Table of Contents
Overview
Key Concepts in Aeroacoustics
Aeroacoustics is fundamentally the study of noise generation resulting from aerodynamic forces interacting with surfaces, particularly in the context of turbulent fluid motion and periodically varying flows. This discipline has evolved significantly since its inception in the 1950s, when the foundational concepts were established alongside the advent of the jet age.[4.1] Although a complete scientific theory for the generation of noise by aerodynamic flows remains elusive, the field primarily relies on the aeroacoustic analogy proposed by Sir James Lighthill. This analogy reformulates the governing equations of fluid motion into a form that resembles the wave equation of classical acoustics, allowing for the analysis of sound generation and propagation.[2.1] The pressure generated in aeroacoustic phenomena can reach levels around 1034 MPa, influenced by the interplay of airspeed and sound.[1.1] The analysis of aeroacoustics encompasses various aspects, including the inertial effects of fluid flow, non-linear acoustic generation processes, and sound generation or attenuation due to viscous forces.[2.1] As a distinct branch of fluid mechanics, aeroacoustics has developed its own scientific and technological missions, focusing on both the modeling of sound generation and its outward propagation.[3.1] In practical applications, the aerospace industry has made strides in integrating noise reduction strategies into aircraft design. For instance, the Boeing 787 Dreamliner employs advanced airfoil designs and winglet technology to minimize aerodynamic noise during takeoff and landing, thereby enhancing fuel efficiency and passenger comfort.[9.1] However, the challenge remains to balance aerodynamic efficiency with noise reduction, as modifications aimed at reducing noise can inadvertently affect aircraft performance.[10.1] The industry is increasingly adopting advanced engine designs, aerodynamic optimizations, and active noise control systems to address the pressing need for quieter aircraft amidst growing air travel demand.[15.1] Furthermore, the integration of aeroacoustic research into urban planning is becoming increasingly relevant, particularly in the context of Urban Air Mobility (UAM). Noise generated by rotorcraft poses significant barriers to the acceptance of UAM operations in populated areas, necessitating effective noise mitigation strategies.[8.1] Research in soundscape design can inform urban planning processes, contributing to the development of more livable and healthier urban environments.[7.1] Overall, the field of aeroacoustics continues to evolve, driven by the need for innovative solutions to manage noise in both aviation and urban contexts.History
Origins of Aeroacoustics
Aeroacoustics, a specialized branch of acoustics, focuses on the study of noise generated by turbulent fluid motion and aerodynamic forces interacting with surfaces. This field encompasses the mechanisms of sound generation, which can arise from turbulence in flows, resonant effects in cavities, or vibrations of structural boundaries.[48.1] The origins of aeroacoustics can be traced back to significant advancements in acoustics and fluid dynamics throughout the 19th and 20th centuries. The early foundations of aeroacoustics were laid in the 19th century, marked by pivotal discoveries such as John William Strutt, 3rd Baron Rayleigh's comprehensive work, "Theory of Sound" (1877). This influential text explored sound waves in detail, including their reflection, refraction, and diffraction, thereby providing essential insights that would later inform the study of sound in fluid flows.[46.1] Additionally, the mid-19th century saw the emergence of specialized acoustical instruments, notably crafted by Rudolph Koenig in Paris, which facilitated experimental acoustics and contributed to the understanding of sound phenomena.[47.1] The formal advent of aeroacoustics as a distinct discipline began in the early 20th century, particularly during the jet age of the 1950s. This period marked a significant evolution in the field, as researchers began to model both the generation and propagation of sound in fluid flows, leading to the establishment of aeroacoustics as a recognized area of study within fluid mechanics.[3.1] Sir James Lighthill's introduction of the acoustic analogy in 1952 provided a theoretical framework for analyzing jet noise, which has since become a cornerstone of aeroacoustic research.[58.1] As the field progressed, computational methods emerged as a transformative force in aeroacoustics. The development of computational aeroacoustics has enabled researchers to simulate complex noise generation scenarios, including jet noise and noise from wall-bounded flows such as airfoils and turbomachinery.[57.1] These advancements have significantly enhanced the understanding of noise propagation and have informed modern strategies for noise reduction in aviation, emphasizing the importance of aerodynamic optimization and innovative noise-cancellation technologies.[41.1]Contributions of Sir James Lighthill
Sir James Lighthill made groundbreaking contributions to aeroacoustics, focusing on noise generation from turbulent fluid motion and aerodynamic forces. His pioneering research established the foundation for understanding how these factors interact with surfaces to produce sound, which is vital in designing quieter aircraft and vehicles. The principles of aeroacoustics are also crucial in the construction of wind turbines, buildings, and bridges, where reducing vibrations and noise is essential.[78.1] [78.1] Beyond theoretical advancements, Lighthill emphasized the importance of experimental validation of theoretical predictions. For example, recent studies have demonstrated the effectiveness of coupled Helmholtz resonators in noise mitigation, using practical setups like microphones to measure sound levels in relevant environments.[77.1] Lighthill's legacy continues to inspire ongoing research and development in aeroacoustics, underscoring the enduring impact of his work on contemporary engineering challenges.Recent Advancements
Current Research Trends
Recent research in aeroacoustics has increasingly focused on the integration of computational fluid dynamics (CFD) with aeroacoustics, leading to the establishment of computational aeroacoustics (CAA) as a critical interdisciplinary field. CAA is dedicated to investigating sound generation and propagation arising from various aeroacoustic problems, emphasizing the need for a comprehensive understanding of the differences in length scales within the computational domain.[86.1] Recent advancements in CAA have included the development of high-resolution methods, artificial selective damping, and high-quality numerical boundary conditions, which are essential for accurately simulating aeroacoustic phenomena.[87.1] Additionally, hybrid approaches have gained particular attention, wherein the turbulent noise source field is computed separately from the far-field calculations, thereby enhancing the accuracy of noise predictions.[85.1] These developments underscore the importance of employing specialized CAA methods, as standard CFD schemes are generally inadequate for addressing the complexities of aeroacoustic problems.[87.1] Moreover, the application of advanced mathematical models, such as spectral proper orthogonal decomposition (SPOD), has been explored to construct low-order models for broadband turbulent flows. These models leverage optimality and coherence properties to better understand complex nonlinear fluid dynamics, which is crucial for addressing jet noise and other forms of turbulence.[92.1] In addition to computational advancements, there has been a notable shift in the design philosophy of aircraft, where aeroacoustics has become a central consideration rather than an afterthought. This evolution is reflected in the development of quieter aircraft designs that balance performance, efficiency, and noise reduction. Techniques such as geometric shape optimization and passive control methods have been prioritized by manufacturers for their reliability in reducing noise from turbofan engines.[90.1] Furthermore, regulatory frameworks, such as those enforced by the Federal Aviation Administration (FAA), have driven the aviation industry to adopt innovative noise-cancellation technologies and aerodynamic optimizations.[89.1]Novel Noise-Reduction Techniques
Recent advancements in aeroacoustics have led to the development of novel noise-reduction techniques that are crucial for enhancing the acceptance of supersonic aircraft in civil aviation. Effective noise reduction techniques are essential for mitigating the impacts of aircraft noise, thereby improving comfort for passengers and communities near flight paths.[96.1] Among these techniques, the use of sound-absorbing materials has emerged as a significant strategy to reduce noise transmission in supersonic aircraft.[96.1] Research indicates a growing need to explore new types of liners and materials that can further improve noise reduction capabilities. Porous materials, in particular, are considered promising candidates for this purpose.[97.1] The integration of advanced materials, along with aerodynamic optimization and innovative noise-cancellation technologies, plays a vital role in designing quieter aircraft.[98.1] Moreover, regulatory frameworks, such as those enforced by the Federal Aviation Administration (FAA), necessitate adherence to noise standards, which compel the aviation industry to prioritize noise reduction in both new aircraft designs and retrofitting existing fleets.[98.1] This regulatory pressure drives innovation in noise reduction technologies, leading to significant advancements in the aerospace sector aimed at achieving quieter skies.[98.1]In this section:
Applications
Military Applications
