Shock-Tube Boundary-Layer Effects on Reflected-Shock Conditions with and Without CO2

The disturbances created by boundary layers behind incident shock waves are minimal but are multiplied in the postreflected-shock region and contribute to nonideal behaviors in this region. In this study, a boundary-layer model was used to confirm the link between predicted incident-shock boundary-layer growth and postreflected-shock pressure rise in shock tubes for a wide variety of nonreacting mixture compositions and experimental conditions. The results show that boundary-layer growth and, consequently, postreflected-shock pressure rise are strongly affected by the incident-shock Mach number and specific heat ratio gamma of the mixture. In this study, mixtures of Ar, N-2, and 0.21N(2)/CO2 were examined at experimental conditions of approximately 1400-1800 K at an average pressure of 1.73 atm. Although each mixture (with differing gamma) experienced the same range of postreflected-shock conditions (T-5 and P-5), the Mach number span for each mixture was different. This Mach number byproduct of matchingT(5) and P-5 for each mixture was a major cause of differences in boundary-layer growth behavior and resulting postreflected-shock pressure rise, with the CO2-laden mixture producing the largest postshock pressure (and temperature) rise. Additionally, the measured pressure rise for the high-CO2-content mixtures was an order of magnitude greater than for mixtures of pure Ar at the same experimental (T-5 and P-5) conditions.