# How do you calculate flue Y+?

## How do you calculate flue Y+?

Choose the named selection for which you want the Y+ and then see the Y-axis for Overall Y+ value. Steps: You have to go to results>plot>histogram form the tree (as shown in figure). Select Turbulence and Wall Yplus from the drop down menu.

## What is the value of y+?

The y+ value is a non-dimensional distance (based on local cell fluid velocity) from the wall to the first mesh node, as you can see in the image below. To use a wall function approach for a particular turbulence model with confidence, we need to ensure that our y+ values are within a certain range.

What is a Y+?

y+ is a non-dimensional distance. It is often used to describe how coarse or fine a mesh is for a particular flow pattern. It is important in turbulence modeling to determine the proper size of the cells near domain walls. The turbulence model wall laws have restrictions on the y+ value at the wall.

### How does Openfoam calculate y+?

To get the yPlus, you can only do it as a post treatment (because you need to compute the velocity first). To get it, simply type “yPlusRas” or “yPlusLes” depending of your turbulence model. You can also write “yPlusLes -h” to get some help.

### What should y+ Be?

When using low-Re models or any models with enhanced wall treatment, the average Y+ value should be on the order of ~1 to ensure we are capturing the laminar sub-layer. When using wall function models, the Y+ value should ideally be above 15 to avoid erroneous modelling in the buffer layer and the laminar sub-layer.

What is first cell height?

This first cell height is practically the distance between the wall and the first grid point. (The characteristic length in most simple terms is the approximate length traversed by the flow over the body, for external flows. For internal flows, it is equal to the hydraulic diameter.)

#### What is Y+ fluent?

y+ is a non-dimensional distance. It is often used to describe how coarse or fine a mesh is for a particular flow pattern. It is important in turbulence modeling to determine the proper size of the cells near domain walls.

#### What is Wall function?

Wall functions are equations empirically derived and used to satisfy the physics in the near wall region. The first cell center needs to be placed in the log-law region to ensure the accuracy of the results. Wall functions are used to bridge the inner region between the wall and the turbulence fully developed region.

What should my y+ Be?

Staying above 35 is ideal although the upper Y+ limit and the accuracy of the results will also be based on the global mesh quality. A mesh sensitivity study should be run to understand this. To raise the Y+, the thickness of the boundary layer (mesh enhancement) could be increased.

## What is a good y+ value?

Generally when you building grid for RANS model of k-epsilon the target value of y+ should be between 30 and 300. The y+ depends on friction velocity u*=sqrt(Tw/rho) where Tw is wall shear stress, element distance to the nearest wall and local kinematic viscosity.

## What is Y+ CFD value?

How do Wall functions work?