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

Chapter 3.0 Vehicle Design
3.3 Wing Aerodynamics
Figure 3-99: Forces (Newtons) Time History for Simulation with Blowing
3.3.1.5.5 Conclusions Stemming from CFD Analysis
The overall lift of the flapping wing has contributions from the physical wing shape, the virtual
camber created by the leading edge vortex, and the extended flow attachment due to the blowing
of the trailing edge plus the additional circulation and lift caused by blowing. The CFD simulation
is not accounting fully for the effects of the blowing at this point in its development. Also,
while the LEV is seen to form in animations, it is fleeting, either disassociating at the particular
station simulated along the wing, or existing dynamically at different stations at different points
in time during the flapping cycle. This too is a subject for further empirical investigation in the
wind tunnel using a particle imaging velocimeter (PIV). Such measurement will provide an
actual 3-D view of the LEV and will be used to update and validate both the CFD models and
the analytical model that presently accounts for the flapping aerodynamics based on physical
wing shape, but does not yet consider LEV effects or blowing effects.
Without flapping, the use of the blown flap is observed to reduce the upper surface separation
and increases the lift by a substantial factor. In cases with flapping, the CFD model shows a
major portion of the lift being supplied by the flapping process itself. The blown flap continues
to be helpful in directing the trailing edge flow in a more downward direction when compared to
corresponding case without blowing, however the overall effect on lift is relatively small since
the most significant portion of the lift is coming from the flapping. This is consistent with the
CFD model operating at a suboptimal point in the design space relative to both blowing and perhaps
LEV formation. All of the indicators are favorable however the point of best performance
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