Characterization of a Free-Molecular Pressure Probe employing Gas-Kinetic Simulation

Free-molecular pressure probes are employed to deduce particle flux in highly rarefied flow fields, such as the farfield or the backflow region of a plume expanding into vacuum. Analytical approaches to model the probe behavior are known in the literature for some time now. Numerical methods such as DSMC however allow to conduct investigations into the probe response in regimes inaccessible to analytical approaches. Besides, the numerical results may be compared to theoretical models in order to test their fidelity. We computed the response of a probe with slot orifice to a highly rarefied, parallel flow with varying molecular speed ratio. We confirmed the negligible influence of the speed ratio on probe response for low angles of attack, but observed significant deviations from theory as the angle of attack approaches 90o.