# Dimensionless wall distance (y plus)

(Difference between revisions)
 Revision as of 09:53, 17 December 2008 (view source)Peter (Talk | contribs)m (Reverted edits by C4tdaRlile (Talk) to last version by Jola)← Older edit Latest revision as of 15:43, 28 March 2014 (view source)Jchawner (Talk | contribs) (One intermediate revision not shown) Line 10: Line 10: 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. 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. - *[http://www.simuserve.com/cfd-shop/GOODIES/YPLUS.HTM Viscous Grid Spacing Calculator] + * [http://www.pointwise.com/yplus/ Y+ Calculator] - : Another y+ estimation script by CHAM. Uses a slightly different approximation formula but also works great. + : 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:

$y^+ \equiv \frac{u_* \, y}{\nu}$

Where $u_*$ is the friction velocity at the nearest wall, $y$ is the distance to the nearest wall and $\nu$ is the local kinematic viscosity of the fluid.

$y^+$ 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.