Onset Of Vortex Shedding From A Bluff Body Changing From Square Cylinder To Flat Plate

Calculations of unsteady 2D flow around bluff body have been carried out. The shape of bluff body is changing from square cylinder to flat plate. The time discretization was implicit and a second order upwind scheme was employed. The Strouhal number and drag coefficient variations with Reynolds number were documented for the two-dimensional region. Results indicated that, as the cylinder aspect ratio is smaller than 0.5, drag coefficient will increase with Reynolds number increases. On the opposite, if the cylinder ratio is larger than 0.5, drag coefficient decreases when Reynolds number increases. Interestingly, for the 0.5 aspect ratio case, when Reynolds number increases, drag coefficient decreases at the beginning and then increases at about Re = 70. A monotonic increase in St with increase in Reynolds number was observed. The critical Reynolds numbers for onset of vortex shedding were obtained by numerical simulation and curve fitting. It is found that, bluff body changing from square cylinder to flat plate, critical Reynolds number decreases. The relationships between Reynolds number and Strouhal number, as well as drag coefficient were obtained by curve fitting. The critical Strouhal number and critical drag coefficient were calculated by extrapolation. For the whole range of incidence angles, the onset of vortex shedding generated with a decrease in critical Reynolds number with increasing incidence angle. By using the Stuart-Landau equation, the onset of vortex shedding was investigated, for a solid blockage of 4%.