how iam determine good quality of mesh grid of airfoil using gambit

nuimlabib · June 29, 2009, 04:00

how to determine the good quality of grid mesh of airfoil using gambit to get a good aerodynamic coefficient...please help me..

linnemann · June 29, 2009, 09:02

Hi

Well that is very much a flow dependent issue.

You have to look at your y+ values for the first cell.

If you want to use nearwall modeling you need a y+ below or equal to 1, although the Fluent manual says below 4, as I can recall.

If you only need to resolve the wall shear layer you need a y+ above 30 and preferably below 100, but not higher than 300.

If you have no idea what y+ is please consult the manual as this is very important for this kind of problem. Searching google for "law of the wall turbulence" you will find information why this is important.

also the book "Bruce R. Munson, Donald F. Young and Theodore H. Okiishi - Fundamentals of Fluid Mechanics" or "Schlichting, Hermann; Gersten, K. - Boundary-layer Theory" are good reads on the topic.

Back to you question,

you don't know if your mesh is sufficiently fine/coarse before you have set it up and have a converged solution in Fluent / other CFD. Fluent has built in features which can refine the mesh based on some values eg. y+, so maybe this would be an idea.

Regards

linnemann · June 29, 2009, 09:11

ooops double post

June 29, 2009, 04:00	how iam determine good quality of mesh grid of airfoil using gambit	#1
nuimlabib New Member labib Join Date: Jun 2009 Posts: 25 Rep Power: 17	how to determine the good quality of grid mesh of airfoil using gambit to get a good aerodynamic coefficient...please help me..

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June 29, 2009, 09:02		#2
linnemann Senior Member Niels Nielsen Join Date: Mar 2009 Location: NJ - Denmark Posts: 556 Rep Power: 27	Hi Well that is very much a flow dependent issue. You have to look at your y+ values for the first cell. If you want to use nearwall modeling you need a y+ below or equal to 1, although the Fluent manual says below 4, as I can recall. If you only need to resolve the wall shear layer you need a y+ above 30 and preferably below 100, but not higher than 300. If you have no idea what y+ is please consult the manual as this is very important for this kind of problem. Searching google for "law of the wall turbulence" you will find information why this is important. also the book "Bruce R. Munson, Donald F. Young and Theodore H. Okiishi - Fundamentals of Fluid Mechanics" or "Schlichting, Hermann; Gersten, K. - Boundary-layer Theory" are good reads on the topic. Back to you question, you don't know if your mesh is sufficiently fine/coarse before you have set it up and have a converged solution in Fluent / other CFD. Fluent has built in features which can refine the mesh based on some values eg. y+, so maybe this would be an idea. Regards

June 29, 2009, 09:11		#3
linnemann Senior Member Niels Nielsen Join Date: Mar 2009 Location: NJ - Denmark Posts: 556 Rep Power: 27	ooops double post