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The bleed slot is necessary for the
requirement of the hypersonic quiet flow all over the world. The aim of the bleed
slot is to decrease the influence of the disturbances from the contraction of
the quiet nozzle to the boundary layer downstream of the throat, so that the
boundary layer of the nozzle could be maintained as laminar flow. The main
parameters of the bleed slot include the distance from lip to throat (DLT) and
the width of slot (WS). Various values of those parameters will affect the
performance of the slot by changing the suction intensity of the bleed slot.
Two kinds of the bleed slots in the world are compared in this paper and the
aerodynamic design of the bleed slots is optimized based on the Purdue-type
slot. The influences of the various values of those parameters to the flow
field around the throat are analyzed and the optimizing results of DLT and WS
are consistent with those relative data designed for the slot of the
Boeing/AFOSR Ma 6 Quiet Tunnel.
Maximum expansion angle is the primary parameter
for the design of expansion section of hypersonic quiet nozzle. According to
the quantity of maximum expansion angle, expansion section could be classified
as fast expansion and slow expansion. In order to diminish the effect of instability
of Görtler vortex, gradually, slow expansion was employed for quiet nozzle design.
Based on the favorable pressure effect, the maximum expansion angle is
optimized in this paper, and a considerable selective session of maximum
expansion angle is obtained. The trend that slow expansion is employed instead
of fast expansion is explained, and a new method is established for aerodynamic
optimization of expansion section contour in a quiet nozzle.
This paper presents quiet zone
design using ultrasonic transducers for local active control in pure tone
diffuse fields. Most of researches in local active noise control used
conventional loudspeakers for the secondary sources to produce quiet zones.
Recently ultrasonic transducers have been used for the secondary sources to
control the plane wave in active noise control. However there is no research
related to active noise control in diffuse fields using ultrasonic transducers.
Therefore this study uses ultrasonic transducers for the secondary sources to
control the diffuse fields. The quiet zone produced using ultrasonic transducers
in single tone diffuse fields has been analyzed through simulations in this work.
The results showed that quiet zones created using ultrasonic transducers were
larger than those created using conventional loudspeakers. This is due to the
fact that the audible sound pressure produced by the ultrasonic transducers
decays slowly with the distance. Therefore the secondary field created by an
ultrasonic transducer could fit the primary field better and the larger zone of
quiet could be obtained using the ultrasonic transducer. Also the audible sound
produced by the ultrasonic transducers is directional; therefore the sound
pressure amplification outside the quiet zones was lower.？