Analysis of Air Plasma Flows in Magnetoplasmadynamic Arcjet Testing

摘要

The influence of the electrical input power of a magnetoplasmadynamic arcjet on the flow translational temperature and velocity is investigated. From a nominal testing condition, representing the 78.8 km altitude trajectory point on the Hayabusa re-entry, the electrical power is varied from 146 kW to 189 kW and the temperature and velocity are measured using a system coupling a spectrometer and a Fabry-Perot interferometer to determine the Doppler broadening and Doppler shift of the atomic emission lines. The atomic nitrogen translational temperature is measured using four different emission lines resulting in a median temperature value of 10700 K for the nominal test condition. The atomic oxygen temperature is measured using the 777 nm triplet with a median temperature value of 16350 K. A reason for the higher temperature of the oxygen has not been determined, however, this is in line with results previously obtained on a different plasma generator. The temperatures of both the nitrogen and oxygen increase approximately linearly with electrical input power. The effect of the power increase is significantly larger on the nitrogen temperature with a measured increase of 38 K / kW (0.35 % / kW) compared to the oxygen increase of 24 K / kW (0.15 % / kW). This is thought to be due to the direct energy transfer from the arc into the nitrogen whereas the oxygen is energised through particle collisions downstream of the arc. The measured velocities were the same for nitrogen and oxygen. For the nominal condition the velocity was measured at 3350 m / s. The velocity also increases approximately linearly with the electrical power increase. The velocity increase was determined to be 22 m / s / kW (0.66 % / kW). When considered as a percentage this is a stronger effect than seen in the temperature increases.