CFD Utilities Files

RADIAL_INTERP_2D Description:

The original RADIAL_INTERP reads a single-layer 3-space volume grid and a
related surface grid to produce a new volume grid with that exact surface.
It takes advantage of a situation common to CFD for reentry vehicles where
all blocks have k = 1:nk from the wall to the outer boundary. For each new
surface pt., it performs a surface interpolation giving fractional coord-
ates (p,q) within some cell (i,j) of some surface patch n. Then it applies
the same surface interpolation at every k plane for k = 2:nk at that (i,j)
of block n.  Along the way, any discrepancy between the new target surface
point and the best interpolated surface point is either decayed towards
zero at the outer boundary or retained at every k plane.

All of these interpolations are necessarily bilinear because of the rapid
structured surface search technique used.  This is not as bad as it sounds,
because RADIAL_INTERP always substitutes the desired new target surface
point for each interpolated surface point, and decays any mismatch (or not,
as already explained).

Note that the number of k planes remains unchanged in the output 3D grid.

2D Analogue:

RADIAL_INTERP_2D performs a similar, simpler function for the 2D case using
linear interpolations with the same sort of correction if needed at the
surface and decay options away from the surface.  It also includes part of
the functionality of REFINE_GRID by allowing the radial distributtion type
and/or the number of points in the off-wall direction (j) to be changed.

Expected DPLR2D-related Usage:

If a coarsened 2D grid needs reclustering in the off-wall direction during
the flow calculation, the result no longer matches every nth point of the
original fine grid.  Therefore, the requirement that prompted this utility
is to recluster that fine grid in the equivalent manner, which has typical-
ly involved cell-Reynolds-number-based spacing at the wall.  Preserving the
same relative spacing in the radial direction while (normally) doubling the
number of cells is the right choice, along with recovering the original
surface grid exactly, which simpler use of REFINE_GRID would not guarantee.

For convenience, the desired surface grid may be the j = 1 line of a 2D
volume grid (1 or more blocks), or it may be a simple generatrix (one curve
in (x,y)-space, with any third coordinate ignored).

XYZ Conventions:

Since the DPLR postprocessor extracts only x and y for a 2D grid, the input
volume grid to be interpolated may be either 2D/xy or 3D/xyz with z all 0.
The DPLR preprocessor ignores any z coordinates if they are present for 2D
input grids, so the output grid here includes z = 0 for compatibility with
other utilities.  Thus y is "up" for input and output files here.

Control:

A handful of prompts suffice.

History:

Feb. 2-5, 2012  D.A.Saunders  Initial design and implementation.
Nov. 6,   2015    "     "     Introduced determine_grid_form and -dim.
                              Writing 3D output is inconsistent with
                              FLOW_INTERP_2D, so make it an option.

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