CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Low Reynolds K Epsilon Launder Sharma Model Functions Doubt...

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   January 10, 2012, 12:58
Unhappy Low Reynolds K Epsilon Launder Sharma Model Functions Doubt...
  #1
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Hi folks,

I am trying to implement the Low Reynolds K Epsilon Launder Sharma Turbulence Model in 3D from scratch because I will need to some changes later on to implement two phase modeling.

However I have some doubts about the E and D model functions, as seen in the wiki section: http://www.cfd-online.com/Wiki/Low-Re_k-epsilon_models.

I am unsure if these functions only apply to the YY axis, or do I need to use a gradient for them?? For D the gradient is pretty straightforward, but for E
I am struggling a bit? Do I have 3 or 6 terms for the gradient, because the partial derivatives change depending on which axis you differentiate first...

Hope it's clear and someone can help..

Cheers!

Rui
RSilva is offline   Reply With Quote

Old   January 10, 2012, 14:30
Default
  #2
Administrator
 
jola's Avatar
 
Jonas Larsson
Join Date: Jan 2009
Location: Gothenburg, Sweden
Posts: 171
Rep Power: 10
jola is on a distinguished road
Send a message via MSN to jola Send a message via Skype™ to jola
y in those formulas refers to the direction normal to the wall. Hence, in a 3D code it will be dependent on how the wall is oriented and will be a combination of x,y and z.
jola is offline   Reply With Quote

Old   January 10, 2012, 18:38
Default
  #3
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Thank you for your reply jola!

Could you suggest some articles or thesis or anyother source that has
those equation so that I can better understand?

Cheers!

Rui
RSilva is offline   Reply With Quote

Old   January 11, 2012, 11:23
Default
  #4
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Also, regarding the extra source terms:

for two dimensional pipe flow and assuming flow in the x-direction, the normal is y.

However, in 3D and pipe flow in the z-direction, both x and y are normal to the flow.

I am not quite understanding how to combine the three coordinates in the extra source terms.

Could you please provide some more details.

Thank you.

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   January 12, 2012, 12:45
Default
  #5
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
I guess I have some progress...

So, I believe that for 3D the extra source term:

E\epsilon =\left (\frac{\partial^{2} u }{\partial x^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} u }{\partial y^{2}} \right)^{^{2}}+\left (\frac{\partial^{2} u }{\partial z^{2}} \right )^{^{2}} + \left (\frac{\partial^{2} v }{\partial x^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} v }{\partial y^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} v }{\partial z^{2}} \right )^{^{2}} + \left (\frac{\partial^{2} w }{\partial x^{2}} \right  )^{^{2}}+\left (\frac{\partial^{2} w }{\partial y^{2}} \right  )^{^{2}}+\left (\frac{\partial^{2} w }{\partial z^{2}} \right )^{^{2}}
+ 2 \left [ \left (\frac{\partial^{2} u }{\partial x \partial y} \right )^{^{2}} + \left (\frac{\partial^{2} u }{\partial x \partial y} \right )^{^{2}}+ \left (\frac{\partial^{2} u }{\partial z \partial y} \right )^{^{2}}\right ] + 2 \left [ \left (\frac{\partial^{2} v }{\partial x \partial y}  \right )^{^{2}} + \left (\frac{\partial^{2} v }{\partial x \partial y}  \right )^{^{2}}+ \left (\frac{\partial^{2} v }{\partial z \partial y}  \right )^{^{2}}\right ] +2 \left [ \left (\frac{\partial^{2} w }{\partial x \partial y}  \right )^{^{2}} + \left (\frac{\partial^{2} w }{\partial x \partial y}  \right )^{^{2}}+ \left (\frac{\partial^{2} w }{\partial z \partial y}  \right )^{^{2}}\right ]

Is this a correct assumption?
I think it's a bit long when compared with the two dimensional case, however it seems logical when I look at the general expression:

2\mu \mu _{T}\left (\frac{\partial^{2} u_{i} }{\partial x_{j} \partial x_{k}}   \right )^{2}

I wonder if it's correct for the 3D case...

Can anyone provide some input?

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   August 1, 2013, 07:55
Default
  #6
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
hi Rui,

Did you manage to apple the model in two phase model?



Quote:
Originally Posted by RSilva View Post
I guess I have some progress...

