PIV Investigation of Flow Structures Around Rotating Circular Cylinders with Dimpled Surfaces

Flow around rotating cylinders with dimples has been evaluated at a Reynolds number of Re = 2000. It has been determined since the rotational influence was more effective for lower Re values. Angular dimple distributions have been considered as 15° ≤ β ≤ 60°. Different rotation rates have also been evaluated from α = 0 to α = 1.26 as lower rotation rates for the current Re were significant to suppress the vortex shedding. Particle Image Velocimetry (PIV) results have been compared by those of a bare cylinder. The wake regions have been shrunk due to dimpled surfaces. Excluding the case of α = 0.42 for a bare cylinder (4.5%), the regions had tendency to approach the bodies. The highest displacement (-78.9%) to the cylinder has been attained for β = 15° with α = 1.26 as observed. The lowest value (-5.6%) has been obtained by α = 0.42 for β = 45° by approaching the cylinder. For the influence of passive flow control, the cases without rotation have been regarded and β = 60° was more dominant. For the wake lengths, the changes for F and S locations have also been exhibited in the wake regions as these points affecting the length of recirculation bubble were substantial. As interpreted from the vorticity results, peak values were more dominant in the cylinder wakes. Since the rotation rates were increased, these regions tended to shrink. It is related to the presence of fluctuations in the wake regions. The displacements of maximum turbulence kinetic energy values have been shown for the level of turbulence intensity. Turbulent intensity has been enhanced in the regions closer to the bodies except the stationary cases of β = 30° and β = 45°. Nevertheless, the forced rotation was more effective.