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how to set y value(distance nearest to the wall) in blockMesh

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Old   April 27, 2011, 07:20
Default how to set y value(distance nearest to the wall) in blockMesh
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Robert Ong
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Hi All,

I've been playing around with the simpleGrading, unfortunately the y I'm after is still far compared to what I want.

Another thing is I have different y values throughout my domain (inlet, outlet, bottom, etc), so do I need to average them out or just consider the highest y value in a particular domain?

Thanks very much for your time and attention.

Regards,
Robert
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Old   April 27, 2011, 08:47
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what do you mean with y value, do you mean your yPlus value? what kind of mesh are you working with? just simple blocks?
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Old   April 27, 2011, 09:04
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Hi Roman,

I meant the y value (not yPlus) used in this formula yPlus=uStar*y/nu. Alternatively, you can also use this http://geolab.larc.nasa.gov/APPS/YPlus/

Yes, I am just dealing with the simple hexagonal blocks with a hemipshere object in the middle which I meshed using cellSet and setSet command after having exported it from the STL file.

Thanks and regards,
Robert
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Old   April 28, 2011, 03:24
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you can calculate your dimension of the cell in wall direction with this

yDim = r / [nCells *{ (l/s)+1} ]

where r is the block length in direction of stretching, nCells, the number cells you want in this direction (l/s) is the ratio between largest an smallest cell, meaning your expansion ratio.

the center will the be the y that you need for the yStar or yPlus calculation your are looking. Therefore, just divide by 2.

if you think you get too many cells you can use the tool
Code:
refineWallLayer
to split only the cells at the wall.
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