A panel free-wake code with boundary layer method for helicopter simulations

Abstract

UPM, DLR's unsteady panel and free-wake code for helicopter simulations, is being modernized and extended in order to provide a modern mid-fidelity tool suitable to support the industrial helicopter development process. Two major tasks in this process were the implementation of approximate boundary layer analysis methods and the calculation of unsteady pressures on arbitrary bodies. This paper shortly describes UPM and the newly implemented methods. Then, results of verification and validation calculations are presented, including isolated airfoil, wing, rotor and fuselage test cases. Finally, a complete helicopter configuration is simulated and compared to experimental wind tunnel results of the GOAHEAD campaign. The results show that the approximate boundary layer methods are able to identify flow separation regions and provide reasonable friction force estimates for a wide range of applications. Nevertheless, the limits of the methods become apparent in cases where viscous effects lead to strong nonlinear behavior. The complete helicopter simulation also shows a good agreement with experimental data in general. But here, too, individual flow regions reveal the limits of the underlying theory. If these limits are kept in mind, UPM can be a valuable tool and support the helicopter development process in many regards.