FSI and flutter
 

Hi all!

Does anybody know if it's possible to model flutter in the new ansys 12. I have access to both cfx and FEM solvers.
I have my wing and I want to examine if there is any risk for flutter in subsonic, transonic (thypical transonic dip) and supersonic regions.

Regards
POP

Yes, it is possible.

Well, Thanks for you short, but honest reply:)
Could you please give me brief info on where I can find documentations for such simulations?

There are example on general FSI in the CFX examples. For information on how to do this sort of FSI I would look in the open literature, there should be plenty of studies on wing flutter. It is not my field so I cannot help you directly.

Flutter visualization in Ansys CFX
 

There is indeed a Tutorial on Fluid Structure Interations, tutorial: Oscillating plate. This deals with a forced vibration of a plate in a 2D plane. However, I think flutter can be quite a bit more difficult to obtain. I am dealing with the same challenge.

I would like to visualize potential flutter phenomena occuring with free hanging slender pipes with pump up fluid. At a certain fluid velocity I expect a certain instability of the pipe. This probably require a small initial deflection, but then the fluid will do the work.

Is there somebody who has experience with flutter type of phenomena in Ansys CFX and knows the best way to deal with it.

One of the questions I have have is which turbulence model to use.

Thanks in advance.

Riser stability analysis in Ansys CFX
 

The problem I am trying to understand is related to earlier observed unstable behaviour of flexible risers aspirating fluid via their free-hanging end, applied in the offshore industry like the Cold Water Pipe for OTEC.

One of the explanations of the unstable behaviour to occur, is flutter near the free-hanging fluid inlet. The pipe with a certain small initial deflection/excitation relative to its neutral vertical position, causes the fluid to make an angle when entering the pipe. This yield in an exchange of momentum, which can lead to flutter.

I expect the flow near the inlet of the pipe to be of crucial importance and I am looking for ways to gain a better understanding of what is happening with Ansys CFX.

What would be the best approach to tackle this topic? Do you have advises for me?

Thanks in advance.

hi:
i am intrested in such fields too,but i have a general question:
in the cfx FSI tutorial such as oscilating plate the deformation of the solid domain is important but for the problems mentioned above such as flutter and vibration of pipes deformation is not beeing discusssed and vibration of solid domain is important...how can vibration be modeled in workbench and cfx?
regards

In V12 you have a number of approaches available. It supports rigid body motion through both deforming mesh and immersed bodies (this is a beta feature) - the body stays rigid but moves around and no FEA solver is required. If the body needs to deform then you need to go to FSI where the CFX solver is coupled with the ANSYS FEA solver. This allows the body to deform at the cost of significantly increased solver run time.

Thanks alot for your useful replies.good luck.regards

There is a fair bit in the literature for wing flutter. The classic case is the AGARD 445 wing, since experimental data exists. Googling for this returns plenty of info. ANSYS also has an FSI training course.

http://www.ansys.com/services/ts-cou...85&Location=NA

FSI for shock absorber
 

Hi Glenn,
i am working on 2 way coupled Fluid structure analysis of a twin tube shock absorber using ANSYS12.0 (Mechanical and CFX), and now getting error like......Fatal error in requesting total mesh displacement from structural part. Is any one know the reason behind this, ur answer will be very much helpful for me.....

hi mallya, I was getting same error some days back,there can be two possible reasons,the first is that your mesh is very distorted,try to map mesh the geometry. and secondly you may have copied the workbench case files here and there, just start a new case and just save it at default location and then dont transfer files here and there