Optimal control efficiency characteristics and wide-speed-range aerodynamic design optimization method for grid fins of launch vehicle

Wide-speed-range grid fins design is one of the key technologies for re-use of sub-stages of launch vehicle. In the course of a substage return flight, grid fins experience subsonic, transonic, supersonic, and other speed regimes. In different speed regimes, the control efficiency and aerodynamic characteristics of grid fins are completely different, and even contradictory, which makes the aerodynamic design of grid fins with high efficiency face great challenges. To address the above problems, this paper applies the aerodynamic design optimization method based on machine learning surrogate model to carry out aerodynamic optimization design of grid fins in subsonic, transonic and supersonic typical states respectively, and obtains the optimal aerodynamic shape in different speed regimes. The flow mechanism of the optimal control efficiency of the grid fins in different speed regimes is analyzed and revealed, which can provide guidance for the subsequent design. Because of the different optimization mechanisms of different speed regimes, there are contradictions between the optimal designs of different speed regimes. In view of the above contradictions, the multi-objective aerodynamic design optimization of wide-speed-range grid fins is carried out, taking into account the influence of sub, tran and supersonic speed regimes. The optimization results significantly improve the wide-speed-range aerodynamic performance of grid fins and improve the optimal control efficiency of grid fins.