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quarkz November 18, 2006 23:31

Correct way to generate grids for boundary layer
 
Hi,

I need to generate grid which are fine enough to capture the boundary layer for my laminar external airfoil flow. Then I'm going to use my 2D FVM NS solver to get the solutions.

Is this way correct?:

1 use flat plate approximation formula of Blasius ie delta y (boundary layer thickness) = 5*x/sqrt(Re), x=characteristic length.

2. knowing my problem's Re, I can get delta y.

3 assumming I'm using 20 pts to capture the boundary layer, each grid spacing is delta y/20.

4. hence, i generate a grid whereby there's 20 rectangular cells of equal thickness of delta y/20 away from the airfoil wall. after that, the cells' thickness increases to reduce the no. of cells required.

Is this a reasonable way to capture the boundary layer accurately?

Thanks!


Munikrishna November 19, 2006 01:58

Re: Correct way to generate grids for boundary lay
 
For Laminar flows, this is reasonable way; this is how I also generate laminar grids.

Bounecer November 19, 2006 10:46

Re: Correct way to generate grids for boundary lay
 
I'm simulating flow about airfoil. With grid generation technic I'm solving NS equations over a domain of radius 20xchord.But i don't give any particular treatment to the boundary layer zone.

mar November 20, 2006 11:42

Re: Correct way to generate grids for boundary lay
 
Even in the boundary layer you can enlarge the normal grid spacing using a stretching function.


quarkz November 23, 2006 22:43

Re: Correct way to generate grids for boundary lay
 
so is there any optimal spacing no. for the boundary layer? most of the time i see ppl using around 30. is this the same for different RE no.? At higher Re (5e3 - 5e4), must the spacing no. for increased?

btw, enlarging the grid spacing with a stretching function may make the computation more accurate but the matrix will take a longer time to solve.

Ahmed November 24, 2006 00:25

Re: Correct way to generate grids for boundary lay
 
Have a look at the following book: Boundary Layer Analysis by Joseph A. Schetz. It has a collection of FORTRAN codes to solve this and other Boundary Layer problems, he used 50 nodes in a case similar to yours Wish you nice reading


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