COMPUTATIONAL STUDY OF HIGH-SPEED PLASMA-FLOW IMPINGING ON AN ENTHALPY PROBE

Enthalpy probe measurements in supersonic plasma flows are subject to various sources of error which are difficult to quantify experimentall y. The relative importance of several such errors has been assessed by means of detailed two-dimensional numerical simulations of high-speed plasma flow impinging on an enthalpy probe. The simulations show that moderate uncertainties in upstream pressure and composition (i.e., de gree of ionization) can lend to significant errors in the velocity and temperature inferred from the measurements. These errors tend to be l arger irt velocity than temperature. A second potential source of erro r is that enthalpy probe data are generally interpreted by means of si mplified analytical relations which neglect the effects of finite-rate ionization, internal electronic excitation, thermal radiation, probe cooling, and probe sampling. The importance of these effects was also assessed, and the resulting errors were not significant under the cond itions examined. We conclude that enthalpy probe measurements in super sonic plasma flows are useful in situations where the upstream pressur e and degree of ionization are known to reasonable accuracy.