'Tweak' Your Grid! That's All It Needs

‘Tweak’ is a small feature that can make a major difference between a grid and a bunch of points on which you can't compute an accurate or converged CFD solution. This command was introduced in the Pointwise Version 16.04. According to the dictionary, tweak means to “adjust or fine-tune,” and that's exactly what it does on Fidelity Pointwise. With Tweak, you can move any grid point in the x, y, or z direction. Tweak is a handy command that is part of your toolkit. It's not something you're likely to use every day, but it'll be there when you need it. A few situations where tweaking can help are:

• Projection onto convoluted surface shapes
• Floating boundaries in the solvers
• Extrusions
• Importing a grid from another program
• Pyramid insertion

Tweak Your Surface Meshes

Tweaking is as simple as clicking on a point and dragging it to a new location using the point placement tools. When tweaking a grid point on a surface grid (Figure 1), the cell edges connected to that point are highlighted so you can see the shape of the new cells relative to the old.

Figure 1. Highlighted edges illustrate the relative shapes of the old and tweaked cells

Improve Your Grid Quality

Tweaking a structured grid can provide a slight improvement to the cells' minimum included angle property over what you get automatically from the solver's orthogonality boundary condition (Figure 2).

Figure 2. Illustrates subtle improvements to the grid quality.

Eliminate Tent Cells With a Tweak

Tweak also is handy for getting rid of "tent" cells that cause the Jacobian metric to indicate skewing. Tent cells most frequently occur along the connector shared between two adjacent and co-planar faces of a block. By tweaking a few points, you can make those cells non-planar and thereby improve the Jacobian metric.

Tweak Your Volume Grids As Well

Here, the cutting plane tool from Examine is used to provide cuts through the mesh on which you choose the point to be tweaked. Figure 3, illustrates the display of volume cells for both structured and unstructured meshes.

Figure 3. Cutting planes are used for tweaking volume grid points

Tweak One or Two Cells to Fix a Big Grid

Block point tweaking is useful for improving the cell quality of literally one or two cells in a structured grid with hundreds of thousands of points. Running the solver is overkill in this case, and with a few tweaks, you can repair show-stopping grid quality issues. This is true for unstructured blocks because of the nature of the Delaunay algorithm for point insertion: it's a bit less predictable than solving Poisson's equation on a structured grid.

Watch the Youtube Video below to learn how the Tweak command helps in improving grid quality.

To learn more about the 'Tweak' command in Fidelity Pointwise, read the article Sometimes All Your Grid Needs Is a Little Tweak by clicking the button below.