CFD Online Logo CFD Online URL
Home > Forums > Siemens

Low-Re and second order discretization

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

LinkBack Thread Tools Display Modes
Old   May 11, 2006, 08:47
Default Low-Re and second order discretization
Posts: n/a
Hi guys,

I'm running the following simulation: starting from an impinging turbulent jet (Re=3000), the flow later goes in a radial diffuser increasing its static pressure (Re=300). The numerical model has got an y+ around 7. By using the first order discretization scheme, and adopting the k-e High Reynolds Number with standard wall functions I've obtained a good convergence and good results. By using the first order discretization scheme, and adopting the k-e Lowh Reynolds Number with hybrid wall functions turbulence model I've obtained better convergence and better results.

To improve the numerical accuracy I've tried to use a second order discretization scheme, but the residuals reach asymptotic values and remain very high (most of all k and e). I've tried LUD, QUICK, CD and MARS with different blending factors, but things don't change. I have also tried the k-w Low Reynolds Number turbulence model and obtained the same bad results.

Furthermore, I have refined the mesh in order to have the y+ close to unity, but nothing change.

What I could do?

  Reply With Quote

Old   May 11, 2006, 10:16
Default Re: Low-Re and second order discretization
Posts: n/a
This is just a rough advice. It is probably more important to apply second order discretisation to velocities than using it for k-e equations. There are a few reasons for this: 1. all transport equations depends on velocity field. 2. for k-e equations, specially k, usually the dominant terms are production and dissipation, that is convection is smaller than these terms. 3. Higher order schemes are usually unbounded and can result in negative values for k and e, which due to the enforcement of positiveness, can cause convergence difficulty.
  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
2nd order time discretization with dynamic mesh Jack FLUENT 1 October 28, 2008 09:07
2nd Order Discretization and Streamwise Periodic Will FLUENT 0 August 29, 2008 12:01
4th order discretization of 2nd order difference dusky.He Main CFD Forum 3 February 14, 2007 09:00
first order time, second order space sven CFX 1 October 27, 2005 13:05
Higher order discretization on staggered grid Chandra Shekhar Main CFD Forum 9 January 27, 2005 17:31

All times are GMT -4. The time now is 11:46.