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?

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.

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

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").

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

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

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