Glow Discharge-Tracer Technique for Velocity Profile Measurement in Hypersonic Boundary Layer Flows

Spark-tracer technique using glow discharge is presented to measure velocity profiles across boundary layers around models in hypersonic flows. At first, a high voltage and high frequency discharge circuit and a discharge electrodes system used in the measurement are described. Next, to demonstrate the capability of the technique, the measurement of a velocity profile across a flat plate boundary layer is performed. The experimental result agrees well with the computational one based on the Navier-Stokes equations. Moreover, to clarify characteristics of the high frequency glow discharge generated in hypersonic flows, discharge gap voltage and current measurement is carried out and the follows are concluded. A positive column region is used as a tracer in the technique. Its characteristics are affected by retained ions in the column and also by the column length. Finally, from the fact that the experimental and numerical velocity profiles agree well, we may conclude that 1mJ of electric energy which is released in an impulsive discharge does not disturb the flow.