CFD Utilities Files

FLOW_INTERP_2D Description:

   This program interpolates a 2-space flow field solution from one PLOT2D
   multiblock grid to another.  The solution should be provided at all
   vertices of the grid.  (Both files may in fact be cell-centered forms
   of the underlying computational grid, but they are always treated as
   though they are vertex-centered.)  The same underlying geometry is
   assumed to be represented by both the solution grid and the target grid,
   but the outer boundaries, block counts, and/or point distributions may
   differ.
 
   Lines of sight (perhaps from LINES_OF_SIGHT_2D) are likely to be the
   target grid blocks (one 2-space line per block), as needed for radiative
   heating calculations from axisymmetric solutions.  Tabulated forms of
   the output are provided in this case (as determined by ni = 1 for all
   target blocks).  Otherwise, the interpolated flow is output as a PLOT2D
   function file.
 
Further Notes Inherited From The Earlier 3-Space FLOW_INTERP:

   >  Ideally, all target grid points will be contained by the grid
      associated with the given flow solution.
   >  For target points outside the solution grid, the nearest soln. cell
      is used.  Thus, extrapolation is explicitly avoided.
   >  The ADT (Alternating Digital Tree) technique used ensures efficiency
      no matter how many of the target pts. are outside the searched grid.
   >  Note that application to different geometries (even slightly
      perturbed ones) is NOT appropriate:  boundary layer point
      distributions are all-important, and the real-space interpolations
      performed here will not preserve the boundary layer flow variables
      (or gradients, especially) anywhere the two surface grids differ
      more than infinitesimally.
   >  See SURFACE_INTERP for interpolating 3-space surface datasets in
      Tecplot form.

Algorithm:

   >  For each block in the target grid:
      >  Read the target grid block.
      >  If this is the first target block, perform some initialization:
         >  Build the solution grid search tree from all cells of all
            blocks.  This requires insertion of z = 0 in the solution
            grid in order to use the 3-space structured surface form of
            the ADT scheme.
      >  For each point in the target block:
         >  Locate the nearest solution cell by searching the ADT.
         >  Interpolate the flow solution to the current target point using
            the best solution cell found.  The interpolation is "bilinear"
            within a single cell.  (This familiar formulation is not really
            linear because it contains nonlinear terms, but the effect is
            (bi)linear if the cell is perfectly rectangular.)
      >  Output the interpolated solution.

Control:

   A few prompts suffice.
   This version allows for adding further options requiring further
   prompts.

    First special option, prompted by shock-normal lines of sight:
      Tabulate the component of velocity along each line of sight?

History:

   03/24/04-08/22/08  D.A.S.  3-space FLOW_INTERP evolution.
   02/24/12-02/27/12    "     2-space adaptation as FLOW_INTERP_2D.
   07/24/13             "     Meeting a requirement for V.n along lines
                              of sight is best done here, but it calls
                              for further prompts.  Todd suggested that
                              we allow for other future possibilities
                              with the initial new prompt.
   08/06/2013           "     All ADT variants have been merged into a
                              module with generic build & search calls.
Author:

   David Saunders, ERC, Inc./NASA Ames Research Center, Moffett Field, CA