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how to deal with high speed jet when the Ma>1? |
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#1 |
New Member
Jietuo
Join Date: Jul 2016
Posts: 25
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Hello!
I use converge 2.3.10 to simulate DI gas engines. When I reduce the diameter of gas nozzles while mass flow rate remains unchanged, the gas jet speed becomes very high and exceeds sound speed. As we know, when Ma >1, choke will happen near the outlet of nozzles. In my case, the timestep declines into #e-7 which is too small to let my case finished within a reasonable time. In the time.out, the timestep is limited by dt_cfl mostly and by dt_piso occasionally. what can I do to let myself out of such a dilemma? Thank you for your advice~ |
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#2 | |
Senior Member
Blanco
Join Date: Mar 2009
Location: Torino, Italy
Posts: 193
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Quote:
Btw, are you using the total energy solver for this case? It is specifically suited for high speed flows |
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#3 | |
New Member
Jietuo
Join Date: Jul 2016
Posts: 25
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Quote:
From what you suggest, I need to coarsen my model mesh or use the total energy solver, right? I have two questions. First, I have done the sensitivity study of mesh size before and found a suitable embedding strategy for my previous case. If I do this again, I need to revalidate the pressure trace and emission statistics which may be time-consuming. Alternatively, can I change Simulation Time Parameters to solve this problem? Second, which parameter should I change to use the total energy solver? can you tell me more detail about this solver? |
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#4 | ||
Senior Member
Blanco
Join Date: Mar 2009
Location: Torino, Italy
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Quote:
Quote:
You can switch on the total energy solver by putting to 1 the solve_total_energy_flag in inputs.in. You can find more details on the total energy solver in the paragraph 4.3 of the manual (and I remember some slide in the advanced training material too, new features of v2.3). |
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#5 | |
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Jietuo
Join Date: Jul 2016
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Thanks a lot ![]() |
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#6 |
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Afiqah Hamzah
Join Date: Jul 2016
Posts: 12
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#7 |
New Member
Jietuo
Join Date: Jul 2016
Posts: 25
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I don't know how to turn on this function. I think it may be related to software version. I am using CVG 2.3.10. What about you?
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#8 |
Senior Member
Blanco
Join Date: Mar 2009
Location: Torino, Italy
Posts: 193
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If you're using linux you have to redirect converge output to a text file during the run, e.g.
converge-2.3-.... > log.out & You can also set verbosity level in inputs.in Sent from my HUAWEI TAG-L01 using CFD Online Forum mobile app |
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#9 | |
Senior Member
Tobias
Join Date: May 2016
Location: Germany
Posts: 283
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Quote:
In this case check the screen print in the log file as Blanco suggested. You can also change the command in windows to write the text output to a file. Simply add > log.txt after he command |
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#10 |
New Member
Afiqah Hamzah
Join Date: Jul 2016
Posts: 12
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Yes you are right. I am using v2.3.6. I already have the output in a text file, just wondering why I don't have the time.out file.
Thanks |
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#11 |
Senior Member
Sameera Wijeyakulasuriya
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 117
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CONVERGE writes the time.out file starting from v2.3.10. Its a good idea to read the release notes from time to time to get updated on the bug fixes that has been happening.
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#12 |
New Member
Afiqah Hamzah
Join Date: Jul 2016
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Thanks for the reply Sam. Would you recommend updating the software to the latest version each time there's a new release?
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#13 |
Senior Member
Sameera Wijeyakulasuriya
Join Date: Jan 2016
Location: Convergent Science, Madison WI
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This is a good question that a lot of the people in the forum can learn from. Let me try to answer this below:
1. If you are in the middle of a project, then you should try not to upgrade the executable unless you find out that there's a bug in the version you are using, that affects your project results. If the system you are simulating is sensitive to small perturbations, then changing the executable can result in a different (yet valid) realization of the results. This might affect your project progress if you swap the executables in the middle of the project 2. Read release notes periodically to find out the bug fixes and improvements that has been done to the code. If the bug fixes in the newer versions of the executables do not affect your project, do not change executable in the middle of the project. 3. If you are going to start a new project then this would be a good time to read the release notes to figure out if you want to upgrade the executable or not. 4. CONVERGE typically releases minor versions monthly and a major version yearly. Hope this helps, |
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Tags |
gas engines, gas jet, high speed injection, timestep |
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