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March 9, 2014, 00:22 |
question about the channel395 tutorial
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#1 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 13 |
Hi, all
I have just installed OF-2.1.1 which contains channelFoam solver. I'm doing a channel simulation. So firstly I want to clarify the accuracy of this solver. I ran the Allrun script in the channel395 tutorial and noticed something strange. 1. As for the case, Re_tau=395, nu=2e-5m^2/s, so u_tau=7.9e-3m/s and thus the pressure gradient can be calculated, gradP=u_tau^2/h=6.24e-5m/s^2, h is the half-width of the channel,h=1m. However, when monitoring the pressure gradient, the pressure gradient varies all the time and maintains a tendency to fall down and down. I'm confused that how can we identify the solution to reach a statical turbulent flow? 2. In the tutorial case, there are 2 folders, "0" and "0.org", take a look at into the "0" folder, it can be seen that all the initial fields are specified by nonuniform values. The only utility I know is the perturbU which can generate a parabolic velocity field for channel flow, but I don't know how to generate a proper "p" or "nusgs" field. Can someone figure it out? |
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March 9, 2014, 02:01 |
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#2 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 13 |
After a period of searching , I continue my calculation for a much longer time, the velocity at the domain center oscillating around 0.15m/s(the Ubar=0.1335m/s), about 1.1times. So this is exactly what it should be. The first problem is solved.
However, I'm still not quite understand the second problem. How can we initialize the p ,nusgs fields? Or my misunderstanding, just perturbU required for the velocity field? |
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March 9, 2014, 08:13 |
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#3 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 13 |
In fact, if I use perturbU utility without change as this
Code:
// Expected turbulent Re(tau) Reynolds number with respect to utau Retau 395; // Streamwise component of flow. 0=x, 1=y, 2=z streamwise 0; // Spanwise component of flow. 0=x, 1=y, 2=z spanwise 2; // Halfheight of channel. This is the direction normal to both streamwise and // spanwise directions. h 1.0; // Set (overwrite) velocity to laminar profile setBulk false; // Perturb velocity with some cosine like perturbations perturb true; // Perturbation properties //wall normal circulation as a fraction of Ubar/utau duplus 0.25; //spanwise perturbation spacing in wall units betaPlus 200; //streamwise perturbation spacing in wall units alphaPlus 500; //transverse decay sigma 0.00055; //linear perturbation amplitude as a fraction of Ubar epsilon 0.005; |
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May 7, 2017, 08:48 |
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#4 |
Member
Robert Ong
Join Date: Aug 2010
Posts: 86
Rep Power: 15 |
Hi Huang,
Have you got the answer on the second part of your question? I'm very interested to know the answer. Thanks, Robert |
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May 7, 2017, 23:20 |
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#5 | |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 13 |
Quote:
It has been a long time after I investigated the channel flow case. In my opinion, the fields are generated by a fully developed case so that the user can quickly has an idea of the right flow field. Xianbei |
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May 8, 2017, 00:34 |
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#6 |
Member
Robert Ong
Join Date: Aug 2010
Posts: 86
Rep Power: 15 |
Hi Huang,
So, if the 0 folder has been defined a posteriori then what is the purpose for defining parameters in the 0.org folder? Thanks, Robert |
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May 8, 2017, 03:09 |
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#7 |
Senior Member
Huang Xianbei
Join Date: Sep 2013
Location: Yangzhou,China
Posts: 302
Rep Power: 13 |
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