# Physically unrealistic result

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 April 14, 2017, 09:58 Physically unrealistic result #1 New Member   steve Join Date: Apr 2017 Posts: 3 Rep Power: 6 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

April 14, 2017, 10:05
#2
Senior Member

Kushal Puri
Join Date: Nov 2013
Posts: 183
Rep Power: 9
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

 April 14, 2017, 23:36 #3 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 4,122 Rep Power: 50 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 New Member   steve Join Date: Apr 2017 Posts: 3 Rep Power: 6 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 Senior Member     Kal-El Join Date: Apr 2017 Location: Finland Posts: 150 Rep Power: 6 I think the cube (atmosphere) should be bigger .. much bigger

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

 May 16, 2017, 05:52 #7 New Member   ishan sharma Join Date: Nov 2016 Posts: 4 Rep Power: 6 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