Powerflow simulations of helicopters in blade-vortex interaction conditions

Abstract

The scope of this paper is to assess the accuracy of the Lattice-Boltzmann/Very Large Eddy Simulation Method to predict the aerodynamics and aeroacoustics of helicopter rotors in strong Blade-Vortex Interaction conditions, and to validate a computational approach to include the effects associated to the rotor blade deflections into the numerical setup. The numerical flow solution is obtained by solving the explicit, transient and compressible Lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOWR . The acoustic far-field is computed by using the Ffwocs-Williams & Hawkings integral solution applied to a permeable surface encompassing the whole helicopter geometry. The employed benchmark configuration is the 40% geometrically and aeroelastically scaled model of a BO-105 4-bladed main rotor tested in the open-jet anechoic test section of the German-Dutch wind tunnel in the framework of the HART-II project. In the present study, only the baseline operating condition of the HART-II test, without Higher-Harmonic Control enabled, is considered. Simulations are performed either assuming a fully-rigid blade motion or a computational strategy, based on a combination of a velocity wall boundary condition applied on the blade surface and fluid body-forces fields applied in proximity of the blade leading- and trailing-edge, to partially retrieve the effects related to the experimental blade flap and torsion deformations, respectively. The impact due to the inclusion of the blade elastic deformations into the computational setup on control settings, unsteady air-loads and noise footprint predictions is outlined.