CFD Utilities Files

LINES_OF_SIGHT Description:

   For a list of surface points (grid indices or (x,y,z) coordinates) and
   the associated volume grid, generate lines of sight - i.e., straight
   lines normal to the surface and extending to the outer boundary with
   point distributions close to those of the local radial grid lines.
   The results are saved in PLOT3D multiblock form (one line of sight per
   block) compatible with the earlier FLOW_INTERP, which can perform the
   flow interpolations and tabulations that are normally what are really
   desired for application to hypersonic flows.

   This version can also read a structured surface grid for the target pts.
   to simplify using a thinned form of the relevant volume grid's surface.

   This version has the option to produce lines parallel to Ox rather than
   normal to the wall.  Most recently, it also has the option to produce
   lines normal to the outer shock boundary, which may be the best choice
   for tangent-slab radiation calculations.

   For the Ox-parallel option, the targets are assumed to be in list form.

   It is understood that body pts. will normally be confined to forebodies,
   since aft-body points are unlikely to have solutions in the usual sense.

Assumptions (probably generalizable, but they may never need to be):

   o  The structured volume grid contains one layer of blocks, with k = 1
      at the wall.  This simplifies determination of the inner and outer
      boundary patches.  (To overcome these restrictions, one could use the
      boundary condition data employed by the relevant flow solver.)

Strategy:

   o  Prompt for all inputs (no control file).

   o  Read the entire volume grid and extract the inner & outer boundaries
      as multiblock surface grids.

   o  For all lines of sight, search the inner boundary and save the
      relevant patch number and cell indices.

   o  Build a new search tree from the outer boundary.

   o  For each line of sight:

        If body-normal:

          > Construct a 2-point line normal to the wall with length that of
            a local radial line.  This should be at least as long as the
            straight line distance to the outer boundary.  (Actually, it
            may need to be longer off the shoulder of a capsule.)

          > Intersect the line with the outer boundary and transform the
            point distribution of the radial grid line to the relevant
            portion of the straight line.

        If shock-normal:

          > Simply apply the ADT search utility to each body point and the
            outer grid boundary: this finds the closest point on the shock
            boundary, and the associated line is orthogonal to it.

          > Discretize the 2-point line very simply.

        If parallel to Ox:

          > Adjust body-normal method to work with unit vector (-1,0,0)'
            instead of the unit normal at the body point, and perform the
            same intersection calculation and discretization.

Input surface point format (read to EOF):

   Either                            or                          or

   n   i   j                         x   y   z             nb
   n   i   j                         x   y   z             ni  nj  1
   n   i   j                         x   y   z             ni  nj  1
   :   :   :                         :   :   :             :   :   :
                                                           x11 x12 x13 ...
   where n = block number and k = 1 is implied.            ...............

History:

   10/07/05  D.A.Saunders  Initial design.
   11/14/05    "     "     Fixed a bug in allocating radial_lines(ib).
   11/22/05    "     "     Expanded the range of t for INTSEC6 to 2, not
                           1.1; added the option to read a structured
                           surface grid rather than a list of indices or
                           coordinates.
   08/21/09    "     "     If a point entered via patch indices were at an
                           upper index boundary, the surface normal utility
                           was not being given the lower-left cell indices.
   07/11/13    "     "     Dinesh Prabhu proposed making the lines of sight
                           orthogonal to the shock as the proper thing to
                           do for tangent-slab radiation calculations.  The
                           earlier body-normal and Ox-parallel options have
                           been retained.
   08/06/13    "     "     All ADT variants have been combined into a
                           module for distribution reasons (generic build
                           & search calls).
   08/16/14    "     "     A trailing comment in the body-point file allowed
                           indices to be interpreted as reals if the last
                           line comment contained a period.  This has been
                           remedied.
   11/11/14    "     "     Tabulate x,y,z with body point indices to help
                           plotting of radiative heating along surfaces.
   08/25/17    "     "     A 20-meter search range was occasionally not
                           enough.  Make it 20 diameters as it should have
                           been from the start for aft body points.
   09/05/17    "     "     The calculation of diameter was flawed for left
                           half body.

Author:  David Saunders, ELORET/NASA Ames Research Center, CA
                         ERC, Inc. at ARC (through 06/2015).
                         AMA, Inc. at ARC    (from 07/2015).