CFD Utilities Files

LINES_OF_SIGHT_2D Description:

   This is the 2D analogue of the the earlier LINES_OF_SIGHT 3-space
   utility.  It can handle either an (x,y) dataset with z = 0 assumed or
   an (x,y,z) dataset with z assumed constant (and ignored).

   For a list of surface pts. (grid indices or (x,y) coordinates) and the
   associated 2D 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 PLOT2D multiblock form (one line of sight
   per block, ASCII) compatible with FLOW_INTERP_2D, which can perform
   the flow interpolations and tabulations that are normally what are
   really desired for application to hypersonic flows.

   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.

   It is understood that body points 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 2D volume grid contains 1 layer of blocks, with j = 1
      at the wall.  This simplifies determination of the inner and outer
      boundary curves.  (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 2D volume grid (ASCII|binary, 2D|3D; any zs ignored).

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

   o  For each line of sight:

        If body-normal:

          > Construct a 2-pt. line normal to the wall with length that of a
            local radial grid line.  This should be at least as long as the
            straight line distance to the outer boundary.

          > 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 NEAREST_CURVE_POINT utility to each body point
            and the outer grid boundary: this finds the closest pt. on the
            shock boundary, and the associated line is orthogonal to that
            boundary.

          > Discretize the 2-point line very simply.

        If parallel to Ox:

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

Input surface point format (ASCII, read to EOF):

   Either                                      or

   n   i                                       x   y
   n   i                                       x   y
   n   i                                       x   y
   :   :                                       :   :

   where n = block number and j = 1 is implied.

XYZ Conventions:

   Since the DPLR postprocessor extracts only x & y for a 2D grid, the
   input volume grid to be interpolated may be either 2D/xy or 3D/xyz
   with z all 0.  Thus y is "up" for input and output files here.

Control:

   A handful of prompts suffice.

History:

   10/07/05  D.A.Saunders  Initial implementation of 3-space LINES_OF_SIGHT.
   02/14/12    "     "     LINES_OF_SIGHT_2D adapted from the 3D form.
   07/09/13    "     "     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, and the starting guesses for
                           line-line intersections have been improved.

Author:  David Saunders, ERC, Inc. at NASA Ames Research Center, CA