Experimental and numerical investigation of flow structure of grooved cylinder

Making modifications to a cylinder is one of the most effective ways to change the flow in the cylinder wake region. This study aimed to investigate experimentally and numerically the flow structure of the wake region of a smooth cylinder and rectangular grooved cylinders (roughness coefficients are epsilon/D = 0.02, 0.04, and 0.06, epsilon is the roughness height, and D is the diameter of the cylinder) by using the Particle Image Velocimetry (PIV) and the Computational Fluid Dynamics (CFD). Numerical studies were conducted with the Reynolds-averaged Navier-Stokes (RANS) equations. The experimental studies were performed at Re = 5000 in an open water channel, while the numerical studies were performed at Reynolds numbers in the range of 5000 <= Re <= 20000. A good agreement was observed between the experimental and the numerical results in terms of the time-averaged patterns, time-averaged velocity profiles, and Strouhal numbers. The saddle points of the rectangular grooved cylinders were closer to the surface compared to those of the smooth cylinder. The results revealed that the time -averaged drag coefficient reduced by 30% for the largest groove roughness (epsilon/D = 0.06) at Re = 20000. In conclusion, the present study shows that rectangular grooved cylinders are effective in reducing the time -averaged drag coefficient.