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March 3, 2017, 16:30
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Mach number not available for contour
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#1 |
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New Member
Justin B.
Join Date: Mar 2017
Posts: 7
Rep Power: 9  |
Hello,
I am a relatively new user and I am modeling a high velocity pipe system with n2 and I am interested in plotting contours of Mach number. However, I do not see Mach number as an option under velocity contours. I am currently modeling the system using the Redlich-Kwong real gas formulation. Is the Mach number contour only available using the ideal gas formulation? |
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March 4, 2017, 12:58
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#2 |
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Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,674
Rep Power: 66 |
You are right, the Mach number is available only for the ideal gas.
You can calculate the sound speed. See 8.2.6 User-Defined Real Gas Models in the Fluent customization manual. There's a UDF template to calculate the sound speed. Btw, I'm not sure but I think in CFD post you might be able to get Mach number. |
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June 25, 2018, 01:41
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why dont we get mach number for real number in fluent (CFD)
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#3 |
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New Member
maharaja vijayaram gajapathi raj college of engineering
Join Date: Jun 2018
Posts: 3
Rep Power: 7 |
i am computing for cd nozzle with a rotating element in it.
when my material density options were in real gas i did not get mach number. nut when i tried for ideal gas i got mach number. so my question is why don't we get mach number for real gas and why we get it for ideal gas in fluent(CFD) |
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June 25, 2018, 02:24
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#4 | |
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Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,674
Rep Power: 66 |
Quote:
For an arbitrary substance the speed of sound is arbitrary. Hence for a real gas (i.e. an arbitrary substance) you have to also define the speed of sound. So Fluent doesn't give you a Mach number. You have to do some extra work to get the Mach number for a real gas. I recommend to look at custom field functions. |
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June 25, 2018, 09:12
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#5 |
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New Member
maharaja vijayaram gajapathi raj college of engineering
Join Date: Jun 2018
Posts: 3
Rep Power: 7 |
Can I know what kind of work I have to do so that I will get Mach number for real gases
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June 25, 2018, 10:38
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#6 |
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Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,674
Rep Power: 66 |
It depends how complicated is your equation of state for the speed of sound. But supposing that you somehow have the speed of sound, you can create a custom field function that takes the local velocity magnitude divided by the sound speed. This custom field function takes a few button clicks and probably 1 minute to do.
If your sound speed is ideal gas law like (i.e. sqrt(kRT) style) then it also can be done easily in a custom field function. |
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June 26, 2018, 03:02
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#7 |
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New Member
maharaja vijayaram gajapathi raj college of engineering
Join Date: Jun 2018
Posts: 3
Rep Power: 7 |
ok, thank you so much. i got the mach number for my problem
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