Effect of Water Vapor Injection on Plasma Reduction in Hypersonic Flow

Communication blackout is an immense challenge for reentry spacecraft, compromising mission safety. The direct simulation Monte Carlo method with the quantum-kinetic ionization reaction model is used to simulate the ionization flowfield with air–water-vapor injection around RAM C-I (the first flight of the Radio Attenuation Measurement experiments). This study focuses on the three-dimensional flowfield structure and electron number density distribution influenced by water vapor injection, aiming to identify regulation patterns and lay a foundation for further investigation of control mechanisms. Parametric studies are conducted by varying key factors, including the injection pressure ratio, injection velocity, injection temperature, injection angle, injection orifice radius, vehicle’s angle of attack, and the mole fraction of hydrogen ions in the injected water vapor. The elevating effect of the injection is evaluated by comparing the flowfield characteristics across different conditions. Single-factor analysis quantifies the influence of each variable on the electron number density. Through a combined optimization strategy, a reduction of the maximum electron number density at the observation point by one order of magnitude is achieved with a mass flow rate of only 3.38 g/s.