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flow over a cylinder 2D

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Old   March 10, 2010, 18:52
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  #21
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karine
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U can do the mean values on Matlab (or excel)
If u want to have the means all over the domain, iterate again in Fluent for 1 period of time and dont forget to put yes for data sampling in the iterate menu
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Old   March 10, 2010, 19:01
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Behrang Asgharian
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Hi
Thanks. The matlab or excel choice work good.
After checking the data sampling in the iterate menu. Where exactly should we go to after the iteration is over?
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Old   March 10, 2010, 21:13
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karine
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AFter u go to plotxy or display contours menus. U choose Unsteady statistics .
( if ure flow is stationnary, i think it is better for u to do the means values over 4-5 periods....)
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Old   March 10, 2010, 21:26
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Behrang Asgharian
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Thanks a lot
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Old   March 24, 2010, 19:34
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Behrang Asgharian
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Hi Again!
How can I initialize the domain using UDF? I mean, for example: I am modeling acoustic oscillating flow which is inherently unsteady so I need to initialize it and after some time it produces sinusoidal curves for velocity and pressure. the problem is that I have to wait for the case to reach that quasi steady state (I mean oscillating with constant frequency and constant amplitudes). If there is a way to initialize with the theoretical sinusoidal pressure distribution throughout the domain, it will definitely reach the quasi steady state faster and that's time-saving. Any suggestions?
Thanks
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Old   March 24, 2010, 20:40
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Micael Boulet
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Hi Arash,
I have a little comment about your mesh. You can improve it by using unstructured tetrahedral cells. The boundary around the cylinder can be regular, though, thanks to boundary layers utility in Gambit.

---------
Edit: sorry, I mean unstructured quadrilateral

Last edited by Micael; March 26, 2010 at 09:12.
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Old   March 25, 2010, 16:55
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karine
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Hi
i dont know how to do this...sorry
i can suggest that u use large time steps so u can get a quick solution
After getting this 'bad' solution, u can use smaller time steps
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Old   March 25, 2010, 17:34
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Behrang Asgharian
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Hey!
Thanks for taking the time to answer this. I did that once. The thing is when i use big time steps it gets steady but the amplitudes are not correct and when I change delta t to a small one then, it gets unsteady again and takes some time to become steady. I think the amplitude problem with big delta t's is due to numerical diffusion. Do you think so?
Thanks
Behrang
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Old   March 25, 2010, 19:44
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karine
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Hi
In fact , u will have a bigger numerical diffusion ( truncation error) and u will miss some of the flow motion. If u use a time step dt, u cant correctly simulate any motion with a time charachteristic less then dt/2 (shannon's theorem)
( U may be also violating the stability limits of ure scheme, what will give rise to wiggles)
Regards
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Old   June 6, 2010, 23:29
Default Problem with flow rate enthalpy sign
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Behrang Asgharian
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I believe you can help me with this.
I put some Lines (from the menu 'surface-line') on my model in order to monitor the enthalpy flow rate. I use the flow rate integral which is
integral of rho*h*u.dA
the absolute values are OK but the sign is negative when it must be positive. I think this has got something to do with the inner product of u.dA.
Does anybody know how I should define the monitor line in order to get positive enthalpy flow rates?
By the way, if I use 'surface-rake' instead of 'surface-line', what will happen?
Thanks
Behrang
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Old   June 16, 2010, 19:40
Default Saving a particular profile and load it in another case
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Behrang Asgharian
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Hi
I am running a case for which I need to give Fluent an initial condition. My question is: Can I save for example density throughout a case and load it in another case with different boundary conditions but with the same mesh? You know, I don't want all the data. I just need a part of it. Is this possible in Fluent???
Thanks
Behrang
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