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

Angle of
attack
α
6°
4. Numerical Results
Table 2. Computational parameters
Reynolds
number
Re
= U C / υ
∞
∞
16
Mach
number
M
Grid nodes
N × N × N
5
10 0.2 840 × 90 × 120
The numerical simulations include three cases: uncontrolled flow separation (baseline
case), flow separation control with a pair of passive vortex generators (Case 1), and flow
separation control with a pair of active vortex generators (Case 2). The flow conditions
and mesh used are exactly the same for all three cases. The numerical simulation results
are summarized and compared in the following subsections.
4.1 Baseline Case
In the baseline case, the vortex generators are at their fully retracted position. The
typical feature of the flow field can be seen from a side view of the isosurface of
instantaneous spanwise vorticity with ω = 30 as depicted in Fig. 10. The separation of
y
free shear layer from the airfoil surface, vortex shedding from the separated shear layer,
reattachment of the shear layer, and breakdown to turbulence in the boundary layer can
be seen clearly in the figure.
Fig. 10. Isosurface of instantaneous spanwise vorticity ( ω = 30 )
Fig. 11 shows the time- and spanwise-averaged velocity vectors at every third
streamwise grid location and the contours of streamwise velocity. The time-average was
performed over a time period of 15 ∞ U C / . The contours of the reversed flow with
negative streamwise velocity are plotted in a dark color. The mean flow field in Fig. 11
ξ
η
y
ζ