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-   -   boundary layer meshing (http://www.cfd-online.com/Forums/fluent/29016-boundary-layer-meshing.html)

santosh October 24, 2001 13:00

boundary layer meshing
 
hi,

I am trying to simulate turbulent flow over an gas turbine blade.I tried to apply boundary layer at the blade surface to have better control while refining.

when I used a particular boundary mesh I had problems in convergence.but,when I increased the no.of rows in the boundary layer and made it thick,the solution converged beautifully.

Can somebody explain this phenomenon,and also give any advice on boundary layer meshing?


john October 26, 2001 12:42

Re: boundary layer meshing
 
What was your y+ ? If it is too low and you use standard-wall-models, the "solution" often does not converge.

santosh October 28, 2001 03:18

Re: boundary layer meshing
 
hi,

thanks for the reply,but if the solution does not converge,and I compute the y+ after some iterations,will the y+ indicate the correct trend?

santosh

Jonas Larsson October 28, 2001 08:50

Re: boundary layer meshing
 
There is no clear answer to that, it depends on how "not-converged" your solution is and what causes it not to converge.

However, you can quite easily estimate the y+. There is even a small java-script on the net which allows you to do it interactively - you can find a link to it on this site ( http://www.cfd-online.com/Resources/calcs.html#misc, the link is named "viscous grid spacing calculator").

david October 29, 2001 08:42

Re: boundary layer meshing
 
A) u can mesh based on y+ and y* B) what do u mean by correct trend ? do u mean if it is 600 at some stage of calculation, does it mean the correct solution even though it decreases over large number of iterations ?

DC

santosh October 31, 2001 08:53

Re: boundary layer meshing
 
hi,

by correct trend what I mean is that say,the calculation proceeds to 200 iterations and then diverges,if I estimate y+ value at this point,how correct is this estimate?

santosh

david November 1, 2001 18:54

Re: boundary layer meshing
 
A) At any stage you calculate y+, it will give the correct value B) At that point even though it's within (if) the limit, it doesn't necessarily mean that the solution of the prob is correct


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