Real gas effects on thermally choked ram accelerator performance

Abstract

A one-dimensional performance analysis code has been modified to account for real gas effects in the combustion zone of the thermally choked ram accelerator. Previous computational studies utilized the ideal gas equation of state and underpredicted experimentally measured thrust values as a function of Mach number. The post-combustion pressure in the ram accelerator is on the order of a few ten MPa and in this regime it is no longer appropriate to ignore intermolecular interactions. Including a compressibility factor to account for these real gas effects provides a much better match with experimental data. The current research code incorporates the following equations of state: ideal gas, Boltzmann, Percus-Yevick, and a direct solution to the virial expansion in which the virial coefficients are computed using the Lennard-Jones and Stockmayer potentials. The ideal gas equation of state performs well for initial fill pressures up to 1.0 MPa, while the Boltzmann and direct virial model perform adequately for fill pressures up to 5.0 MPa. The Percus-Yevick model also performs well for ram accelerator fill pressures up to 5.0 MPa and is expected to accurately model fill pressures up to a few ten MPa.