Simultaneous Computation of Surface and Volume Sources for Fan Broadband Noise with the Random-Particle-Mesh Method

Abstract

The relative contribution of broadband noise has steadily increased over the last decades
\nas the mechanisms creating tones are now well understood and can be efficiently reduced.
\nFor fan-design capabilities an interim or intermediate solution is needed between restrictive
\nanalytical models and full-resolved costly simulations.
\nEwert et al.1 proposed an affordable way to simulate broadband noise with a CAA solver
\nin the time domain while accounting for the complex geometry and background flow. The
\nRandom-Particle-Mesh (RPM) method reconstructs the turbulent fluctuations based on a
\nRANS calculation. Turbulence source is coupled to the Acoustic Perturbation Equations
\nsolved by a CAA solver. The approach was applied sucessfully for slat noise and generic
\ntrailing-edge noise problems.
\nOur investigations showed that this coupling method does not work sufficiently for lead-
\ning edge noise of generic airfoil configurations if the vortex sound sources are determined
\nfrom an incident vorticity field that does not include the additional effect of scattered
\nvorticity shed from the trailing edge of the airfoil due to the presence of a Kutta condition.
\nThe objective of this article is to extend and validate the coupling between the RPM
\nand the CAA domain to explicitly include the enforcement of the Kutta condition into
\nthe CAA model for homogeneous and potential flow. This is achieved by adding another
\ndomain which computes the vorticity–wall interaction.
\nTheoretically the approach should be sufficient to separate the surface from the volu-
\nmetric sources. This works very well for a flat plate. But we apply this on a NACA0012
\nairfoil in potential flow which gives unreasonable results. We discuss the issue and offer
\nideas for this cause.