Investigation of a simplified aerodynamic modelling technique for noise predictions using FW–H propagation

Abstract

This paper addresses the influence of the elastic rotor blade deformation and the aerodynamic interference from the fuselage on the rotor aerodynamics, including rotor noise characteristics. A BO105 main rotor/fuselage configuration is chosen for the numerical simulations. An unsteady aerodynamic code based on free wake three-dimensional panel method (UPM) is used to account for nonlinear effects associated with the mutual interference between main rotor and fuselage. Airbus Helicopters’ (formerly: Eurocopter) rotor code (HOST) is coupled with this aerodynamic code (UPM) to account for the effect of elastic blade deformation. The effect of the fuselage is simulated using two fuselage models in aerodynamic code, (1) potential theory in the form of a panelized fuselage and (2) an analytic fuselage influence formulation derived from isolated fuselage simulation. The advantage of (2) is in its computational efficiency. The aerodynamic modelling is then coupled with an aero-acoustic post-processing tool based on the Ffowcs-Williams–Hawkings (FW–H) approach for evaluating the noise propagation to the far-field. This toolchain is then evaluated in different flight conditions to assess the usability of this approach in the design process. In descending flight, the acoustic prediction is completed at a very mature level, as the blade vortex interaction is well captured. In climb, the major noise peak is underpredicted, while the overall directivity agreement is well matched. In forward flight, due to a phase shift in the airloads prediction, parts of the loading noise directivity are not well captured. The onset of transonic effects further degrades the results obtained at the front of the rotor. For the investigated flight cases, the analytical fuselage formulation brought very similar results to the panelized fuselage model, therefore proving its worthiness for further accelerating the simulation in these flight conditions.