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Old   January 29, 2011, 16:40
Default Flow over a cylinder
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I am simulating a (1-way FSI) flow over a cylinder case. My case is very similar to the one way FSI and mesh deformation Ch-22 tutorial. My question is that I need to validate my displacements but the disp observed is very low. What can be the reason ??? Is there a problem with the .CEL expression written???
The water flows in the positive x direction and displacement in the transverse (i.e y) direction is to be measured ?????

I am attaching the .CCL file.

Thank you.
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File Type: txt CEL expression.txt (670 Bytes, 38 views)
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Old   January 29, 2011, 16:58
Default wall shear data in result file ???
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In the ANSYS CFX reference guide Ch: 14 Functions in ANSYS CFX Pg. 150 says the following;

In all case if the wall shear data exist in the result file, the viscous force is added to the calculated force.

How do I do this ?????

Thank you very much.
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Old   January 30, 2011, 05:45
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First post - http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

Second post - It is done by default, is it not?
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Old   January 3, 2012, 22:31
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Quote:
Originally Posted by vmlxb6 View Post
I am simulating a (1-way FSI) flow over a cylinder case. My case is very similar to the one way FSI and mesh deformation Ch-22 tutorial. My question is that I need to validate my displacements but the disp observed is very low. What can be the reason ??? Is there a problem with the .CEL expression written???
The water flows in the positive x direction and displacement in the transverse (i.e y) direction is to be measured ?????

I am attaching the .CCL file.

Thank you.

Hi, Did you solve why the disp is very low?
I have also exactly same problem. if you figure out what the problem is, please kindly let me know it.

Best Regards
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Old   January 3, 2012, 23:21
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Quote:
Originally Posted by colopolo View Post
Hi, Did you solve why the disp is very low?
I have also exactly same problem. if you figure out what the problem is, please kindly let me know it.

Best Regards

The first thing to do is use realistic values of spring stiffness (k) & damping values (c). I had actually assumed the values of k & C. The best paper to validate your simulations would be by Anagnostopoulos & bearman - "Response Characteristics of a vortex excited cylinder at low Re number". It is the only experimental paper I know that performed VIV at Re as low as 100. Also you might have low displacements because you vibrations must be in the lower or initial branch. Try to run simulations in the upper branch instead. Use the Strouhal relation given by Roshko (1988) to find the velocity at which your system vibrates in 2P mode of vortex shedding.

If you need any papers related to VIV or any help with CFX just let me know, send me an email at vmlxb6@mail.mst.edu

Hope that helped.
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Old   February 3, 2012, 00:34
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Quote:
Originally Posted by vmlxb6 View Post
The first thing to do is use realistic values of spring stiffness (k) & damping values (c). I had actually assumed the values of k & C. The best paper to validate your simulations would be by Anagnostopoulos & bearman - "Response Characteristics of a vortex excited cylinder at low Re number". It is the only experimental paper I know that performed VIV at Re as low as 100. Also you might have low displacements because you vibrations must be in the lower or initial branch. Try to run simulations in the upper branch instead. Use the Strouhal relation given by Roshko (1988) to find the velocity at which your system vibrates in 2P mode of vortex shedding.

If you need any papers related to VIV or any help with CFX just let me know, send me an email at vmlxb6@mail.mst.edu

Hope that helped.
Thank you. I solved viv simulation with laminar model at low Re number but I have same problems if I use turbulence model at a little bit high re number (4*E04). I used fine mesh (y+~1) with sst model and c and k are used as exactly same value as wind tunnel test. but it yield very small displacement (10E-6 order). before starting transient simulation, I ran steady flow to check cd. value of cd is same as the results of wind tunnel test.
then I turn on transient and put my ccl expression. the cylinder does not move ...

do you have any idea about this situation?

Best Regards,



have you been experienced simulation at high re n
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Old   February 3, 2012, 12:08
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Am sorry but I have never encountered such a problem.
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