Monte Carlo computation of rarefied supersonic flow into a pitot probe

Abstract

Pitot probes are commonly used to make measurements in high-speed gas flows in wind tunnels and vacuum chambers. In supersonic flow, a shock wave forms in front of the probe. In the continuum flow regime, the Rayleigh pitot probe equation is used to describe nonisentropic pressure losses across this shock. Under the rarefied flow conditions typical of supersonic plumes produced by spacecraft propulsion systems, the continuum theory is inaccurate. Hence, pressure corrections are needed to make use of pitot probe measurements in these flows. Currently, there is no general analytical theory describing this behavior. In the present study, the direct simulation Monte Carlo method is used to simulate rarefied, supersonic flow of nitrogen into a representative pitot probe geometry in order to predict these pressure corrections. Numerical results are compared with experimental data and are found to show good agreement qualitatively and quantitatively. Pressure corrections computed at very low probe Reynolds numbers are found to be consistent with free molecular limits calculated using collisionless gas theory.