Noise Generated by a Leading Edge in Anisotropic Turbulence

Turbulence interaction noise is a main aeroacoustic noise source mechanism. It often dominates the noise generation, as for example in rotor-stator configurations of fans and air condition units. Besides numerical models, there exist a number of analytical models for the prediction of this type of noise. Most of these models are based on the assumption of an ideally homogeneous and isotropic turbulence. In a practical situation, however, this assumption may not be justified. For example, when measurements are performed in a wind tunnel where perforated plates or meshes are used to generate a turbulent flow, the resulting turbulence may be inhomogeneous and anisotropic. This is especially true in close proximity to the grids.The aim of the paper is to compare the noise generated at flat plates and airfoils both in inhomogeneous, anisotropic turbulence as well as in homogeneous, isotropic turbulence. To this end, detailed hot-wire measurements were performed in an aeroacoustic open jet wind tunnel in order to characterize the grid-generated turbulence. The resulting turbulence parameters were then used as input for a simple noise prediction model. Finally, the predicted noise was compared to the results from acoustic measurements performed with a microphone array.