  The present study primarily focuses on the effect of jet spacing and strut
geometry on the evolution and structure of the large-scale vortices which play
a key role in mixing characteristics in turbulent supersonic flows. Numerically
simulated results corresponding to varying parameters such as strut geometry
and jet spacing (Xn=nDj such that n=2, 3 & 5) for square jet of height Dj=0.6
mm is presented in the current study, while the work also investigates the
presence of the local quasi-two-dimensionality for the X2(2Dj) jet spacing;
however, the same is not true for higher jet spacing. Further, the tapered
strut (TS) section is modified to the straight strut (SS) for investigation,
where the remarkable difference in flow physics is unfolded between the two
configurations for similar jet spacing (X2: 2Dj). The instantaneous density and
vorticity contours reveal the structures of varying scales undergoing different
evolution for the different configurations. The effect of local spanwise
rollers is clearly manifested in the mixing efficiency and the jet spreading
rate. SS configuration exhibits excellent near field mixing behavior amongst
all the arrangements. However, in case of TS cases, only X2(2Dj) configuration
performs better due to the presence of local spanwise rollers. The qualitative
and quantitative analysis reveals that near-field mixing is strongly affected
by the two-dimensional rollers, while the early onset of wake mode is another
crucial parameter to have improved mixing. Modal decomposition performed for SS
arrangement sheds light into the spatial and temporal coherence of the
structures, where the most dominant structures are found to be the Von-Karman
street vortices in the wake region.
