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-   -   Turbulence viscosity ratio (http://www.cfd-online.com/Forums/fluent/29963-turbulence-viscosity-ratio.html)

Fernando July 1, 2002 11:54

Turbulence viscosity ratio
 
Hi to all. I am trying to self-teach myself with FLUENT but I am having some problems with the simulation. When I start the iterations, a message saying "turbulence viscosity is limited by turbulence viscosity ratio in ....cells" comes up all the way to the end of the iterations and the number of cells where this hapeens does not seem to converge I have tried many different meshes, refined here and there. It is a 2-D jet discharge in a cross flow, being both of the order of 70m/s. Also the y+ is ridiculously high, around 80000, and it does not seem to come down as I refine the mesh. If any of you could give me some ideas on how to takcle this problem I would appreciate it a lot. Thanx.

Alammar July 1, 2002 13:12

Re: Turbulence viscosity ratio
 
Try a boundary-layer mesh with Gambit. Also, if you expect steady state, try low-velocity initial conditions.

alain July 2, 2002 04:45

Re: Turbulence viscosity ratio
 
Check if you have a correct scaling for your geometry.

By default fluent use meter as default unit and if your geometry is in mm that exactly that happen : high y+, high viscosity ratio and divergence.

You can change the scale in menu/mesh/scale.

Alain

Puck July 21, 2002 10:00

Re: Turbulence viscosity ratio
 
why cant you jus increase the limit for viscosity ratio?

Puck July 21, 2002 10:06

Re: Turbulence viscosity ratio
 
Is there a certain technique to do boundary layer mesh? cos when i apply a boundary layer, meshing got error. how to tackle this?


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