Aeroacoustics is integral to the development of military aircraft, particularly in enhancing stealth capabilities. Stealth technology represents a significant advancement in military strategy and aircraft design, incorporating principles aimed at minimizing an aircraft's visibility to radar and other detection systems.[148.1] Stealth aircraft are specifically engineered to reduce their detectability, utilizing specialized shapes and materials that contrast sharply with conventional aircraft, which reflect radar waves in multiple directions.[148.1] This transformative technology fundamentally alters the dynamics of aerial engagements, providing strategic advantages in military operations.[148.1] Furthermore, ongoing research and development in stealth technology focuses on advancing methods to further minimize the detection of military aircraft, thereby enhancing their effectiveness and capabilities in aerial warfare.[148.1] The integration of stealth technology with other advanced technologies significantly boosts operational effectiveness in these military applications.[148.1] Recent advancements in stealth technology have increasingly focused on enhancing the effectiveness and capabilities of military aircraft in aerial warfare. Research and development efforts are directed towards improving methods that reduce the detection of military aircraft, thereby providing strategic advantages in military operations.[150.1] The integration of stealth technology with other advanced technologies further enhances operational effectiveness in aerial engagements.[148.1] In addition to traditional stealth measures, innovations in aeroacoustic technologies have emerged as vital components in enhancing the stealth capabilities of military aircraft. These advancements include the application of aerodynamic design principles, specialized enclosures, and insulation techniques that contribute to the overall reduction of noise emissions.[152.1] Such innovations not only aim to improve operational stealth and survivability but also address environmental concerns and regulatory requirements.[152.1] European nations are at the forefront of developing advanced stealth aircraft, such as the Eurofighter Typhoon and F-35 Lightning II, which incorporate cutting-edge stealth technologies alongside artificial intelligence and directed energy weapons.[151.1] The Future Combat Air System (FCAS), a collaborative Franco-German project, exemplifies the commitment to creating sixth-generation fighter aircraft that leverage these advancements.[151.1] As military aviation continues to evolve, the integration of aeroacoustic technologies will remain essential in maintaining a strategic edge in aerial warfare.Civilian Applications
Aeroacoustics has significant civilian applications, particularly in the assessment and management of noise produced by various air vehicle operations. One of the primary areas of focus is the evaluation of noise generated by drones, which has become increasingly relevant as their use expands in urban environments and for commercial purposes. The study of drone noise is essential for ensuring compliance with community noise regulations and for minimizing disturbances to residents.[118.1] Aeroacoustics is a specialized field that focuses on the study of noise produced by turbulent fluid motion in complex flows, with applications spanning both military and civilian domains. In civilian contexts, it includes drone noise assessment and the evaluation of acoustic interactions in combustion and chemical processes.[118.1] Research in this area aims to understand how turbulent fluid motion contributes to noise generation, which is essential for developing quieter and more efficient propulsion systems.[118.1] Additionally, tailoring aircraft design to enable low-noise flight performance has been shown to significantly impact overall flight performance, highlighting the importance of advanced noise reduction techniques in aerospace engineering.[119.1] Moreover, the integration of innovative techniques, such as active noise control systems that generate anti-noise to counteract unwanted sound, is being explored to further mitigate noise from aircraft engines and nacelle ducts. These systems can adapt their acoustic properties in real-time to optimize noise reduction across varying operating conditions.[121.1] Such advancements are critical in balancing the demands of aviation technology with the need to minimize the impact of aviation noise on surrounding communities.[125.1]In this section:
Theoretical Framework
Aeroacoustic Analogy
Aeroacoustic analogy plays a pivotal role in the theoretical framework of aeroacoustics, focusing on the mechanisms of sound generation within fluid flows. Central to this framework is Lighthill's equation, which provides a foundation for modeling sound production in turbulent environments by incorporating factors such as wall influences, flow unsteadiness, and the nonlinear interactions between turbulent velocity fields and sound waves.[153.1] The challenge of predicting sound in fluid flows stems from the nonlinearity of the governing equations, particularly in high-speed scenarios where inertial forces overshadow viscous effects.[154.1] To address these complexities, advanced mathematical models like the generalized acoustic analogy have been developed. This model effectively integrates mean flow propagation and source anisotropy, offering a comprehensive description of broadband turbulence.[155.1] In practical applications, the generalized acoustic analogy has been utilized in high-speed jet scenarios, such as those in the SILOET experiment by QinetiQ. This statistical model, grounded in Goldstein's theory, leverages the covariance of fluctuating Reynolds stresses and enthalpy source terms.[173.1] Numerical methods employed in these models facilitate the prediction of turbulent jet noise by simplifying the governing equations for sound propagation, thus reducing computational demands.[158.1] These methodologies underpin the development of physics-based, reduced-order noise prediction techniques, advancing our understanding of sound propagation in complex fluid flows, especially concerning jet noise.[160.1] The evolution of turbulent jet-noise models, from Lighthill's acoustic analogy to modern approaches, underscores the significance of sound generation and mean-flow propagation effects and their interactions.[159.1] This framework is crucial for understanding jet noise in complex fluid flows, serving as a robust engineering tool for predicting jet mixing noise and analyzing problems characterized by three-dimensional propagation effects.[161.1]Governing Equations in Aeroacoustics
The governing equations in aeroacoustics are primarily derived from Lighthill's acoustic analogy, which reformulates the fluid dynamic equations into an inhomogeneous wave equation. This transformation allows for the description of sound generation by turbulent flows, addressing the complexities inherent in such phenomena. Lighthill's formulation is particularly significant as it provides exact solutions to the Navier-Stokes equations, with the source term of the wave equation being crucially important within turbulent flow regions, thereby representing the flow-induced noise source.[171.1] In the context of turbulent two-phase flow, Lighthill's theory incorporates the effects of one phase on the other through monopole, dipole, and quadrupole distributions, which are essential for accurately modeling sound generation.[168.1] However, the application of Lighthill's equation is not without challenges. It is based on the assumption of static media with respect to the observer, which may not hold true in scenarios involving moving bodies and flow media, such as in the case of fans or compressors where duct flow significantly influences sound generation.[169.1] Lighthill's analogy serves as an exact reformulation of the fluid dynamic equations into an inhomogeneous wave equation, effectively addressing the generation of sound as well as acoustic nonlinearity, convection, refraction of sound waves by the flow, and attenuation due to thermal and viscous actions.[172.1] This comprehensive approach highlights the complexities involved in sound generation, particularly in turbulent flows where these factors must be carefully considered. The source term in Lighthill's equation not only accounts for these elements but also poses challenges for researchers when applying the equation to real-world scenarios, as it requires a nuanced understanding of the interplay between these various factors.[172.1]Challenges And Future Directions
Emerging Noise Sources
Emerging noise sources in aeroacoustics present significant challenges, particularly in the context of increasing air traffic and stringent environmental regulations. Four major areas of concern have been identified in computational aeroacoustics: the prediction of tonal and broadband noise generated by both rotating and stationary cascades, the optimization of nozzle designs—including features such as tabs and chevrons—to mitigate jet noise, the propagation and radiation of noise from lined bypass ducts, and the prediction and minimization of combustor noise.[194.1] Additionally, the development of new open-rotor contra-rotating power plants alongside conventional ducted turbofan designs highlights the ongoing technological issues in the quest to reduce aeroengine noise.[196.1] The interaction of flow turbulence with noise generation is another area of concern, as these turbulent flows can produce acoustic waves that may lead to the formation of new turbulent structures, a phenomenon known as self-noise.[195.1] This complexity is compounded by the need to address noise propagation and radiation from lined bypass ducts, which requires advanced modeling and simulation techniques to accurately predict acoustic behavior.[194.1] Recent advancements in experimental methodologies have significantly enhanced our understanding of emerging noise sources in aeroacoustics. A focus on the preparation of experimental setups for studying full-scale models has been emphasized, particularly regarding measurement techniques for velocity and pressure quantification, which are essential for addressing complex aeroacoustic challenges.[229.1] These techniques are crucial for tackling difficult problems in the field and contribute to a deeper comprehension of the mechanisms behind aeroacoustic noise generation. As air traffic volumes are predicted to increase rapidly, the challenge of reducing aeroengine noise becomes increasingly pressing, particularly in light of stricter environmental regulations.[196.1] The ongoing transformation of the aeroacoustic field has been significantly influenced by the adoption of new experimental and simulation techniques by both academic and industrial stakeholders.[197.1] These advancements are crucial for addressing the emerging noise sources associated with both conventional ducted turbofan designs and the development of new open-rotor contra-rotating power plants.[196.1]Regulatory Impacts on Research and Development
