CFD simulation of helicopter rotor in the Vortex Ring State regime

The Vortex Ring State studies have received recently a renewal of interest because of the definition of steeper approach trajectories for city landing that lead to flying condition closer to VRS boundaries. In past years, numerical aspects with empirical methods or analytical models have been studied and experiments have been made in order to better understand the physics of the phenomenon. In this study, the elsA CFD solver was used in order to solve the Euler equations. A sweep in vertical descent speed was performed with different grids with an aim to evaluate the capability of the solver to capture the Vortex Ring State. Firstly, we evaluate the accuracy of the flow field representation with one quarter rotor and a complete rotor configurations. Then, unsteady phenomena and non periodicity related in published works on VRS are studied with time-consistent simulations. Furthermore, we analyze the grid resolution on the representation of the global aspect of the VRS. Finally, the modelisation of the blade root vortex and its effect on CFD simulations of the VRS phenomenon is performed.