how to apply totalPressure BC for more stability?

immortality · April 8, 2013, 17:13

I have an inlet patch that want to total pressure be constant on it.
but the pressure goes very low and velocity goes very high.
how to correct this situation?
is there another way to apply constant total pressure without this instability problem?
experiences are appreciated.thanks.

vbchris · April 8, 2013, 21:55

what are your other BC's? whats the mesh look like?

immortality · April 9, 2013, 04:50

hi
Its a rectangular(2d) tube with large length tha initially is full of air.one side opens to high pressure fluid and i expect a shock wave to originate (like shock tube)
I want to write total pressure code by myself.
But i'm not sure about which variables should be read from domain(extrapolate from internal domain) and which should set a formula for them.
I assumed so far that velocity be read from internal domain at have set isentropic relations for pressure and temperature(by knowing total values of p and T) But it seems somewhat unstable.
I read a thesis and it seems that p should be extrapolated from inside.but i think in this manner may no shock comes to existence because pressure on patch and internal domain will be the same.
Which combination is true and i should assign?
Thanks.

immortality · April 9, 2013, 16:47

i tested second scenario when p is zeroGradient.but its like U zeroGradient and U goes very high.
How should use total pressure then?
Has anyone any experience to share?

immortality · April 10, 2013, 05:54

has anyone had some experience or can help anyway or any hint or thought?!

April 8, 2013, 17:13	how to apply totalPressure BC for more stability?	#1
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	I have an inlet patch that want to total pressure be constant on it. but the pressure goes very low and velocity goes very high. how to correct this situation? is there another way to apply constant total pressure without this instability problem? experiences are appreciated.thanks.

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April 8, 2013, 21:55		#2
vbchris Member Chris L Join Date: Sep 2012 Posts: 53 Rep Power: 13	what are your other BC's? whats the mesh look like?

April 9, 2013, 04:50		#3
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	hi Its a rectangular(2d) tube with large length tha initially is full of air.one side opens to high pressure fluid and i expect a shock wave to originate (like shock tube) I want to write total pressure code by myself. But i'm not sure about which variables should be read from domain(extrapolate from internal domain) and which should set a formula for them. I assumed so far that velocity be read from internal domain at have set isentropic relations for pressure and temperature(by knowing total values of p and T) But it seems somewhat unstable. I read a thesis and it seems that p should be extrapolated from inside.but i think in this manner may no shock comes to existence because pressure on patch and internal domain will be the same. Which combination is true and i should assign? Thanks.

April 9, 2013, 16:47		#4
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	i tested second scenario when p is zeroGradient.but its like U zeroGradient and U goes very high. How should use total pressure then? Has anyone any experience to share?

April 10, 2013, 05:54		#5
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	has anyone had some experience or can help anyway or any hint or thought?!