On leading-edge vortex attachment in rotary systems: Incident flow effects

The mechanism governing the stable attachment of the leading-edge vortex (LEV) in rotating systems has been believed to be rooting in a balance between the rate vorticity production from the leading-edge shear layer and the convection of vorticity-bearing mass from within the LEV to the surrounding flow field. In such a relation, the accumulation of vorticity within a vortical structure is regulated by convective influences effectively draining the structure of circulatory strength. This work numerically investigates the shear rate-convection balance assertion in low-aspect ratio rectangular flat plates undergoing unidirectional rotation in a steady freestream. The freestream is oriented parallel to the rotational axis and the effect of advance ratio on the resulting flow structures is compared with a rotary plate operating in a quiescent fluid. Depending on advance ratio, the incidence angle of the plate is adjusted to maintain a constant effective attack angle of $\alpha=45^\circ$ based on plate tip speeds. Of interest is the response of the system over a Reynolds number range $Re=\left[ 10^2:10^3\right]$ where axial flow prominence shifts from aft of the leading-edge vortex to within the structure.