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vmlxb6 January 29, 2011 16:40

Flow over a cylinder
 
1 Attachment(s)
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.

vmlxb6 January 29, 2011 16:58

wall shear data in result file ???
 
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.

ghorrocks January 30, 2011 05:45

First post - http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

Second post - It is done by default, is it not?

colopolo January 3, 2012 22:31

Quote:

Originally Posted by vmlxb6 (Post 292773)
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

vmlxb6 January 3, 2012 23:21

@ colopolo
 
Quote:

Originally Posted by colopolo (Post 337763)
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.

colopolo February 3, 2012 00:34

Quote:

Originally Posted by vmlxb6 (Post 337771)
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

vmlxb6 February 3, 2012 12:08

Am sorry but I have never encountered such a problem.


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