- The calculations are based on empirical correlations and may still require iterations to meet Y+ requirements
- The calculation is based on fully-developed regime. In developing regime, coarse mesh is required and hence the estimated mesh height will hold true for developing region also.
- The calculation is applicable to TURBULENT flows only
- The material properties (viscosity and density) are calculated based on specified fluid
- The mesh requirements are different for vertex-based formulations (CFX) and cell-centred formulations (Fluent & STAR CCM+)
- For identical mesh, boundary conditions and material properties, CFX will result in Y+ value approx. twice of that in Fluent, if Y+ ≥ 30 everywhere
- If Y+ of flow results in a range 10 ~ 30, the value reported in CFX will not be closer to twice that reported in Fluent. This is because of "scalable" formulation in CFX.
- For 2D geometries, a thickness of 1.0 [m] is assumed to estimate velocity from specified volumetric or mass flow
- The steps required to estimate the first layer height is described below:
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.
- The diameter is 100 [mm] and
- the 1st layer height used in CFD simulation is 1.0 [mm]
The material properties used in CFX and Fluent are described below.
The turbulence model used are:
The good level of convergence was achieved:
The calculation was repeated in CFX using velocity profile specified by exponential function V0
] keeping all other parameters constant. The reported value of Y-plus has reduced from 33.2 to 24.2.
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