Regulatory frameworks significantly influence research and development (R&D) efforts in the field of aeroacoustics, particularly in the United States. The Federal Aviation Administration (FAA) enforces noise standards that govern aircraft operations, including specific restrictions on flight paths and times.[198.1] These regulations compel the aviation industry to prioritize noise reduction in the design of new aircraft and the retrofitting of existing fleets with quieter technologies.[198.1] To address these challenges, the FAA has established various programs aimed at understanding and mitigating noise impacts, including the Continuous Lower Energy, Emissions, and Noise (CLEEN) program, which focuses on developing certifiable aircraft technology that can reduce noise levels by up to 32 decibels (dB) relative to the standards set by the International Civil Aviation Organization.[201.1] Through these initiatives, the aerospace industry is making significant progress toward achieving quieter skies while balancing regulatory compliance with technological innovation.[201.1] The FAA has initiated various programs aimed at understanding noise impacts and identifying solutions to mitigate them. One notable initiative is the Continuous Lower Energy, Emissions, and Noise (CLEEN) program, which seeks to develop certifiable aircraft technology that can reduce noise levels by 32 decibels (dB) relative to the standards set by the International Civil Aviation Organization.[201.1] Such regulatory measures not only set benchmarks for noise reduction but also encourage the development of a broader portfolio of noise reduction technologies. This, in turn, justifies the establishment of lower regulatory noise levels and increases the likelihood of proactive implementation by industry stakeholders.[200.1] In terms of specific noise reduction strategies, various control approaches have been developed to address noise generated by turbofan engines. These include active control, geometric shape optimization, and passive control methods, with the latter two being favored by manufacturers due to their reliability and effectiveness.[199.1] The ongoing research and development in these areas are essential for creating next-generation low-noise turbofan engines, which align with regulatory expectations and market demands.[199.1] International Regulatory Cooperation refers to the collaborative efforts among countries to harmonize regulations and standards across various sectors. This cooperation is pivotal in addressing transnational challenges, such as climate change and public health crises, which require coordinated responses for effective solutions.[208.1] Noise regulations vary significantly across countries, shaped by local living conditions, urban planning, and specific noise issues. Some nations impose limits on acceptable decibel levels in residential areas, while others implement quiet hours or employ strategic planning to mitigate noise.[209.1] Achieving global harmonization necessitates that regulatory agencies agree on developing, implementing, and adopting uniform guidelines and technical standards focused on quality, safety, and efficacy.[210.1] However, the political agendas of individual countries often hinder the timely updating of regulations to align with international guidelines, as these agendas may not prioritize global harmonization.[210.1]In this section:
Research Methodologies
Theoretical Approaches
Aeroacoustics research employs various theoretical approaches to model and predict noise generated by fluid flows. One significant method is the generalized acoustic analogy, which integrates mean flow propagation and source anisotropy effects into a unified framework for broadband turbulence description. This model is particularly useful in jet noise applications, where it accounts for contributions from both fine-scale turbulence and large-scale coherent structures to far-field noise.[261.1] The formulation of this analogy begins with Goldstein's principles, rearranging the Navier-Stokes equations into Linearized Euler Equations. This rearrangement allows for the inclusion of nonlinear terms that represent analogous acoustic sources, thereby providing a consistent framework for analyzing convection effects on acoustic sources and refraction effects on sound propagation.[262.1] In practical applications, the generalized acoustic analogy has been implemented in various experimental conditions, such as the Strategic Investment in Low-carbon Engine Technology (SILOET) experiment. Here, the model utilized statistical methods based on the covariance of fluctuating Reynolds stresses and enthalpy source terms, demonstrating its effectiveness in real-world scenarios.[263.1] Additionally, the field of aeroacoustics encompasses a range of topics, including sound generation from turbulence and interactions with solid boundaries, as well as the effects of source convection and inhomogeneities in the medium. These aspects are critical for developing predictive models that accurately reflect the complexities of aerodynamic sound generation.[266.1]Computational Techniques
Recent advancements in computational aeroacoustics (CAA) have significantly transformed the methodologies employed in predicting and mitigating noise in various engineering applications, particularly in aviation and automotive design. CAA has evolved independently from computational fluid dynamics (CFD), addressing unique computational challenges that are not typically considered in CFD.[248.1] This independence has led to the development of specialized algorithms and methods tailored for aeroacoustic problems, which often involve vastly different length scales within the computational domain.[249.1] Key advancements in CAA include the introduction of high-resolution methods, artificial selective damping techniques, and the establishment of high-quality numerical boundary conditions.[249.1] These innovations are crucial for accurately simulating flow-induced noise, as they enhance the precision of numerical predictions by addressing issues such as turbulent intensity and length scale disparity.[241.1] Furthermore, the integration of wave number analysis has proven beneficial, as it not only quantifies errors associated with discretized computational methods but also aids in the optimization of computational schemes.[249.1] The integration of Computational Aeroacoustics (CAA) with Computational Fluid Dynamics (CFD) has significantly advanced our understanding of sound generation mechanisms, particularly through the application of the Navier-Stokes equations. This coupling allows for the identification of sound sources, such as those produced by vortex rings, thereby enhancing noise prediction and mitigation strategies in various engineering applications.[239.1] Recent developments in this field have been exemplified by the collaborative efforts between DNW and DLR, which led to the design of low-noise fan stators and turning vanes. These innovations were achieved through extensive use of high-fidelity CFD tools and new optimization methods for acoustic layout.[240.1] Furthermore, the field of CAA is characterized by its active research and numerous industrial applications, highlighting the importance of integrating advanced computational methods with experimental techniques to improve the design and certification of aerospace vehicles.[247.1] A recent study by NASA emphasizes the critical role of high-performance computing (HPC) in enhancing the impact of CFD on these design processes.[250.1]Educational And Institutional Contributions
Academic Programs and Research Centers
Numerous academic programs and research centers contribute significantly to the field of aeroacoustics, fostering education and innovation. The AeroAcoustics Research Consortium (AARC), established in 2001 by NASA Glenn Research Center in collaboration with industry partners, aims to advance technologies that mitigate the environmental impact of noise from commercial aircraft. This consortium facilitates a collaborative environment where NASA and industry partners engage with international researchers to overcome technical barriers in noise-reduction technologies, thereby benefiting all stakeholders involved.[291.1] In addition to the AARC, various universities offer specialized programs in aeroacoustics. For instance, Penn State's Graduate Program in Acoustics encompasses a wide range of topics, including underwater acoustics, signal processing, and structural vibration, thereby preparing students for diverse careers in the field.[289.1] Similarly, Georgia Tech's Daniel Guggenheim School of Aerospace Engineering is recognized as one of the oldest and largest educational programs in aerospace engineering, providing students with hands-on experience and opportunities to engage in practical design projects.[290.1] NASA also plays a pivotal role in educational initiatives through its University Leadership Initiative, which recently awarded $5.7 million to a multi-university partnership led by Boston University. This initiative aims to develop quieter vertical lift air vehicles and involves collaboration among several institutions, including Virginia Tech and Embry-Riddle University.[284.1] Such partnerships not only enhance research capabilities but also prepare students for future challenges in aeroacoustics. Furthermore, the Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee actively promotes the interests of the aeroacoustics community in Europe, supporting both scientific and industrial advancements in the field.[277.1] This committee's efforts contribute to a broader understanding and application of aeroacoustic principles across various research and industrial contexts.Collaborative Research Initiatives
