Numerical investigations of the wake behind a confined flat plate

The two-dimensional flow around a confined flat plate is simulated with the spectral element code, Nek5000. Direct numerical simulations were carried out at low Reynolds numbers Re (between 10 <= Re <= 200) and various blockage ratios beta (between 0.1 <=beta <= 0.9) and compared with the confined two-dimensional circular cylinder flow previously reported by Sahin and Owens (2004). Four distinct flow regimes are observed for the flow over a confined flat plate. The first is a steady symmetric wake where the vortices are evenly distributed along the centerline of the channel. The second is an unsteady symmetric regime which upon time-averaging the instantaneous flow field, the wake profile is symmetric. The third is an asymmetric steady wake where the flow is steady but the vortices in the wake are skewed towards one of the channel walls. The first three have been reported for the confined flow over a circular cylinder. However, a fourth flow regime defined as unsteady asymmetric wake is found for a flat plate at beta = 0.8. This flow regime was not reported in prior studies on the confined flow over a confined cylinder. Analysis using linear stability analysis is also reported in this paper which confirms the trends reported in this paper. Effects of the confinement on the wake of a flat plate on the hydrodynamic forces such as the mean drag coefficient and Strouhal number have also been documented for the same range of Re and beta and compared with the flow over a confined cylinder.