# Dimensionless wall distance (y plus)

(Difference between revisions)
 Revision as of 17:43, 11 May 2006 (view source)Jola (Talk | contribs)m (Dimensionless wall distance moved to Dimensionless wall distance (y plus))← Older edit Revision as of 13:37, 18 May 2006 (view source)Jola (Talk | contribs) (Added external links to y plus estimators)Newer edit → 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://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! + + *[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:

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

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 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.