# Dimensionless wall distance (y plus)

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<math>y^+</math> is often refered to simply as ''y plus'' and is commonly used in boundary layer theory and in defining the [[Law of the wall|law of the wall]]. | <math>y^+</math> is often refered to simply as ''y plus'' and is commonly used in boundary layer theory and in defining the [[Law of the wall|law of the wall]]. | ||

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+ | == Estimation of y plus == | ||

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+ | The following online tools can be used to estimate the necessary grid spacing in order to obtain a desired y plus: | ||

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+ | *[http://geolab.larc.nasa.gov/APPS/YPlus/ Viscous Grid Spacing Calculator] | ||

+ | :A JavaScript that helps you to estimate at what normal distance from a wall you should place your first grid-line. This is one of those wonderful little tools that saves you from learning a formula! | ||

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+ | *[http://www.simuserve.com/cfd-shop/GOODIES/YPLUS.HTM Viscous Grid Spacing Calculator] | ||

+ | : Another y+ estimation script by CHAM. Uses a slightly different approximation formula but also works great. | ||

[[Category:Dimensionless parameters]] | [[Category:Dimensionless parameters]] |

## Revision as of 13:37, 18 May 2006

A non-dimensional wall distance for a wall-bounded flow can be defined in the following way:

Where is the friction velocity at the nearest wall, is the distance to the nearest wall and is the local kinematic viscosity of the fluid.

is often refered to simply as *y plus* and is commonly used in boundary layer theory and in defining the law of the wall.

## Estimation of y plus

The following online tools can be used to estimate the necessary grid spacing in order to obtain a desired y plus:

- A JavaScript that helps you to estimate at what normal distance from a wall you should place your first grid-line. This is one of those wonderful little tools that saves you from learning a formula!

- Another y+ estimation script by CHAM. Uses a slightly different approximation formula but also works great.