Propagation Speed of the Frontal Head Through Lock-Exchange Density Current in Cold Fresh Water: Simulations without the Effect of Back-reflected Waves

Abstract

The behaviour of warm water discharged at 4\(^{\circ}\)C through lock-exchange in cold fresh water was investigated numerically, fixing lock volume at the centre of the domain. This investigation as presented here is practical and can also enhance policy making towards the protection of the aquatic ecosystems. Though, the aim of this study is to better fathom and as well, gain more insight into such ows. Our results have shown a speedy movement of the lock volume at the centre of the domain with a leading head at two front on the oor which resulted in a hat shape within the first few time frame. Fluid movement in the second phase is independent of the back reflected waves. We were able to identify two regimes of ow with a stepwise decreasing velocity in the second phase. Our results have shown that velocity with which the current travels with in the second regime is higher within the first time frame as compared to those with the effect of back reflected waves. One major factor that is responsible for decrease in the velocity here is mixing. Previous results have also shown that the front velocities in the collapsing phase are independent of lock volume. But this seem not to be the same here because fluid movement in the first phase (regime) is not totally independent of the lock volume and its position here, where density difference is as a result of temperature. However, our scaling power laws here in the second phase show some variations with previous studies where we have effect of back reflected waves. But results in the collapsing phase here are in strong agreement with those in the first phase of our previous simulations with small lock volume. Generally, the spreading behaviour here is dependent on lock volume, barrier position, density difference and Reynolds number.