Description of the DLR grids for the first High Lift Prediction Workshop

March 30, 2010
Simone Crippa; simone.crippa@dlr.de

The grids were created at the DLR Institute of Aerodynamics and Flow Technology, Braunschweig, using Solar v14.1.3.

Content
Description of the following grids:
trap21_coarse_yNeg.cgns
trap21_medium_yNeg.cgns
trap21_fine_yNeg.cgns
trap21_config8_yNeg.cgns
trap21_brackets_yNeg.cgns

Where in the naming scheme, 
"trap21" reflects the internal denomination of the grid family;
for case1, the three levels "coarse", "medium", "fine";
for case2, the same meshing approach as for case1/medium, but applied to configuration 8;
for case3, the same meshing approach as for case1/medium, but with additional slat/flap brackets. 
The grids were generated after a xz-plane mirroring of the geometry, then mirrored back to the negative y-coordinate system as in the original CAD data.

For all grids, the meshing guidelines (version: June 11, 2009) were fulfilled as far as the meshing package allowed to. Taking reference to the points given in the gridding guideline, in detail:

a)1-3) based on trial computations, to achieve y+ values around unity on the coarse grid level, the first cell height was decreased to:
coarse: dy=6e-05"
medium: dy=4.16017e-05"
fine: dy=2.8845e-05"

b) to improve the similarity of the grid family, the following amount of constant spacing layers are used
coarse: 3
medium: 4
fine: 6

c) Ratio of number of points:
fine/medium=2.9957
medium/coarse=3.0038

d) Guideline fulfilled

e)1) Partially fulfilled for all grids. Due to an automatic, local growth rate modification, the coarse mesh features regions with a growth rate>1.25. Given a target growth rate, the final range for the three grid levels are:
coarse: 1.012308 - 1.372266 (target: 1.25); 
medium: 1.000915 - 1.237712 (target: 1.16638701);
fine: 1.000213 - 1.159547 (target: 1.11218237).
Surface distribution of growth rate is shown in additional plots, 'comparison_trap21_CMF_LocalGrowthRatioSmoothed_*.png'.
e)2-3) Variable growth rate not possible.

f) Guideline fulfilled

g)1-4) Guideline fulfilled

h) Guideline fulfilled

i) Guideline fulfilled

j) NA

k) NA

The near-field, advancing-front step resulted in the following numbers of wall-normal layers.
coarse: 35 
medium: 51
fine: 74
whereby the last layer is subsequently converted to pyramids/tetrahedra for a smooth overlap to the far-field, advancing-front tetrahedral mesh.


For the generation of the grid for case2, the same mesh sources were used as for the case1/medium grid. To transform the source field of the flap, the operation deployed/config1 - to - stowed - to - deployed/config8 was used.


For case3, on top of the case1/medium source field, mesh sources were added covering the brackets.


For some comparative plots, see the files '{isoback,flap,brackets}_comparison*png'


The grid point counts are summarized hereafter; for a complete grid elements breakdown and quality distribution, see the additional files 'trap21_*_ElementQuality.txt'.
coarse: 12306950
medium: 36967871
fine: 110745950
config8: 37062155
w/brackets: 39705152