A Mach 4 wind tunnel for plasma / boundary layer interaction studies

The focus of this study is to present preliminary results of a plasma/boundary layer interaction investigation and determine if significant fluid dynamic interactions and mechanisms are present. The aim is to provide experimental results that will afford a greater fundamental understanding of the primary fluid dynamic mechanisms. Three types of plasmas / plasma actuators were evaluated for their prospective influences: a capactively-coupled radio frequency discharge that pulses at a frequency of 13.56 MHz, a pulsed plasma from an arc discharge, and a laser-induced optical breakdown. In addition to the type of plasma, the effectiveness of plasmas with varying discharge times was explored in this study. The potential of each actuator and its effect on the Mach 4 supersonic boundary layer are evaluated through emission photography, Schlieren imaging, and high-frequency pressure measurements at 40 mm (1.57″) and 60 mm (2.36″) downstream of the discharge. The array of measurement techniques is not only valuable to quantify characteristics of the flow field altered by the plasma, such as downstream pressure distribution and the presence of vortical structures in the boundary layer, but could also be useful in providing valuable quantitative information for comparison with future computational modeling efforts.