# Reynolds Number of a non-uniform duct

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 February 10, 2020, 04:10 Reynolds Number of a non-uniform duct #1 Senior Member   Raza Javed Join Date: Apr 2019 Location: Germany Posts: 182 Rep Power: 2 Hello Everyone, I have a question relating to the calculation of the Reynold number. If I have a non-uniform duct or may be a pipe, and at the inlet of the pipe, the cross-section area will be different, and as the length of the pipe increases, the area and the shape of the pipe changes. Now, in this case if I want to calculate the Reynolds number to check whether my flow will be laminar or Turbulent. Do I need to just consider the area of the pipe at the inlet and calculate the Reynolds number or is there any other way to calculate it in this case? Thank you for your help. Raza

 February 11, 2020, 00:19 #2 Member   Glenn Carlson Join Date: Oct 2012 Location: US Posts: 44 Rep Power: 9 Hi, Raza. The critical Reynolds number dividing laminar and turbulent flow regimes was found from experiments with long round pipes. Flow in non-uniform ducts may show recirculation, separation, or other phenomena that don't arise for long straight pipe. Therefore, the well-known Re.crit = 2000 should not be assumed correct for other shaped pipe. If a non uniform pipe has a long straight section, it begins to make sense to apply a Reynolds numbee in that section. But, otherwise, IMO, the Reynolds number is not particularly useful for non-uniform pipes. Regards, Glenn Last edited by gcengineer; February 11, 2020 at 01:43.

February 11, 2020, 04:05
#3
Senior Member

Raza Javed
Join Date: Apr 2019
Location: Germany
Posts: 182
Rep Power: 2
Quote:
 Originally Posted by gcengineer Hi, Raza. The critical Reynolds number dividing laminar and turbulent flow regimes was found from experiments with long round pipes. Flow in non-uniform ducts may show recirculation, separation, or other phenomena that don't arise for long straight pipe. Therefore, the well-known Re.crit = 2000 should not be assumed correct for other shaped pipe. If a non uniform pipe has a long straight section, it begins to make sense to apply a Reynolds numbee in that section. But, otherwise, IMO, the Reynolds number is not particularly useful for non-uniform pipes. Regards, Glenn

Hi Glenn,

Thank you so much for your reply.

As I am modelling the air Flow, in this case, if I want to check whether the flow will be laminar OR Turbulent, what could be the possible approach to do that?

Thank you.

 Tags laminar, reynolds number, turbulence

 Thread Tools Search this Thread Search this Thread: Advanced Search Display Modes Linear Mode

 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 OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post [snappyHexMesh] Error snappyhexmesh - Multiple outside loops avinashjagdale OpenFOAM Meshing & Mesh Conversion 53 March 8, 2019 10:42 thomas. OpenFOAM Running, Solving & CFD 9 March 30, 2016 07:45 Sargam05 OpenFOAM 16 April 30, 2013 17:18 [swak4Foam] Air Conditioned room groovyBC Sebaj OpenFOAM Community Contributions 7 October 31, 2012 15:16 Wolle OpenFOAM 2 April 11, 2011 08:32

All times are GMT -4. The time now is 09:32.

 Contact Us - CFD Online - Privacy Statement - Top