Injector Geometry Effects on Cryogenic Coaxial Jets at Supercritical Pressures

Abstract

The effects of LOX post recess length on the mixing characteristics of coaxial jets, such as the inner-jet-core length and jet spread angle, were investigated under supercritical pressures. In experiments, cryogenic nitrogen/gaseous helium coaxial jets were visualized using the shadowgraph technique. The LOX post recess enhanced the mixing of the inner nitrogen jet when its length was longer than one LOX post exit diameter. The outer helium jet also expanded as the recess length increased. In addition to the effects of LOX post recess, it is also noted that the inner nitrogen jet had sinusoidal structures only in coaxial injection cases. In numerical simulations, the numerical model for Reynolds-averaged Navier-Stokes (RANS) simulations was in the first place validated by comparing RANS results with Direct Numerical Simulation results of a temporally developing mixing layer at supercritical pressures. Unsteady RANS simulations of coaxial jets at supercritical pressures were conducted in the cases with and without the LOX post recess. As in experiments, the inner jet core in the case with the recess was shorter than that in the case without the recess. These effects of recess were most likely due to the enhancement of the inner mixing layer instability inside the recess region.