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how to accurately simulate flow around cylinder

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Old   March 11, 2014, 09:28
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Dear Alexey,

I tried many changes in the attached folder, but the figures of velocity, drag and lift don't look like for laminar flow. I followed the information about velocity, drag and lift coefficients given in

http://onlinelibrary.wiley.com/doi/10.1002/fld.1683/pdf

Any idea please?

Many thanks in advanced.
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Old   March 11, 2014, 11:41
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Well,

1. You've shown wrong geometry in the PDF you've attached. Maybe it's not so important..

2. Cdrag is more or less the same as in paper. The sign is opposite due to error in dragAxis settings. Clift and vertical velocity component are also more or less the same. See attached figures. Even though I've run the simulation with Re=200.
Attached Images
File Type: png 1-3.png (28.1 KB, 34 views)
File Type: png 1-3-130-150.png (33.5 KB, 25 views)
File Type: png 1-5.png (30.3 KB, 23 views)
File Type: png 1-5-130-150.png (27.3 KB, 15 views)
File Type: png 1-6.png (30.5 KB, 16 views)
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Old   March 11, 2014, 11:50
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Dear Alexey,

could you check my mistakes in the attached file please. Why I did't get the figures you shown?

Yours it seems me are absolutely right.
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File Type: gz circularCylinderNew.tar.gz (4.7 KB, 9 views)
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Old   March 11, 2014, 11:57
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Cause you're running the case for Re = 1000.
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Old   March 11, 2014, 12:03
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No I'm running for Re = 100.
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Old   March 11, 2014, 12:14
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OK, you're running the case for Re = 100 (if you'd like to think so, why not). Though I still wonder why you think that you're running the case for Re = 100.

Then I guess, the problem is in your OpenFOAM installation. Or maybe in the hardware, you're using. So to get the same plots, you just need to change hardware, reinstall OpenFOAM. And surely after everything will be OK.

Dixi.
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Old   March 11, 2014, 12:26
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Dear Alexey,

many thanks. I will reinstall OpenFOAM. I just have couple of inquiries please
1. could you please go through my previous folder that sent in post number 36 to check if everything is ok or not?

2. What do cm, cl(f), and cl(r) refer to in forceCoeffs.dat?

Regards
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Old   March 11, 2014, 12:50
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In fact it was sarcasm about re-installation of OpenFOAM cause I just wonder why you don't want just to calculate U*D/Nu.

I've already posted source file names where forceCoeffs are calculated, you should check them yourself.

EDIT: And also for some reason you've got center of rotation set wrong.
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Old   March 11, 2014, 12:55
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Dear Alexey,

many thanks for your help.
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Old   March 12, 2014, 03:15
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Dear Alexey,

I reinstalled OpenFOAM in different machine, unfortunately, nothing changed. I'm still confused. I got the same results for velocity, lift and drag coefficients. Could you please help me to get the mistakes in the last attached folder?

Many thanks for your help.
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Old   March 12, 2014, 05:41
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Hi,

Quote:
Originally Posted by Maimouna View Post
I reinstalled OpenFOAM in different machine, unfortunately, nothing changed. I'm still confused. I got the same results for velocity, lift and drag coefficients. Could you please help me to get the mistakes in the last attached folder?
That was easy part. But well, at least you've excluded possible software and hardware problems

Now, the part that is not so easy:

1. How do you calculate Reynolds number?
2. Where is the center of your cylinder? (As the cylinder is the thing that is rotated by the flow, CofR is used to calculate moments (http://en.wikipedia.org/wiki/Pitching_moment))
3. If you change location of CofR to (VERY-LARGE-NUMBER, VERY-LARGE-NUMBER, 0), what will happen with your forceCoeffs.dat?

Try rereading the article to see if initial and boundary conditions you're using in simulation is the same as the ones authors used (hint: as you're initial statement of the problem actually differs from the description in the article, they should be slightly modified).

Start with physics and mathematics, not with software and its settings.
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Old   March 14, 2014, 10:00
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Dear Alexey,

I tried many ways to get the results for drag and lift coefficients that you got. But I still confused about the result that I got. It was totally different than yours.

To calculate Reynolds number, I fixed u = 1, D = 1, and changed nu = 0.001.

For CofR, lRef, and Aref I put
CofR = (4.5 4.5 0) which is the center of the cylinder
lRef = 1.0 which is the diameter length
Aref = 1.0 which is the area D*D

Also,
rhoInf = 1000
liftDir (0 1 0)
dragDir (1 0 0)
pitchAxes (0 0 1)

Whats the mistake please?
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Old   March 14, 2014, 10:11
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Maybe, I'm completely wrong, but I thought that Re = U*D/nu, the U is freestream velocity, D, for the case of vortex street, is diameter of the cylinder, nu is fluid kinematic viscosity. So, if we take your values, Re will be 1000, not 100.
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Old   March 14, 2014, 10:19
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Sorry nu = 0.01 not 0.001.

What do you think I have to change? Any idea please.
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Old   March 14, 2014, 10:22
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I don't know, post your case files again. Cause last time I've checked them, nu was 1000, CofR was in some strange place.
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Old   March 14, 2014, 10:41
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I attached, look at it please.

Many thanks in advanced
Attached Files
File Type: gz circularCylinderNew.tar.gz (4.8 KB, 11 views)
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Old   March 14, 2014, 10:50
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And plots of your results, please.

Also if you really want...
1. to have BCs like in the article you've posted link to, you should change BC on the walls from fixedValue to slip.
2. to have a mesh like in the article, you should introduce mesh grading towards the center-line of the channel.

Though these changes will just slightly change the results.
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Old   March 14, 2014, 10:56
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I posted the result that I got.

I will try another some changes now to see the progress.

I'll keep you in touch.
Attached Images
File Type: jpg Drag_Today.jpg (92.1 KB, 17 views)
File Type: jpg Lift_Today.jpg (95.1 KB, 11 views)
File Type: jpg Velocity-Today.jpg (95.0 KB, 3 views)
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Old   March 14, 2014, 11:12
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Oh, I've missed it. Why you've decided that CofR if (4.5 4.5 0)? Center of cylinder is (4.5 0 0).
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Old   March 14, 2014, 11:24
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Yaaah, ok. I changed CofR to (4.5 0 0) and walls to slip in 0/U and 0/p.

It's running now. I'm going to inform you about the results.
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