Experimental study on the vertical motion of colliding gravity currents

Abstract

Predicting the consequences of colliding gravity currents remains one of the most significant challenges in geophysical fluid dynamics. While the collision phenomenon has long been established through field observations, irregular natural occurrence and measurement limitations denied a comprehensive quantitative analysis of its dynamics. Herein, we experimentally studied colliding gravity currents to describe the collision dynamics and quantify essential parameters that are difficult to measure in nature. Visualization techniques and particle image velocimetry were deployed to monitor the flow evolution and obtain the flow field of the colliding gravity currents. Results revealed that as gravity currents propagated into proximity, vertical motions developed along the respective fronts’ leading edge and became enhanced as the currents merged at collision. Although both symmetric and asymmetric collisions initiated a significant vertical displacement of the mixed fluid, the lifting pattern was dependent on the ratio of reduced gravities of the colliding currents. The displaced fluids reached maximum vertical velocity at low height; however, the velocity reduced as the displaced fluids approached maximum heights. The maximum height attained by the displaced fluid was a significant fraction of the initial fluid depth in the lock, regardless of the reduced gravity ratio. This paper quantifies the vertical motion of the displaced fluid during the collision process, describes the relationship between relevant current parameters and the vertical motions, and provides valuable preliminary contributions toward improving the overall understanding of collision dynamics at the frontal boundary.