I'm trying to simulate VORTEX INDUCED VIBRATIONS in Flow Around A Rigid Cylinder. The diameter (D) and mass of the cylinder are 0.5 m and 35.78 g, respectively. The spring stiffness is 69.48 kN/m, the damping coefficient is 0.0039 Ns/m and Re=200. I've been trying various UDF since past 2 weeks but everytime m not able to simulate any oscillation so it would be of great help if you kindly provide the UDF.
What software do you want to solve the problem? Fluent? CFX?...?
Maybe if you were more specific on what your problem is, someone might be able to help you without providing a UDF (User Defined Function, right?) directly.
E.g., do you see vortex shedding in your simulation? Does your cylinder move at all? Do you want to impose a forced motion, or is the cylinder free to vibrate?
the cylinder should be undergoing Vortex Induced Vibration sir
I know that Arbind Prasad Acharya.
Vortex-Induced Vibration (VIV) is closely related (a consequence, one could say) to vortex shedding. So, again, do you see vortex shedding in your CFD simulation?
Also, VIV will typically happen with a body free to move, but it is common to study the aeroelastic properties of a system related to VIV by imposing forced motions. This is done in experiments and also in CFD simulations. So, what are you doing? Free vibrations or forced vibrations?
If anything is not clear please let me know. But if you answer with a one-line sentence I will not be able to help you further I am afraid :)
No sir I don't see vortex shedding in my simulation, I'm using a Turbulence k-epsilon model with standard conditions, I'm using a test fluid with Density 1kg/m3, viscosity 1Pa.s and inlet velocity of 400ms-1 to simulate flow for Re=200 and the diameter of the cylinder is 50cm. The inlet is specified as Velocity inlet and the Outlet is specified as Pressure Outlet.
I'm looking towards implementing free vibrations. The cylinder is free to vibrate along y-axis.
I regret for the inconvenience caused sir.
These are the the velocity contours that I had obtained sir for Flow Around
the cylinder
Okay, thanks for the detailed answer :)
So, as I see it, your problem has nothing to do with the UDF, but with the fluid solution.
Vortex shedding may take some time to develop in your simulation, maybe you could try running for more iterations. If you see your wake shape is still evolving, for sure you need more time (see this video for an example of what I mean https://youtu.be/8mgU-kVpaw0). Unfortunately I could not say how many iterations you need, maybe someone else can help you with this.
okay sir, thank you for the response. I'm re-starting the simulation process right from the geometry and will update here regarding the simulation if I'm getting the vortex shedding or not. I'll be giving 4000 timesteps this time for simulating the flow. And sir do let me know what should be the process after that to make free vibration of the cylinder.
Just as a side note: you should be able to continue your simulation without having to start from the beginning. There should be a restart option or something similar. Sorry for not being more specific, I haven't used Fluent for a long time, but you should be able to find the details by yourself.
Regarding the VIV. I would say you should try for yourself, and if you run into specific problems many people will be happy to help :)
Hi
If you want to simulate the motion of the sphere due to fluid flow, there is an example in Fluent's Problems with a UDF. Also, in older versions of Fluent, it was necessary to install the C++ compiler separately through the Visual Studio program. With the UDF changes given for this Fluent example, you can customize it for your model.
- Badges
- Science topic