Impacts Of Toporaphic Variations On Hydrody-Namics Of Gravity Currents In Stratified Environments

Gravity currents,are flows driven by the density difference between the flow and its ambient environments,occurring in natural and practical environments.From generation to disappearence,gravity currents usually propagate a long distant.The topographic variations have an important influence on the propagation of gravity currents.The variation of the bottom slope will change the hydrodynamics of gravity currents and even the separation location from the slope when the gravity currents propagating in stratified environments(such as reservoirs,lakes,oceans),which may change the damage depth of gravity currents on underwater structures.Therefore,it is of great value to engineering practice.In this paper,we used a two-tank system to create linear stratified water and used rectangular and triangle obstacles to simulate the topographic variation.By using high-speed camera and particle image velocimetry(PIV)method,a series of experiments were conducted to investigate the propagation of lock-exchange gravity currents encountering various obstacles.The dissertation focused on the flow characteristics and the hydrodynamic characteristics(such as,velocity field,vorticity field and streamline)of gravity currents at the cross-section near the obstacle.By introducing the factors of stratification coefficient and mass centroid coefficient,considering the change of effective buoyancy to reflect the driving force,the head velocity formula of gravity currents down a ramp in stratified water with and without obstacles was improved.An empirical formula for calculating the proportion of buoyancy contained in the head of gravity currents was established.Using the experimental data,the separate depth formula of gravity currents from the ramp by considering the impacts of obstacles was established.The calculation results of the formula are in good agreement with the experimental data obtained from the experiment(such as,head velocity and separation depth).The present study provides scientific references for the researches,such as the transport and diffusion of pollutants in complex topography environment,seabed structures protection and reservoir deposition.