Interdisciplinary collaboration plays a crucial role in enhancing educational programs in aeroacoustics, as evidenced by various initiatives aimed at bridging the gap between academia and industry. The InterPBL research project at Aalborg University exemplifies this approach, focusing on improving interdisciplinary collaboration in engineering education. This project highlights the benefits of integrating diverse disciplines to foster innovative problem-solving and enhance learning outcomes in engineering contexts, including aeroacoustics.[278.1] The collaboration between academia and industry is crucial for economic growth and development, as it facilitates the conversion of knowledge and innovation into practical applications and innovative products.[281.1] The Academia-Industry Collaboration Plan Design Model highlights the necessity of planning structured collaboration processes, which includes defining time constraints for both long-term and short-term relationships. This approach aids in understanding the nature of projects pursued by researchers and practitioners.[280.1] By fostering such collaborations, the model supports the research and development of market solutions and technological improvements that benefit both sectors.[280.1] Public-private partnerships have also emerged as a significant avenue for advancing noise reduction technologies in aerospace. For instance, the FAA has led initiatives that involve 100% cost-sharing from industry partners to develop technologies aimed at reducing fuel burn, emissions, and noise. These partnerships enable the acceleration of certifiable aircraft and engine technologies through ground and flight test demonstrations.[288.1] Additionally, collaborations between NASA and industry stakeholders have resulted in substantial advancements in aircraft engine and airframe technology, significantly reducing noise levels produced by aircraft.[295.1] The geared turbofan, developed through collaboration between industry and NASA, is set to significantly reduce both fuel consumption and noise emissions in aviation.[292.1] This partnership has led to advancements in aircraft engine and airframe technology that have substantially decreased the noise produced by aircraft, with potential for further reductions as ongoing research progresses.[295.1] Additionally, regulatory frameworks for aircraft noise are typically established through partnerships with the industry, indicating that current policies may need to adapt to address the noise generated by emerging air vehicles.[294.1] Thus, the collaboration between NASA and industry stakeholders not only fosters technological innovation but also plays a crucial role in shaping regulatory policies related to aircraft noise.In this section:
References
[1] Aeroacoustics - an overview | ScienceDirect Topics — Aeroacoustics is the science of acoustic noise generation caused by aerodynamic forces interacting with surfaces. Pressure reaches around 1034 MPa pressure through a combination of air speed and sound.
[2] Aeroacoustics - Wikipedia — Although no complete scientific theory of the generation of noise by aerodynamic flows has been established, most practical aeroacoustic analysis relies upon the so-called aeroacoustic analogy, proposed by Sir James Lighthill in the 1950s while at the University of Manchester. whereby the governing equations of motion of the fluid are coerced into a form reminiscent of the wave equation of "classical" (i.e. linear) acoustics in the left-hand side with the remaining terms as sources in the right-hand side. The first term ρ v i v j {\displaystyle \rho v_{i}v_{j}} describes inertial effect of the flow (or Reynolds' Stress, developed by Osborne Reynolds) whereas the second term ( p − c 0 2 ρ ) δ i j {\displaystyle (p-c_{0}^{2}\rho )\delta _{ij}} describes non-linear acoustic generation processes and finally the last term τ i j {\displaystyle au _{ij}} corresponds to sound generation/attenuation due to viscous forces.
[3] Advances in aeroacoustics research: recent developments and ... — Aeroacoustics continues to be a subject of active research now nearly 70 years since its genesis in the 1950s at the dawn of the jet age. Although fundamentally a branch of fluid mechanics, aeroacoustics has grown into a discipline of its own right with well-defined scientific and technological missions, namely modelling both the generation and outward propagation of sound, and more critically
[4] Aeroacoustics - Wikipedia — Aeroacoustics is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces. Noise generation can also be associated with periodically varying flows.
[7] PDF — Finally, important design criteria for urban planning and development could be derived from the findings of soundscape research. A soundscape design guide could help to integrate the acoustic environment into the planning and design process and thus contribute to more livable and healthier cities.
[8] Flight Path Planning for Minimization of Total Noise Exposure in Urban ... — Noise generated by rotorcraft is a major barrier to the acceptance and integration of Urban Air Mobility (UAM) operations in populated areas. Annoyance due to rotorcraft noise increases with the noise level as well as the total duration and frequency of exposure. As such, noise annoyance serves as an important metric for the impact of Urban Air Mobility operations. This paper presents a method
[9] Noise Reduction Strategies through Airfoil Design Modifications — Several aircraft manufacturers and have implemented these noise reduction strategies with notable success: Boeing 787 dreamliner: Incorporates advanced airfoil designs and winglet technology to minimize aerodynamic noise during takeoff and landing, improving both fuel efficiency and passenger comfort.
[10] Effective Noise Reduction Techniques in Aircraft Design and Operations — Aerodynamic design poses significant restrictions on noise reduction strategies. Modifications to reduce noise can inadvertently affect the aircraft's performance, such as speed and fuel efficiency.
[15] Aeroacoustics: Exploring How Planes Are Designed to Be Quieter — In the context of aviation, it focuses on understanding and mitigating the noise produced by aircraft during various phases of flight. Designing quieter aircraft involves a combination of aerodynamic optimization, advanced materials, and innovative noise-cancellation technologies. Optimize Designs: Iteratively improve aircraft components to reduce noise. Federal Aviation Administration (FAA) Regulations: In the United States, the FAA enforces noise standards for aircraft operations, including restrictions on flight paths and times. These regulations drive the aviation industry to prioritize noise reduction in new aircraft designs and retrofit existing fleets with quieter technologies. Through a combination of advanced engine designs, aerodynamic optimizations, active noise control systems, and strict regulatory frameworks, the aerospace industry is making significant strides toward quieter skies.
[41] Aeroacoustics: Exploring How Planes Are Designed to Be Quieter — In the context of aviation, it focuses on understanding and mitigating the noise produced by aircraft during various phases of flight. Designing quieter aircraft involves a combination of aerodynamic optimization, advanced materials, and innovative noise-cancellation technologies. Optimize Designs: Iteratively improve aircraft components to reduce noise. Federal Aviation Administration (FAA) Regulations: In the United States, the FAA enforces noise standards for aircraft operations, including restrictions on flight paths and times. These regulations drive the aviation industry to prioritize noise reduction in new aircraft designs and retrofit existing fleets with quieter technologies. Through a combination of advanced engine designs, aerodynamic optimizations, active noise control systems, and strict regulatory frameworks, the aerospace industry is making significant strides toward quieter skies.
[46] Making waves | Royal Society — The nineteenth century saw further advances, including the discoveries of John William Strutt, 3rd Baron Rayleigh FRS, whose Theory of sound (1877) is regarded as one of the most significant contributions to acoustics. In this comprehensive work, he explored sound waves in detail, including their reflection, refraction, and diffraction.
[47] Seeing Sound in the 19th Century - University of Toronto — In the mid-19th century, Paris was at the heart of the scientific instrument making world. In a busy field of craftsmen, Rudolph Koenig was the sole maker of acoustical instruments (Pantalony, 12), keen to sell experimental acoustics to buyers stocking demonstration cupboards across North America and Europe (Pantalony 13).
[48] A Brief History of Acoustics - SpringerLink — Aeroacoustics, a branch of physical acoustics, is the study of sound generated by (or in) flowing fluids. The mechanism for sound or noise generation may be due to turbulence in flows, resonant effects in cavities or wave-guides, vibration of boundaries of structures etc.
