CFD Utilities Files

SHADOWGRAPH Description:

   For a real gas CFD solution on a structured or unstructured grid in 3-
space, construct an image that simulates an experimental shadowgraph.
Options for interferograms and schlieren are also [to be] provided.

   [Actually, only the mixture density is treated at present (ns = 1), and
it is unlikely that distinguishing the species densities (and their deriv-
atives) would produce perceptible differences in the images.  In the case
of FUN3D, where the derivatives must be included with the density,
handling multiple species could also involve much larger files for
negligible gain.]

   [Interferograms have not been implemented yet.  Simulated schlieren and
shadowgraphs can both be obtained via Tecplot gray-scale contouring of the
various functions written to quadratures.f[u] - see a sample layout.]

Control File (Standard Input):

   SHADOWGRAPH Control File
   1              ! Image type    1|2|3 = shadowgraph|schlieren|interfrgrm.
   1              ! Grid type 1|2|3|4|5 = P3D|P3D/iblnk|DPLRovrst|FUN3D|VTK
   3              ! Dimensions      2|3 = 2D/(x,z)|3D/(x,y,z)
   mygrid.gu      ! Grid file name|FUN3D/US3D file name|@name -> FUN3D list
   F              ! Formatted?      T|F = ASCII|unformatted
   myflow.fu      ! Flow data file name (mixture density or blank, density)
   F              ! Formatted?      T|F = ASCII|unformatted
   F              ! ASCII results?  T|F = ASCII|unformatted
   0.  1.  0.     ! Unit view vector;  0. 1. 0. => no rotation of CFD data
   2000 2000      ! Image pixel counts
   999. 999.      ! Image width, height; CFD units; 999. => grid bbox vals.
   999. 999. 999. ! Image center (x,y,z) before any rotation; 999. => "   "
   10.            ! Distance of shadowgraph image from the exiting rays
   999999.        ! Clip image data further than this # st. devs. from mean

Notes:

   o  Input flowfield datasets for structured grids need only one function,
      density, except that DPLR overset cases have blanking information as
      function 1 and density as function 2.  Partial derivatives are
      computed by SHADOWGRAPH.
   o  Unstructured datasets are expected to include density as function 1
      and the partial x/y/z derivatives of density as functions 2, 3, 4.
   o  US3D introduced a VTK (Virtual ToolKit) unstructured binary format
      that allows for cell-centered and/or vertex-centered function data.
      SHADOWGRAPH handles one or the other, but not both at the same time.
   o  US3D datasets are expected to contain x/y/z coordinates at grid pts.
      and function data at the cell centers.  This program detects cell-
      centered data and interpolates it to the vertices via inverse
      distance-weighted averaging.
   o  Cart3D datasets as written at NASA Ames are expected to have both the
      grid coordinates and the function data at cell centers, and this is
      no different from having both at the vertices as far as SHADOWGRAPH
      is concerned.
   o  Both US3D & Cart3D can employ grid type 5 (VTK unstructured binary),
      which (like the earlier-handled FUN3D format but with different
      node-numbering conventions) allows for cells that are tetrahedra,
      hexahedra, prisms, or pyramids.

History:

   Jan-Mar 2010  DAS     Initial implementation of some capabilities
                         published for program CISS by Leslie Yates in
                         AIAA Journal Vol. 31, No. 10, October 1993:
                         "Images Constructed from Computed Flowfields."
   04/13/10      DAS     Option to read integration data from a prior
                         run rather than regenerate it before testing
                         changes to the image construction details.
   04/15/10       "      After too much effort trying to get useful
                         images from actual deflections and accumulated
                         pixel counts, it appears that contour plots of
                         the integrated quantities (1/n)(dn/dx) and
                         (1/n)(dn/dz) in gray-scale provide schlieren
                         images corresponding to horizontal & vertical
                         knife edges respectively, while the magnitude
                         of this vector pair simulates a shadowgraph.
   04/19/10       "      Choosing to do spline integrations along the
                         lines of sight comes at a high price: each
                         line requires scanning the entire flow field.
                         [A 2000 x 2000 case for a Shuttle solution
                         with 8,143,360 grid cells takes 4.5 hours.]
                         Therefore, an option to use the trapezoidal
                         rule (as in CISS) is also provided, allowing
                         each cell of the flow field to be visited
                         just once for the rays that intersect it.
                         The above case now takes 4.5 minutes, and the
                         differences are imperceptible everywhere
                         except along the top of the OMS pod. Puzzling.
   04/28/10       "      PLOT3D/iblank option implemented.
   05/05/10       "      A large OVERFLOW grid shows that the bounding
                         box of the grid can be way too big to define
                         the imaged region.  Retain that option, but
                         provide for confining the image to smaller
                         regions.  Also, Bil Kleb suggested using a
                         unit vector to allow any view direction.
   06/30/10       "      The 04/13/10 option for reprocessing the
                         integrated data is retained but should not be
                         needed following the 04/15/10 realization.
                         Entering a non-defaulted image center is best
                         done in the input grid coordinate system.
                         This means entering three coordinates, even
                         though only the rotated x & z are the only
                         ones used to define the output image center.
                         Note that rotations are about a line through
                         the origin of the input grid coords.
   07/09/10       "      Filled in the FUN3D option (FieldView data
                         format, 32-bit, unformatted).  The whole
                         program can safely be compiled for 32-bit
                         arithmetic.
   07/28/10       "      PLOT3D input files are now processed one block
                         at a time.  One price paid is having to read
                         (and possibly rotate) the grid twice in order
                         to default the image size, but worse is the
                         impact on program modularity.  Now, several
                         steps are interleaved rather awkwardly and
                         more variables are moved to the highest level
                         for inheritance by the internal procedures.
                         The spline quadrature option had to be killed,
                         and so did the reprocessing option.
   08/02/10       "      Wondering about the 5.*machine_epsilon by
                         Jan-Renee Carlson prompted use of x1 - eps
                         for the i2 test, to err on the safe side
                         as for i1; likewise for j2 (symmetric now).
   08/03/10       "      Extended the FUN3D case to allow multiple
                         input files, one zone per file, via a list
                         of file names indicated by @<list file name>.
   11/04/10  D. Saunders Incorporated DPLR overset case, requiring that
           ERC, Inc./ARC flow function 1 = blank, function 2 = density,
                         and igrid_type = 3.
   07/07/11       "      Added US3D/VTK unstructured grid option
                         (igrid_type = 5).  Cart3D data is expected to
                         use the same format as well.
   07/12/11       "      VTK hexagon and prism cells needed translating
                         to FieldView's node-numbering convention.
   07/15/11       "      If cell-centered VTK function data are found,
                         convert to cell vertices in-place.
   07/19/11       "      Realized the intended (1/n) factor in the
                         integrated quantities was unintentionally
                         missing.  Results appear identical, though,
                         because n is very close to 1, and the partial
                         derivatives dominate.
   07/20/11       "      The documentation above now covers files from
                         Cart3D solutions, which can employ the same
                         VTK format as US3D but can omit the conversion
                         of function data here from cell centers to
                         cell vertices because both the coordinates and
                         the functions are cell-centered (but can be
                         treated as though they are vertex-centered).
   07/24/11       "      The VTK cases were incrementing the il pointer
                         at the end of each cell case, forgetting the
                         tests for cycling (skipping the cell) above.

Author:  David Saunders, ELORET Corporation/NASA Ames Research Center, CA