The efficient use of CFD in Rotorcraft Optimization

Computational Fluid Dynamics enables the accurate prediction of the flow about complete rotorcraft configurations. However, depending on the complexity of test case under consideration the execution time of a single CFD computation may be prohibitive. Therefore, efficient optimization strategies are required. Two examples of recent optimizations by DLR are reported: A first example is given by the optimization of a helicopter fuselage to minimize drag. The adjoint equations are solved to efficiently compute the design sensitivities for up to 200 design variables and to find the optimum with a gradient based optimizer. A second example is given by the multi-objective optimization of a helicopter rotor blade using ten design variables. The Pareto-front for the goal functions hover and forward flight performance is predicted by surrogate based optimization. A variable-fidelity approach combining low- and high fidelity predictions is employed to reduce the number of required high-fidelity samples.