pressure in function of time

dzuodoka · February 4, 2011, 05:58

Here is the thing:

I have transient flow with CHT through the pipe. Pressure and temperature are in function of time and when it's coming to change parameter of pressure then appears a problem with overflow and temperature has been clipped.

For being more clear:

from 0 s to 480 s pressure equals 14.7 psi
from 481 to 520 s pressure equals 56.4 psi
and so on ....

the problem appears in solver from 450 s
time step 30 s

any advice ?

ghorrocks · February 4, 2011, 06:12

You will have to give more details if we are to help. Is the flow compressible? Show a drawing of the geometry.

dzuodoka · February 4, 2011, 06:45

Flow is compressible.
Turbulence model SST.

ghorrocks · February 4, 2011, 06:58

Can you explain your diagram? I do not know what it means.

dzuodoka · February 4, 2011, 08:03

It's the pipe connection with closing wall inside (no flow through this wall only CHT). My aim is to find out what is the change temperature on this wall depening on time. I got three boundary conditions and after three hours the mass flow outlet is opened and I wrote expressions including pressure, temperature and mass flow in function of time. The problem appears in the simulation when the parameters are changed.

Function of pressure:

ghorrocks · February 5, 2011, 06:05

You are probably getting transient compressible flow stuff happening, like shock waves due to the rapid pressure changes. I would round the pressure history off to be more realistic.

I still have no idea what you are trying to model.

February 4, 2011, 05:58	pressure in function of time	#1
dzuodoka New Member Rafał Kryjak Join Date: Jul 2010 Posts: 11 Rep Power: 16	Here is the thing: I have transient flow with CHT through the pipe. Pressure and temperature are in function of time and when it's coming to change parameter of pressure then appears a problem with overflow and temperature has been clipped. For being more clear: from 0 s to 480 s pressure equals 14.7 psi from 481 to 520 s pressure equals 56.4 psi and so on .... the problem appears in solver from 450 s time step 30 s any advice ?

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February 4, 2011, 06:12		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	You will have to give more details if we are to help. Is the flow compressible? Show a drawing of the geometry.

February 4, 2011, 06:45		#3
dzuodoka New Member Rafał Kryjak Join Date: Jul 2010 Posts: 11 Rep Power: 16	Flow is compressible. Turbulence model SST.

February 4, 2011, 06:58		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Can you explain your diagram? I do not know what it means.

February 4, 2011, 08:03		#5
dzuodoka New Member Rafał Kryjak Join Date: Jul 2010 Posts: 11 Rep Power: 16	It's the pipe connection with closing wall inside (no flow through this wall only CHT). My aim is to find out what is the change temperature on this wall depening on time. I got three boundary conditions and after three hours the mass flow outlet is opened and I wrote expressions including pressure, temperature and mass flow in function of time. The problem appears in the simulation when the parameters are changed. Function of pressure:

February 5, 2011, 06:05		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	You are probably getting transient compressible flow stuff happening, like shock waves due to the rapid pressure changes. I would round the pressure history off to be more realistic. I still have no idea what you are trying to model.