Comparison of Higher-Order CFD Modelling with an unsteady Panel Method

Kurzfassung

One major difficulty in the design of quiet rotor blades is the correct numerical prediction of blade vortex interaction (BVI) noise in descent flight. Current second order spatial discretization schemes inherently have too much numerical dissipation to correctly conserve vorticity in the computational fluid dynamics (CFD) simulation. Higher order methods have proven their worthiness to alleviate this problem, yet are costly in terms of computational resources. In this paper, the 4th order implicit compact Pade scheme based on the finite differece formulation of the RANS equations is employed to convect the vortices in the simulation. The approach is paired with the classical finite volume approach with the Jameson-Schmidt-Turkel (JST) scheme. The robustness and flexibility of the JST scheme are exploited in the near field of the rotor blades and fuselage, while in the mid- and farfield the Pade scheme is utilized. This approach is validated against the experimental data of the HART II wind tunnel campaign. Opposing this higher order approach, a classical Panel method with a free wake model is investigated. It allows for the computation of results at similar quality of the higher order CFD scheme, however at a much reduced price. In this paper the effect of grid densities for all methods is analyzed along with the direct comparison of them for the resolution of BVI noise in descent flight of the HART II test case.