Physically unrealistic result

cfd_steve · April 14, 2017, 09:58

hi all,Fluid inlet is the entrance of the cylinder. There is an obstruction inside the cylinder over which the fluid flows.The cube at the end of the cylinder is created to model the atmosphere. After running the case, the results look unrealistic due to the reversed flow. I have tried with two different boundary conditions on the cube:1. Pressure outlet2. Outflow.The boundary conditions were given on five faces of the cube. I have also tried giving the boundary condition only on one face opposite to where the cylinder ends. However the results look unrealistic. Is there any other wayto model the atmosphere at the end of the pipe?? Refer images.Geometry 1.PNGVelocity contour (mid plane) 2.jpg

Kushal Puri · April 14, 2017, 10:05

Quote:

Originally Posted by cfd_steve

hi all,Fluid inlet is the entrance of the cylinder. There is an obstruction inside the cylinder over which the fluid flows.The cube at the end of the cylinder is created to model the atmosphere. After running the case, the results look unrealistic due to the reversed flow. I have tried with two different boundary conditions on the cube:1. Pressure outlet2. Outflow.The boundary conditions were given on five faces of the cube. I have also tried giving the boundary condition only on one face opposite to where the cylinder ends. However the results look unrealistic. Is there any other wayto model the atmosphere at the end of the pipe?? Refer images.Geometry Attachment 55332Velocity contour (mid plane) Attachment 55333

just try to patch the values in the cube (modeled as atmospherre) after initiallization. Keep pressure outlet boundary conditions on all the six faces, which are visible.

Values to be patch

Pressure : 1bar
x vlocity : 0
y velocity : 0
z velocity : 0
tke : 1
rate of dissipation : 10
temperature : atmospheric temperature

Hope this will work

LuckyTran · April 14, 2017, 23:36

The 6th face of the cube should be a pressure inlet, because the exiting jet from the pipe will entrain flow with it. Unless there really is meant to be a wall there, then you just need to make your cube much bigger so that reversed flow doesn't occur.

cfd_steve · April 19, 2017, 07:59

Kushal,
I have tried to patch the values as you mentioned. But the results show no change.

Tran,
Did you mean the face opposite to the cylinder outlet as the 6th face?

KaLium · April 25, 2017, 07:59

I think the cube (atmosphere) should be bigger .. much bigger

Mehakkar · April 25, 2017, 11:04

Try to make the bigger cube

Sent from my ASUS_Z00LD using CFD Online Forum mobile app

ishan2033 · May 16, 2017, 05:52

Dear Kushal,

I am modelling A stilling Basin in Fluent but Velocity at outlet is coming out to be greater than the inlet and also velocity contour shows velocity at top portion of outlet but Streamlines are not present there. Please help.

Thank you

Ishan
https://drive.google.com/open?id=0By...Dd6dmE1LWxHT0k

April 14, 2017, 09:58	Physically unrealistic result	#1
cfd_steve New Member steve Join Date: Apr 2017 Posts: 3 Rep Power: 9	hi all,Fluid inlet is the entrance of the cylinder. There is an obstruction inside the cylinder over which the fluid flows.The cube at the end of the cylinder is created to model the atmosphere. After running the case, the results look unrealistic due to the reversed flow. I have tried with two different boundary conditions on the cube:1. Pressure outlet2. Outflow.The boundary conditions were given on five faces of the cube. I have also tried giving the boundary condition only on one face opposite to where the cylinder ends. However the results look unrealistic. Is there any other wayto model the atmosphere at the end of the pipe?? Refer images.Geometry 1.PNGVelocity contour (mid plane) 2.jpg

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April 14, 2017, 23:36		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	The 6th face of the cube should be a pressure inlet, because the exiting jet from the pipe will entrain flow with it. Unless there really is meant to be a wall there, then you just need to make your cube much bigger so that reversed flow doesn't occur.

April 19, 2017, 07:59		#4
cfd_steve New Member steve Join Date: Apr 2017 Posts: 3 Rep Power: 9	Kushal, I have tried to patch the values as you mentioned. But the results show no change. Tran, Did you mean the face opposite to the cylinder outlet as the 6th face?

April 25, 2017, 07:59		#5
KaLium Senior Member Kal-El Join Date: Apr 2017 Location: Finland Posts: 150 Rep Power: 9	I think the cube (atmosphere) should be bigger .. much bigger

April 25, 2017, 11:04		#6
Mehakkar Member Mehak Join Date: Jan 2017 Posts: 31 Rep Power: 9	Try to make the bigger cube Sent from my ASUS_Z00LD using CFD Online Forum mobile app

May 16, 2017, 05:52		#7
ishan2033 New Member ishan sharma Join Date: Nov 2016 Posts: 4 Rep Power: 9	Dear Kushal, I am modelling A stilling Basin in Fluent but Velocity at outlet is coming out to be greater than the inlet and also velocity contour shows velocity at top portion of outlet but Streamlines are not present there. Please help. Thank you Ishan https://drive.google.com/open?id=0By...Dd6dmE1LWxHT0k