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chtMultiregionFoam, Temperature is not changing

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Old   June 7, 2018, 05:15
Default chtMultiregionFoam, Temperature is not changing
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Muhammad Waqas
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Hello Everyone,


I am studying heat transfer between solid and fluid and for this purpose i have taken chtMultiregionHeater as an example.To get familiarize with the solver, i have created a simple example with two cylinders (axial cut is shown in attachment). The inner cylinder has been set as solid and fluid (water) is entering from bottom of external cylinder and leaving from top. I didn't use any heat source (removed toposetDict). I have just set the internal field for solid cylinder as 400K. I was expecting decrease in solid temp. due to heat transfer. But after 100 sec there was no change in temp.

My geometry is quite big (forgot to scale down the cylinder) 15m bigger cylinder and the velocity is 1m/s. So fluid will take 15 sec to pass through the domain.
I didn't change any default parameter of chtMultiRegionHeater except P and P-rgh (both changed from 0 to 100000).
Moreover, I ran two simulations, one with g = 9.81 and one almost withoutgravitation (g = 0.1).
In both cases, it is looking like fluid in not passing through the domain. I have attached my velocity contour at 0 and 100 sec.
I am using OF5x Ubuntu 17.10
May be someone could give an expert opinion or point out my mistake

Thank you
Attached Images
File Type: jpg T_100sec.jpg (20.5 KB, 82 views)
File Type: jpg vel_0sec.jpg (23.7 KB, 77 views)
File Type: jpg vel_100sec.jpg (22.2 KB, 65 views)
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Old   June 7, 2018, 05:20
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My changeDictionaryDict for both solid and fluid re attached here.
Attached Files
File Type: txt changeDictionaryDict_fluid.txt (4.7 KB, 37 views)
File Type: txt changeDictionaryDict_solid.txt (1.6 KB, 20 views)
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Old   June 8, 2018, 09:55
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You can not set p and p_rgh at the same time. p should be calculated everywhere. Another point is that you setting the pressure at the wall. Why? This should be zeroGradient.
Why is the inlet inletOutletCondition for k? Why is the wall inletoutlet for U?
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Old   June 11, 2018, 05:55
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Hello Bloerb,


Thank you so much for your reply. I couldn't work on weekend on my case. Actually I had not changed boundary and took default values from multiregionHeater tutorial. As you mentioned, my BC are messed up. I will correct my BC and will run simulation once again.
I have one confusion regarding P and P_rgh. As per my understanding P_rgh is the external pressure (normally atmospheric pressure) but P is our operating pressure. Shouldn't I specify P at one point either inlet or outlet to determine operating pressure. At other points It will be calculated accordingly.
Please correct me, If I am wrong or having wrong understanding of P and P_rgh.


Regards
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Old   June 13, 2018, 02:53
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Hello waqas,
Have you solved your problem? When I want to simulate water flowing through tube using chtMultiRegionSimpleFoam, I also get a unreliable results. Besides, I don't know whether the solver can solve incompressible fluid. Could you please give me some suggestions? Thanks a lot in advance!
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Old   June 13, 2018, 04:13
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Hello Qin,


Yes, it also solves for incompressible fluid. It is very difficult to say anything about your results without any information regarding your case.
As far as my simulation is concerned, I didn't try yet. Most probably I will run my simulation today then I will update here. But in my case, the problem is with my BC setting (as Bloerb mentioned above).


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Old   June 13, 2018, 04:56
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Hello Waqas,

The configuration files of my case are attached as follows. https://github.com/QinHao810/OpenFOA...tube_tworegion They are almost the same as the tutorials, just the fluid thermodynamic properties are changed. So I have no idea how to modify them further. Could you please have a sight on them and give some comments? Thank you very much!
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Old   June 13, 2018, 05:46
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Hello Qin,


First of all, I am not an expert as well. So, I could give you some suggestions based on my understanding and experience .


1) You are using gravitational acceleration (g = 0), I was reading somewhere on the forum, if you set g = 0, it may cause problem. If you really want to neglect g, you may set a very small value (I don't know, may be 0.01 or 0.1)


2) In your changedictionaryDict, liquid_outlet for both P and P-rgh are zero. If you have P and P_rgh at outlet zero, then what would be the pressure at inlet, negative? That doesn't make sense to me.
As I mentioned above in my #4, according to my understanding P is operating pressure and P_rgh is external pressure.


3) There are many extra boundary fields in your "0" folder. I guess you should remove those extra fields to keep it simple and straight.


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Old   June 13, 2018, 10:10
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Hello Waqas,

Thank you for your quick reply. I will try it again according to your suggestions.

Regards, Qin
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Old   June 19, 2018, 05:37
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Hi Muhammad,

there are many threads regarding p and p_rgh.

p = p_rgh + rgh

So, you define only p_rgh with values and the p you define to be calculated.

Robin
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