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

how is TKE defined?

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

Like Tree2Likes
  • 1 Post By stud-many
  • 1 Post By sbaffini

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 22, 2020, 18:17
Post how is TKE defined?
  #1
New Member
 
dimitri koletsos
Join Date: May 2020
Posts: 3
Rep Power: 6
dkoletsos is on a distinguished road
I understand that the turbulent kinetic energy is defined as k=1/2(<u_i*u_i>)
where does the factor of 1/2 come from? Is this pure convention? Has an integral been taken? Is there a more general equation, an averaging equation that brings in the factor 1/2?
dkoletsos is offline   Reply With Quote

Old   May 23, 2020, 08:01
Default
  #2
New Member
 
Malte
Join Date: Nov 2017
Posts: 20
Rep Power: 9
stud-many is on a distinguished road
As a kinetic Energy is defined as 1/2 m c**2 , it makes sense to define the tke as 1/2sum(ui'ui'). i guess it would also make sense to multiply this with the fluid-density. wouldn't it? I was only working on incompressible turbulent flows so far. for me, it was pretty handy not to have the density in there
dkoletsos likes this.
stud-many is offline   Reply With Quote

Old   May 23, 2020, 09:00
Default
  #3
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 2,192
Blog Entries: 29
Rep Power: 39
sbaffini will become famous soon enoughsbaffini will become famous soon enough
Send a message via Skype™ to sbaffini
There are several possible answers to this, but for all of them it really is a matter of convention. When you look at it from the fluid mechanics point of view, you really just need to look at it from the following perspective:

\phi \frac{\partial \phi}{\partial t} = \frac{1}{2}\frac{\partial \phi^2}{\partial t}

as the factor really comes out from differentiation. This is for the general kinetic energy. When you apply any average or filter to that, you end up with its turbulent counterpart that, obviously, has the same factor.

From a more general perspective in mechanics, having the factor and the mass in the definition makes it an exact differential which is cool for some manipulations.
dkoletsos likes this.
sbaffini is offline   Reply With Quote

Reply

Tags
turbulent kinetic energy

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
User defined memory value changing minhoabc FLUENT 2 June 22, 2017 07:28
Not defined orientation change while running SU2_CFD mdawson25 SU2 4 May 11, 2017 10:52
why CPtr_ defined as SlicedGeometricField, whereas magSfPtr_ as GeometricField? Jerryfan OpenFOAM Programming & Development 1 July 6, 2016 22:02
fetal overflow in user defined cavitation model unclewallcn CFX 15 January 20, 2016 23:17
definition of TKE and its relationship to buoyancy winter Main CFD Forum 0 December 10, 2007 17:34


All times are GMT -4. The time now is 00:10.