A Fundamental Study on Instability of Stratified Shear Flow in Gravity-Currents

The instability phenomenon called Lobes and clefts structure that appears frontal line of gravity current is investigated by performing computational fluid dynamics (CFD) and a small-scale experimental fluid dynamics (EFD) in laboratory. In computation under no-slip condition, inverse stratified condition that less dense fluid lies under more dense fluid appears at bottom surface of channel as advancing of gravity current head. Periodic convective structures occur by this unstable stratified condition, and they make frontal line of gravity current head rippling. And if front line of gravity current has no ripple just after the lock releasing, germination of periodic convective structure can be confirmed. By flow visualization experiments of lock-exchange flow in vertical and horizontal planes, characteristics of ripples is good agreement with computational results and periodic convective structures inside head of gravity current can be confirmed. It is found that this convective structure have an important role for progress of three dimensionality of gravity current and mixing process at density.