CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Prandtl mixing length vs Isotropic assumption

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

LinkBack Thread Tools Display Modes
Old   March 23, 2000, 23:53
Default Prandtl mixing length vs Isotropic assumption
Mohammad Kermani
Posts: n/a

In Prandtl mixing length hypothesis, which is almsot the background of all zero equation models, the turbulent fluctuataions throughout the whole computational domain are modeled as:

u' =. v' =. l*du/dy (=. is appoximation sign)

But ( u' =. v' ) is exactly the definition of isotropic turbulent.

My question: Does not this a violate the anisotropicicity fact of the turbulent close to the wall? i.e. how the Prandtl mixing length hypothesis justifies the anisotropic turbulent close to the wall?

Thanks for your comment.

  Reply With Quote

Old   March 26, 2000, 15:47
Default Re: Prandtl mixing length vs Isotropic assumption
Bob Anderson
Posts: n/a
If this were true, and the only weakness of the mixing length hypothesis, it would be doing pretty well. The mixing length hypothesis is not meant to be any sort of rigorous derivation by any means.

That being said, I think the development is only contingent upon \overline{u'} and \overline{v'} being related by a constant. That constant doesn't have to be particularly small. In fact, it doesn't even have to be constant, since the mixing length is a function of y. You could split off any portion of the y dependence in l and consider it to be part of the relationship between u' and v' if you like.

  Reply With Quote


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
How to define the turbulence intensity and mixing length at an outlet (for k-eps)? david39 OpenFOAM Running, Solving & CFD 6 February 2, 2011 04:01
Turbulence mixing length value eva Main CFD Forum 1 February 27, 2009 15:19
Mixing length models and zero-hvac model in fluent sarah_ron FLUENT 0 November 28, 2004 00:29
mixing length mukkarum Main CFD Forum 4 July 25, 2002 05:16
Prandtl Mixing length Vs. Isotropic turbulent Mohammad Kermani Main CFD Forum 0 March 24, 2000 00:06

All times are GMT -4. The time now is 16:01.