Computational Analysis of High-Altitude Ionization Gauge Flight Measurements

The rarefied, three-dimensional flows experienced during the turbulent oxygen mixing experiment (TOMEX) at altitudes between 85 and 143 km are simulated using the direct simulation Monte Carlo (DSMC) method. The present study focuses on ionization gauge measurements obtained by TOMEX. The payload is, thus, modeled in detail, and the simulations employ complex meshes. The simulations show that a bow shock wave is generated in front of the payload at low altitude that becomes diffusive at higher altitudes. When the altitude increases, the pressure in the channels of the ionization gauge and the pressure variation around the payload are both decreased. The DSMC results agree very well with data predicted by compressible flow theory and free molecular theory when applicable. Comparison between the DSMC results and the TOMEX flight data shows generally good agreement.