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Andrew Parker August 22, 2001 08:18

Turbulent transition
 
Can anybody tell me if it is ok to split my grid into laminar and turbulent regions? I am modeling a hydrofoil; does this violate any physical rules? It's just that I get better results if I split my grid.

Cheers

Andy

Mary August 22, 2001 12:24

Re: Turbulent transition
 
The turbulance equations are just models. Can I use toothpicks and popsicle sticks to model my bridge? Noone knows your system better than you and the more accurate the model, the closer the results are to reality.

Dave August 23, 2001 17:52

Re: Turbulent transition
 
if you are trying to model a wind tunnel experiment for example the transitional point (or line) is often forced by adding roughness to the aerofoil surface.

this is so simulate the transition in flight at a high reynolds number. therefore if the transition point is know you should force it by using a laminar region.

note .. some turbulence models may not let you split the grid like this i.e. spallart-allmaras

Andrew Parker August 24, 2001 08:55

Re: Turbulent transition
 
As far as I can see the Spalart-Allmaras model does allow this, in fact I have been told that if I enforce a laminar zone before the transition point then the turbulence model can not be k-epsilon, as there is no value of k at the beginning of the transition, and it will not be modeled probably. However, I am thinking that it may not be right to a have a laminar region as if my hydrofoil was in water at 10 m/s the water in front of it would be turbulent anyway.

Cheers

Andy

Peter August 25, 2001 16:00

Re: Turbulent transition
 
The mesh choice depends actually on the region you are interesting in. If you have strong interest in the turbulent regions, use then a mesh for turbulent cases, and study the areas you are interested in.


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