# What if coase mesh at the boundary?

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 September 20, 2004, 18:42 What if coase mesh at the boundary? #1 GER Guest   Posts: n/a For a turbulence flow, if I am not interested in flow next to wall, can I use coarse mesh at the bounday (in normal direction of wall)? Also, from model aspect, do I have to use fine grid if the model does not use a wall function? Thanks a lot for your valuable input. Ger

 September 21, 2004, 09:03 Re: What if coase mesh at the boundary? #2 ag Guest   Posts: n/a 1. No - behavior at and near the wall is probably the major influence on the flow. 2. Yes - see answer to 1. You need to have a y+ value of about 1 if you do not have wall functions. Otherwise you are wasting CPU cycles.

 September 22, 2004, 12:16 Re: What if coase mesh at the boundary? #3 amol palekar Guest   Posts: n/a If you are not interested in flow near the wall, then why dont you change the boundary conditions at the wall to extrapolation. This way your computational domain will also be small. That should work for flow away from wall and which is not affected by the wall. -amol

 September 22, 2004, 16:35 Re: What if coase mesh at the boundary? #4 ag Guest   Posts: n/a The original poster states that his interest is in turbulent flow. Ignoring the wall (a major source of turbulence) seems rather odd to me.

 September 22, 2004, 18:02 Re: What if coase mesh at the boundary? #5 amol palekar Guest   Posts: n/a I think that may depend on problem at hand. if we have a jet type of configuration which is not wall bounded then i guess effect of wall may no matter. so may be if GER tells abt the particular problem we may know more. amol

 September 23, 2004, 19:31 What if only interested in large scales #6 GER Guest   Posts: n/a I meant that we are interested in large scale motion of turbulence flows in which wall effects cannot be ignored. What's your idea? Ger

 September 23, 2004, 23:57 Re: What if only interested in large scales #7 amol palekar Guest   Posts: n/a In that case I guess you would need fine enough grid to resolve the trubulence as ag had mentioned. -amol

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