Application and Results

To improve the grid 1x the grid enlargement tool was applied to a portion of the structured layer surrounding the airfoil and the wake. The initial grid was enlarged by the factors two, four and six in each case yielding three additional grids. The resulting grid for an enlargement factor of six is shown in Figure 18(a) and compared to the initial grid in Figure 18(b). Flow solutions were obtained on these grids. The results are shown in the polar curves plot in Figure 19. The polar curve shows that an enlargement by factor two affects the prediction of lift coefficients by about 85% by reducing the difference to the reference grid 8x from 4.0 lift counts to 0.60 lift counts. The drag coefficient is affected by a change of about 44% by reducing the difference to 8x from 9.20 drag counts to 5.10 drag counts.

Further enlarging the structured layer by factor four and more reverses the im – provment as revealed by the polar curve plot. This has to be attributed to the fact that a stronger enlargement reduces the effective resolution in the structured layer,

(a) Grid derived from the initial grid after an enlargement by a factor of six

(b) Initial grid 1x Fig. 18 Initial grid 1x compared to the grid with enlarged structured layer by a factor of six

2

c

since the enlargment does not introduce additional points but redistributes present points over a wider area.