Wake of forced flow around elliptical leading edge plates

Previous investigations have shown that flows around rectangular plates with transverse forcing involve interactions between vortices shed from the leading and trailing edges and vortex merging in the wakes. The Strouhal number of vortex shedding at which peak base drag occurs varies with chord-to-thickness ratio in a stepwise fashion, similar to the self-sustained oscillations at low Reynolds number for unforced flows. In the present study, the leading edge flow separation and vortex shedding is eliminated by using plates with elliptical leading edges, and the trailing edge flow is examined through particle image velocimetry. In particular, the response of the trailing-edge vortex shedding and the base pressure coefficient to applied transverse oscillations of different Strouhal number and amplitude is measured. Substantial variation in the base pressure coefficient is found, with peaks appearing at the natural shedding frequency and at a harmonic. The effect of the forcing on the wake dimension and the strength of the wake vortices is quantified using particle image velocimetry. Three-dimensional structures in addition to the two-dimensional Kármán vortices in the wake are also visualized.