Numerical studies on small rotor configurations with validation using acoustic wind tunnel data

Abstract This paper addresses the acoustic and aerodynamic characteristics of small rotor configurations, including influence rotor–rotor interactions. For this purpose, a Rotor/Rotor/Pylon configuration is chosen for both test numerical simulations. The wind tunnel experiments on various were performed in DLR’s Acoustic Wind Tunnel Braunschweig (AWB). involve isolated rotors, rotors tandem coaxial hover forward flight. simulations, an unsteady free wake 3D panel method (UPM) used to account non-linear effects associated with mutual interference among configurations. effect pylon simulated using potential theory form panelized body. Finally, sound propagation into far field calculated FW–H code APSIM, UPM blade surface pressure as input. validation effort supported by CFD TAU steady simulations selected cases. results indicate that noise at passing frequency (BPF) its higher harmonics dominant source present selection. extra subharmonics between two BPFs appearing are caused geometric discrepancy blades well motor noise. Broadband also observed experiment, but contribution overall very can be neglected. simulation scattering from support system cases indicated about 1–3 dB polar microphones. In configuration, interferences particularly visible cause more complex directivity. There almost no change time-averaged inflow applying phase angles. condition, hover, delay does not maximum level. flight, level radiation. position downstream key radiation, therefore, avoiding interaction upstream reduce