CFD Online Logo CFD Online URL
Home > Forums > FLUENT

Reynolds similarity question

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

LinkBack Thread Tools Display Modes
Old   July 22, 2009, 05:09
Default Reynolds similarity question
New Member
Join Date: Jul 2009
Posts: 2
Rep Power: 0
cmbv is on a distinguished road
I am trying to simplify a multi-component, high temperature and pressurized flow into air at atmospheric conditions.
I heard and have read that two flows are similar as long as their Reynolds numbers match.
So I set up a very simple model a single 25cm channel with a cross sectional area of ~1x1 mm.
I ran this model for the flow with all the components, at a high pressure and a high temperature and then I also ran it for air at atmospheric conditions.
Then I did this very simple calc:
m2 = (mu2*m1) / mu1 where ms are flow rates and mus are viscosity 1 & 2 refer to the two different flows (gas mixture and air)
This are not remotely turbulent they are both in fact very laminar, and both Reynolds numbers match very well.
However when it comes to measuring the pressure drop, they defer by almost an order of magnitude: 7 Pa (air case) and ~70 Pa.
Why is this? Is it not possible to use this for measuring pressure drops this way? How about the distribution of flows, in case there are splits and separations; will they both give you similar right results?
I have tried all sorts of things, most diffusion models, running all the turbulent models turning turbulence off, running incompressible flows, inviscid, double precision, etc All of these have given me an order of magnitude difference.
Do you know why?
cmbv is offline   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
Unanswered question niklas OpenFOAM 2 July 31, 2013 16:03
Reynolds stresses without velocity correlations? Phil Main CFD Forum 1 October 2, 2006 04:29
Obtaining Reynolds Number in FLUENT Emmanuel FLUENT 1 April 21, 2006 17:53
A question about the low Reynolds number k-model Haribort CFX 0 December 27, 2001 02:49
question K.L.Huang CD-adapco 1 March 29, 2000 04:57

All times are GMT -4. The time now is 11:09.