| Summary: | 碩士 === 國立中興大學 === 機械工程學系 === 85 === The effects of upstream local disturbances on the aerodynamic
characteristics ofan airfoil pitching at a constant-rate is
studied experimentally.The experimentswere conducted in an open-
type wind tunnel.The test model was the NACA 0012 airf-oil. The
disturbed flow field was produced by a thin rod placed upstream
of thetest airfoil. The surface pressures of the airfoil were
measured to examine its aerodymamic performance under various
test conditions. The results demonstrate that the upstream
disturbances, produced by the rod parallel to or below the pit-
ching axis, have significant influence on the static airfoil at
higher angles of attack, causing a delay in stall angle and an
increase in maximum lift coeffi-cient. For the dynamic airfoil,
such disturbances also leads to a delay in lift and moment
stall. The largest influence occurs when the rod is located
below the pitching axis of the airfoil. For higher pitch rates,
it is found that the upstr-eam influence on the airfoil retains
but is less intensified. Different horizon-tal locations of the
rod make no discernable effects on the pressure distrib-utions
for the dynamic cases. The lift coefficient plateau phenomenon
happenswhen the airfoil is operated at pitch rates higher than
k=0.01. The LCP becomesunclear when the rod is located below
the pitching axis, and meanwhile there appears a smooth
pitching moment stall rather than a sharp drop observed for the
undisturbed case.
|
|---|
