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Turbulrnt flow past cylinder

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Old   October 21, 2013, 06:34
Post Turbulrnt flow past cylinder
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Hi Foamers
I want simulate the flow past circular cylinder with very high reynolds no of order 10000 and above. Could you please tell which solver can be used to handle these turbulent flows. ?????
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Old   October 22, 2013, 08:46
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That depends on what you want to study in your simulations, please be a bit more specific. Ideally, Have a look at this first:

How to give enough info to get help

Al the best,

A
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Old   October 23, 2013, 03:29
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Thomas Reviol
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Hi,

I simulated such a case a few month ago.

And as expected, with RAS-Models the problem of the karman vortex street will result in relativ "bad" values. My intention was to show the phenomenon of this flow, so a RAS-Model was sufficient to me.

But if you want to compare your results with a test case, or you want to analyze drag-coefficients or something else, you should choose a better turbulence modelling. For example the DES- or even the LES-Model. but I have no experience with these models.

Have fun with the Karman vortex street :-)

Regards

Thomas
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Old   October 23, 2013, 05:30
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The standard solver can be found at: http://www.openfoam.com/features/standard-solvers.php

For turbulence models have a look at:
http://www.cfd-online.com/Wiki/Turbulence_modeling
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Old   October 23, 2013, 23:51
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Hi TReviol,

I would like to know which solver did u use to run RAS-models ?
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Old   October 24, 2013, 03:23
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Hi,

I used pisoFoam. I needed different grids to find out an appropriate grid-distance. Further more the timeStep was difficult to estimate. I used an correlation of Reynolds No. and Strouhal No. (for an example follow this link). I reached good results with kOmegaSST - but only for "coarse" grids. For fine grids and kOmegaSST the flow phenomenon was overestimated.

At least I analyzed the time averaged values for p and U and compared them with an test-Case. I also repeated all my effort with fluent and CFX to demonstrate the failure off RAS-turbulence-modelling when calculating high turbulent detachment flow.

Here are my results: karman.jpg


Thomas
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Old   October 24, 2013, 05:29
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Hi TReviol,
I want to simulate the same case but the geometry is Circular Cylinder instead of Square cylinder for the Re no of the order 10,000 and greater and want to use simpleFOAM with k-epsilon turbulent model.
Does it give comparably good results ????
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Old   October 24, 2013, 07:30
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Hi,
simpleFoam will not be sufficient, because simpleFoam is a steadyState solver. You have tho solve transient flow phenomenons.

Regards Thomas
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Old   October 25, 2013, 05:46
Default yPlusRAS problem
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Hi
I used simpleFOAM with standard k-epsilon model for Flow past circular cylinder .
Re = 10^6
Velocity = 10 m/s
Kinematic Viscosity = 10^-5
Walls = slip condition
But y+ value is going far beyond.
Can anybody help me how to get rite value of y+ ??
Attached Images
File Type: jpg Screenshot from 2013-10-25 14:51:24.jpg (43.8 KB, 22 views)
File Type: jpg Screenshot from 2013-10-25 14:59:44.jpg (69.9 KB, 28 views)
File Type: jpg BOUNDARIES.jpg (99.2 KB, 32 views)
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Old   October 25, 2013, 05:55
Default o files of simpleFOAM
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Hi
Kindly find the attached 0 file for reference
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File Type: zip 0.zip (58.9 KB, 26 views)
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Old   October 25, 2013, 08:08
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Thomas Reviol
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Hi,

in my case, the front and back faces were set as a cyclic-conditions. The other initial conditions of my case look similar to your conditions. But maybe a better choice is necessary for better agreement with empirical Data (e.g. inletOutlet and totalPressure conditions).

Yor question about y+ values may be answerde with this link.

Regards

Thomas
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Old   October 29, 2013, 06:50
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Hi TReviol,

Could u please share your pimpleFOAM case set up ?

Regards,
Sam Ho
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Old   October 29, 2013, 06:57
Post Specifying Boundary Conditions in pimpleFOAM
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Hi Foamers,

I am stuck up with specifying Boundary conditions like
K, epsilon, nut, nuTilda for the flow past cylinder with following conditions...
Kinematic viscosity = 10^6 m2/s
Re = 2.5 x 10^5
free stream velocity = 0.25 m/s

Kindly help me
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Old   October 29, 2013, 07:33
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Thomas Reviol
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Hi,

have a look at this link.

But choose your characteristic length carefully. I always initialize with the "Fluent" formulas. Fluent scales the characteristic length with a factor. I think the factor is 0.07, but I am not sure.

In many cases, you doesn't need to initalize the turbulent viscosity. So maybe you can delete the file nut (and even nuTilda, when you have choosen kEpsilon).

Thomas
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Old   October 29, 2013, 07:59
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Thank you TReviol
I will set up the case with these information and if any problem i will post on this link.
Kindly help me in that case
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Old   November 8, 2013, 04:49
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Quote:
Originally Posted by TReviol View Post
Hi,

have a look at this link.

But choose your characteristic length carefully. I always initialize with the "Fluent" formulas. Fluent scales the characteristic length with a factor. I think the factor is 0.07, but I am not sure.

In many cases, you doesn't need to initalize the turbulent viscosity. So maybe you can delete the file nut (and even nuTilda, when you have choosen kEpsilon).

Thomas
Hi
Please look in to the following link and help me to resolve the issue.
http://www.cfd-online.com/Forums/openfoam-solving/126061-turbulrnt-flow-past-cylinder-new-post.html
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