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March 10, 2010, 18:52 |
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#21 |
Senior Member
karine
Join Date: Nov 2009
Posts: 158
Rep Power: 16 |
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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March 10, 2010, 19:01 |
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#22 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
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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March 10, 2010, 21:13 |
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#23 |
Senior Member
karine
Join Date: Nov 2009
Posts: 158
Rep Power: 16 |
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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March 10, 2010, 21:26 |
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#24 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
Thanks a lot
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March 24, 2010, 19:34 |
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#25 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
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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March 24, 2010, 20:40 |
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#26 |
Senior Member
Micael
Join Date: Mar 2009
Location: Canada
Posts: 156
Rep Power: 18 |
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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March 25, 2010, 16:55 |
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#27 |
Senior Member
karine
Join Date: Nov 2009
Posts: 158
Rep Power: 16 |
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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March 25, 2010, 17:34 |
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#28 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
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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March 25, 2010, 19:44 |
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#29 |
Senior Member
karine
Join Date: Nov 2009
Posts: 158
Rep Power: 16 |
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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June 7, 2010, 00:29 |
Problem with flow rate enthalpy sign
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#30 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
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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June 16, 2010, 20:40 |
Saving a particular profile and load it in another case
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#31 |
Member
Behrang Asgharian
Join Date: Oct 2009
Posts: 38
Rep Power: 16 |
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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