Experimental and simulation investigation on flow structures and energy transfer of rectangular jets with different aspect-ratios in crossflow

Turbulent mixing of the jet in Crossflow (JICF) is significantly influenced by the jet aspect ratio (AR), which alters the generation and evolution of coherent vortex structures and thereby affects flow characteristics and energy transfer, posing challenges for prediction and control. In this study, a combination of wind tunnel flow visualization experiments and large eddy simulations (LES) is employed to systematically investigate the effects of rectangular jet AR variation on flow structures and energy transfer under non-isothermal conditions. The results indicate that JICF exhibits typical coherent structures: the hanging vortex is the dominant factor governing the jet penetration depth (dJP) and an increase in AR delays its breakdown. The dJP increases by 46.42% at X/d = 1 as AR increases from 0.32 to 3.14. The horseshoe vortex primarily influences the jet width and the formation of the wake vortex, and its structural integrity is negatively correlated with AR. The counter-rotating vortex pair (CVP) is proposed as a pseudo-sequential structure composed of external vortex rings and a pair of line vortices. In the far field, the CVP core becomes more stable with increasing AR, accompanied by a reduction in temperature fluctuation amplitude. When the AR increases from 0.32 to 3.14, energy dissipation at X/d = 10 increases by 28.78%, and turbulent kinetic energy (TKE) decay in the shear layer is accelerated. This study provides theoretical guidance for optimizing jet orifice geometry to regulate vortex evolution, thereby enhancing mixing and cooling efficiency in industrial and aerospace applications, contributing significantly to performance improvement and energy consumption reduction.