ENTHALPY PROBE PERFORMANCE IN COMPRESSIBLE THERMAL PLASMA JETS

Enthalpy probe measurements in compressible argon/helium thermal plasm a jets are compared with results from high spectral resolution laser l ight scattering. In the laser scattering measurement the plasma temper ature and velocity are determined directly from high-resolution line-s hape analysis of light scattered by the plasma. The technique yields a n unambiguous determination of gas or kinetic temperature without the assumption of local thermodynamic equilibrium. Velocity is determined directly from the measured Doppler shift. The enthalpy probe is a comb ination stagnation probe and flowing calorimeter. Gas temperatures and velocities are calculated from measured values using both frozen flow and equilibrium flow assumptions for the stagnation process. Over the Mach number range examined, the assumption of isentropic, frozen comp osition stagnation best matches the laser results. In the jet peripher y a significant streamline displacement is caused by the presence of t he probe. The displacement, which is a function of the nondimensional radial velocity gradient, distorts the velocity and temperature result s in the wings of the profiles. In the core of the jets examined, prob e measurements in both subsonic and supersonic compressible flows show excellent agreement with laser scattering results.