Test Gas Slug Characterization for Large-Scale Shock Tube Facility

Abstract

An experimental methodology for characterizing the available test gas slug is presented for a gas-driven shock tube. The method employs simple models for theoretical and experimental estimates of the available test gas slug at the time of interaction of the contact surface with the reflected shock wave, avoiding any direct measurement of driver gas in the tube. The measure of this interaction length is estimated against the primary shock Mach number over the entire operating range of a large-diameter shock tube. The trends of driver gas mixing show a strong relation to the theoretical predictions. The trends also suggest that mixing of the contact surface gases in the large shock tube is independent of driver gas composition and could depend largely on diaphragm opening times. The same analysis is also used on a smaller-diameter shock tube, in which resulting trends are readily explained by the known behavior of the contact surface from previous studies. The larger tube data also indicate a laminar boundary layer growth proportionality which can be used to reduce data further. This leads to available test gas slug quantification as a function of the produced shock Mach number alone. The experimental measurement requirements for this method are that of a regular shock tube calibration setup with wall-mounted pressure sensors, which makes it very convenient to implement in any shock tube for preliminary analysis.