[57] The third golden age of aeroacoustics - AIP Publishing — The present review covers the latest evolution of computational aeroacoustics, the field that deals with the noise generated by fluid flows and its propagation in the medium. Aeroacoustics, Acoustic noise, High-lift device, Landing gear, Aerodynamics, Lattice Boltzmann methods, Navier Stokes equations, Subsonic flows, Supersonic flows, Turbulence simulations Current status of jet noise predictions using large-eddy simulation Large-eddy simulations analysis of supersonic heated jets with fluid injection for noise reduction Trailing edge noise prediction using large eddy simulation and acoustic analogy Direct numerical simulation of turbulent flow past a trailing edge and the associated noise generation Computation of trailing-edge flow and noise using large-eddy simulation Synthetic turbulence methods for computational aeroacoustic simulations of leading edge noise Broadband noise predictions on the ACAT1 fan stage using large eddy simulations and analytical models
[58] PDF — The acoustic analogy introduced by Lighthill to study jet noise is now over 50 years old. In the present paper, Lighthill's Acoustic Analogy is revisited together with a brief evaluation of the state-of-the-art of the subject and an exploration of the possibility of further improvements in jet noise prediction from analytical methods, computational fluid dynamics (CFD) predictions, and
[77] Case studies on aeroacoustics damping performances of Coupled Helmholtz ... — To demonstrate the procedures and quantify the aeroacoustics damping performances of coupled Helmholtz resonators, an experimental study 61 is conducted as a case study. Here, six microphones were distributed, three upstream and three downstream, and utilized in Helmholtz resonators attached to a pipe with a grazing flow present.
[78] Knowledge Center - Aerospace | GRAS Sound and Vibration — Aeroacoustics is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces. Aeroacoustics is important in the design of aircraft, vehicles, wind turbines, and even buildings and bridges to minimize vibrations and noise. Learn more about that with our additional resources.
[85] Computational Prediction of Flow-generated Sound — Abstract This article provides a critical review of computational techniques for flow-noise prediction and the underlying theories. Hybrid approaches, in which the turbulent noise source field is computed and/or modeled separately from the far-field calculation, are afforded particular attention. Numerical methods and modern flow simulation techniques are discussed in terms of their
[86] Recent advances of computational aeroacoustics - shu.edu.cn — ABSTRACT：Computational aeroacoustics (CAA) is an interdiscipline of aeroacoustics and computational fluid dynamics (CFD) for the investigation of sound generation and propagation from various aeroacoustics problems.In this review, the foundation and research scope of CAA are introduced firstly. A review of the early advances and applications of CAA is then briefly surveyed, focusing on two
[87] Recent advances in computational aeroacoustics - ScienceDirect — They include the development of high resolution CAA methods, artificial selective damping and high quality numerical boundary conditions. Wave number analysis not only can yield an absolute error incurred in the use of a discretized computational method but also offers a way to develop optimized computation schemes. Before discussing how to solve aeroacoustics problems numerically or simulate them computationally, an approach generally referred to as computational aeroacoustics (CAA), it is important to recognize and to have a good understanding of these differences. CAA methods must be designed to deal with problems with greatly different length scales in different parts of the computational domain. To be able to compute or simulate aeroacoustics problems accurately and efficiently, standard CFD schemes, designed for applications to fluid problems, are generally not adequate.
[89] Aeroacoustics: Exploring How Planes Are Designed to Be Quieter — In the context of aviation, it focuses on understanding and mitigating the noise produced by aircraft during various phases of flight. Designing quieter aircraft involves a combination of aerodynamic optimization, advanced materials, and innovative noise-cancellation technologies. Optimize Designs: Iteratively improve aircraft components to reduce noise. Federal Aviation Administration (FAA) Regulations: In the United States, the FAA enforces noise standards for aircraft operations, including restrictions on flight paths and times. These regulations drive the aviation industry to prioritize noise reduction in new aircraft designs and retrofit existing fleets with quieter technologies. Through a combination of advanced engine designs, aerodynamic optimizations, active noise control systems, and strict regulatory frameworks, the aerospace industry is making significant strides toward quieter skies.
[90] Development and progress in aeroacoustic noise reduction on turbofan ... — To reduce noise generated from turbofan engines-powered aircraft, a number of control approaches have been developed. Because they are considered the most reliable and effective noise reduction methods, the geometric shape optimization and passive control are preferable by the engine manufacturers. The research and development progress made on the active control, passive control, and geometric shape optimization are reviewed and discussed, aiming to provide an useful guidance on next-generation low-noise turbofan engines. To attenuate these noises in engineering applications, noise reduction approaches such as i) active control, ii) geometric shape optimization, and iii) passive control (including acoustic boundary control) have been suggested . Moreover, the geometric shape optimization and the passive control are preferable by the engine manufacturers since they are considered the most reliable and effective noise reduction methods .
[92] A stochastic SPOD-Galerkin model for broadband turbulent flows - Springer — The use of spectral proper orthogonal decomposition (SPOD) to construct low-order models for broadband turbulent flows is explored. The choice of SPOD modes as basis vectors is motivated by their optimality and space-time coherence properties for statistically stationary flows. This work follows the modeling paradigm that complex nonlinear fluid dynamics can be approximated as stochastically
[96] Effective Noise Reduction Techniques in Aircraft Design and Operations — Effective Noise Reduction Techniques in Aircraft Design and Operations - Aeroplane Tech Effective noise reduction techniques help mitigate these impacts, enabling broader acceptance and integration of supersonic aircraft into civil aviation markets. Effective noise reduction techniques employed in supersonic aircraft can significantly enhance comfort for both passengers and people living near flight paths. Sound-absorbing materials are specialized substances designed to reduce noise transmission in various environments, including supersonic aircraft. Implementing noise reduction techniques in supersonic aircraft presents several challenges that must be addressed for effective outcomes. Future directions in noise reduction for supersonic aircraft hinge on innovative strategies that combine technology, engineering, and materials science. The pursuit of effective noise reduction techniques in supersonic aircraft is critical for enhancing the sustainability and acceptance of supersonic travel.
[97] PDF — Aircraft noise reduction : AIRBUS industrial needs in terms of new materials for nacelle liners Journées scientifiques de l'ONERA - January 16th, 2003 ... there is a need to investigate new type of liners and/or new materials to improve noise reduction. Porous materials remain good candidates ! Optimum impedances Resistance and reactance of
[98] Aeroacoustics: Exploring How Planes Are Designed to Be Quieter — In the context of aviation, it focuses on understanding and mitigating the noise produced by aircraft during various phases of flight. Designing quieter aircraft involves a combination of aerodynamic optimization, advanced materials, and innovative noise-cancellation technologies. Optimize Designs: Iteratively improve aircraft components to reduce noise. Federal Aviation Administration (FAA) Regulations: In the United States, the FAA enforces noise standards for aircraft operations, including restrictions on flight paths and times. These regulations drive the aviation industry to prioritize noise reduction in new aircraft designs and retrofit existing fleets with quieter technologies. Through a combination of advanced engine designs, aerodynamic optimizations, active noise control systems, and strict regulatory frameworks, the aerospace industry is making significant strides toward quieter skies.
[118] Aeroacoustics | Ole Miss - University of Mississippi — Aeroacoustics focuses on the study of noise produced by turbulent fluid motion in complex flows. This specialized field focuses on the study of noise produced by turbulent fluid motion in complex flows and has wide-ranging applications, from military initiatives such as noise reduction in jet propulsion and analysis of noise from ballistic missile launches, to civilian uses including drone noise assessment and evaluation of acoustic interactions in combustion and chemical processes. The study explores how the contoured insert influences the acoustic properties of the jet, aiming to lower noise levels associated with afterburning in high-speed aircraft. This study quantitatively assesses the acoustic field produced by a laboratory-scale heated jet with high Mach numbers, using microphone arrays to map the sound pressure levels across the jet's field.
