Shahab Abbaszadeh

           M.Sc Graduated Student in Mechanical Engineering

            Sharif University of Technology

 Researches

Large Eddy Simulation of Continuous Density Current impinging on Obstacles

 

As a particular form of stratified fluid motion in nature, density currents have attracted the interest of many researchers in the past decades. These types of flows are formed whenever a fluid with specific density begins to move through another fluid with different density called ambient fluid. Prediction of turbulent density currents propagation, especially because of their remarkable influence on the environment, is one of the researcher's interests in geophysics and engineering over the past decades. Density currents have many variant applications both in industry and nature. Sandstorm in deserts, turbidity currents in oceans and avalanches are some natural examples of these currents. On the other side, leakage of dense gas into the atmosphere due to reservoir Fracture, ventilation in buildings and spread of wastewater and cooling water into the sea are considered as the industrial examples. In nature, when density current is moving on a loose bed, usually the surface of the bed is not smooth. The existence of natural or man-made obstacles has different influences on the physical behavior and structure of density current.

The interaction of density currents with naturally occurring topography or engineering structures is one of the important aspects of density currents behavior that needs to be analyzed. In the present study, the 3-D density current propagating over bottom-mounted cylinders has been studied numerically using LES method. Unlike many previous works, this research has been studied the "continuous" form of density currents. Continuous density currents clearly have more temporal continuity than the lock-exchange type which causes some parameters such as sedimentation and friction potential become more significant in this type of density currents.

In this investigation, the influence of the change in obstacles number and geometry on the fundamental parameters of the flow is investigated. The continuous density current propagating over obstacles is simulated and analyzed in following cases: channel without obstacles, with one obstacle (Square, Triangle and dune) and with two obstacles (Square-Square). The bottom surface of the straight channel is smooth and has 1% slope and the height of all obstacles is 0.86 of the inlet height. The simulations provide detailed information on the flow instabilities and structure of the current, the quasi-steady state distributions of velocity, concentration, pressure, bed shear stress and temporal evaluations of the front velocity, backward flow (Bore), vorticity and energy balance.

The results generally show that in the case of having more than one obstacle, the first obstacle determines the conditions of upstream flow and it makes the flow less turbulent in this region; however, the conditions of the obstacles downstream is intensely dependent on the last obstacle. In the case of using obstacles with different geometries and equal height, it can be mentioned that the change in geometry is only influential in the areas around the obstacles and downstream of that.

 

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