Actuator disk for helicopter rotors in an unstructured flow solver

Motivated by the demand for a fast flow simulation tool that takes the interaction between a rotor and a helicopter fuselage into account, an actuator disk boundary condition suited for helicopter rotors in forward flight has been implemented in the unstructured grid DLR TAU code. The time-averaged effect of the rotor, which accelerates the flow and adds energy to the fluid, is imposed using source terms in the Navier-Stokes equations. The actuator disk is located in the grid. The transfer of this approach, previously implemented in the structured grid DLR FLOWer code, involved adapting the strategy to the unstructured framework. It is shown that propeller simulation results are in agreement with FLOWer results and simple one-dimensional theory predictions. Moreover, the rotor in forward flight cases prove the robustness of the implementation and resemble FLOWer results. Further development involved testing the implementation in parallel mode, and a more sophisticated rotor force distribution is applied instead of a constant pressure jump. Finally, a comparison of the viscous flow field around the EC145 helicopter computed by TAU and FLOWer is performed. It shows that there is good agreement between the two codes in predicting the effect of the actuator disk on the fuselage pressure distribution.