Measurements of Vortex Stretching on Two-Dimensional Rotating Plates with Varying Sweep

The vortex growth around plunging and flapping profiles of varying sweep angle was studied with three-dimensional particle tracking velocimetry and direct-force measurements. For plunging kinematics all sweep angles tested resulted in the same force coefficient history and circulation history. Therefore, it was concluded that nominally two-dimensional spanwise flow has no effect on vortex growth or force history. However, when flapping kinematics were introduced, vortex growth was reduced due to vorticity convection. Vorticity convection for flapping cases could be modulated with the nominally two-dimensional spanwise flow. Reduced circulation for rotating cases corresponded to reduced force coefficient histories. No relationship between vortex stretching and vortex strength was observed at the Rossby number considered in this study. Through an analysis of the vorticity transport equation it was concluded that spanwise flow must be accompanied by gradients in vorticity magnitude in order to limit vortex growth