Geometry in FASTEST

As described in chapter 2.1.3, CVs are identified by their index ijk (with i=1,...,ni; j=1,...,nj and k=1,...,nk). The coordinates (x(ijk),y(ijk),z(ijk)) for CV ijk are related to the east-north-top-edge. The midpoint coordinates are stored in vectors xc(ijk),yc(ijk),zc(ijk). Figure 2.1 shows the 2d-case: the cross marks the east-north-top-edge (related to x,y,z), the black circle markes the CV-midpoints (xc,yc,zc). This holds for indices i=2,...,ni-1; j=2,...,nj-1; k=2,...,nk-1.

Figure 2.1: Definition of coordinates

(for a better understading look also in calgrd.F).

Block boundaries

The following referrs to CVs with indices i=1, i=ni-1 and i=ni (accordingly to j and k).
Block boundaries are devided into patches (so patches are 2dimensional arrays). Patches may be boundary condition patches (lying on the physical boundary of the domain) or connectivity patches (lying on the interface of two adjacent blocks). In figure 2.1 the southern and eastern block boundaries are BC-patches and the northern and western boundaries are connecitvity patches.

Figure 2.2: Grids in FASTEST

• Boundary condition patch
  In CVs with indices i=1 and i=ni boundary condition values are stored. The coordinates of these CVs are the same as the coordiantes of the physical boundary. The length in x-direction is equal to zero, so the boundary CVs are 2dimensional. CVs with i=2 and i=ni-1 define the first and the last CV-layer of the block where values are obtained by calculation and are not defined by boundary values.
  Coordinates for CVs with index i=ni are identical to those with index i=ni-1 (those CVs are necessary for connectivity patches).
• Connectivity
  In connectivity patches, CVs with index i=1 and i=ni contain the so-called ghost CVs, which are necessary for block communication (see figure 2.1). Values like velocities, pressure etc of CVs with i=2 are copied to the ghost cells of the west neighbour block (in CVs with i=ni) so that values are available for the calculations in the neighbour block.
  So these rows of CVs (i=ni in the western block and i=2 in the eastern block) have the same coordnates.
  CVs with i=2 and i=ni-1 are the first and the last row of CVs where values are obtained by calculation and not by block communication.
• Boundary Condition and Connectivity lying on the same boundary
  See figure 2.2. On the southern boundary (boundary condtion) values are exchange via ghost cells between the connectivity patches (east/west boundary). These ghost cells are defined like ``normal'' boundary CVs and have length zero in direction of the physical boundary. .