Enter the absolute distance from the wall, kinematic viscosity, and friction velocity into the calculator to determine Y+.

## Y+ Formula

The following formula is used to calculate Y+

Y+ = (y*u) / v

• Where Y+ is the local reynolds number
• y is the absolute distance from the wall
• v is the kinematic viscosity
• u is the friction velocity

## What is Y+?

Definition:

Y+ is a term used in computational fluid dynamics (CFD) to describe a “local Reynolds number” of flow near a wall.

Y+ is dimensionless and unitless.

## How to calculate Y+?

Example Problem:

The following example problem outlines how to calculate Y+ in a fluid dynamics problem.

First, determine the absolute distance from the wall being analyzed. In this case, the distance is .35.

Next, determine the friction velocity near the wall. In this example, the friction velocity is 5.

Next, determine the kinematic viscosity of the fluid. For this problem, the kinematic viscosity is measured to be 1.25.

Finally, calculate Y+ using the formula above:

Y+ = (y*u) / v

Y+ = (.35*5) / 1.25

Y+ = 1.4