# Dimensionless wall distance (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: | The following online tools can be used to estimate the necessary grid spacing in order to obtain a desired y plus: | ||

+ | |||

+ | *[http://www.cfd-online.com/Tools/yplus.php Y+ Wall Distance Estimation] | ||

+ | : A y+ wall distance estimation script provided by CFD Online. Uses the free-stream velocity and gas-data to estimate the wall distance needed to obtain a desired y+ value at a certain boundary layer length. This is one of those wonderful little tools that saves you from learning a formula! | ||

*[http://geolab.larc.nasa.gov/APPS/YPlus/ Viscous Grid Spacing Calculator] | *[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. | + | :A JavaScript that helps you to estimate at what normal distance from a wall you should place your first grid-line. Variants suitable for compressible flow using total conditions and Mach number also available. |

- | *[http://www. | + | * [http://www.pointwise.com/yplus/ Y+ Calculator] |

- | : | + | : An online calculator written in Javascript for computing the distance of the first grid point off the wall to achieve a desired Y+ value for given flow conditions. iOS and Android versions also available. |

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

## Latest revision as of 15:43, 28 March 2014

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 y+ wall distance estimation script provided by CFD Online. Uses the free-stream velocity and gas-data to estimate the wall distance needed to obtain a desired y+ value at a certain boundary layer length. This is one of those wonderful little tools that saves you from learning a formula!

- A JavaScript that helps you to estimate at what normal distance from a wall you should place your first grid-line. Variants suitable for compressible flow using total conditions and Mach number also available.

- An online calculator written in Javascript for computing the distance of the first grid point off the wall to achieve a desired Y+ value for given flow conditions. iOS and Android versions also available.