Hi,

I have created a cicular cross section in GAMBIT to model a cylinderical structure and had exported the mesh file to FLUENT. I am trying to determine the natural frequency of the cylinder in FLUENT? Do you know any command in FLUENT that can determine the natural frequency, either both in air or water?

Thanks KWong

You don't need Fluent to do this. If your Reynolds number is between 2000<Re<200000 then you can just assume a Strouhal number of 0.2 and go from there.

If i do not need FLUENT to do this, then what do i use??

Thanks

For a cylinder in crossflow the Strouhal number, S = fD/U, (f = frequency, D = cylinder diamter, U = mean flow velocity) is pretty much constant for Reynolds numbers from 2000-200000. Just solve for the frequency.

[saeedjack]

i modeled an external flow with fluent 6.1, how i can find natural frequency of it? if its possible or not?
and what is exactly output of acoustic model in fluent?

[ringtail]

Originally Posted by saeedjack

i modeled an external flow with fluent 6.1, how i can find natural frequency of it? if its possible or not?
and what is exactly output of acoustic model in fluent?

First, start the unsteady simulation of the flow until the flow become stable. I mean the vortex shedding become regular. Then monitor the lift of the cylinder for some time. After that, Do FFT to the lift data, and you will get a peak frequency. Generally, it is the natural frequence.