Influence of flight/jet parameters on drag and heat reduction characteristics of opposing jet under real gas effects

Hypersonic vehicles experience significant aerodynamic drag and thermal loads during high-speed flight, where vibrational and electronic energy excitation of surrounding gas molecules, along with chemical reactions such as dissociation and ionization, make real gas effect non-negligible. As a novel active thermal protection method, opposing jet technology has attracted considerable research attention. Therefore, it is essential to conduct a detailed investigation of drag and heat reduction capabilities of opposing jet under real gas effects. Based on numerical simulation methods, this study compares the performance of opposing jet systems under different gas models, and finds that compared to other models, the non-equilibrium thermochemical gas model provides more accurate predictions of drag and heat flux on blunt bodies, making it more suitable for analyzing aerodynamic thermal environments in high-speed aircraft. Therefore, a two-dimensional compressible Navier-Stokes equations and a thermochemical non-equilibrium gas model are employed to simulate the flow field of the opposing jet system under various flight conditions. The effects of real gas effects and flight/jet parameters on the flow field structure, aerodynamic drag, and heat of a blunt body are investigated. Results indicate that an increase in flight Mach number significantly raises total temperature and pressure, with the total drag coefficient increasing by 29.30% and the total heat flux increasing by 8.53 times when the flight Mach number increases from 8 to 12. The presence of a flight angle of attack disrupts the symmetry of the flow field, with a wall pressure difference of 2.57 times and a heat flux difference of up to 16.17 times between the windward and leeward sides at an angle of attack of 10°. Increased flight altitude decreases the total pressure of free-flow, resulting in a reduced free-flow intensity and enhanced jet-flow penetration capability. As the flight altitude increases from 32 km to 36 km, the maximum pressure of the blunt body decreases by 36.34 kPa, and the maximum heat flux decreases by 1.32 MW/m². Increasing the jet pressure ratio significantly improves the total drag and heat flux. At a jet pressure ratio of 0.014, the system demonstrates optimal drag and heat flux reduction, with the total drag coefficient and heat flux reduced by 41.32% and 73.55%, respectively, compared to no-jet conditions. Changes in jet temperature have a significant impact on the near-wall temperature distribution. While increasing the jet temperature has little effect on total drag coefficient, it increases total heat flux, thereby reducing the overall drag and heat reduction efficiency of the system.