  Effect of large-scale vortical structure on mixing and spreading of shear
layer is numerically investigated. Two strut configurations namely Straight &
Tapered strut at two convective Mach numbers (Mc = 1.4 & 0.37) for two jet
heights (0.6 & 1mm) are investigated. Hydrogen jet is injected through a
two-dimensional slot in oncoming coflow at Mach 2. Excellent agreement between
simulated and experimental data is witnessed, whereas the instantaneous data
reveal the presence of various large-scale structures in the flow field. From
the instantaneous field, it becomes apparent that both the geometries have
different vortical breakdown locations. It is also noticed that an early onset
of vortex breakdown manifests itself into the mixing layer thickness
enhancement, effect of which is reflected in overall mixing characteristics. It
becomes evident that the shear strength plays an important role in the near
field mixing. The higher shear strength promotes the generation of large
vortices. The analysis shows that SS-0.6 case offers highest mixing efficiency
being dominated by relatively large-scale structures. Eigenmodes obtained
through Proper Orthogonal Decomposition (POD) confirm the presence of
dominating structures and shed light into the series of events involved in
vortex pairing/merging and breakdown. Dynamic modal decomposition (DMD) also
strengthens the observation made through the POD.
