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CHAPTER 8
CONCLUSIONS AND OBSERVATIONS
Summary
Unsteady fluid-structure reaction (FSR) computational fluid dynamics (CFD) solutions of
a viscous, rigid, full-scale F-16 are computed and analyzed for prescribed rigid-body pitch and
roll oscillations for tip-launcher, clean-wing, and wing-only cases, simulating the torsional and
bending nature of limit cycle oscillation (LCO) mechanisms, respectively. There are a number of
interesting features seen in the flow upon examining the surface pressure coefficient, Cp,
Mach=1 iso-surface, vorticity magnitude iso-surface, Lissajous, and wavelet plots for 1Hz ± 2.0°
and 8Hz ± 0.5° pitch and roll oscillations. Significant shock-induced separation and tip and
strake (aircraft cases) vortices are observed for all motion cases. Lagging trends relative to
aircraft/wing motion are exhibited for all cases when animating the vorticity magnitude, Mach=1
boundary, and surface Cp; and when examining the Lissajous plots of -Cp vs. local displacement
and associated wavelet transform plots.
The F-16 aircraft roll cases indicate that the presence of the tip launcher has a significant
effect on the strength and location of the shock on the upper surface of the wing. Additionally,
the strake vortices maintained a relatively constant position and magnitude throughout the
oscillatory cycle. The tip vortices also exhibited a lag in their growth with respect to the aircraft
motion. F-16 aircraft pitch cases exhibit significant inboard shock separation. The presence of
the tip launcher during the pitch oscillation limits the amount of inboard separation seen; and
again shows strengthening and relocation of the shock on the wing. The strake vortices
demonstrate a much more active oscillatory nature during pitch oscillation, and it is believed
they are a factor in the inboard shock separation. It is seen in the pitch cases that the vortices’
motion also lags behind that of the aircraft.
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