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Shock tube simulation in Fluent

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Old   August 27, 2018, 22:19
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hi, i tried your udf and i get wrong pressure distribution i get separate regions but not as written in the text file i get very small pressures like between 10e-8 and 10e-5.
What you have replied is a rather old thread. By any chance did you choose incompressible fluid rather than ideal gas in your setup?
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Old   August 28, 2018, 00:14
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that's a possibility i am gonna repeat the steps again, and make sure i don't miss anything. honestly i didn't choose either of them.
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Old   August 28, 2018, 00:24
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What you have replied is a rather old thread. By any chance did you choose incompressible fluid rather than ideal gas in your setup?

can i upload a video to youtube showing the steps i am going through and maybe you can spot the error?
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Old   August 28, 2018, 01:57
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What you have replied is a rather old thread. By any chance did you choose incompressible fluid rather than ideal gas in your setup?

here is the video of what i did in fluent

https://youtu.be/DZOyHQQs4rk
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Old   August 28, 2018, 02:36
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You have to set the material property for the computation. By default the fluid is assumed to be incompressible but you have to change it to ideal gas law in this case. Also, please make sure that your domain range is exactly as the comment of the UDF stated.
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Old   August 28, 2018, 02:45
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You have to set the material property for the computation. By default the fluid is assumed to be incompressible but you have to change it to ideal gas law in this case. Also, please make sure that your domain range is exactly as the comment of the UDF stated.

IT WORKED, i changed the density from constant to ideal gas and the changed the solver from pressure driven to density driven, and i got a nice contour, it looks better, i still need to tweak some variable a little bit, i believe the domain is right it's like this:
[X]: from 0 to 10 meters

[Y]: from -0.1 to 0.1 meters

[Z]: from -1 to 1 meters
i tried with low resolution mesh of 20x20x1
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Old   August 29, 2018, 01:19
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You have to set the material property for the computation. By default the fluid is assumed to be incompressible but you have to change it to ideal gas law in this case. Also, please make sure that your domain range is exactly as the comment of the UDF stated.



so i just discovered that somehow after initializing using the udf, i get wrong densities right away
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File Type: png density issue.PNG (34.5 KB, 9 views)
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Old   August 29, 2018, 02:23
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What fluid do you use in your computation? Did you type in the code rather than copy& paste? The pressure ratio is 10 (1e5 versus 1e5) and the temperature ratio is 1.25, which according to the ideal gas law will lead to a density ratio of 8, no matter whatever the fluid is. But in your figure, the density ratio is no more than 1.5, so in your code either the temperature ratio is not 1.25, or the pressure ratio is not 10.
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Old   September 6, 2018, 01:21
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What fluid do you use in your computation? Did you type in the code rather than copy& paste? The pressure ratio is 10 (1e5 versus 1e5) and the temperature ratio is 1.25, which according to the ideal gas law will lead to a density ratio of 8, no matter whatever the fluid is. But in your figure, the density ratio is no more than 1.5, so in your code either the temperature ratio is not 1.25, or the pressure ratio is not 10.



hi, i am sorry. i just didn't set the operation pressure to zero, i finally got extremely accurate results using ausm scheme. thank you, but i am still not sure what the operating pressure means, is it like the static or atmospheric pressure? thanks
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