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Old   October 11, 2016, 07:56
Default Gas simulation setup
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Hello guys,

I am a beginner in using Converge and CFD software as well. I want to simulate the internal flow of a nozzle in order to investigate the cavitation phenomena. I will use C7H16 as fuel and air as ambient gas. I am not quite sure about setting up the gas simulation. Is the equation of state, critical temperature and pressure only influenced by the air or also by the vapor of C7H16? Do I need a .dat file for the critical conditions?

I guess it is a very basic question, but I already searched for an answer in the user manual and the theory manual of Converge and could not find anything.

Best regards
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Old   October 11, 2016, 11:19
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Hi,

First of all, welcome to the Converge world!

Converge actually takes vapors as source terms in the transport equations. You need to have C7H16 in thermal.dat for its thermodynamic properties, and in mech.dat for mechanism. If you don't know how to setup, you can load our example cases in STUDIO as reference.

Hope this answer helps.

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Originally Posted by GNKK View Post
Hello guys,

I am a beginner in using Converge and CFD software as well. I want to simulate the internal flow of a nozzle in order to investigate the cavitation phenomena. I will use C7H16 as fuel and air as ambient gas. I am not quite sure about setting up the gas simulation. Is the equation of state, critical temperature and pressure only influenced by the air or also by the vapor of C7H16? Do I need a .dat file for the critical conditions?

I guess it is a very basic question, but I already searched for an answer in the user manual and the theory manual of Converge and could not find anything.

Best regards
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Old   October 12, 2016, 02:57
Default Further question
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Hey Xieshengbai,

thank you for the fast reply, but I still do not fully understand. I am aware that I have to use the therm.dat and the mech.dat to define the fuel I want to use. My question is about the step where I have to choose the equation of state. Do I need a crit_conditions.dat file for air and vapor or only for air? And do I need gas transport data for air and vapor?

I hope you can understand what I mean. Thanks in advance.

Best regards
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Old   October 12, 2016, 11:39
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Hi,

Now I see what you really meant. For the equation of the state, even if there are vapors, you can still use the default critical values, which can be understood as an approximation for the mixed gas.

Alternatively, to be more accurate, you can provide species-dependent values including the vapor species using a file as you mentioned, which will be like the following

# species crit_temp crit_pres acentric_factor
DEFAULT xxxx xxxx xxxx
N2 xxxx xxxx xxxx
O2 xxxx xxxx xxxx
C7H16 xxxx xxxx xxxx
...

For each species in the mechanism not listed, it will get the "DEFAULT" values.

Please let me know if you still have any question. Thank you.



Quote:
Originally Posted by GNKK View Post
Hey Xieshengbai,

thank you for the fast reply, but I still do not fully understand. I am aware that I have to use the therm.dat and the mech.dat to define the fuel I want to use. My question is about the step where I have to choose the equation of state. Do I need a crit_conditions.dat file for air and vapor or only for air? And do I need gas transport data for air and vapor?

I hope you can understand what I mean. Thanks in advance.

Best regards
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Old   October 13, 2016, 06:12
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Hey Xieshengbai,

thanks again for the fast reply. Your answer really helps me. I am still not sure which data I have to insert via the gas.dat. Is there also the possibility to define the gas transport data for several species?

Thanks in advance.

Best regards
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Old   October 13, 2016, 11:01
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Actually, gas.dat is species independent. Instead, you can define species dependent diffusion via transport.dat. Please check "Mixure-averaged diffusion" in STUDIO to enable the file. It follows the CHEMKIN format and you can find some instructions in the manual. Hope it answers your question.

Quote:
Originally Posted by GNKK View Post
Hey Xieshengbai,

thanks again for the fast reply. Your answer really helps me. I am still not sure which data I have to insert via the gas.dat. Is there also the possibility to define the gas transport data for several species?

Thanks in advance.

Best regards
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Old   April 30, 2019, 12:27
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Hey Xieshengbai,

im also a beginner in Converge. Ive got similar question like GNKK and i read your Posts it helps me. And i have a little question: The Transport.dat data for the "Mixure-averaged diffusion" is like below formated?

"h2o 2 572.400 2.605 1.844 0.000 4.000
h2o2 2 107.400 3.458 0.000 0.000 3.800"

Cuz i used to importe file like this as gas.dat and that made no sense when i plot the gas transport data with Studio.

So something like this should be importer as Transport.dat? i guess.

Thanks in Advance!
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Old   April 30, 2019, 12:49
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Yes, the format you used should be for transport.dat. In gas.dat, there is no distinct gas species since it uses the same properties for all.

Quote:
Originally Posted by stark_zh View Post
Hey Xieshengbai,

im also a beginner in Converge. Ive got similar question like GNKK and i read your Posts it helps me. And i have a little question: The Transport.dat data for the "Mixure-averaged diffusion" is like below formated?

"h2o 2 572.400 2.605 1.844 0.000 4.000
h2o2 2 107.400 3.458 0.000 0.000 3.800"

Cuz i used to importe file like this as gas.dat and that made no sense when i plot the gas transport data with Studio.

So something like this should be importer as Transport.dat? i guess.

Thanks in Advance!
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