Effects of Air Blowing on Turbulent Flow Over a Circular Cylinder

Abstract

This study analyzes the flow over a two-dimensional (2D) circular cylinder at a turbulent Reynolds number of 20,000 and its control by air blowing from several slots located on the surface of the cylinder, computationally. CFD simulations are performed by using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and Spalart-Allmaras turbulence model. Uncontrolled flow simulation results are validated using the experimental results available in literature for drag coefficient, Strouhal number, time-averaged pressure coefficient distribution on the circumference of the cylinder and mean velocity values at the downstream. Air blowing from several slots located on the cylinder is used as an actuator for forcing the flow. Blowing from four slots located on the circumference of the cylinder with a velocity magnitude of 50% of the free stream velocity yields a drag reduction of 23% compared to the uncontrolled case. Additionally, near wake region is further examined by application of Proper Orthogonal Decomposition (POD) technique. A Fast Fourier Transform (FFT) based spatial filtering procedure is employed in order to separate the effects of small-scale turbulent structures in the wake region. The FFT-filtered snapshot-based POD analysis shows that approximately 99% of the total energy of the flow can be represented by considering only the most energetic first two modes where the effects of von Karman vortex street can be seen appropriately both for uncontrolled and controlled flow cases.