Estimate height of the 1st layer height of the mesh as per recommended y+ value of the chosen solver, a better guess than choosing an arbitrary value. Here is Excel version: Y-Plus and Boundary Layer Height Estimation using Excel


The default values have been specified to avoid arithmetic errors. Please ensure you specify all the values as per the operating conditions chosen in simulation. The default value of y+ is set = 30, appropriate for most high-Re turbulence models. In case a low-Re turbulence model such as SST is being used, change this value to 1 or maximum 5.
Select the type of geometry:
Select the working fluid:
Select mode of specifying velocity scale:
Specify velocity scale in [m/s] or [m3/s] or [kg/s]:
Specify cross-section area in [m2] - ignored if velocity is specified:
Select solver type: 1=Vertex-based (CFX), 2=Cell-centre based (Fluent):
Specify length scale of flow: hyd. dia. (Ducts) or length of the (Flat) plate [m]:
Specify working temperature of the fluid in [°C]:
Specify 'absolute' working pressure (required in case of air only) in [bar]:
Specify desired mean value of y+:
In order to demonstrate the effect of the cell-based and vertex-based scheme, simulations were performed using same mesh, material properties, solver and boundary conditions. The area-averaged value of Y-plus matched the observations described above. The mesh used is shown below. Mesh for Pipe Flow - Section

Mesh for Pipe Flow - Wall
The material properties used in CFX and Fluent are described below.
Material properties in CFX

Material properties in Fluent
The turbulence model used are:
Turb. Model in CFX

Turb. Model in Fluent
The boundary conditions at inlet and outlet are shown below.
Inlet Boundary in CFX

Outlet Boundary in CFX

Inlet Boundary in Fluent

Outlet Boundary in Fluent
The good level of convergence was achieved:
Convergence in CFX

Convergence in Fluent

Conclusion:

The contour plots for the Y-plus are shown below. Based on the flow conditions and material properties, following are derived parameters:
Y-plus value in CFX

Y-plus value in Fluent
Contour of Y-plus in Fluent
The calculation was repeated in CFX using velocity profile specified by exponential function V0*[1-(r/R)7] keeping all other parameters constant. The reported value of Y-plus has reduced from 33.2 to 24.2.
Y-plus value in CFX


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