Heat and drag reduction of single and combined opposing jets in hypersonic nonequilibrium flows

Abstract

To establish a method of achieving effective thermal protection and drag reduction in hypersonic flows with an opposing jet under a low flow rate, this study compared three single and two combined jets. For a single jet, nozzles of different sizes (nozzles 1, 2, and 3) were investigated. The influence of the effective area of the annulus jet was studied for the combined jet, consisting of a circular jet and an annulus jet. A 2.6%-scale Apollo capsule was investigated with these jets in hypersonic flows at Mach 19 and an altitude of 60 km using a transient numerical method. Considering nonequilibrium effects (vibrational excitation and chemical reactions), the heat and drag reduction mechanisms of these single and combined jets in hypersonic flows were explored using a nonequilibrium Navier–Stokes–Fourier numerical approach. The results indicated that nonequilibrium effects exist in the shock wave and wake regions. The size of the nozzle in the single jet and the effective area of the annulus jet in the combined jet influence the heat and drag reduction. A single jet with an excessively small nozzle size considerably decreases the effects of heat and drag reduction. Compared with a single jet, the combined jet cannot reduce the aerodynamic drag at a low flow rate owing to the dispersion of the jet. However, a combined jet with a larger area of the annulus jet can effectively reduce the aerodynamic heat to 68%, whereas three single jets can considerably enhance the surface heat flux.