So, I believe that for 3D the extra source term:

E\epsilon =\left (\frac{\partial^{2} u }{\partial x^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} u }{\partial y^{2}} \right)^{^{2}}+\left (\frac{\partial^{2} u }{\partial z^{2}} \right )^{^{2}} + \left (\frac{\partial^{2} v }{\partial x^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} v }{\partial y^{2}} \right )^{^{2}}+\left (\frac{\partial^{2} v }{\partial z^{2}} \right )^{^{2}} + \left (\frac{\partial^{2} w }{\partial x^{2}} \right  )^{^{2}}+\left (\frac{\partial^{2} w }{\partial y^{2}} \right  )^{^{2}}+\left (\frac{\partial^{2} w }{\partial z^{2}} \right )^{^{2}}
+ 2 \left [ \left (\frac{\partial^{2} u }{\partial x \partial y} \right )^{^{2}} + \left (\frac{\partial^{2} u }{\partial x \partial y} \right )^{^{2}}+ \left (\frac{\partial^{2} u }{\partial z \partial y} \right )^{^{2}}\right ] + 2 \left [ \left (\frac{\partial^{2} v }{\partial x \partial y}  \right )^{^{2}} + \left (\frac{\partial^{2} v }{\partial x \partial y}  \right )^{^{2}}+ \left (\frac{\partial^{2} v }{\partial z \partial y}  \right )^{^{2}}\right ] +2 \left [ \left (\frac{\partial^{2} w }{\partial x \partial y}  \right )^{^{2}} + \left (\frac{\partial^{2} w }{\partial x \partial y}  \right )^{^{2}}+ \left (\frac{\partial^{2} w }{\partial z \partial y}  \right )^{^{2}}\right ]

Is this a correct assumption?
I think it's a bit long when compared with the two dimensional case, however it seems logical when I look at the general expression:

2\mu \mu _{T}\left (\frac{\partial^{2} u_{i} }{\partial x_{j} \partial x_{k}}   \right )^{2}

I wonder if it's correct for the 3D case...

Can anyone provide some input?

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   August 5, 2013, 10:05
Default
  #7
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Hello Kanarya,

yes I was. I am using it now in my simulations.

How can I help you?

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   August 5, 2013, 10:40
Default
  #8
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Rui,
do you have already publish some results?
Or do you have some comparison with the classical methods with wall function!
I already did it for single case but I have some difficulties to apply damping function to the wall with solid included case. Can you give me some reference about it?

thanks a lot
Quote:
Originally Posted by RSilva View Post
Hello Kanarya,

yes I was. I am using it now in my simulations.

How can I help you?

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   August 5, 2013, 11:24
Default
  #9
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Hello Kanarya,

I'm finishing a paper on the subject but is not yet pusblished.

I can try and point in the right direction, but I cannot as of now provide you with some of the coding. I'm sure you understand.

So, the papers that helped me out were the following:

- C. M. Hrenya [1995] Comparison of low Reynolds number κ—ε turbulence models in predicting fully developed pipe flow

- J. J. Costa [1999] Test Of Several Version For The k-e Type Turbulence Modelling

- On the Mixture Model for Multiphase Flow

Also, remrmber that meshing is always an issue.

Hope this helps and let me know if you need anything.

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   August 5, 2013, 11:48
Default
  #10
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Rui,

Thanks for the quick answer!
Did you use mixture approach or dispersed one?
What is your application e.g gas-solid , gas-liquid, dense or dilute?
Because I am simulating gas solid CFB system and I want to include in both equation source term which includes the momentum interchange between two phases!

Thanks a lot again!
Quote:
Originally Posted by RSilva View Post
Hello Kanarya,

I'm finishing a paper on the subject but is not yet pusblished.

I can try and point in the right direction, but I cannot as of now provide you with some of the coding. I'm sure you understand.

So, the papers that helped me out were the following:

- C. M. Hrenya [1995] Comparison of low Reynolds number κε turbulence models in predicting fully developed pipe flow

- J. J. Costa [1999] Test Of Several Version For The k-e Type Turbulence Modelling

- On the Mixture Model for Multiphase Flow

Also, remrmber that meshing is always an issue.

Hope this helps and let me know if you need anything.

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   August 5, 2013, 11:52
Default
  #11
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Hi,

I'm using the Mixture Model because Im modelling a solid-liquid dense suspension.

Since you are gas-solid, I recomend the works of Elghobashi (I believe it is spelled this way).

