A series of lock-release experiments are carried out to investigate the hydrodynamics of weakly and strongly stratified two-layer gravity currents (GC) on a flat bottom. A particle image velocimetry (PIV) system combined with an optical method is used to obtain the mixing process, front velocity, and velocity profiles of the two-layer GCs, focusing on the effect of the initial height ratio and lock aspect ratio. For a weakly stratified two-layer GC, the two layers mix thoroughly earlier with a higher initial height ratio and lock aspect ratio. A theoretical model is improved to predict the time that is necessary for the thorough mixing during the propagation of weakly stratified two-layer GCs. For a strongly stratified two-layer GC, a higher initial height ratio leads to a larger velocity of the upper layer because of the larger initial density difference, which results in a shorter time for the upper layer to outrun the lower layer. After the upper layer outruns the lower layer, the current has a constant-velocity phase and then a deceleration phase. The present investigation indicates that the maximum velocity in a vertical velocity profile of a strongly stratified two-layer GC is located at the position near to, or higher than the upper limit for single-layer GCs due to the smaller drag resistance at the upper boundary.

为了研究平底弱和强分层两层重力流（GC）的流体动力学，进行了一系列锁定释放实验。使用粒子图像测速（PIV）系统结合光学方法获取两层GC的混合过程、前速和速度剖面，重点关注初始高度比和锁定纵横比的影响。对于弱分层的两层 GC，两层较早彻底混合，具有较高的初始高度比和锁定纵横比。改进了理论模型以预测弱分层两层 GC 传播过程中彻底混合所需的时间。对于强分层的两层 GC，较高的初始高度比导致较大的上层速度，因为较大的初始密度差异导致上层跑出下层的时间较短。上层跑出下层后，电流先是等速阶段，然后是减速阶段。目前的研究表明，由于上边界的阻力较小，强烈分层的两层GC的垂直速度剖面中的最大速度位于接近或高于单层GC上限的位置.