Numerical Investigation of Secondary Vortex Structures in a Rotor Wake

This work uses high fidelity simulations to study the development of secondary vortices in a rotor wake. The focus is on investigating how temporal convergence affects the development of the secondary vortices, but the effect of off-body grid structure, rotation and resolution is also studied. The effect of sub-iteration convergence is investigated by performing a parametric study with the ring vortex problem. It is found that not only is the vortex breakdown minimized when all flow solvers are sufficiently converged, but the solution to the rotating and stationary torus is identical as well. A convergence and grid structure/resolution analysis is done on the geometry used in previous experiments. For relatively high flow solver sub-iteration convergence, the off-body grid structure and grid rotation has little effect on the development of the secondary vortex structures. Only small differences occur between the stationary and rotating torus due to the more dissipative rotating torus. However, at low solver sub-iteration convergence, larger differences occur between the torus and no torus grid structures. Since the secondary vortices are developed by the interaction of the vortex sheet with the primary vortex structure, when the sub-iteration convergence or grid resolution is not high enough, the vortex sheet and primary vortex is broken down and therefore, results in less secondary vortices.