CFD Online URL
[Sponsors]
Home > Forums > FLUENT

How to define turbulent diffusion coeff. for UDS

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 14, 2005, 22:19
Default How to define turbulent diffusion coeff. for UDS
  #1
John
Guest
 
Posts: n/a
I need to use a User Defined Scalar in turbulent flow. However I could not find where I could define turbulent diffusion coefficient for UDS as we usually did, for example, TKE Prandtl number.

I have thought an idea to define diffusion coefficient in the Properties of Materials. But I guessed it was for physical properties instead of properties related to turbulence.

Thanks a lot for your help!

  Reply With Quote

Old   October 15, 2005, 13:04
Default Re: How to define turbulent diffusion coeff. for U
  #2
Wael
Guest
 
Posts: n/a
I think using DEFINE_DIFFUSIVITY
  Reply With Quote

Old   October 15, 2005, 17:21
Default Re: How to define turbulent diffusion coeff. for U
  #3
John
Guest
 
Posts: n/a
If your idea is correct, transport of User Defined Scalar in turbulent flow is not same treated as other scalars such as temperature.

Because the transport of User Defined Scalar in turbulent flow is actually treated in laminar flow, I have to use DEFINE_DIFFUSIVITY to define turbulent diffusion coefficient for UDS by myself.

Is my understanding right?

  Reply With Quote

Old   October 17, 2005, 04:59
Default Re: How to define turbulent diffusion coeff. for U
  #4
RoM
Guest
 
Posts: n/a
Yes, thats right. Although turbulent diffusion tends to overwhelm laminar diffusion so you can neglect it in high Re flows.

Fluent uses the follwing turbulent difusion coefficients

Species transport model (includes laminar+turbulent diffusion)

Diff_coeff=D_lam*C_R(c,t)+C_MU_T(c,t)/0.7 with D_lam = laminar coefficient

Non premixed combustion (full turbulent)

Diff_coeff=C_MU_T(c,t)/0.85

RoM
  Reply With Quote

Reply

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
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 07:20
NOT Mass converges on Turbulent Diffusion Flame Yoon Main CFD Forum 0 February 8, 2007 09:17
low turbulent reynold number C-CARE CFX 4 March 12, 2004 07:36
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 07:13
Diffusion Coef. of a Scalar C.H. Huang Main CFD Forum 2 August 18, 1999 04:48


All times are GMT -4. The time now is 10:38.