Numerical study of a fully confined supersonic slot impinging jet from bleed system

Abstract

A supersonic slot jet issuing from a bleed system and impinging into a plenum is numerically investigated to deepen our understanding of the flow field and heat transfer of a fully confined impinging jet. The air of the slot jet is forced to exhaust from a plenum in unidirection, resulting in a fully confined configuration. It is of significant practical interest because of its presence in the bleed systems of a scramjet or other related applications. Three primary factors are surveyed, i.e., impingement angle, impingement distance, and back pressure at the plenum exit. The results show that the supersonic slot jet spontaneously generates a plate shock standing on the impingement wall and a strong jet shock on the right side of the jet core. On the left side, the jet shear layer can directly impinge the wall because of the pressure self-adaption effect of a recirculation region. The jet shock and jet shear layer result in two peaks of Stanton number. As the impingement angle increases, the jet shock weakens gradually and moves toward the impingement region of the shear layer until the shock disappears. And thus a single heat peak occurs in place of the previous two peaks. When the downstream flow of the plenum is choked, a wall jet pattern is exhibited because of the formation of a large scale recirculation region. The walls suffer severe aerodynamic heating as the plenum back pressure increases. In particular, the impingement wall endures the maximum thermal load at a certain back pressure at which the jet reduces to the sound speed. The plenum should be controlled to keep the back pressure below this threshold so that the slot walls Stanton number won't increase further. And the plenum should be designed as high as possible to relieve its thermal load.