Towards Accurate Prediction of �Blade-Vortex-Interactions on Helicopter Rotors with Higher-Order Accurate Spatial Discretization Methods

Kurzfassung

In flow simulations of helicopter configurations the blade-vortex-interactions have a significant influence on the prediction of rotor blade loads and also on the trim state. To ensure accurate results, the vortex transport within the flow field has to be physically correct without a premature decay of vortical structures due to numerical dissipation. To realize a physically correct vortex transport in flow simulations with the unstructured DLR TAU code, very fine computational grids may be required to minimize the numerical dissipation, but this leads to an extensive computational effort. A more efficient simulation method for vortical flows is the fourth-order-accurate spatial discretization method implemented in the DLR-FLOWer code, commonly entitled as the FLOWer4 flow solver variant. This method implements a PADE scheme on structured rectilinear grid, so that grid generation for complex configurations may be difficult and costly. To overcome the disadvantages of these simulations methods, the TAU and the FLOWer4 code should be coupled for accurate rotor flow simulations by using an unstructured near-body grid associated to the TAU code and a Cartesian background grid associated to the FLOWer4 code. The transfer of the flow data at the coupling boundaries is realized by an external code coupling module. Additionally the trim state of the helicopter and the blade deformation has a significant impact on the rotor blade tip vortices, which should also be considered in this work, by a further coupling of the flow solution method to the comprehensive rotor code HOST. This code is coupled loosely to the flow solver, so that the rotor blade loads of a full revolution are used to calculate a new trim state and blade deformation data for the following rotor revolution, until a converged trim state is achieved. Within the DLR project DIGITAL-X both aspects of realistic rotor flow simulations are addressed by a coupled simulation approach allowing for accurate prediction of blade-vortex-interactions on helicopters.