Numerical study of a hydrodynamic instability excitation for bluff body wake control

Effects of spatially uniform and spanwise-discrete disturbances generated by steady suction on the surface of a cylinder are investigated. The wake flow was studied experimentally using flow visualization and hot-wire measurements, and numerically solving Navier-Stokes equations. The numerical and experimental results complement each other to overcome some of the limitations associated with each approach. The discrete perturbations cause the formation of streamwise vortices and suppression of the formation of spanwise vortices, which most probably results in the attenuation or elimination of vortex induced vibrations of the cylinder. It is shown that the suppression of the Kelvin Helmholtz instability is not due directly to suction but rather the formation of streamwise vortices. The formation and spatial evolution of streamwise vortices are discussed, and the phenomenon is linked to a hydrodynamic instability. The results obtained from numerical simulation are in good agreement with the experimental results, validating the reliability of using URANS to resolve the primary instabilities of the flow. Cylinders with different spanwise porosity are studied for the near and far wake characteristics. Also the critical suction coefficient and perturbation wavelengths above which the instability is excited are reported and compared to previous wake control techniques.