  The lift-off characteristics of supersonic streamwise vortex in oblique
shock-wave/jet interaction (OS/JI for short), extracted from a wall-mount ramp
injector in scramjet, is studied through Large-eddy simulation method. Shocked
helium jet is deformed into a pair of streamwise vortex with a co-rotating
companion vortex showing the lift-off characteristic immediately after shock.
Based on the objective coordinate system in frame of oblique shock structure,
it is found that the nature of three-dimensional lift-off structure of a
shockinduced streamwise vortex is inherently and precisely controlled by a
two-stage growth mode of structure kinetics of a shock bubble interaction (SBI
for short). The striking similar structures between OS/JI and SBI support the
proposition that the lift-off of streamwise vortex is the result of a
underlying two-dimensional vortical motion. By considering the first stage
impulsive linear growth rate, an improved vortex propagation model suitable for
SBI is proposed and validated. The lift-off phenomena of both numerical OS/JI
case in this paper and wall-mounted ramp injector cases in literature are well
explained under the two-stage structure kinetics model of SBI. This model
further predicts that for higher free stream Mach number (M > 5), increasing
ramp compression shows little effect on elevating streamwise vortex while
evident lift-off may occur for lower Mach number (M < 3.5), which offers the
new way for preliminary design of streamwise vortex-based ramp injector in
scramjet.
