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

Turbulent Channel validation case - Pressure gradient

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

Like Tree1Likes
  • 1 Post By sbaffini

LinkBack Thread Tools Display Modes
Old   July 8, 2015, 08:22
Question Turbulent Channel validation case - Pressure gradient
New Member
Join Date: Jul 2015
Posts: 1
Rep Power: 0
ZviH is on a distinguished road

I'm trying to validate an LES code using DNS data by Moser for the fully-turbulent channel case.

I have seen some posts about it here before, but I can't find how the pressure gradient is determined to reproduce the DNS Re_tau values. This is not specified anywhere as far as I know and I'd like to keep the trail-and-error steps to a minimum...

For example, the DNS data shows that Re_Tau of ~550 for Lref and Uref of 1 is achieved with a bulk Re of 10,000 - but no pressure is prescribed.

Just to point out something:
I've seen posts like this, where the pressure gradient is modified on-the-fly (although I'm not clear exactly how to use the difference of mean flow rates) - however shouldn't the flow be driven by a constant gradient?
If I do need to get the pressure gradient corrected - I need to base that on the mean-velocity given by the DNS data, where the mean velocity in the LES case take a while to converge, won't it cause stability issues in the beginning (rapid change of the pressure gradient)?


Last edited by ZviH; July 8, 2015 at 11:33.
ZviH is offline   Reply With Quote

Old   July 8, 2015, 13:04
Senior Member
sbaffini's Avatar
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 784
Blog Entries: 17
Rep Power: 21
sbaffini will become famous soon enough
Long story short:

1) Most DNS use a fixed mass flow rate (instead of pressure gradient), that' s why the pressure gradient is not specified.

2) If your channel has height H=2, rho=1, mu=1/Re_tau then dp/dx=-1 will work for any given value of Re_tau. Note that this is only true in DNS, where the exact channel flow equations (should) hold.
LES is almost there (depending on the resolution, SGS model, etc.) and you can double-check by actually computing u_tau from your mean velocity profile. This should be 1 with these parameters and no errors (i.e., DNS).
FMDenaro likes this.
sbaffini is offline   Reply With Quote

Old   July 8, 2015, 16:11
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,564
Rep Power: 40
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
I am quite sure this issue has been already discussed in other posts in cfd-online forum....
FMDenaro is offline   Reply With Quote


channel flow, turbulence

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
Problem with divergence TDK FLUENT 11 July 31, 2016 06:03
static vs. total pressure auf dem feld FLUENT 17 February 26, 2016 14:04
Compare the pressure of potential flow and a turbulent case of cylinder ooo OpenFOAM Running, Solving & CFD 0 August 2, 2013 07:25
Pressure Driven Supersonic Flow in Converging-Diverging Nozzle cdm OpenFOAM Running, Solving & CFD 4 July 21, 2013 16:24
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00

All times are GMT -4. The time now is 02:45.