16100lectre48_cj - facilitated by an unstructured grid may...

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Structured vs. Unstructured Grids The choice of whether to use a structured or an unstructured mesh is very problem specific (as well as company/lab specific). The answer is one of engineering judgement. Here are some of the issues: (1) Complex geometry : unstructured grid generation is usually much faster than structured grid generation. However, if the geometry is only slightly modified from a previously existing geometry with a structured grid, then structured grid generation can occur very rapidly. For a problem which is different from previous applications: Structured grid : man weeks to 1 man month Unstructured : man hours to a few days (2) Accuracy : For simpler problem such as airfoil (single element) or an isolated wing, structured grids are generally more accurate per unknown than unstructured. However, for more complex flows, the adaptivity
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Unformatted text preview: facilitated by an unstructured grid may allow more accurate solutions. (3) Convergence CPU time : structured grid calculations usually take less time than an unstructured grid calculation because, to date, the existing algorithms are more efficient. 1 1 1 1 1 1 1 1 1 , 1 1 1 − + − − − + − + + + + + − ij i ij j i j i ij j i j i j i j i ( )⇐ j i U , data stored in a “2-D” array ( ) ⇐ i U data stored in a “1-D” array So, in order to calculate a residual for all, the neighboring states must be known. Structured : neighbors found by adding/subtracting 1 from cell indices. Unstructured : requires storage of cell-to-cell pointers. ⇒ More storage, slower execution of code. 12 14 11 13 15 10 0 2 9 1 3 8 6 4 7 5...
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