Meshing for CFD and FEA facilitates accurate simulation of flow or other physical phenomena.
Meshing discretizes a complex object into well-defined cells where the governing equation can be assigned so that the solver can easily simulate physical behavior.
A high-quality mesh is fine and geometrically well-defined to ensure accuracy and convergence in speedy simulations.
When performing computational analysis of a structural or fluid simulation using computational fluid dynamics (CFD) or finite element analysis (FEA), meshing plays an important role. Mesh simply breaks down the object to be simulated into smaller cells that have the ability to accurately define the geometry of the object. The governing equation can be associated with each cell, which helps in the simulation of the flow in that discrete space. With a high-quality mesh, numerical analysis can be ensured with accuracy and precision.
In this article, we will discuss in detail the role and importance of meshing in CFD and FEA and examine how high-quality meshing can be achieved with a CFD simulation package.
The Importance of Meshing for CFD and FEA
We know that the basic difference between FEA vs. CFD is that FEA is generally the preferred method for structural analysis and limited fluid problems, while CFD provides computational analysis support for fluid flow problems. Meshing, however, provides a similar kind of function for both types of analysis. During the meshing process, the complex geometrical object is discretized into a number of cells with a distinct number of nodes. These cells have predictable shapes and can properly capture the physical shape of the object. CFD solvers can perform structured, unstructured, or hybrid meshing with 2D (triangle, quadrilateral) or 3D (tetrahedral, hexahedron, etc.) nature and varying densities while meshing a structure.
The major importance of meshing in CFD or FEA lies in the ability to solve the governing partial differential equations in the allocated cell. Computational solvers cannot solve equations when directly applied to the entire object due to the complexity or irregularity of the shape. Hence, with meshing, the partial differential equations are applied to each individual cell with mathematically defined volumes. Solving for these individual equations provides the solution for the complete simulation.
Best Practices for High-Quality Meshing
Creating a high-quality mesh is key to the accuracy of the simulation. Here are some ways you can create a high-quality mesh to achieve accurate simulation results.
Mesh Geometry and Its Metrics
Mesh should be well-defined with no intersections or outliers. Depending on the geometry of the object being used in the analysis, the mesh geometry can have hexahedral, tetrahedral, pyramidal, or quadrilateral sections. Complex geometries generally use hexahedral or tetrahedral meshes. The quality of these shapes can be analyzed through metrics such as skewness and aspect ratio. It is generally preferred to have:
- ➞ Minimal skewness. Highly skewed cells decrease the accuracy of the solution.
- ➞ Suitable aspect ratio depending on the cell location and stability of the flow. It is generally preferred to have an aspect ratio between 0.25 to 5 for the flow away from the boundary walls.
- ➞ Change in volume between the adjacent cells should be minimal.
Especially for CFD fluid flow simulation, the mesh geometry should be solid and watertight enough for the CFD solver to identify the appropriate flow domain for internal and external flow simulation.
It is generally true that higher mesh density produces a more accurate solution. Finer mesh can accurately depict the stress gradients. However, before increasing the mesh density, it is to be noted that more cells mean more time to solve the governing equation. This can take up more disk space and slow down the computational speed of the solver. This also raises the question of cost-effectiveness.
Thus, for an efficiency purpose, only the density near critical points with higher stress levels can be adjusted while keeping the overall cell size constant. This can increase the accuracy of the simulation while keeping the cost within limits.
When meshing for FEA or CFD, a convergence study helps to identify the mesh density required to achieve convergence. Once the result obtained by running the simulation has converged, the subsequent change in mesh size has little to no effect on the result. The result obtained from the convergence study has maximum accuracy for the given mesh.
Fine Meshing With a Commercial Solver
Engineers and system designers working with complex CFD and FEA analysis can use commercial solvers for complex simulations. Tools such as Pointwise from Cadence can support various mesh types and techniques for high fidelity CFD simulation in a wide range of industries. With seamless meshing, you can ensure higher-order accuracy for your critical applications in no time.