Block-structured mesh generation involves splitting the domain (assumed 3D) into several 6-sided blocks. Each block is then divided into a number of hexahedral-shaped cells.
There are some popular strategies for specifying the structure of blocks around boundaries of particular shapes. The most general approach uses blocks which extend outwards from sections of the boundary into the domain. For a cylinder in cross-section, 4 blocks are typically used as shown below by the blocks whose edges are oriented at to the horizontal.
The domain extends away from the cylinder with additional blocks connected to those that encircle the cylinder. The mesh is usually graded starting with small cell heights on the cylinder surface, which gradually increase with distance from the surface. The main weakness of this block structure is the abrupt transition in non-orthogonality from to at the outer vertices of the inner blocks, indicated in the ﬁgure.
The ﬁgure above shows the structure of the mesh of 40,000 cells used in Sec. 8.4 for a cylinder of diameter . Each element represents 1010 = 100 cells in the actual mesh. There are 80 layers of cells around the cylinder, with grading that gives a centre height of in cells adjacent to the cylinder surface.
A mesh inside a cylinder, e.g. a pipe, can use a similar structure in which the inner vertices of the curved blocks are connected to form a single block along the centre, as shown above.