# Dimensionless wall distance (y plus)

(Difference between revisions)
 Revision as of 15:11, 11 May 2006 (view source)Jola (Talk | contribs)← Older edit Revision as of 21:36, 12 June 2011 (view source)Peter (Talk | contribs) Newer edit → (4 intermediate revisions not shown) Line 6: Line 6: $y^+$ is often refered to simply as ''y plus'' and is commonly used in boundary layer theory and in defining the [[Law of the wall|law of the wall]]. $y^+$ is often refered to simply as ''y plus'' and is commonly used in boundary layer theory and in defining the [[Law of the wall|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: + + *[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] + :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. [[Category:Dimensionless parameters]] [[Category:Dimensionless parameters]]

## Revision as of 21:36, 12 June 2011

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.