Blade Tip-Vortices of a Four-Bladed Rotor with Axial Inflow

The vortex system of four rotating and pitching DSA-9A blades was examined numerically and experimentally. Numerical computations were performed using DLR's finite-volume solver TAU and were validated against experimental data gathered using particle image velocimetry (PIV) carried out at the rotor test facility in Gottingen (RTG). Algorithms deriving the vortex position, swirl velocity, circulation and core radius were implemented. Hover-like conditions with a fixed blade pitch were analyzed giving a good picture of the static vortex system. These results are used to understand the vortex development for the unsteady pitching conditions, which can be described as a super-positioning of static vortex states. The use of a zonal DES approach reduced numerical dissipation and improved physical modelling of the vortex development.