An investigation into vortex growth and stabilization for two-dimensional plunging and flapping plates with varying sweep

A simple analytical model for leading-edge vortex (LEV) growth is proposed and tested, based on the transport of vorticity-containing mass through the shear-layer. The two-dimensional case is validated using time-resolved Particle Image Velocimetry. As a precursor to developing a model for finite wings, the effect of varying spanwise flow on a nominally two-dimensional profile is investigated by imposing plunging and flapping motions on high aspect-ratio flat-plate profiles of sweep angles Λ=+45°,−45°Λ=+45°,−45° and 0°. By varying sweep angle, both coinciding and opposing gradients of spanwise vorticity stretching and convection were tested. It was shown that nominally two-dimensional spanwise flow has no effect on vortex strength and thus force history for plunging kinematics. However, force histories for flapping kinematics were dependent on sweep angle suggesting that spanwise flow regulates vortex strength when coupled with gradients in effective incidence.