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 asistas October 22, 2011 10:26

saline gravity current

Hello!

I'm trying to model the gravity current of brine in clean water ambient. It's a 2D model. To define brine I changed the density and viscosity of water and saved it as a different material.
I'm using k-epsilon RNG for turbulence and 3 phase Eulerian for multiphase. I'm defining air at the top of water in order to see the wave movement at the top surface. I defined air as primary phase, water and brine as secondary phases. There are 3 boundary conditions: inlet, pressure outlet at the top just for air and no-slip wall. Initially there is only two materials defined on the surface body; water and air on top of it. The gravity current I wanted to model is constant flux. So, I defined an inlet and patched brine to it. The inlet is only 3 cm high and velocity of brine is supposed to be about 0.10 m/s. So, I'm not sure whether it is proper for me to use turbulent model or not.

My problem is brine is accumulating in front of the inlet, instead of flowing under the water. I tried to enable drag and lift forces, surface tension between water-air and brine-air, near wall treatments, manipulated operating conditions, meshing sizes. I could not improve the model!

 doronzo October 22, 2011 11:03

Re

Hello

I'm interested in this problem, I have a ''similar'' case posted here as how simulating a water-particle current into sea

Are you modeling the water as a pseudo-fluid, i.e. the water properties are modified to account for the presence of brine, or is the brine an independent phase?

Why not using VoF to see how the interface moves?

Anyway, I think the balance between initial shear velocity and the tendency of the brine to settle, through its density, is important. Thanks

Regards

 asistas October 24, 2011 09:54

Quote:
 Originally Posted by doronzo (Post 329014) Hello I'm interested in this problem, I have a ''similar'' case posted here as how simulating a water-particle current into sea Are you modeling the water as a pseudo-fluid, i.e. the water properties are modified to account for the presence of brine, or is the brine an independent phase? Why not using VoF to see how the interface moves? Anyway, I think the balance between initial shear velocity and the tendency of the brine to settle, through its density, is important. Thanks Regards

I defined saline as an independent secondary phase.
I tried VoF too but the result was same. I could not observe a gravity current. The saline is only accumulating and pushing the water. I decided to go with Eulerian because I thought maybe Eulerian would be a better solution method considering the relative velocity of saline wrt water.

Initially there is no saline in the surface body, I've never thought of defining initial shear velocity. How can I do that? Do you think it would be a better idea if I define salt and water instead of saline and water?

Thank you!

 doronzo October 24, 2011 13:18

Re

My expertise is on gas-particle gravity currents, so I don't know exactly how to approach to this problem at best.

Anyway, I generally start with a velocity constant with height, which means the shear velocity is the same as for the velocity at all heights. Then, the flow moves over a preliminary surface (not of interest for my purpose), in order to develop a turbulent boundary layer, which is actual and common in my cases.

Check for your initial conditions. Also, is your model ''two-way coupled''? I generally use DPM model, and sometimes the particles decouple having high inertia. Thanks

Regards

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