Numerical Simulation of Broadband Noise from Airfoil-Wake Interaction

Abstract

LES of airfoil interaction with a turbulent wake is performed in a rod-airfoil configuration to investigate the generation of broadband as well as tonal noise. A NACA 0012 airfoil at zero angle of attack is located one chord length C behind a cylindrical rod of diameter 0.1C. The chord Reynolds number is 480, 000 and free-stream Mach number is 0.2. The LES flow results, including velocity statistics and energy spectra at various locations, are compared with experimental data and show reasonable agreement. Acoustic radiation is computed using Lighthill’s equation solved by a boundary-element method. The results show good agreement with experimental far-field measurements in terms of spectral peaks as well as broadband contents. Acoustic source mechanisms are investigated and the relative importance of various source regions compared. It is found that although the airfoil generally dominates the rod in sound generation, the relative strength is highly directional and frequency dependent. Trailing-edge noise is weak relative to leading-edge noise at low frequencies but it becomes a major contributor to the total noise at higher frequencies. Turbulent flow over the hull of marine vehicles and their control surfaces interacts with the rotating blades of a downstream propeller and generates sound. The strength and characteristics of the interaction sound are strongly dependent on the incoming turbulence, which is highly inhomogeneous and complex. The sound radiated from this type of interaction consists of two components: a tonal component associated with periodic blade passage and broadband sound due to blade interaction with a broad range of turbulence scales. The classical gust response theory based on inviscid flow and empirical correlations for homogeneous and isotropic turbulence is deficient for predicting such complex interactions. High-fiedality numerical simulations such as large-eddy simulation (LES) are needed to accurately characterize the incoming turbulent flow and its interaction with a lifting surface.