Thermodynamic Scaling of Supersonic Retropropulsion Flowfeilds

Abstract

The scaling of steady supersonic retropropulsion shock position and curvature is experimentally examined for a series of conical nozzles at the end of a cylindrical forebody at zero angle of attack. An experimental apparatus was constructed that for the first time allowed the influence of gas molecular weight, temperature and ratio of specific heats to be examined in addition to thrust, pressure, and mass flow ratees. It is revealed that the shape of the bow shock is close to self-similar regardless of gas composition and jet Mach number. In contrast to earlier studies, that suggest that thrust coefficient scales shock standoff distance, we find an additional dependence on the jet to freestream Mach number ratio, the product of which was found to collapse shock standoff distance data. In addition, explicit functions of gas molecular weight, temperature, ratio of specific heats derived from control volume analysis were found to scale the mass flow rate ratio and collapse the current dataset equally well for our data. Mach number ratio was also used to collapse the data but was not explicitly supported from the same control volume analysis. Additional comparisons to higher freestream Mach number data from the literature suggest the mass flow rate scaling is slightly superior, however further study is needed to determine scaling sensitivity to freestream Mach number and small geometric differences.