LINEAR-STABILITY ANALYSIS OF THE NEAR WAKE OF A FLAT-PLATE

Depending on the structure of the surface roughness, the supersonic wake of a flat plate is either turbulent or contains large vortical structures. The time-averaged velocity profiles of two different turbulent and one vortical wake are measured. Applying the concept of locally absolute and locally convective instability to the measured profiles the differences in the stability characteristics of a turbulent and a vortical wake is turned out. From these results a resonator model for vortex generation in the wake is proposed. The global instability criterion by Chomaz et al. [12], is experimentally verified and extended to a new necessary and sufficient criterion. The influence of Mach number, momentum thickness of the near wake, and plate thickness on the stability characteristics and the vortex shedding frequency are discussed and qualitatively compared with experimental results.