Which mesh size should be set for a numerical wind flow analysis?

Answer

The density and quality of the finite solid mesh have a significant impact on the accuracy of the results. The denser is the mesh, the more accurate are the results. However, the computing time and the requirements of the computer memory increase with the denser mesh at the same time.

The mesh of RWIND Simulation can be divided into 3 categories:

CategoryMesh DensityMesh CellsCalculation TimeHigh-Performance Computer
Alow≤ 1 million
several minutes
≤ 4 GB RAM
Bmiddle-sized1 - 10 million
several hours
≤ 16 GB RAM
Chigh10 - 50 million
several 10 hours
≤ 64 GB RAM


In RWIND Simulation, the mesh density is organized globally in the "Simulation Parameters" dialog box. The mesh density can be defined in the range between 10% and 100%.

Figure 02 - Simulation Parameters

However, to increase the calculation efficiency in the wind tunnel area, the program does not generate a mesh with the constant mesh density, but automatically generates a finer mesh in the immediate surrounding of the models, that the wind flows around, than in the remaining area.

The size of the mesh refinement of each model is controlled by 5 levels of detail in the "Edit Model" dialog box. The refinement level can be defined here with the steps 0‑4.

Figure 03 - Level of Detail

By default, the program sets the global mesh density of 20% with Level 2 of the mesh refinement for the model. This setting usually results in a network distribution of Category A with 300 to 700,000 cells. With this large-meshed configuration of Category A, the program gives a basic display of the flow field and the pressure distribution on the wind-swept model within a very short time.

Figure 01 - FE Mesh for Solids

After checking all input data and compression reactions on the model, it is possible to quickly switch to the mesh of Category B in the mentioned dialog boxes by increasing the mesh density and the mesh concentration level to determine a qualitatively superior result.

By using the finer mesh refinement options and levels, it is also possible to achieve the mesh of Category C.
During the development of the RWIND Simulation program, we tested successfully the mesh configurations of this kind (≥ 50 million) on a corresponding computer. However, we do not yet recommend this configuration as the increased accuracy of the results gained in this way is not in equilibrium with the computer requirement required for this purpose. In the next development phase of RWIND Simulation, we plan to use a customized mesh in the boundary layer to fully use the mesh of Category C and to offer transient flow models with more accurate turbulence models.  

Keywords

Mesh size Mesh Turbulence CFD Wind flow Mesh category

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Compatible Programs RWIND Simulation
RWIND Simulation 1.xx

Stand-Alone Program

Stand-alone program for numerical simulations of wind flow around buildings or any other objects. The generated wind loads acting on these objects can be imported into RFEM / RSTAB programs for static and dynamic analysis.

Price of First License
2,690.00 USD