Determining thruster plume impingement forces and free stream dynamic pressure from impact pressure measurements at transitional Knudsen numbers
This paper presents a comprehensive theoretical numerical, and experimental investigation of the phenomena encountered when analyzing exo-atmospheric plume impingement loads. An analytic model combined with Monte Carlo simulations is used to study the relationship between the force induced on a body surface and the pressure measured within a cylindrical pressure tap set in the body. This model is compared with data obtained in the plume of a small nitrogen thruster. Both data and model show that the pressure measured within the pressure tap may be as much as three times less than the actual force on the body surface. In addition, a new method is introduced for determining the free-stream speed ratio within a plume from pressure measurements. Finally, a theoretical model is developed to predict the perturbing effect of an invasive measurement on the plume flowfield. This theory can be used to extract the true undisturbed free-stream quantities from experimental data for use in code validation. Comparison between the theory and historical data is excellent.
