Role of Jet Spacing and Strut Geometry on the formation of Large Scale Structures & Mixing Characteristics

TL;DR

This study investigates how jet spacing and strut geometry influence large-scale vortex formation and mixing in turbulent supersonic flows, revealing that strut design and jet spacing significantly affect flow structures and mixing efficiency.

Contribution

It provides new insights into the effects of jet spacing and strut geometry on vortex structures and mixing characteristics in turbulent flows, including the comparison between tapered and straight strut configurations.

Findings

Straight strut (SS) exhibits superior near-field mixing.

Optimal jet spacing (X2) enhances local spanwise rollers and mixing.

Flow structures are dominated by Von-Karman vortices in the wake region.

Abstract

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.