Despite the evolution of computer processing capability, improving the efficiency of numerical simulations remains critical. In CFD simulations, the key factor impacting solution quality is meshing. A mesh spacing that does not resolve local variations in the flow variables introduces a discretization error. On the other hand, if the mesh is overly refined, the computational time and effort are needlessly increased. Mesh element types and data structures also impact the human hours and skills required to generate a mesh and the cost per unit of accuracy.
Figure 1. Comparison between Local Error-based and Output-based Adaptation Technology.
Mesh adaptation (which can be local error-based or output-based), as depicted in Figure 1, is a common technique employed to help improve simulation efficiency. Unstructured mesh adaptation has been used to reduce the mesh size to reach the desired solution accuracy. This technique enables significant improvements in processing time, memory requirements, and storage needed. However, without access to the underlying CAD data, adaptation is limited only to improving off-body grid resolution. While the mesh adaptation technique in Fidelity CFD respects the geometry, improves the mesh quality, adapts to the near-wall shear layers, and reduces run-time for improved CFD solutions.
Usual challenges using mesh adaptation for improved mesh quality are as follows:
Fidelity Pointwise is a mesh generation solution that offers ample flexibility in mesh construction techniques and mesh styles. This flexibility is the meshing philosophy of the Fidelity CFD meshing tool and allows it to be applied to a wide range of workflows. The Pointwise mesh adaptation technology separates the meshing and solving steps in a coordinated and automated manner enabling refinement of the mesh as per the developing flow solution or based on the objective of the application (as shown in Figure. 2)
Figure 2. Mesh adaptation of a diamond airfoil for two different objectives, i.e., adapted for drag (left) and adapted for shock propagation (right).
This automatic mesh refinement tool is used only in those regions where the mesh is deficient. It starts by creating a baseline flow solution, and by using this flow solution, an estimate of the error corresponding to the deficiencies in the mesh size is determined. This step is repeated quite a few times to get a better hold of the mesh discretization error. For high-quality CFD meshing, this method can also be used on off-body voxel meshing for uniform and excellent resolution of the off-body features, specially to capture the wake region. In Figure 3, the wake shear layer mesh for the sedan is refined using the mesh adaption tool.
Figure 3. Mesh refinement to define off-body features.
The Fidelity Pointwise mesh adaptation tool
To learn more about mesh adaptation in Pointwise, request a free trial license.