[119] Reduction of Aircraft Noise by Wing Design and Add-On Technologies — For example, Koch demonstrates, that tailoring the aircraft design to enable low-noise flight performance has a significant impact on flight performance. In order to achieve significant noise
[121] PDF — In engine and nacelle ducts the character of turbo-machinery noise depends on the aircraft and engine operating conditions, so that significantly improved noise attenuation could be achieved by Approach: Generate anti-noise with opposite phase, controlled in real time to achieve optimum reduction of fan noise at source at all conditions Key issues: • Design, manufacturing & integration complexity • Affordable micro-controllers • Potential weight penalty • In service reliability & maintenance Approach: Generate anti-noise with opposite phase, controlled in real time to achieve optimum reduction of fan noise at source at all conditions Key issues: • Design, manufacturing & integration complexity • Affordable micro-controllers • Potential weight penalty • In service reliability & maintenance Main Menu 21 replacing or complementing passive liners by systems capable of adapting their acoustic properties to match the in-duct sound field.
[125] GAO-08-216T, Aviation and the Environment: Impact of Aviation Noise on ... — A Number of Efforts Are Underway or Planned to Reduce the Impact of Aviation Noise: To reduce the impact of aviation noise, FAA, in conjunction with NASA, aircraft and aircraft engine manufacturers, airlines, airports, and communities, follows what the International Civil Aviation Organization refers to as its "balanced approach."
[148] The Evolution and Impact of Stealth Technology in Aviation — The evolution of stealth technology in aviation marks a significant advancement in military strategy and aircraft design. Stealth technology in aviation incorporates several principles designed to minimize an aircraft’s visibility to radar and other detection systems. These aircraft exemplify the transformative nature of stealth technology in aviation, fundamentally altering the dynamics of aerial engagements and enhancing strategic advantages in military operations. Advancements in stealth technology are increasingly focused on enhancing the effectiveness and capabilities of military aircraft in aerial warfare. Research and development in stealth technology for aviation focuses on advancing methods to minimize the detection of military aircraft. The integration of stealth technology in aviation with other advanced technologies significantly enhances operational effectiveness in aerial warfare.
[150] The Evolution and Impact of Stealth Technology in Aviation — The evolution of stealth technology in aviation marks a significant advancement in military strategy and aircraft design. Stealth technology in aviation incorporates several principles designed to minimize an aircraft’s visibility to radar and other detection systems. These aircraft exemplify the transformative nature of stealth technology in aviation, fundamentally altering the dynamics of aerial engagements and enhancing strategic advantages in military operations. Advancements in stealth technology are increasingly focused on enhancing the effectiveness and capabilities of military aircraft in aerial warfare. Research and development in stealth technology for aviation focuses on advancing methods to minimize the detection of military aircraft. The integration of stealth technology in aviation with other advanced technologies significantly enhances operational effectiveness in aerial warfare.
[151] The Evolution of Stealth Technology in Modern Military Aircraft — The Evolution of Stealth Technology in Modern Military Aircraft European nations are developing advanced stealth aircraft, AI-powered fighters, and radar systems, enhancing precision strikes in military aviation, including the Eurofighter Typhoon and F-35 Lightning II. This technology has seen significant advancements in Europe, with several nations developing cutting-edge stealth aircraft to maintain their military edge. The Future Combat Air System (FCAS), a joint Franco-German project, aims to create a sixth-generation fighter aircraft incorporating advanced stealth technologies, artificial intelligence and directed energy weapons. European nations have developed cutting-edge radar technologies tailored to identify stealth aircraft. AI-driven algorithms analyse extensive sensor data to identify and track stealth aircraft with greater precision, showcasing Europe's commitment to leading advancements in defence technology.
[152] Advanced Noise Reduction Technologies: A Comprehensive Guide — Furthermore, the integration of aerodynamic design principles, specialized enclosures, and insulation techniques has contributed to the overall reduction of noise emissions in military aircraft. These innovations aim not only to enhance operational stealth and survivability but also to address environmental concerns and regulatory requirements.
[153] Basic Theoretical Aeroacoustics Models - Wiley Online Library — This chapter discusses the main theoretical developments which constitute the basis of aeroacoustics. It presents the derivation of Lighthill's equation, as well as subsequent developments that make it possible to take into account, for example, the influence of walls or flow unsteadiness, as well as the nonlinear coupling between turbulent velocity fields and sound waves.
[154] 2 - Theoretical Background: Aeroacoustics - Cambridge University Press ... — Introduction to aeroacoustics Owing to the nonlinearity of the governing equations it is very difficult to predict the sound production of fluid flows. This sound production occurs typically at high-speed flows, for which nonlinear inertial terms in the equation of motion are much larger than the viscous terms (high Reynolds numbers).
[155] Advances in aeroacoustics research: recent developments and ... — Different mathematical approaches to jet noise modelling include the generalized acoustic analogy that takes into account mean flow propagation and source anisotropy effects within a single unified description of broadband turbulence. Motivated by jet flow physics, the two-source model proposes empirical fine-scale and large-scale spectra to account for the contributions of fine-scale turbulence and large-scale coherent structures to far-field noise, respectively. An extensive survey of different contributions in the area of high-fidelity jet flow and noise modelling based on LES is given by Brés & Lele . The review discusses a broad range of common issues pertinent to jet noise applications—from boundary conditions, grid generation and high-performance computing, through turbulence modelling, to details of the far-field noise prediction schemes and the flow solution analysis based on the LES data.
[158] Numerical Methods for Jet Noise Predictions Using the Generalized ... — Numerical methods used in several implementations of the Generalized Acoustic Analogy for the prediction of turbulent jet noise are discussed. The equation governing sound propagation in the analogy formulation is presented along with analytical simplifications to reduce the computational burden of obtaining solutions. Numerical methods for the resulting boundary-value problem for two classes
[159] Understanding jet noise - JSTOR — Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for
[160] PDF — are planned which will include additional functionality for the code and more complex test cases. 1.0 Introduction Acoustic analogy approaches to the analysis of flow-generated noise can provide a basis for the development of physics-based, reduced-order noise prediction methods. In their practical implementation,
[161] Prediction of jet mixing noise with Lighthill's Acoustic Analogy and ... — Prediction of jet mixing noise with Lighthill's Acoustic Analogy and geometrical acoustics Carlos R. S. Ilário; ... enabling the application of the method to jet noise problems with inherently three-dimensional propagation effects. ... The method presented herein can be applied as a relatively low cost and robust engineering tool for
[168] Sound generation by turbulent two-phase flow | Journal of Fluid ... — Sound generation by turbulent two-phase flow is considered by the methods of Lighthill's theory of aerodynamic noise. An inhomogeneous wave equation is derived, in which the effects of one phase on the other are represented by monopole, dipole and quadrupole distributions.
[169] Lighthill's Equation - an overview | ScienceDirect Topics — 1.5 Generalized Lighthill's equation Lighthill's equation exists under the assumption of static media with respect to the observer. However, in some cases, it is necessary to consider the situation with both the moving body and the flow media. For example, for any reasonable noise prediction for a fan/compressor, it is inevitable to include the effect of duct flow on the sound generation. For
[171] The Lighthill Analogy - COMSOL Multiphysics — In Lighthill's seminal work (Ref. 63 and Ref. 64) he transformed (rearranged) the full set of Navier-Stokes equations (momentum and mass conservation) into an inhomogeneous wave equation. The source term of the wave equation only being important within turbulent flow regions and thus representing the flow-induced noise source.
