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

Turbulent flow at walls in complex flows

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

LinkBack Thread Tools Display Modes
Old   March 22, 2000, 03:24
Default Turbulent flow at walls in complex flows
Bo Jensen
Posts: n/a
Hallo all

My question is: How does the cfd-programs deal with the velocity near the wall, when the flow is turblent and not parallel to the surface?

When the flow is parallel the programs either use some kind of law-of the wall or uses these new two-layer models. But what if the flow for exampel is over a backward facing step? (the point where the flow divides and a part goes in the recirculation zone just after the expansion and the main part flows down thorugh the channel). Or a jet hitting a wall??


  Reply With Quote

Old   March 22, 2000, 04:28
Default Re: Turbulent flow at walls in complex flows
Dietmar Giebert
Posts: n/a
Dear Bo,

by using wall functions, you have to split the mean velocity vector (at the node closest to the wall) in its vertical and parallel component. The component parallel to the wall is the quantity you have to use in the wall function approach. For recirculating flows the normalized quantity in the u+ definition is formulated as: u+=v_par / u_tau = v_par / (c_mue**0.25 * sqrt(k)) (1). This is done to avoid singularity at separation and reattachment points where the wall shear stress is zero. In eqn. (1) the assumption u_tau = c_mue**0.25 * sqrt(k) has been introduced which is valid for flows in local equilibrium.

When you resolve the boundary layer with a two layer model ,as far as the velocity is concerned, you can treat the velocity at the cell closest to the wall like the velocity at the other grid points.



  Reply With Quote

Old   March 23, 2000, 23:42
Default Re: Turbulent flow at walls in complex flows
Mohammad Kermani
Posts: n/a
Is the wall function also used for the zero-equation models as well, or it is just for the one or two equation models?


  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
Inlet turbulent boundary condition: external flows ROOZBEH FLUENT 3 August 28, 2015 15:34
spectrum: LES of a turbulent channel flow finally goes to turbulent liu OpenFOAM Running, Solving & CFD 6 November 1, 2011 02:00
PhD in turbulence Hans Main CFD Forum 14 October 8, 2001 03:03
Instability and Vortex/roll structure Z. Zeng Main CFD Forum 3 May 10, 2000 05:18

All times are GMT -4. The time now is 04:29.