Physical Insights into Downsized Nozzle Geometry for Microwave Electrothermal Thruster via Evolutionary Algorithms

Microwave electrothermal thrusters, characterized by considerably high thrust and a broad specific impulse range, offer advantages over other electrothermal thrusters in terms of operational lifetime, thruster efficiency, and propellant selection. However, the complex phenomena associated with the multi-physics behavior of microwave electrothermal thruster operation pose challenges in optimizing system components. One notable challenge arises in miniaturized nozzles, caused by discernible boundary layer effects, necessitating meticulous consideration in the design process. Multi-objective design optimization is performed by incorporating fluid dynamic simulation coupled with evolutionary algorithms supported by surrogate model predictions. This approach enables nozzle design optimization to maximize performance with respect to flow velocity, thereby enhancing thrust and specific impulse. The flowfields within the nozzle and their effects on performance are scrutinized for selected optimal geometries, offering valuable insights into key design factors. Considerable effects of the nozzle divergent angle and throat radius on performance have been found, as they play a crucial role in shaping the flowfield at the nozzle, consequently influencing thrust generation. Covariance-based sensitivity analysis is performed to identify key design variables and understand their interactions and interdependencies in the physical characterization and modeling of miniaturized nozzles.