Investigation of the drag reduction mechanism for a blunt forebody with opposing and side jets

An opposing jet (OJ) is applied in the drag and heat flux reduction at the blunt leading edge of hypersonic vehicles. The drag reduction capability of the OJ is related to the penetration mode. When the total pressure ratio (PR) of the jet exceeds the critical value, the penetration mode of the OJ transitions from long to short, resulting in a sudden drag spike. This work proposes a novel combined opposing and side jet (OASJ) control method to modify the jet penetration mode. The work employs the finite volume method to solve the Reynolds average Navier–Stokes equations, using the two-equation k–ω shear stress transport turbulence model to analyze the detailed flow field structures of the OJ and OASJ methods at various PR values. Compared with OJ, the OASJ method introduces complex three-dimensional recirculation zones, which could limit the development of the shear layer at the OJ boundary, causing the extension to a higher value of the pressure ratio range for sustaining the long penetration mode (LPM). Thus, the drag coefficient of the blunt body simultaneously decreases. However, with a further increase in the pressure ratio, the LPM of the OASJ will change to the short penetration mode, leading to a worse drag reduction performance than that of the OJ.