Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 83 === The active control of separated and unsteady flow over NACA
633-018 cross section airfoil at high angle of attack is
studied experimentally by means of a leading-edged periodic
oscillating flap located near the separation point.
Theparameters here investigated include the forcing frequency
of the flap, the angles of attack of the airfoil and the
Reynolds number herein is 1.9 × 10^5. The contents of this
experiment include the comparisons of the pressure
distributions along the wing with and without excitation, the
frequency spectrum analysis of the fluctuation pressure along
the upper surface of the airfoil, the dynamic variations of the
aerodynamic properties with the flap oscillating and the vortex
convection speed along the airfoil. The results indicate that
the periodic excitation indeed have the ability to synchronize
and enhance the strength of the shedding vortices over the
airfoil when the oscillating frequency is close to the vortex
shedding frequency in the wake region. The enhanced shedding
vortices increase the adverse flow strongly and lower the
pressure distribution over the upper surface. Thus, the
excitation causes the increases and the periodic variations
both in lift and drag. Besides, from the variations of the
fluctuation pressure along the upper surface of the airfoil, we
can calculate the ratio of the vortex convection speed and the
freestream speed is from 0.67 to 0.87.
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