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Vortex sound due to a flexible boundary backed in the presence of in a low mach number flow across a drum like silencer

'Vortex sound due to a flexible boundary backed in the presence of in a low mach number flow across a drum like silencer'
Vortex sound in the presence of a low Mach number flow across a drum-like silencer S. K. Tanga) Department of Building Services Engineering, The Hong Kong Polytechnic University, Hong Kong, China (Received 28 April 2010; revised 13 February 2011; accepted 16 February 2011) The sound generated by a vortex propagating across a two-dimensional duct section with fl exible walls (membranes) in an infi nitely long rigid duct conveying a fl ow is investigated numerically using the matched asymptotic expansion technique and the potential theory. The effects of the initial vortex position, the mechanical properties of the fl exible walls, and the mean fl ow on the sound generation are examined in detail. Results show that the presence of a vortex inside a uniform mean fl ow can strengthen or attenuate the sound generation, depending on the phase of the membrane vibration when the vortex starts vigorous interaction with the membranes and the strength of the mean fl ow. The results tend to imply that there is a higher chance of sound amplifi cation when a vortex stream is moving closer to the lighter membrane under a relatively strong mean fl ow or when the mean fl ow is weak. The chances of sound amplifi cation or attenuation are equal otherwise. V C2011 Acoustical Society of America. [DOI: 10.1121/1.3562567] PACS number(s): 43.28.Ra, 43.40.Rj, 43.50.Nm [JWP]Pages: 2830–2840 I. INTRODUCTION The air conditioning and ventilation system is one of the major noise sources in a modern heavily serviced commer- cial building. The noise from the air handling unit of the sys- tem, which basically consists of a powerful fan, propagates into the building interior through the ductwork which at the same time conveys the treated air to the occupied zones within the building. There are also exhaust fans which extract the used air inside the building out of the building. Duct noise control is therefore an important duty of a build- ing services engineer. The conventional method to attenuate these noises is by using dissipative silencers in which the porous materials inside them damp the noise by converting the acoustical energy into heat.1The acoustical performance of these mate- rials at low frequencies is not satisfactory, and thus attenuat- ing the low frequency noise from the fans in the air conditioning and ventilation ductwork by using porous mate- rials is not cost-effective. The topic of low frequency duct noise attenuation has attracted the attentions of many researchers and engineers over the past few decades. There have been efforts on understanding the performances of vari- ous reactive components in the noise control2,3and on the use of combined dissipative and reactive methods for the noise attenuation.4Active cancellation methods using adapt- ive digital fi lters have also been explored (for instance, Can- evet5and Nelson and Elliott6). The use of vibro-acoustic technique for noise attenua- tion has also been investigated. Ford and McCormick7dem- onstrated t
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Vortexsoundduetoaflexibleboundarybackedinthepresenceofinalowmachnumberflowacrossadrumlikesilencer
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本文标题:Vortex sound due to a flexible boundary backed in the presence of in a low mach number flow across a drum like silencer
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