[172] PDF — Introduction Lighthill's analogy is an exact reformulation of the uid dynamic equations into an inhomogeneous wave equa-tion. Thereby, the source term not only accounts for the generation of sound but also acoustic non-linearity, con-vection, and refraction of sound waves by the ow, as well as attenuation due to thermal and viscous actions. To compute the ow-induced sound, one needs Lighthill
[173] Generalized Acoustic Analogy Modeling of Hot Jet Noise — A generalized acoustic analogy model is implemented for the hot and cold static high-speed jet cases corresponding to conditions of the Strategic Investment in Low-carbon Engine Technology (SILOET) experiment performed by QinetiQ. The model is statistical and based on the covariance of fluctuating Reynolds stresses and enthalpy source terms in accordance with Goldstein's theory. These
[194] Future challenges in computational aeroacoustics for fan broadband and ... — To- ward this end, four major challenge areas exist for computational aeroacoustics: (i) prediction of tonal and broadband noise by rotating and stationary cascades, (ii) optimization of nozzle design (tabs, chevrons) for jet noise, (iii) noise propagation and radiation from lined bypass ducts and (iv) prediction and minimization of combustor
[195] PDF — rrent challenges for acoustic engineering teams to address. These sources re triggered by mechanisms with several interaction levels. Aeroacoustics typically represents this class of problems, where the flow turbulences generate the noise sources, producing acoustics waves that may trigger the creation of new turbulent structures (self-noise
[196] Modern Challenges Facing Turbomachinery Aeroacoustics — In this review we describe current scientific and technological issues in the quest to reduce aeroengine noise, in the face of predicted rapid increases in the volume of air traffic, on the one hand, and increasingly strict environmental regulation, on the other. Alongside conventional ducted turbofan designs, new open-rotor contra-rotating power plants are currently under development, which
[197] Fereidoun Farassat Aeroacoustic Symposium - Home — Aeroacoustic Symposium In memory of Fereidoun Farassat, this symposium is organized to discuss future challenges in aeroacoustics. In the last decade, a profound transformation of the aeroacoustic field has been fostered by the progressive adoption of new experimental and simulation techniques by both academic and industrial players.
[198] Aeroacoustics: Exploring How Planes Are Designed to Be Quieter — In the context of aviation, it focuses on understanding and mitigating the noise produced by aircraft during various phases of flight. Designing quieter aircraft involves a combination of aerodynamic optimization, advanced materials, and innovative noise-cancellation technologies. Optimize Designs: Iteratively improve aircraft components to reduce noise. Federal Aviation Administration (FAA) Regulations: In the United States, the FAA enforces noise standards for aircraft operations, including restrictions on flight paths and times. These regulations drive the aviation industry to prioritize noise reduction in new aircraft designs and retrofit existing fleets with quieter technologies. Through a combination of advanced engine designs, aerodynamic optimizations, active noise control systems, and strict regulatory frameworks, the aerospace industry is making significant strides toward quieter skies.
[199] Development and progress in aeroacoustic noise reduction on turbofan ... — To reduce noise generated from turbofan engines-powered aircraft, a number of control approaches have been developed. Because they are considered the most reliable and effective noise reduction methods, the geometric shape optimization and passive control are preferable by the engine manufacturers. The research and development progress made on the active control, passive control, and geometric shape optimization are reviewed and discussed, aiming to provide an useful guidance on next-generation low-noise turbofan engines. To attenuate these noises in engineering applications, noise reduction approaches such as i) active control, ii) geometric shape optimization, and iii) passive control (including acoustic boundary control) have been suggested . Moreover, the geometric shape optimization and the passive control are preferable by the engine manufacturers since they are considered the most reliable and effective noise reduction methods .
[200] PDF — • Increasing the available portfolio of noise reduction technology would stimulate all insertion paths: o Justifies the setting of lower regulatory noise levels o More likely to be proactively implemented by industry o More possibilities for retrofitting • Emphasize: o Healthy discovery portfolio o Focused development: Feasibility
[201] Aircraft Noise - Federal Aviation Administration — Aircraft and airport noise programs Aircraft and airport noise programs The Federal Aviation Administration (FAA) has developed a variety of programs aimed at increasing the understanding of noise impacts, identifying solutions to reduce those impacts, and educating the public on the issues and our ongoing efforts. The FAA works with the aviation community to control aircraft noise. The FAA established the Continuous Lower Energy, Emissions, and Noise (CLEEN) program to develop certifiable aircraft technology that reduces noise levels by 32 decibels (dB) cumulative, relative to the noise standards set by the International Civil Aviation Organization. For questions about FAA noise abatement studies and sound insulation programs, please contact the appropriate FAA Regional Offices for more information. On a scale of 1-5, how would you rate your confidence in using FAA.gov as your main source of U.S. aviation information?
[208] Enhancing Global Standards Through International Regulatory Cooperation — International Regulatory Cooperation refers to the collaborative efforts among countries to harmonize regulations and standards across various sectors. This cooperation is pivotal in addressing transnational challenges, such as climate change and public health crises, which require coordinated responses for effective solutions.
[209] Understanding Global Residential Noise Regulations — Noise Regulations in Different Countries. Rules about noise are based on how people live, how cities are built, and the specific noise problems in each place. Some countries limit acceptable decibel levels in residential areas, while others have quiet hours or use thoughtful planning to reduce noise.
[210] Barriers and Challenges for Global Regulatory Harmonization — Talking about global harmonization implies that all regulatory agencies agree upon developing, implementing, and adopting the same guidelines and technical standards focused on quality, safety, and efficacy, that would be eventually applied by each Regulatory Agencies on the respective countries. There are several global initiatives intended to drive harmonization and development, such as: Asian-Pacific Economic Cooperation (APEC), International Council for Harmonization (ICH), The International Pharmaceutical Regulators Programme (IPRP), Pan American Network for Drug Regulatory Harmonization (PANDRH). Regional regulation – Each country possesses its regulatory framework and sometimes it is not updated according to the international guidelines because global harmonization is not contemplated by the political agenda of Presidents, Congresses, Senators, and Prime Ministers. E-Submissions ### Post-event Report: Global Pharmaceutical Regulatory Affairs Summit 2020 Read More east
[229] Course "Experimental techniques for aeroacoustics" — Experimental techniques for aeroacoustics The course deals with the preparation of experimental setups meant for the study of full scaled models. By starting with the approach to address a usually difficult problem, the course will then continue presenting the salient aspects of measurement techniques for velocity and pressure quantification.
[239] Recent Advances in Aeroacoustics - MDPI — The use of various forms of the Navier-Stokes (NS) equations in CFD (Computational Fluid Dynamics) can be coupled to the identification of the sources of sound in CAA (Computational Aeroacoustics). A good example of CFD/CAA applied to the NS equations is noise generation by a vortex ring.
[240] Computational Aeroacoustics - an overview - ScienceDirect — The novel design of the airline and the turning vanes as well as the low noise fan stator was developed by DNW in close cooperation with the DLR and was the result of extensive use of high fidelity CFD tools, incorporating new optimization methods for acoustic lay-out. In a study of a possible active control technology , a coupled aerodynamic and aeroacoustic analysis using the DLR numerical methods TAU and APSIM was performed to assess the potential of pylon trailing edge blowing to achieve a reduction of unsteady blade and rotor loadings and corresponding noise emissions caused by the installation of the powerplant on the aircraft.
[241] Full article: Concise review: aerodynamic noise prediction methods and ... — On the other hand, computational aeroacoustics (CAA) deals with the use of application of numerical methods to analyse flow-induced noise more accurately. The problems posed on the accurate prediction of aerodynamic noise are the important issues such as turbulent intensity and length scale disparity.
[247] PDF — This is the aim of computational aero acoustic (CAA). Hence, the field of CAA may be defined to be the domain between computational fluid dynamics (CFD) and classical acoustics. This is an active topic of research embossed by many industrial applications.
[248] Computational Aeroacoustics: An Overview of Computational Challenges ... — Abstract The objective of this paper is to present an overview of recent advances in computational aeroacoustics (CAA). During the last decade, CAA has developed quite independent of computational fluid dynamics (CFD). There are computational issues that are unique to CAA and are, generally, not considered in CFD. In this paper, these issues are discussed and explained. In CAA, there is a
[249] Recent advances in computational aeroacoustics - ScienceDirect — They include the development of high resolution CAA methods, artificial selective damping and high quality numerical boundary conditions. Wave number analysis not only can yield an absolute error incurred in the use of a discretized computational method but also offers a way to develop optimized computation schemes. Before discussing how to solve aeroacoustics problems numerically or simulate them computationally, an approach generally referred to as computational aeroacoustics (CAA), it is important to recognize and to have a good understanding of these differences. CAA methods must be designed to deal with problems with greatly different length scales in different parts of the computational domain. To be able to compute or simulate aeroacoustics problems accurately and efficiently, standard CFD schemes, designed for applications to fluid problems, are generally not adequate.
