How to choose the Boundary Layer Thickness, Boundary Layer Mesh and No of Boundary Layer in CFD
Hi,
I Performing a CFD analysis for an Air blower Model. Here I meshed Model with some Element size and Tetra 3d Mesh Type. But here How to choose the Boundary layer mesh Size, No of layer and thickness.
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Altair EmployeeMost, if not all, the turbulence models in AcuSolve are valid from Y+ on the order of 1, to Y+ of 300, with proper transitioning between the various boundary layer regions. A lower Y+ will give better accuracy at the higher simulation cost of more mesh. For most model types a layer-to-layer growth ratio of 1.2 to 1.3 is best. We also want a smooth size transition from the last boundary layer meshed element to the interior. Beyond that, simulations typically require a few runs, reviewing results, Y+, contours, etc, to determine if the current mesh is good enough, or if the mesh needs to be refined/modified in certain areas. It's difficult to provide a one-size-fits-all response.
Hi Thanks for your answers.
Actually , I am new to CFD as Well as Altair Products. I am not aware about Turbulence Modeling and I am not using HM CFD. I am Using Simlab Acusolve and there is no Y+ Option, I am using the Turbulent flow in Flow Type and Spalart Allmaras in Modeling.
At the initial phase of simulations, How to decide the no of layers and its size using Simlab.
I am understood using the Y+ option in HmCFD to choose the BL, but iam not aware in Simlab.
Thanks & Regards,
Sivaprakash V.
For now, you can set the first layer height to 10–15% of the surface mesh size, with a total of 5 layers and a growth rate of 1.2. Make sure that the size transition from the last boundary layer to the volume mesh is smooth as acupro mentioned. You can simultaneously learn about wall functions to gain a better understanding of near wall modelling.
You need to be aware of turbulence models, Reynolds number and wall functions to calculate it.
If you are using HM CFD you can use the following option to define the y+ based boundary layer thickness.
To model the turbulent boundary layer, you can estimate the 1st layer height by setting the y+ value to 30. Use the blade length or duct diameter as the reference length and the maximum expected velocity as the bulk velocity.
You can go through this to learn more about wall functions and near wall modelling/resolving.
https://www.simscale.com/forum/t/what-is-y-yplus/82394
Altair EmployeeMost, if not all, the turbulence models in AcuSolve are valid from Y+ on the order of 1, to Y+ of 300, with proper transitioning between the various boundary layer regions. A lower Y+ will give better accuracy at the higher simulation cost of more mesh. For most model types a layer-to-layer growth ratio of 1.2 to 1.3 is best. We also want a smooth size transition from the last boundary layer meshed element to the interior. Beyond that, simulations typically require a few runs, reviewing results, Y+, contours, etc, to determine if the current mesh is good enough, or if the mesh needs to be refined/modified in certain areas. It's difficult to provide a one-size-fits-all response.
For now, you can set the first layer height to 10–15% of the surface mesh size, with a total of 5 layers and a growth rate of 1.2. Make sure that the size transition from the last boundary layer to the volume mesh is smooth as acupro mentioned. You can simultaneously learn about wall functions to gain a better understanding of near wall modelling.
You need to be aware of turbulence models, Reynolds number and wall functions to calculate it.
If you are using HM CFD you can use the following option to define the y+ based boundary layer thickness.
To model the turbulent boundary layer, you can estimate the 1st layer height by setting the y+ value to 30. Use the blade length or duct diameter as the reference length and the maximum expected velocity as the bulk velocity.
You can go through this to learn more about wall functions and near wall modelling/resolving.
https://www.simscale.com/forum/t/what-is-y-yplus/82394