Determination of the choke pressure of a ram accelerator projectile in subdetonative regime

Operation of the thermally choked propulsive mode provides a high level of acceleration at velocities below the Chapman-Jouguet detonation speed. A one-dimensional modeling of this process has been elaborated which takes into account the real gas effects and yields results that are in good agreement with experimental data at this velocity and acceleration. It also provides an estimate for the pressure level at the thermal choking point that is assumed to occur in the region where the pressure rapidly drops and the oscillatory character of the signal abruptly smoothes out. A fairly good agreement between experimental data and those derived from the one-dimensional modeling based on the ideal gas equation of state was observed. The effects of increasing the initial pressure, however, suggest that a real gas equation of state should be used. The present paper is aimed at providing experimental data on the thermal choking pressure. These values are compared to calculations based on real gas equations of state, i.e. Boltzmann and Percus-Yevick. The thermal choke point pressure in many high-pressure experiments is much lower than the calculated values which brings into question the validity of the criteria for identifying the choke point and/or the accuracy of the pressure measurements under these conditions.