Note: The Configuration
Geometry, Test Cases, and Gridding Guidelines are current as of 31 October
2008, but are subject to changes as developments require. Please check the website
periodically for updates, and/or register with dpw@cessna.textron.com to be notified
directly.
1)
Grids to
be Generated:
a) Grid
Convergence Cases – NASA Common Research Model:
i) Wing-Body-Tail,
iH=0¡: ~3.5 Million, ~10 Million, ~35 Million,
~100 Million Cells/Nodes;
Where iH is the incidence of the
horizontal tail
ii) Coarse
(3.5M), Medium (10M), and Fine (35M) grids are required;
The Extra-fine (100M) grid is optional
b) Trim Drag
Analysis - match Medium grid from Grid Convergence cases
i) Wing-Body
~8
Million Cells/Nodes
ii) Wing-Body-Tail,
iH=-2¡ ~10
Million Cells/Nodes
iii) Wing-Body-Tail,
iH=+2¡ ~10
Million Cells/Nodes
c) RE Study,
Wing-Body-Tail, iH=0¡: Same Family as Medium, but different
viscous spacing as required (See item 2-a-ii below)
2)
Grid
Guidelines:
a) Initial spacing
normal to all viscous walls (RE Based on CREF=275.80Ó):
i) coarse: y+
~ 1.0 dy = 0.001478 (RE= 5M)
ii) medium: y+
~ 2/3 dy = 0.000985 (RE= 5M),
dy = 0.000273 (RE= 20M)
iii) fine: y+
~ 4/9 dy = 0.000657 (RE= 5M)
iv) extra-fine:
y+
~ 8/27 dy = 0.000438 (RE= 5M)
b) Recommended:
generate grids with 2 cell layers of constant spacing normal to viscous walls
c) Total
grid size to grow ~3X between each grid level for grid convergence cases
d) For
structured meshes, this growth is ~1.5X in each coordinate direction
e) Grid
convergence cases must maintain the same grid family between grid levels, i.e.
maintain the same stretching factors, same topology, etc.
f) Growth
rate of cell sizes in the viscous layer should be < 1.25.
g) Farfield located at ~100 CREFÕs
for all grid levels.
h) For the Medium
Baseline Grids:
i) Chordwise
spacing for wing and tail leading edge (LE) and trailing edge (TE) ~0.1% local
chord.
ii) Wing and
tail Spanwise spacing at root ~0.1% local semispan.
iii) Wing and
tail Spanwise spacing at tip ~0.1% local semispan.
iv) Cell size
near fuselage nose and after-body ~2.0% CREF.
i) For the
Coarse and Fine Baseline Grids, the above values should be scaled accordingly.
j) Wing and
Tail Trailing Edge Base
i) Minimum
of 8 cells across TE base for the coarse mesh
ii) Minimum
of 12 cells across TE base for the medium mesh
iii) Minimum
of 16 cells across TE base for the fine mesh
iv) Minimum
of 24 cells across TE base for the extra-fine mesh
k) Be
multi-grid friendly
l) For
unstructured grids designed for vertex based solvers, the spacings
refer to inter-nodal spacings and the resulting grid
sizes are expected to be similar to the structured grid sizes above. For
unstructured grids for cell- centered solvers, the spacings
refer to spacings between cell centers (or surface
face centers), which corresponds approximately to a factor of 2 reduction in
the overall number of surface points compared to the nodal solver case, for a
triangular surface grid (this is based on triangle centroid
separation distance of 2/3h). For tetrahedral cell-centered-solver meshes, the
total number of grid points will be approximately 1/3 of the numbers listed
above.