Stability Analysis of Forced and Unforced Flow Fields around a Cylinder in Crossflow

This study deals with a theoretical analysis, based on flow stability theory, of a canonical flow control problem to delay separation. The system involves a cylinder in crossflow, with flow control that is carried out by means of wall-jets, placed on the surface adjacent to the location of separation. Much of the knowledge about this problem was obtained by examining two-dimensional slot-blowing; however, recent findings demonstrate the potential to utilize an array of three-dimensional wall-jets. Wall-jets on convex surfaces are prone to Görtler instabilities, since the velocity in the outer region decreases away from the wall. The ability to employ the Görtler instabilities to delay separation is assessed. The stability analysis is conducted on measured velocity fields, by means of Particle Image Velocimetry (PIV), provided by our colleagues at the Georgia Institute of Technology. The theoretical approach includes the local Linear Stability Theory (LST) and Parabolized Stability Equations (PSE), where the latter considers the streamwise variation of the flow along the surface of the cylinder. The analysis reveals the dominant frequencies and spanwise wavenumbers of the perturbations, which is essential to inform flow control and guide future experiments.