Large eddy simulation of downslope gravity currents flowing through a cylindrical pile in the two-layer stratified environment

This study employed large eddy simulation coupled with a mixture model to investigate downslope gravity currents (GCs) flowing through a cylindrical pile in the two-layer stratified environment. Sixteen simulation cases were performed, covering a range of ambient stratified strength and pile submergence ratios. Results demonstrate that ambient stratification determines the fate of GCs head upon impinging the pycnocline, leading to underflow-dominated, interflow-dominated, or interflow morphological patterns with increasing ambient stratified strength. The pile disrupts the coherence of GCs head, promoting dilution of the concentration core, and enhancing the vertical redistribution of dense fluid from the underflow into interflow. The vortex-strain structures of GCs inherently transition from lateral bands to longitudinal stripes but are reorganized by the ambient stratification into vortex-stripes intensified, weakened, or suppressed regimes and also adjusted by the pile into a strain-dominated pattern, particularly upstream of the emergent configuration. Acting as a localized energy sink, the pile shortens the dominance period of kinetic energy and enhances the dissipated energy of GCs. The potential-kinetic energy reversal is modulated by internal waves (IWs): locked IWs facilitate bidirectional energy exchange with GCs under weak ambient stratification, whereas launched IWs cause unidirectional energy loss of GCs under moderate and strong ambient stratification. Irreversible mixing quantified by the background potential energy is maximized for the case with a shallow-submerged pile configuration, which optimally balances wake production and wall shear-induced turbulence. The pile reduces the peak friction velocity at GCs head but enhances it downstream via wake effects, with these influences being moderated by ambient stratification. This work provides critical insight into the coupled dynamics of GCs with stratified environments and pile obstacles, offering a valuable foundation for assessing seabed scouring potential and optimizing the design of offshore infrastructures.