Turbulence Characteristics in a Supersonic Cascade Wake Flow

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two–component Laser Doppler Anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 10⁶, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near–wake and the far–wake. The extremities of profiles of both the mean and turbulent wake properties were found to be strongly influenced by upstream shock–boundary–layer–interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23%, and the generally–accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock–boundary–layer–interactions has been superimposed.