No force readings from simulated wind tunnel

  • Last Post 11 March 2019
namlhadkire posted this 01 March 2019

I'm working on a design project testing a light fixture in a wind tunnel to find the coefficient of drag. Everything worked fine up until it came time to calculate the drag force, there were no errors, just a value of zero for the force applied to the body. Initially I thought this was due to a lack of shear force by the wind on the fixture but the body is set to a no slip wall, I'm not entire sure where I'm going wrong. Any help would be appreciated. Attached are images of various groups of settings I believe are relevant.

Attached Files

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Kremella posted this 04 March 2019


Are you running your simulation on Fluent or on CFX? If it is Fluent, are you seeing any Force readings in Fluent before you move your data to CFD post?

Thank you.



namlhadkire posted this 04 March 2019

Hi Karthik, 

No, I'm running this in CFX. 


abenhadj posted this 04 March 2019

Can you Monitor the forces in the solver? Can you change the direction in post?

Best regards,


namlhadkire posted this 04 March 2019

I can't monitor forces in the solver. When in the solver I can't monitor anything. There should be a plot here to measure force but there isn't anything there. I can change the direction in post but there's nothing in any direction, positive or negative. 

namlhadkire posted this 04 March 2019

In addition, I've checked and the fluid is clearly flowing as shown in this image, 

and the walls are set to no slip, however no forces are still present.

namlhadkire posted this 04 March 2019

Is it a possible issue that there's no points of contact between the object and the walls? That's my best guess I have left.

rwoolhou posted this 05 March 2019

Please can you put a plane down the centre-line and plot velocity contours? That'll help diagnose what's going on. Don't display any of the mesh on the plane. 

namlhadkire posted this 05 March 2019

 This clearly isn't right but I'm not sure if this is the cause of the issue or a sub issue created by a mistake in the plane and contour system.

namlhadkire posted this 06 March 2019

Ok so upon further inspection I believe the issue is that the fluid is flowing around inside the outer walls and not inside the tunnel as it was supposed to, but I'm still getting velocity readings inside the fixture itself. Any attempt to reverse it to flow inside the tunnel instead of the walls was met with several errors. Is there some way to change the tunnel to zero thickness so that there's no way to mistake where the flow is supposed to be going?

rwoolhou posted this 07 March 2019

I think you've meshed the solid bits. Can you put a slice through the centre line in Meshing? If that's the case in SpaceClaim or DesignModeler you'll need to create a volume that is the fluid domain, we don't need the metal parts. Then repeat the process (meshing & set up) and I think the data will make sense. 

namlhadkire posted this 11 March 2019


Ok so I redid it as you said and in the CFX Pre it looked much more promising but I got this error. I looked online and people were saying it's a problem with memory so I altered the magazine size to the amount specified earlier on in the run in execution control but nothing changed. Any ideas?