How to create a tank which partially filled with fluid?
I'm conduct a filling simulation which is filling heavier density liquid into a tank which is partially filled with lighter density liquid. Let say the total height of the tank is 10m and partially filled with 3m water. Stratification will happen during filling.
My question is how to create the geometry of this tank and related setting by using Fluent 14.0? |
Hi,
As far as I know, you need to name a body in your geometry / meshing tool. In this case you could create the tank with two different bodies - one "upper" and one "lower" body. Now set some named selections to make these bodies available in Fluent. In Fluent - once you switched on the multiphase model and after initializing - you can patch the volume fraction of fluid i to zero and of fluid ii to 1 in the upper body and vice versa in the lower body. What do you use for geometry and meshing? |
I did try the method that u mentioned above, but the problem I faced is at time=0, the tank is filled with 3m heavier fluid but also the other 7m is already filled with lighter fluid. What I want is at initial stage the tank is filled with 3m heavier fluid only, the rest 7m is filled during filling with lighter fluid, so the total height of fluid inside the tank will increase during filling.
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Remember: You can not have "nothing" inside a volume at any time. Also at t=0 you have to have some kind of fluid above 3m. It sounds like you have to introduce a third fluid (air?) to do what you want.
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That means my problem involved 3 phases, am I right? By the way, how to made my simulation like the height of total fluid inside the tank increase during filling? what I did before is I named the top of the tank as pressure outlet,but it seem like didn't work.
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Bottom filling-the inlet is at the bottom of the tank.
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Then, pressure outlet for the top should be the right thing. What happened? BTW: You should set the backflow fraction of the two liquids to zero at the top to ensure that only air flows back from the top...
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Hi, I faced some problem after my simulation and i attach my result and problem as attachment in this post. Generally my problem are:
1. how to set the inlet with filling rate 10m3/s? 2. why the path of filling doesn’t show? 3. Why the heel with mix and react with bog? What I want is the feed is mix with heel. Thx |
1) Is this something different to the things we discussed? I think we were talking about a three-phase flow.
2) Why do you use a pressure inlet? If you know the volume flux, use a velocity inlet and divide the 10m^3/s by the area of your inlet to get the velocity. 3) What do you mean by 2. 4) What do you insert through the inlet? Can you create a picture of your geometry? I just see colored faces... Is there any symmetry? |
1) what is the difference between three phase with my case?
3) By referring to figure 6, there is a horizontal path from inlet reach the surface of the heel( blue-green-yellow). But this kind of path didn't occur in my simulation(figure 5). 4) Lighter fluid(feed) is filling from the inlet to tank. |
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here is the geometry
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1) Ok. Now, in your last post (picture) you say "this is a closed tank". But it isn't. It is open on the top since you defined it as a pressure outlet.
2) The inlet is just a small half-circle on the ground? What's the size? 3) Bottom and side-wall are defined as "walls" in fluent? BTW: What is "heel"? My dictionary says it is some part of the foot. Nothing else mentioned there... |
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1) i think that is the key for my problem. For my case, i want to model a closed tank( LNG tank). What should i define for a closed tank?
2) the radius of inlet is 0.22m 3)Yes, the bottom and side wall are defined as wall. "Heel" is refer to the fluid which is already inside the tank. "feed" is refer to the fluid which is to be filled to the tank. " BOG" -Boil of gas is the vapor form of fluid. |
What happens to the gas at the top of the real tank during filling? Is it compressed?
to 2) -> then you have an inlet area of about 0.152m^2. To get your desired 10^m3/s you need an inlet velocity of 65.79m/s. No pressure inlet. But what means "heel"? |
1) Boil off Gas generally will be vented out and reliquefy back to Fluid.
"Heel" actually is a term used in Oil and gas industry. Heel in here is means the residual fluid( old LNG) inside the tank before filling the new LNG. LNG- Liquefied Natural Gas The objective of my simulation is to simulate the mixing behavior between 2 different density of LNG. Here is the published paper: https://www.google.com.my/url?sa=t&r...aNp6hvVBT052og |
Ok, if it is vented out, then just use a pressure outlet for the vent, or leave the top as it is...
Now post some pictures after trying again! |
ok, so the total volume of the Fluid( heel+Feed) will increase if i'm defined the top of the tank as pressure outlet?
besides that,by referring to figure 6, there is a horizontal path from inlet reach the surface of the heel( blue-green-yellow). But why this kind of path didn't occur in my simulation(figure 5). |
Maybe because your pressure-inlet was defined incorrectly.
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hi, after redefined the inlet as velocity inlet, the same problem also occur and the contour is similar to figure 2 which is volume faction of feed is 0 within the tank.That means that the feed is no filled into tank. Why this occur?
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At the inlet, did you set the volume fraction of feed to "1" and all others to 0?
Otherwise you will pipe phase 1 as default in, which might be different to feed... |
As I said before, you can use patch to set initial volume fraction of each phase. or use UDF.
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I did set the volume fraction of feed by 1, but same problem occur too.
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here is the setting part 1
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here is the setting part2
Thanks |
Hi,
1) Are you sure about your time step size? With 20m/s at the velocity inlet and dt=60s the fluid will move 1200m each timestep! I am afraid that these settings can't converge... Can you show your residual history? 2) Why don't you set the velocity normal to the surface at the velocity inet, but instead you use a direction vector? EDIT: I just realized that you did some curious things in your calculation settings... Do you know, what all these values mean? Timestep, Number of Iterations, ... |
CFD codes are not like Word, Excel or Powerpoint that you can learn to use on your own and it will be fine. When it comes to CFD, you really need to understand what you are doing (your model, fluid dynamics, numerical methods, etc...). And obviously you are lacking a bit of background.
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This is the first time I'm contact with CFd, I still fresh with it and still got a big room for improvement. I'll spend more to time on it.
Btw, in order to maintain filling rate at 20m/s, what time step and interaction I should use? |
I would: Estimate how far I want to travel the feed during one timestep. Let's say 0.5m.
Now, your time step has to be 0.5m / 20m/s = 0.025s. Then, you set the number of iterations per timestep to 1. This can't work. Since the set of equations is nonlinear, you have to iterate each time step for convergence. I would set the number of iterations to 25 and see how the residuals behave. You could do 10 time steps with these settings and post a picture of the residuals here. Good luck! |
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here is the residual result by using time step of 0.05, Number of timestep=10, and interations/time step=25.
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This looks bad...
How did you initialize your domain? |
How you differentiate between good and bad residual from the graph?
Sorry, I can't understand your question.. Can u further explain to me? |
It looks like some of the residuals nearly don't change at all during these iterations. This should not happen.
What do you use for initialization? There is a button "initialize" at "Solution->Solution Initialization->" Do you use "hybrid"? I would go for "standard" and set every text box to zero. Then, hit "Initialize". Can you post a picture of your mesh? |
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i set all the value as 0 except the temperature=113.
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I still believe that to get the most out of CFD, you need to study it. Everyone can tick boxes but understanding what you are doing is different story. |
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