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   August 5, 2013, 12:00
Default
  #12
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Rui,

thanks for your time and patients!
did you get improvement near the wall without wall treatment (dense mesh) in comparison to classical models?
I am looking forward to read your paper!
thanks!
best!
kanarya
Quote:
Originally Posted by RSilva View Post
Hi,

I'm using the Mixture Model because Im modelling a solid-liquid dense suspension.

Since you are gas-solid, I recomend the works of Elghobashi (I believe it is spelled this way).

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   August 5, 2013, 12:10
Default
  #13
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Yes, I did.

The classic wall function behaves very poorly with particles, at least in solid-liquid case that I study.

Best Regards,

Rui
RSilva is offline   Reply With Quote

Old   September 9, 2013, 05:26
Default
  #14
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Rui,

what do you mean with "Also, remember that meshing is always an issue"?
do we need dense mesh near the wall for damping function as well (like Y+ =1 or Y+ =30). Y+ = 30 should be enough,right?

thanks in advance!

Best!

Kanarya
Quote:
Originally Posted by RSilva View Post
Hello Kanarya,

I'm finishing a paper on the subject but is not yet pusblished.

I can try and point in the right direction, but I cannot as of now provide you with some of the coding. I'm sure you understand.

So, the papers that helped me out were the following:

- C. M. Hrenya [1995] Comparison of low Reynolds number κε turbulence models in predicting fully developed pipe flow

- J. J. Costa [1999] Test Of Several Version For The k-e Type Turbulence Modelling

- On the Mixture Model for Multiphase Flow

Also, remrmber that meshing is always an issue.

Hope this helps and let me know if you need anything.

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   September 9, 2013, 07:00
Default
  #15
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
Hi Kanarya,


I think that for Low Re models you should go for Y+=1.

This is due to the anisotropic behaviour near the wall.

The meshing issue comes from two points: 1) refine mesh until the results do not vary and 2) the RAM limitations for really dense meshes.

Hope this helps.

Best Regards,

Rui

Quote:
Originally Posted by Kanarya View Post
Hi Rui,

what do you mean with "Also, remember that meshing is always an issue"?
do we need dense mesh near the wall for damping function as well (like Y+ =1 or Y+ =30). Y+ = 30 should be enough,right?

thanks in advance!

Best!

Kanarya
RSilva is offline   Reply With Quote

Old   September 9, 2013, 07:17
Default
  #16
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Thanks a lot Rui!
Quote:
Originally Posted by RSilva View Post
Hi Kanarya,


I think that for Low Re models you should go for Y+=1.

This is due to the anisotropic behaviour near the wall.

The meshing issue comes from two points: 1) refine mesh until the results do not vary and 2) the RAM limitations for really dense meshes.

Hope this helps.

Best Regards,

Rui
Kanarya is offline   Reply With Quote

Old   February 17, 2014, 06:59
Default damping function in gas solid multiphase flows
  #17
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Rui,
Did you publish your paper about damping function in gas solid multiphase flows.
can you give me some referance about it?
thanks!
Kanarya is offline   Reply With Quote

Old   February 17, 2014, 10:52
Default
  #18
New Member
 
R. Silva
Join Date: Apr 2011
Posts: 29
Rep Power: 6
RSilva is on a distinguished road
My paper is on Solid-liquid multiphase flows.
I'mm finalizing the paper and will submit it soon.

If I get accpeted for publication I'll share the link here.

I appologize if I gave the wrong impression.


Best Regards,

Rui

Quote:
Originally Posted by Kanarya View Post
Hi Rui,
Did you publish your paper about damping function in gas solid multiphase flows.
can you give me some referance about it?
thanks!
RSilva is offline   Reply With Quote

Reply

Tags
k epsilon, low reynolds, model functions

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
low reynolds number models in Fluent doug Main CFD Forum 6 August 4, 2012 14:39
low Reynolds Model for pipe flow RugbyGandalf OpenFOAM 9 July 4, 2011 11:28
Wall functions for near wall treatment : k - epsilon model fivos Main CFD Forum 4 April 27, 2011 07:44
low reynolds k omega / wall functions stawrogin OpenFOAM 1 March 30, 2011 06:04
SimpleFoam k and epsilon bounded nedved OpenFOAM Running, Solving & CFD 1 November 25, 2008 21:21


All times are GMT -4. The time now is 17:26.