Flow around a circular cylinder placed in an incompressible uniform stream is investigated via two-dimensional numerical simulation in the present study. Some parts of the cylinder are replaced with moving surfaces, which can control the boundary layer growth. Then, the effects of the moving surfaces locations on the power and drag coefficients are studied at various surface speeds. The flow Reynolds number is varied from 60 to 180. To simulate the fluid flow, the unsteady Navier-Stokes equations are solved by a finite volume pressure-velocity coupling method with second-order accuracy in time and space which is called RK-SIMPLER. In order to validate the present written computer code, some results are compared with previous numerical data, and very good agreement is obtained. The results from this study show that some of these surfaces reduce the drag coefficients and the coefficient of the total power requirements of the system motion. The optimum location and the speed of the surfaces which cause the minimizing the power coefficient are also obtained; By observing the results it is found that in all Reynolds numbers, the minimum power coefficient or in other word, the optimum drag coefficient is occurred at surface angle of 70 deg.

Keywords: Circular cylinder, Moving surfaces, Boundary Layer, Power coefficient, Drag coefficient

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