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-   -   Shaking a Can under changing gravity (https://www.cfd-online.com/Forums/fluent/36474-shaking-can-under-changing-gravity.html)

 Optixxx April 22, 2005 21:18

Shaking a Can under changing gravity

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Hi Community

I have a special problem and maybe someone might help me and(or) write me a UDF. I have a Can with fluid domain inside and further is heated up from outside in a process. Additional the Can is now shaked to increase heat transfer and "forced convection"

Question: I have the acceleration function a= w^2*sin(w*t) w(omega)= 17.6 1/s f.e

so under gravity-panel:

y-direction a = 9.81 m/s^2

x-direction: a=17.6^2*sin(17.6*t)

I found nothing in the input-box for ...(t), so for unsteady calculation a udf is needed. Can someone write that short case

Found nothing in help or search.Would be happy abou any help

Thy Optixxx

 Mehdi Ghoddosy April 24, 2005 04:56

Re: Shaking a Can under changing gravity

Dear kenischi: Have your read fluent tutorial no. 15 for using VOF model. It would ontain usefull information for your case. I can send you the case file if needed. regards

 Optixxx April 24, 2005 12:12

Re: Shaking a Can under changing gravity

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Thx Medi for help

Yes in case of domain splitting liquid/gas you are right, because the can has also a headspace of air which canīt be neglegted. So the VOF model is needed, additional the heat equation.

But for moving walls you can only set constant velocity numbers and that isnīt the case. The can is shaked translational (like a piston over a crankshaft)with changing velocities and accerelation over time. So the wall is accerlerated and then liquid and gas too. Therefore iīm sure, this can only be done with an udf, that calculates acceleration every time step, because we have a(t)=....sin(wt). Btw w (omega) is the rotational velocity of the crankshaft. So i need the udf for wall acceleration in wall panel

Has anyone some further ideas

Thx anyway

Optixxx

 edi ghirardi April 26, 2005 03:49

Re: Shaking a Can under changing gravity

You can effectively change the values of gravity components during flow time via an udf or a scheme file. I personally use the second choice. Let me know if you are interested in it. Advantages: you don't need to compile or interpret it. Disadvantage: you have to write an input file that fluent have to read any time step.

Edi.

 Optixxx April 27, 2005 21:05

Re: Shaking a Can under changing gravity

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Thx Edi

for your advice, but i donīt need changing accerleration or velocities in define/conditions, because only the Can get that, inside the Can Fluent calculates swapping over viscosity. The liquid isnīt affected. So i need the wall-panel. Also i can calculate changing velocities over time for the wall, but under moving wall i normally able to set constant speed

Any hints how i can changing velosity, maybe UDF

thx Optixxx

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