Reduction of aeroacoustic noise in turbomachinery by geometrically modified blades

The goal of our project is the reduction of flow noise from fans and ventilators using geometrically modified blades. For this purpose, conventional ventilator blades are altered in two different ways - the first blade by a serrated trailing edge and the second by a wavy leading edge. In this study we will perform and compare numerical simulations using the Navier-Stokes solver OpenFOAM and complementary experimental investigations. Highly-resolved large-eddy simulations (LES) employing the wall adapting local eddy-viscosity (WALE) model are carried out to accurately capture the turbulent flow structures and the aero-acoustic source terms. As a first step, purely aerodynamic simulations of the flow around the unmodified blade and the modified blades are performed. The results of the simulations are compared to experimental data obtained by a particle image velocimetry (PIV) technique. Here, the focus is on the impact of the geometrical modifications on the specific work of the blade. In the next step, the location and the strength of the acoustic sources are investigated in detail with the simple Proudman model. The aim is the analysis of the basic mechanisms of sound generation by the various blade types. In the following simulations we will investigate the far-field sound propagation using Curle’s analogy. The application of this analogy is valid since the Mach number of the flow is comparably small and, therefore, the dominant sound sources can be considered as dipoles. In the oral presentation at the workshop we will present the first results of the numerical and experimental investigations obtained in this project to the community.