Shock-induced supersonic combustion with a streamwise vortex

Abstract

Two hypermixer fuel-injector struts, which can induce streamwise vortices in the middle of a combustor, are used to investigate numerically how the difference of vortex circulation affects the interaction of a streamwise vortex with shock-induced combustion at a Mach number of 3.5. Hydrogen fuel is injected into a combustor at a jet Mach number of 1.5 from the rear of the struts. The separation-restraint (SR) struts used here are SR1 and SR2 with a smaller vortex circulation. Supersonic combustion starts at the point where the reflected oblique-shock waves impinge on the streamwise vortex, and the formed streamwise vortex interacts with the reflected shock waves twice. Although weak vortex breakdowns occur due to the second shock interaction for both struts, strong breakdown that occurs as a result of the first shock interaction appears only in the case of SR1. In terms of vortex breakdown connected with combustion, our results demonstrate that high pressure rises occur close to the vortex breakdown, which can be identified by the integrated helicity, the enstrophy calculated by subtracting the streamwise component, and the occurrence of the subsonic region. In addition, we found that the combustion efficiency of SR2 without strong vortex breakdown was higher than that of SR1. This can be understood by dividing the cross section perpendicular to the main flow into two distinct regions, namely the strut region and the outside region. Although there was little difference in the efficiency calculated on the strut region including the vortex, between the two struts, SR2 was found to be more efficient in the outside region. Therefore, circulation could significantly influence combustion with a streamwise vortex using hypermixer struts.