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 as the mechanisms creating tones are now well understood and can be efficiently reduced. For fan-design capabilities an interim or intermediate solution is needed between restrictive analytical models and full-resolved costly simulations. Ewert et al.1 proposed an affordable way to simulate broadband noise with a CAA solver in the time domain while accounting for the complex geometry and background flow. The Random-Particle-Mesh (RPM) method reconstructs the turbulent fluctuations based on a RANS calculation. Turbulence source is coupled to the Acoustic Perturbation Equations solved by a CAA solver. The approach was applied sucessfully for slat noise and generic trailing-edge noise problems. Our investigations showed that this coupling method does not work sufficiently for lead- ing edge noise of generic airfoil configurations if the vortex sound sources are determined from an incident vorticity field that does not include the additional effect of scattered vorticity shed from the trailing edge of the airfoil due to the presence of a Kutta condition. The objective of this article is to extend and validate the coupling between the RPM and the CAA domain to explicitly include the enforcement of the Kutta condition into the CAA model for homogeneous and potential flow. This is achieved by adding another domain which computes the vorticity–wall interaction. Theoretically the approach should be sufficient to separate the surface from the volu- metric sources. This works very well for a flat plate. But we apply this on a NACA0012 airfoil in potential flow which gives unreasonable results. We discuss the issue and offer ideas for this cause.