A numerical study on mitigation of plasma sheath by droplet injection

A numerical model was developed in which droplet motion, evaporation, and chemical reactions are coupled to evaluate how liquid–water injection influences the temperature and electron density of hypersonic plasma sheaths. Simulations show that cooling lowers the translational–rotational temperature and suppresses ionization, while electron attachment by H2O provides an additional pathway for electron removal. The effectiveness of the injection is highly dependent on altitude and location. High-rate head injection penetrates the shock layer, substantially reducing core electron density and modifying sheath thickness; low-rate shoulder injection effectively decreases local electron density and sheath thickness, thereby creating a stable communication window. In addition, vapor films forming on the vehicle surface further suppress free electrons production. These results demonstrate that water injection is a promising technique for blackout mitigation, but its application requires dynamic optimization with respect to altitude and flow-field conditions.