Response of the Patterson Probe in the Transition Flow Regime

Abstract

The free-molecular impact pressure probe, also known as Patterson probe, is known and applied for more than half a century now to deduce the number flux of a single species in highly rarefied inert flow. While the working principle is conceptually simple, interpretation of the gauge readings may not be, but approximate formulas for evaluation exist. In the context of cold-gas plume flow and interaction experiments with the obvious large variations in Mach and Knudsen numbers, it may not be clear initially, whether the signals measured with the Patterson probe are obtained in free-molecular flow environment, and hence, whether the mentioned evaluation techniques may be employed. A series of numerical experiments have been conducted using the Direct Simulation Monte-Carlo method, to study the response of the Patterson probe to prescribed free-stream conditions in the transitional flow regime. From the computational results we infer analytical expressions that describe the probe response in transitional regime at zero angle of attack.