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J.-A. Faust, Y.S. Jung, J. Baeder, J. Rauleder
In recent years an asymmetric lift-offset compound helicopter model has been developed at the University of Maryland with the objective of improving the overall performance of a conventional medium-lift utility helicopter. The investigated form of lift-compounding incorporates an additional stubbed wing on the retreating fuselage side, which alleviates rotor lift requirements and generates a roll moment that enables increased rotor thrust potential on the advancing side in high-speed forward flight. In the current investigation a numerical model is developed based on the corresponding experimental test case, where three-dimensional unsteady Reynolds-averaged Navier-Stokes equations are solved on overset grids. The simulations employ a fifth-order WENO scheme for spatial reconstruction, second order dual time stepping, a Medida-Baeder boundary layer transition model and a hybrid SA-DDES turbulence model within the in-house CPU-GPU heterogeneous Mercury CFD framework. CSD-CFD coupling is realized using the comprehensive rotor aeromechanics analysis PRASADUM to model blade structural deflection and compute cyclic control angles to achieve rotorcraft trim. Good correlation between the numerical and the experimental models is found in terms of cyclic control angles, rotor thrust and torque predictions. Comparisons between blade structural flap, lag and torsion moments overall are in satisfactory agreement. CFD results show that for an advance ratio of 0.5 with a collective pitch of 10.6° , a vehicle lift-to-equivalent-drag ratio improvement of 47% is attainable using 10.4% wing-lift offset. The CFD-computed flow fields and PIV data provide insights into the multiple dynamic stall vortex formations entering the reverse flow region, and into the wing-rotor interactional aerodynamics.
Deutscher Luft- und Raumfahrtkongress 2020
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