Phase II Final Report - NASA's Institute for Advanced Concepts

Chapter 3.0 Vehicle Design
3.3 Wing Aerodynamics
Table 3-6: Lift and Drag Coefficient Values (Continued)
Case Flow Time(s) C L C d
5 1.9 4.27 0.468
Figures 3-67 through 3-71 show pressure contours at 0.03-s intervals for α = 45.79 o and Reynolds
number = 5,100. The corresponding C L and c d values are shown in Table 3-6. Several
important features can be observed from these results. At this high angle of attack, the wing generates,
a large amount of lift, indicating that extrapolation of high Reynolds number results
would be erroneous, especially because the catastrophic stall pattern of conventional high Reynolds
number airfoils is not present in these cases. The other feature is the large variation of lift
with time. Table 3-6 shows only part of a complete cycle in which the lift varies as shown in
Figure 3-63, the frequency and amplitude differing due to differences in angle-of-attack and
Reynolds number. Note that these large values of lift coefficient are obtained without any wing
kinematics included. The challenge is to establish the relationship between the flow velocity and
the vortex-shedding frequency so that, by choosing appropriate flapping frequency, the wing
would operate in the high C L mode during the entire beat cycle. A detailed review of literature
indicates that similar cyclical variation of C L has been observed experimentally [272].
Figure 3-63: Lift Coefficient Variation,
α = 8.31 o , Reynolds Number = 9,600
Figure 3-64: Drag Coefficient Variation,
α = 8.31 o , Reynolds Number = 9,600
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