Effects of Incomplete Accommodation on Intake Performances of Atmosphere-Breathing Electric Propulsion

Rarefied gas flows inside the intake device of an atmosphere-breathing electric propulsion system are investigated systematically by employing the direct simulation Monte Carlo method and Cercignani–Lampis–Lord model. Two intake devices with different ionization-section radii and four gas–surface interaction cases are considered. The effects of incomplete accommodation on flow features and intake performances are assessed and analyzed in depth. Incomplete accommodation in the normal direction augments the compression ratio, but it creates or intensifies backflow and produces or enlarges the recirculation zone, thus reducing collection efficiency. By contrast, incomplete accommodation in the tangential direction makes the reflected molecules gather at the ionization section, greatly increasing the compression ratio and collection efficiency. The maximum compression ratio of the intake device with a smaller ionization section even exceeds 2000, and the collection efficiency of the larger one reaches nearly 100%. Although incomplete accommodation in the normal direction reduces the friction component of aerodynamic drag, it also augments the pressure component by the same magnitude, eventually leaving the total drag unchanged. By contrast, incomplete accommodation in the tangential direction lowers both the pressure and friction components, thus achieving a considerable reduction in aerodynamic drag. Decreasing the ionization-section radius intensifies the interaction between the freestream and the compression surface, consequently making incomplete accommodation play a more important role in intake flows and performances. The reduction in ionization-section radius also raises the compression ratio at the expense of reducing collection efficiency and increasing aerodynamic drag.