Aerodynamic interactions on Airbus Helicopters' compound helicopter RACER

Abstract

In this thesis, the mutual effects of main rotor, wings, and lateral rotors of Airbus Helicopters' compound helicopter RACER are addressed under different flight conditions. In order to isolate the interactional phenomena, trimmed high-fidelity computational fluid dynamics (CFD) simulations are not only conducted on a detailed representation of the full compound helicopter but also on reduced configurations which are created by removing the respective other components of interest. By comparing the aerodynamic performance of main rotor, wings, and lateral rotors for the different computations, mutual influences can consequently be determined, which are further divided into first- and second-order effects. With the help of a loose coupling between the comprehensive analysis (CA) tool HOST and the CFD solver FLOWer, realistically trimmed free-flight conditions are determined for the relevant flight states. The first of these is RACER's cruise flight at 220kts, which represents the operating condition the compound helicopter was specifically designed for. Due to the elevated advance ratio of over 0.5 and the resulting azimuthal variation of main rotor inflow, a strong asymmetry is witnessed in unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, where most of the interactional phenomena originating from or affecting the advancing side of the rotor disk are significantly stronger than on the retreating side. In order to account for the large regions of separated flow below the wings, RACER's hover as the second flight condition of interest is analysed by means of delayed detached-eddy simulations (DDES). It is not only that second-order effects generally play a more important role for this flight state, but that asymmetries in aerodynamic interactions are not linked to the main rotor and its thrust distribution but rather to the different operating conditions of the lateral rotors where the right-hand rotor generates reverse thrust to provide anti-torque.