[250] High-performance aerodynamic computations for aerospace applications ... — A recent study outlining a NASA vision for computational fluid dynamics (CFD) development emphasizes the importance of high-performance computing (HPC) in increasing the impact of CFD on design and certification of aerospace vehicles.
[261] Advances in aeroacoustics research: recent developments and ... — Different mathematical approaches to jet noise modelling include the generalized acoustic analogy that takes into account mean flow propagation and source anisotropy effects within a single unified description of broadband turbulence. Motivated by jet flow physics, the two-source model proposes empirical fine-scale and large-scale spectra to account for the contributions of fine-scale turbulence and large-scale coherent structures to far-field noise, respectively. An extensive survey of different contributions in the area of high-fidelity jet flow and noise modelling based on LES is given by Brés & Lele . The review discusses a broad range of common issues pertinent to jet noise applications—from boundary conditions, grid generation and high-performance computing, through turbulence modelling, to details of the far-field noise prediction schemes and the flow solution analysis based on the LES data.
[262] Anisotropic source modelling for turbulent jet noise prediction — 2. Formulation. The modelling starts from Goldstein's generalized acoustic analogy , the Navier-Stokes equations are rearranged into Linearized Euler Equations for the propagating quantities, with nonlinear terms representing the analogous acoustic sources.This formulation provides a consistent framework in which the convection effects on acoustic sources and the refraction effects on
[263] Generalized Acoustic Analogy Modeling of Hot Jet Noise — A generalized acoustic analogy model is implemented for the hot and cold static high-speed jet cases corresponding to conditions of the Strategic Investment in Low-carbon Engine Technology (SILOET) experiment performed by QinetiQ. The model is statistical and based on the covariance of fluctuating Reynolds stresses and enthalpy source terms in accordance with Goldstein's theory. These
[266] Basic principles of aerodynamic noise generation — Topics treated include radiation from compact and non-compact multipole sources, Lighthill's theory of sound emission from free turbulence, effects of source convection, sound generation from flow interaction with solid surfaces and inhomogeneities of the medium, and singular perturbation aspects of the aerodynamic sound problem.
[277] Aeroacoustics - an overview | ScienceDirect Topics — The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. The role of the Confederation of European Aerospace Societies Aeroacoustics Specialists Committee (CEAS-ASC) is to serve and support the scientific and industrial aeroacoustics community in Europe. This is a report on some highlights of aeroacoustics research in Europe in 2003, compiled from information provided to the Aeroacoustics Specialists Committee of the Confederation of European Aerospace Societies (CEAS). The role of the Aeroacoustics Specialists’ Committee (ASC) of the Confederation of European Aerospace Societies (CEAS) is to promote and encourage activities on aeroacoustics in the industrial and research communities in Europe.
[278] Interdisciplinary collaboration in engineering education — Interdisciplinary collaboration in engineering education Anette Kolmos, Jette Egelund Holgaard, and Henrik Worm Routhe from Aalborg University discuss findings from the InterPBL research project and highlight the advantages of interdisciplinary collaboration in engineering education InterPBL, a research project at Aalborg University funded by the Grundfos Foundation, seeks to improve interdisciplinary collaboration in engineering education. Understanding and Designing Variation in Interdisciplinary Problem-Based Projects in Engineering Education. Interdisciplinary project types in engineering education. Experienced Learning Outcomes for Interdisciplinary Projects in Engineering Education. https://vbn.aau.dk/da/projects/interdisciplinary-pbl-methodologies-in-engineering-education-and- Open Access Government produces compelling and informative news, publications, eBooks, and academic research articles for the public and private sector looking at health, diseases & conditions, workplace, research & innovation, digital transformation, government policy, environment, agriculture, energy, transport and more.
[280] Strengthening the Bridge Between Academic and the Industry Through the ... — Strengthening the Bridge Between Academic and the Industry Through the Academia-Industry Collaboration Plan Design Model - PMC Planning a collaboration process is imperative; defining a time constraint for long-term and short-term relationships between academia and the industry will eventually aid in understanding the nature of projects that both researchers and practitioners pursue. Academia-Industry Collaboration Plan’s New Approach in Connection With the Triple Helix Model The framework activities for the test set of communications extending the relationship between academia and the industry for collaborative work in the field of research and implementation of that research would be as follows: Academia Industry Collaboration Engineering Process Model Research and development through innovation and creative thinking will provide market solutions and new technological improvements that interest both industry and academia.
[281] PDF — Academia-Industry collaboration is the key step towards the growth and development of economy. The academia is a store house of knowledge and innovation whereas the industry is a sector to convert the knowledge and technique into innovative product. The conversion of research and innovation through universities or research institutions to the
[284] NASA grant funds aeroacoustic research to develop quieter vertical lift ... — NASA has awarded $5.7 million to a multi-university partnership as part of the agency's University Leadership Initiative. The project, led by Boston University over the next three years, will bring together researchers and engineers from Virginia Tech, Embry-Riddle University, Tuskegee University, and industry partner Joby Aviation to focus on developing quieter vertical lift air vehicles.
[288] Federal Programs Advancing Sustainable Commercial Aircraft and Engine ... — These government partnerships and federal cost sharing make it possible for corporate participation in development projects that have both significant technological risk and the potential for large improvements in fuel efficiency, reduced particulate and nitrogen oxide emissions, and noise reduction.
[289] Graduate Program in Acoustics | Penn State Engineering — Penn State's Graduate Program in Acoustics. ... underwater acoustics, signal processing, aeroacoustics, structural vibration, speech and communication, outdoor propagation, computational methods, and much more. ... The Distance Education Program was created in 1987 to give full-time working professionals the opportunity to earn a Master of
[290] Which colleges are the top ones for aerospace engineering? — The university is also near Silicon Valley, providing abundant internship and job opportunities. 4. Georgia Tech: Georgia Tech's Daniel Guggenheim School of Aerospace Engineering is one of the oldest and largest educational programs of its kind in the country. Students here get hands-on experience in labs and can participate in design
[291] AARC | Ohio Aerospace Institute℠ — The AeroAcoustics Research Consortium (AARC) was established in 2001 by NASA Glenn Research Center and Industry partners with the goal of advancing the development of technologies for reducing the environmental impact of noise produced by commercial aircraft. The AARC provides a collaborative environment for NASA and its Industry partners to engage with international researchers in aeroacoustics to work toward the elimination of technical barriers in the development of noise-reduction technologies, at a pre-competitive stage, for their mutual benefit. Projects funded by the AeroAcoustics Research Consortium are selected based on technical proposals submitted by international researchers from academia, industry and government agencies. Research participants are expected to engage in significant interactions with NASA and industry Consortium members during their funding period.
[292] Reducing Aviation Noise, Advancing the Aviation Enterprise — More recently, the geared turbofan—developed by industry in collaboration with NASA—is poised to significantly reduce fuel burn and noise. Tomorrow's Technology, Today's Noise Reduction Strategies . Technology investment is critical to reducing aviation noise, but it can take years for new designs to significantly extend across the
[294] NTRS - NASA Technical Reports Server — Aircraft noise is currently regulated at a national level and typically involves partnerships with the industry to establish regulations. Regulators realize that current policies and procedures may not be appropriate for some of the emerging air vehicles and new procedures may be needed to address UAM noise.
[295] PDF — NASA, in partnership with the aircraft and engine manufacturing industry, has contributed to a number of advancements in aircraft engine and airframe technology that have substantially reduced the amount of noise produced by aircraft and may lead to further reductions, depending on the extent to which current research leads to noise-reducing