It’s All About The Mesh – Cartesian Cut-Cell Approach
Posted by Rob Kaczmarek on August 19, 2013
The CFD mesh is one of the most discussed topics within the engineering community. It can be both problematic and time consuming – not to mention a source of numerous inaccuracies. There are different approaches to meshing but in this blog we are going to take a look at the cut-cell Cartesian approach and some of its benefits.
One of the most obvious benefits of the cut-cell Cartesian approach is the fact that you have a body-fitted mesh. This ultimately means that your mesh fits perfectly with your geometry, reducing the number of inaccuracies that propagate through the rest of the domain. Because of this, the cut-cell Cartesian approach makes handling complex and moving geometries much easier and accurate by cutting the cells rather than stretching and compressing the cells to fit.
Because this method cuts the volume cells at the wall, the mesh resolution is then independent of the geometry resolution. In other words, you can have a high fidelity geometric representation and a very coarse mesh. This can help speed up run-time calculations for one-off “let’s see what happens” designs ultimately aiding in rapid virtual prototyping.
Lack of skewness
Skewness is an inherent issue whenever you have a moving boundary using traditional meshing methods. This is not the case for the cut-cell Cartesian method. The mesh remains stationary and as the geometry moves the cells are cut and no compressing or stretching of the volume mesh occurs. This lack of skewness increases accuracy of the results and makes it the preferred method when dealing with moving geometries.
The other benefit of the cut-cell Cartesian method is added cell refinement at the wall, as this will have a positive impact on accuracy. With other methods, the full grid needs to be provided as an input and the actual surface geometry is no longer available. As a result, the accuracy of the surface location is limited by the resolution in the original grid. Any grid refinement performed during the simulation will cut the existing cells, and any resolution added near walls will not result in a better representation of the actual geometry. On the other hand, using the cut-cell Cartesian method requires the original surface information to be maintained. Thus, grid refinements will improve accuracy in the near-wall flow predictions.