Table of Contents
- 1 What is Wall Y+ value?
- 2 What should y+ value be?
- 3 Which turbulence method is suitable for wall Y+ 5?
- 4 What y+ Should I use in my simulations?
- 5 How do you find y+ in CFX?
- 6 What is non equilibrium wall function?
- 7 How does the near-wall model affect the fidelity of numerical solutions?
- 8 Where is the friction velocity at the nearest wall?
What is Wall Y+ value?
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 should y+ value be?
A value of 2 is typically OK although this might need to be as low as 1, especially when capturing boundary layer heat transfer. 10 boundary layers are typically recommended with SST. Also try changing the layer gradation, switching from auto to approximately 1.4. This can help to reduce the Y+ value.
What is Wall distance in CFD?
Dear mohammad, for a given point in a fluid, the wall distance used in CFD codes is usually computed as the minimum distance between the given point and any of the points on the wall boundaries of the domain, irrespective of the angle formed between the wall and the line connecting the two points.
How do you find y+?
Hi @somaya you check the Y+ value by selecting a turbulence model and then after hybrid initialization or running few iterations you can check the wall Y+ value in XY plots under turbulence section. Choose the named selection for which you want the Y+ and then see the Y-axis for Overall Y+ value.
Which turbulence method is suitable for wall Y+ 5?
k-w and k-epsilon can only have good results(velocity profile, skin friction etc.) when y+ is close to 1. For y+ between 5 and 30, you should use wall function with unified form, such as one that Spalding suggested.
What y+ Should I use in my simulations?
Based on above discussion I would like to give you some guidelines / best practices: Keep Y+ below 10 for viscous dominate flows with separation. Use Y+ < 1 for the transition prediction and heat transfer calculations. Use Y+ < 10 for SST model (omega based models in general)
How do you find the Y+ value in Ansys?
How do you check y+ value in Ansys meshing?
How do you find y+ in CFX?
Re: Checking of Y+ values Click on the ‘…’ box and a window containing many more variables will appear. Scroll down towards the bottom of this list and select ‘Yplus’. Click OK, then click Apply to generate the contour of Y+.
What is non equilibrium wall function?
The nonequilibrium wall functions account for the effect of pressure gradients on the distortion of the velocity profiles. In such cases the assumption of local equilibrium, when the production of the turbulent kinetic energy is equal to the rate of its distruction, is no longer valid.
What is the wall function approach and Y+ value required?
We have learnt that the wall function approach and y+ value required is determined by the flow behaviour and the turbulence model being used. If you have an attached flow, then generally you can use a Wall Function approach, which means a larger initial y+ value, smaller overall mesh count and faster run times.
What is YY+ wall distance estimation?
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!
How does the near-wall model affect the fidelity of numerical solutions?
The near-wall modeling significantly impacts the fidelity of numerical solutions, inasmuch as walls are the main source of mean vorticity and turbulence. After all, it is in the near-wall region that the solution variables have large gradients, and the momentum and other scalar transports occur most vigorously.
Where is the friction velocity at the nearest wall?
Where is the friction velocity at the nearest wall, is the distance to the nearest wall and is the local kinematic viscosity of the fluid. is often refered to simply as y plus and is commonly used in boundary layer theory and in defining the law of the wall .