Turbulence generation and evolution mechanisms induced by herringbone ribs in supersonic mixing layer

To investigate how herringbone ribs modify turbulence generation and evolution in a supersonic mixing layer, large-eddy simulations (LES) are performed for a splitter-plate configuration. The numerical framework is first validated against classical experimental data by comparing normalized velocity and turbulence-intensity profiles obtained using Reynolds-averaged Navier–Stokes (RANS), LES without synthetic inlet turbulence, and LES with synthetic-eddy-method (SEM)-generated turbulent inflow. The downstream evolution of the baseline mixing layer and the local variations in mixing-layer thickness associated with shock–shear-layer interactions are then examined. Herringbone ribs are introduced on the splitter plate, and the baseline and herringbone-ribbed configurations are compared in terms of flow structures, vortex evolution, mean-velocity profiles, turbulence intensities, and dynamic mode decomposition (DMD) characteristics. The results show that the rib-induced geometric perturbations generate periodically distributed near-wall vortical structures and secondary motions. Compared with the baseline configuration, a distinct canonical two-dimensional roll-up stage is not clearly identified in the ribbed case, while three-dimensional vortical structures emerge farther upstream. Recirculating motions downstream of the rib trailing edges are accompanied by enhanced velocity fluctuations, with the initial streamwise turbulence intensity increasing by 60% relative to the baseline configuration. DMD analysis further shows that the herringbone ribs excite high-frequency small-scale disturbances through localized forcing of the shear layer, while sustaining low-frequency large-scale coherent motions with longer temporal persistence. The present findings are specific to the herringbone-rib geometry and inflow conditions considered in this study, and their applicability to other rib configurations and flow conditions requires further investigation.