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which boundary condition is true?

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Old   January 8, 2013, 06:24
Default which boundary condition is true?
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I have used 3 types of boundary conditions with three different results!
The patch i assigned BC on is outflow.these scenarios are examined:
1)firstly pressure is specified through p0 as isentropic formul:


U and T are zero this pressures are obtained less than expected.
2)at second i set

And U and p are assumed zero gradient.
This approach results in more higher pressures.
3)both p and T are specified:

T=T0-(gama-1)/(2*gama*R)*U^2 (as second case)

This approach leads to diverge after 200 iterations.

So as it tooks one month so far and remaind a little time for me why these conditions result so differently?whats the cause or the causes?
Any knowledge,advice and idea is much appreciated.
Thanks for attention.
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