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how to simulate pressure variation wrt time at outlet

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Old   April 20, 2011, 05:08
Question how to simulate pressure variation wrt time at outlet
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Gyanesh Kumar
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i have pressure-time discrete data at pressure outlet of aerospike engine(exactly as rocket climbs up and ambient pressure goes down) and i want to simulate. The inlet pressure is constant say it is 60 bar. how i can simulate it in fluent 6.3.
data are as follows:

time(sec)------------ outlet pressure(pascal)
0 ---------------------101325
1 ---------------------101307
2 ---------------------101352
4 ---------------------101160
-
-
-
-
-
-
94---------------------4373.95
- -
143------------------- 19.9039
- -
200.9------------------0.000732896

Last edited by gyanesh; April 20, 2011 at 05:12. Reason: spaces
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Old   April 20, 2011, 06:02
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You will need to write a UDF for doing this or use a journal file.

There have been some suggestions that this can be done using the profile option, but I think that profile can only manage spatial not temporal variations.
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Old   April 21, 2011, 00:38
Unhappy How to make udf
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Gyanesh Kumar
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i have discrete values of pressure at different time so it is possible by UDF Or should i go for curve fitting.
if it is possible by curve fitting then how to make UDF??
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Old   April 21, 2011, 03:12
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Hi,

It depends at what points you have your values. You will be stepping in time discretely using a finite time step.

So if you have your values at these instants of time(which are whole multiples of your time step) there is no need to for curve fitting and you can do it easily using journal file.

If not interpolation is required.
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Old   April 21, 2011, 03:42
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Gyanesh Kumar
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Hi
thanks for your reply, for better understanding of the problem i am attaching the pressure time history in pdf format.

i have also fitted the curve with help of MATLAB and now i want to make UDF,,how to make it??
Attached Files
File Type: pdf pressure variation1.pdf (26.1 KB, 2 views)
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