Assessment of refinement techniques in aeroacoustic numerical simulations for helicopter rotors

Abstract

Blade vortex interaction (BVI) noise is a major source of noise radiated by helicopter rotor in descent flight. The prediction of BVI noise requires that numerical simulation code can capture and follow small concentrated vortex structures in the midst of large extent of three dimensional time dependent wake structure. The highest possible resolution regarding loads and wake characteristics are expected to capture the tip vortex structure. In order to provide evidence and obtain guideline for high resolution simulations, the isolated main rotor calculation is carried out by partner DLR and NTUA in accordance with HeliNovi work description Task 1.1. The issue of scale refinement in BVI simulations for helicopter configurations is addressed in the NTUA GENUVP code [based on the vortex blob method and DLR UPM-Mantic code based on 3D free wake panel method. Since the highest possible scale refinement will result in severe penalty on computational cost, some numerical techniques are applied in both NTUA GENUVP code and DLR UPM code in order to speed-up the aerodynamic computation without sacrificing general accuracy. Results are presented for the BO105 rotor in descent flight, for four time steps down to 0.5 deg of azimuth angle increment and two panel grids. Aerodynamic and aeroacoustic properties are provided and discussed. The further improvement of BVI simulation by using tip vortex roll-up model is also addressed.