CFD Simulation of Vortex Induced Vibrations near Resonance at Re 10000

Vortex Induced Vibrations of a cylinder near resonace. This was a simulation I did in Fluent using Dynamic Mesh. Observe the 2p mode of shedding and the high amplitude of oscillations

Since I have got many requests for the UDF, here is a link where you can download the UDF from

http://web.ics.purdue.edu/~kumar65/interests.shtml#cfd

Category:

Education

Tags:

• VIV
• Vortex Induced Vibrations
• Fluent
• CFD

[varunlobo1986]

@ Kumar & sagar: How is this a 2 way FSI ?? I am trying to simulate the same thing using CFX. As for what I understand, 2 way FSI is where there is structural deformation (stresses) monitored along with fluid flow. Please correct me if am wrong. For all this while I was thinking it was 1 way FSI. Thank you.

[rkumar310]

@varunlobo1986 : FSI means that the structure "reacts" to the fluid forces. It is not necessary for the structure to deform. In this case, the structure is vibrating due to the fluid forces created from vortex shedding. If you increased the velocity (i.e. Reynolds number), the frequency of vibration would increase due to higher vortex shedding frequency. Thus fluid flow is affecting motion and hence it is 2-way FSI.

[rkumar310]

To add: If on the other hand, you had specified (say sinusoidal) motion for the cylinder and then observed how it affects fluid flow, it is not FSI since the motion of the structure is "independent" of the fluid flowing around it.

As you said, structural deformation is sometimes involved in FSI as well (for eg. deflection of wing due to lift forces) but these type of problems are extremely challenging computationally and involve coupling CFD solver with a structural solver.

[sagga18]

I think it is 2 ways FSI. Could you tell me the concept to write UDF code? Thanks

[rkumar310]

@sagga18: Yes it is 2 ways FSI. It is a mass spring system. The spring stiffness adjusted to match the natural frequency with the vortex shedding frequency (for resonance). The force on the cylinder is computed using Fluent's built-in function Compute_Force_And_Moment from which the acceleration and the velocity is computed. I can send you the UDF if I can get your email id.

[varunlobo1986]

@rkumar310 : How is this a 2 way FSI. I thought a 2 way FSI has structural deformation involved also ????

[rkumar310]

@varunlobo1986 : As I said earlier structural deformation may or may not occur for 2 way FSI.. there could just be a rigid body motion. For example, in this simulation, fluid forces move the cylinder, the movement of the cylinder effects the flow, which in turn again affects the forces on the cylinder.. thus there is a 2-way effect (fluid-> cylinder and cylinder->fluid) and there is a coupling between the two .. coupling implies two-way FSI.

[Mecheng1985]

Hello Rkumar310, sorry I'm bothering you again, but I need your help again. I compiled your UDF, and it ran perfectly. However, I am having problems when my case is iterating; it said negative volumes are present. I think I am not defining correctly my dynamic mesh zone, or I am using a high time step. I wanna ask if you can send me your case file in order to identify my mistakes. My email is angelraf_81@yahoo.com. Thank you so much for all your help and sorry for the inconveniences.

[Mecheng1985]

Hello Rkumar310, I am trying to simulate this case with a lower Re, but I am having problem with the UDF. Please I wanna ask you if you can send me your UDF. My email is angelraf_81@yahoo.com. Thank you for your help.