CFD Online Logo CFD Online URL
Home > Forums > CFX

Reynolds Number Again

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

LinkBack Thread Tools Display Modes
Old   June 2, 2005, 10:03
Default Reynolds Number Again
Posts: n/a
A while some one asked a question about Reynolds number calcualtion in CFX, unfortunately there was no answer, so I thought I will try again. I have been running an external flow simulation. I made 2 models, one a tet dominated mesh without any hex's, and another model with hex dominated meshes, I am getting a higher Reynolds number from the Hex simulated meshes, by the way, I have more volume mesh from the tet dominated model, about 5:1. I am waiting for the wind tunnel report to compare results. Perhaps some one knows how CFX is computing the Re number, perhaps this might help me to figure out the influence of the mesh. Secondly, I am told that Hex mshes for external flows are generally more accurate, has any one tried this or know about it ? Thanks
  Reply With Quote

Old   June 2, 2005, 20:01
Default Re: Reynolds Number Again
Glenn Horrocks
Posts: n/a

The Reynolds number reported in the output file is not a good way to compare results. You should compare results based on the physical quantity you are interested in, such as pressure drop, flow rate, forces on surfaces or whatever.

Hex meshes are in general better than tet meshes, as long as you can generate a good quality hex mesh. A hybrid grid with tets in the domain and prisms at the boundaries is almost as good as a good hex mesh. The problem is that many geometries are very difficult to generate good hex meshes, so in general the hybrid grid method is recommended.

As for comparing the quality of hex, prism and hybrid grids - there is a paper on the CFX-Community site which discusses this.

Regards, Glenn Horrocks
  Reply With Quote

Old   June 2, 2005, 23:34
Default Re: Reynolds Number Again
Posts: n/a
Hi Ogbeni,

The Reynolds number written by the solver is a rough estimate which uses the the cube root of the mesh volume as the length scale and either the average velocity of the boundary conditions or the RMS averaged velocity of the solution as the velocity scale. If density and viscosity vary, then these too are averaged.

Regards, Robin
  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
Problem with decomposePar tool vinz OpenFOAM Pre-Processing 18 January 26, 2011 03:17
Reynolds Number and Heat transfer Coefficient panos_metal FLUENT 0 January 7, 2011 07:37
Low Reynolds Number k-epsilon formulation CFX 10.0 Chris CFX 4 December 8, 2009 00:51
Reynolds Number Matt CFX 0 February 25, 2009 06:40
Trimmed cell and embedded refinement mesh conversion issues michele OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 2 July 15, 2005 04:15

All times are GMT -4. The time now is 21:01.