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Mesh generation in computational fluid dynamics (CFD) must achieve a balance between solution accuracy and simulation convergence time. The generated mesh should be fine enough to accurately resolve the flowfield and, at the same time, should be coarse enough to converge in a reasonable amount of time. Hence, it is essential for the mesh cell sizes to vary across the computational domain, with finer cells being used in boundary layer regions, no-slip walls, and other flow features that need a higher resolution; and larger cells being used elsewhere for computational efficiency. An additional requirement is that the cell size must blend smoothly from fine to coarse.
The three design factors to be taken into consideration for local element size gradation in Fidelity Pointwise are -
Figure 1. Example of distributing user-specific element size along a line shape.
With the mathematics of the RBF defined, one needs only a method for defining the source. In this implementation, sources are defined by geometric primitives called shapes. Shapes can be 0-D (point), 1-D (line, curve, circle), 2-D (circle, quad, disk, polygon), or 3-D (sphere, box, frustum, cylinder, cone, swept polygon). These shapes are created in a sketch-based interface and can overlap with each other and the geometry of the object being meshed.
Implementing radial basis functions and source shapes allows users to apply a priori element size gradation to a tetrahedral mesh. Below are two examples of source shapes used for cell size refinement in the wake region.
In Figure 2, for wake refinement behind an automobile, a source shape is defined. Further, two cell sizes are specified on the source, with a smaller one immediately behind the automobile and a larger one downstream.
Figure 2. A box source in the wake region behind an automobile(top), the box source refines the mesh behind an automobile(bottom).
In Figure 3, the two-volume sources behind the aircraft not only overlap each other but also overlap the aircraft geometry.
Figure 3. Two overlapping sources are placed behind the aircraft – a flat box source is used in the wing's wake region, and a cone source is used behind the engine nacelle(top); the cone source refines the mesh behind the nacelle(bottom).
For more information on cell size gradation in Fidelity Pointwise, read Controlling Localized Element Size Gradation in an Unstructured Mesh by clicking the button below -