This grid is VERY similar to Grid #2 (case3half-struct-1-p2dfmt), 
with the exception that the top wall's shape has been adjusted to 
APPROXIMATELY account for blockage caused by the side plates in 
the experiment.

The medium case3half-struct-4-p2dfmt grid is exactly 
every other point in each coordinate direction of the 
fine case3.struct.4.p2dfmt grid.  Thus, the zone sizes
are as follows:
 397x109
  81x 61
  33x 61
  25x109

Also, all the BCs are the same as described in the roadmap 
file for the fine grid, and the 1-to-1 connectivity is
as follows:

   1-1 BLOCKING DATA:
      NBLI
         3
 NUMBER   GRID     :    ISTA   JSTA   KSTA   IEND   JEND   KEND  ISVA1  ISVA2
      1      1             1    117      1      2    177      1      1      2
      2      3             1      1      1      2      1     61      1      3
      3      1             1      1      1      2      1    109      1      3
 NUMBER   GRID     :    ISTA   JSTA   KSTA   IEND   JEND   KEND  ISVA1  ISVA2
      1      3             1     33     61      2     33      1      1      3
      2      2             1     81      1      2     81     61      1      3
      3      4             1     25      1      2     25    109      1      3

The way to read the above table is to match the number 
from the 1st set with the number from the 2nd set.  For
example, for interface number 1, grid 1 connects with grid 3.
Because this is a 2-D grid, the i-indices ISTA and IEND
are irrelevant.  The j-index from zone 1 from 117-177 
(at k=1) matches up with the k-index from zone 3 from
61-33 (reverse ordering) (at j=33).  The parameters isva1 
and iva2 indicate which index is varying (but because
this is a 2-D grid, the fact that the i-index is varying
(ISVA1=1) is irrelevant)... for interface
number 1 the j-index (ISVA2=2) is varying in grid 1, 
and the k-index (ISVA=3) is varying in grid 3.

Format for the structured grid is PLOT3D-type, formatted, 
MG, 2D:

      read(2,*) nbl
      read(2,*) (idim(n),jdim(n),n=1,nbl)
      do n=1,nbl
        read(2,*) ((x(i,j,n),i=1,idim(n)),j=1,jdim(n)),
     +            ((y(i,j,n),i=1,idim(n)),j=1,jdim(n))
      enddo
