TURBULENT FLOW ACROSS A ROTATING CYLINDER WITH SURFACE ROUGHNESS

The purpose of this study was to investigate the influence of surface roughness on turbulent flow across a rotating cylinder. Although smooth rotating cylinders have been extensively investigated, the influence of surface roughness on flow across rotating cylinders has not been reported yet. The parameters for the analysis were chosen such that the Reynolds number is sufficiently large in order to avoid vortex shedding behind the cylinder, while still sufficiently low to maintain the assumption of incompressible flow. Three different Reynolds numbers (5x10 5 , 10 6 and 5x10 6 ) and rotation rates ( � = 1, 2 and 3) were investigated using four different surface roughnesses (�/D = 0, 0.0011, 0.0045 and 0.009) and a validated CFD model. The drag coefficients decreased with increasing Reynolds number due to the turbulent boundary layer that moves the separation bubble further to the rear of the body. Increasing surface roughness increased the drag coefficient, but this increase became less as the Reynolds number increased. The lift coefficient increased with increasing Reynolds number, surface roughness and rotation rate. The investigated Reynolds number range is very desirable since the drag decreased while the lift increased. Furthermore, the aerodynamic efficiency revealed that the most aerodynamic efficient case occurs at a combination of the largest surface roughness, Reynolds number and rotation rate.