Numerical Study of Passive and Active Flow Separation Control ...

airfoil is shown in Fig. 14. The negative value of C between x = 0.06C and x = 0.285C,
f
indicates the near-wall reversed flow in the separation bubble. Both Fig. 13 and Fig. 14
confirm the observation in Fig. 11 and Fig. 12 in terms of the location and length of the
separation bubble. The abrupt recovery of C from its negative peak to a positive peak
f
between x = 0.25C and x = 0.35C corresponds to transition and reattachment of the
separated flow.
Fig. 13. Mean pressure coefficient of
baseline case
18
Fig. 14. Mean skin friction coefficient of
baseline case
The chord-wise distribution of peak turbulence kinetic energy k is displayed in Fig.
15. The ‘peak’ means the maximum k at each streamwise location. The abrupt increase of
k at xº 0.24C indicates the starting point of transition to turbulence, which is also shown
by the sharp increase of C displayed in Fig. 14. It is clear that transition occurs before
f
the separated flows reattaches, because the mean reattachment point is at x = 0.285C
while transition starts at x º 0.24C.