DYNAMICS OF WAKE BEHIND A LOW ASPECT RATIO PITCHING PLATE

Vectorized numerical simulations of unsteady wake behind a low-aspect ratio (double amplitude to span ratio 0.3) sinusoidally pitching plate (Strouhal number 0.4 and 0.5) are carried out for the Reynolds number, Re = 150,300. A non-staggered finite volume based predictor-corrector type of algorithm employing 2nd-order time integration and spatial schemes is used. The first sign of instability appears on the plate promoting separation which becomes more vigorous with the increase in Reynolds number. At low Reynolds number, the separation bubble originating near the plate diffuses in the near wake region and the whole wake oscillates with the plate. Fully developed vortex shedding from the rear edge of the plate is observed at a higher Reynolds number. The shed vortices are slowly convected and eventually diffuses completely at a large downstream distance. At a higher forced frequency the wake does not alter significantly at a lower Reynolds number. However, vigorous vortex shedding leading to two layers of vortex streets from both the sides of the plate is observed at a higher Reynolds number.