BOUNDARY-LAYER CONTROL OF SEPARATED FLOW OVER CIRCULAR-CYLINDERS - A BEM PARAMETRIC STUDY

A numerical procedure based on the boundary element method (BEM) for solving the time-dependent, incompressible Navier-Stokes equation is developed and presented. The BEM technique allows separate treatment of the kinematics and kinetics as well as offering other additional advantages over the prevailing FDM and FEM techniques. The developed algorithm is used to conduct a parametric study for the boundary layer control of subcritical flow over a circular cylinder. Different boundary layer control systems (such as pure suction, combined suction and blowing, periodic suction, etc.) have been computed to predict the favorable boundary layer control systems for subcritical flow regimes. Standard benchmark problems, including impulsively started unsteady flows over a circular cylinder for several values of Reynolds number, are solved to demonstrate the robustness of the scheme and to evaluate the accuracy of the developed algorithm. The reduction in drag due to either constant or periodic boundary layer suction and blowing is generally shown to be substantial, but depends on the control system used and the values of the control parameters. The variation of the drag with these control parameters is presented in various figures. The sine function distribution of equal blowing and suction at the surface and with a suction discharge coefficient equal to 0.15 was found to be the most economical boundary layer control system in the present parametric study.