Chimera simulations of multibladed rotors in high-speed forward flight with weak fluid-structure-coupling

The state of the art of weak fluid-structure coupling for rotors in forward flight at DLR is presented. The coupling procedure is based on the DLR rotor simulation code S4 and the DLR Navier-Stokes solver for structured grids FLOWer. The method allows trimmed CFD solutions to be produced for rotors in high-speed forward flight with the inclusion of elastic blade deformations and viscous effects. The weak coupling procedure is applied to high-speed forward flight test cases of isolated rotors. 4-bladed rotors are simulated for two cases (7A and 7AD rotor) using the chimera approach. A variation of turbulence models from algebraic to 2-equation models did not show significant differences for these high-speed forward flight test cases with moderate rotor loading. The weak coupling, which includes the transfer of normal forces (cn), tangential forces (ct) and pitching moments (cm) from the CFD code to the rotor simulation code, considerably improved the overall agreement with the existing experimental data compared to the uncoupled computations. The performance difference between the 7A and the 7AD rotor in high-speed forward flight is well predicted.