Investigation of Supersonic Mixing Using Laser-Induced Breakdown Spectroscopy

Abstract

Supersonic mixing enhancement techniques are of considerable interest; typically qualitative observations of shear layer growth rate are used to compare these techniques. A more accurate assessment of the efficiency of various mixing techniques could be made using local species concentrations at specific points. Laser-induced breakdown spectroscopy (LIBS), which can determine local elemental concentrations in a flowfield, is applied to the supersonic mixing problem in this work.

An investigation of mixing caused by cavity-induced resonance was completed in a Mach 2 wind tunnel using LIBS. Calibration experiments showed that LIBS is capable of measuring helium concentrations with ± 5%, ± 15%, ± 25%, and ± 40% fractional error for ranges of 0-25%, 25-45%, 45-75%, and 75-100% helium. Quantitative helium concentration measurements were performed at several points in the flow field. The results showed that cavity-induced resonance caused an increase in the mixing between helium and air in supersonic flow.