Experimental verification of the quasi-steady approximation for aerodynamic sound generation by pulsating jets in tubes

Voice production involves sound generation by a confined jet flow through an orifice (the glottis) with a time-varying area. Predictive models of speech production are usually based on the so-called quasi-steady approximation. The flow rate through the time-varying orifice is assumed to be the same as a sequence of steady flows through stationary orifices for wall geometries and flow boundary conditions that instantaneously match those of the dynamic, nonstationary problem. Either the flow rate or the pressure drop can then be used to calculate the radiated sound using conventional acoustic radiation models. The quasi-steady approximation allows complex unsteady flows to be modeled as steady flows, which is more cost effective. It has been verified for pulsating open jet flows. The quasi-steady approximation, however, has not yet been rigorously validated for the full range of flows encountered in voice production. To further investigate the range of validity of the quasi-steady approximation for voice production applications, a dynamic mechanical model of the larynx was designed and built. The model dimensions approximated those of human vocal folds. Airflow was supplied by a pressurized, quiet air storage facility and modulated by a driven rubber orifice. The acoustic pressure of waves radiated upstream and downstream of the orifice was measured, along with the orifice area and other time-averaged flow variables. Calculated and measured radiated acoustic pressures were compared. A good agreement was obtained over a range of operating frequencies, flow rates, and orifice shapes, confirming the validity of the quasi-steady approximation for a class of relevant pulsating jet flows.     

Broadband sound generation by confined pulsating jets in a mechanical model of the human larynx

Experiments were performed to study the production of broadband sound in confined pulsating jets through orifices with a time-varying area. The goal was to better understand broadband sound generation at the human glottis during voicing. The broadband component was extracted from measured sound signals by the elimination of the periodic component through ensemble averaging. Comparisons were made between the probability density functions of the broadband sound in pulsating jets and of comparable stationary jets. The results indicate that the quasi-steady approximation may be valid for the broadband component when the turbulence is well established and the turbulence kinetic energy is comparatively large. A wavelet analysis of the broadband sound showed that random sound production was modulated at the driving frequency. Two distinct sound production peaks were observed during one cycle, presumably associated firstly with jet formation and secondly with flow deceleration during orifice closing. Most high-frequency sound was produced during the closing phase. Deviations from quasi-steady behavior were observed. As the driving frequency increased, sound production during the opening phase was reduced, possibly due to the shorter time available for turbulence to develop. These results may be useful for better quality voice synthesis.     

Broadband sound generation by confined turbulent jets

Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 20002.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.     

Broadband shock noise reduction in turbulent jets by water injection

The concept of effective jet properties introduced by the author (Kandula M. Prediction of turbulent jet mixing noise reduction by water injection. AIAA J 2008;46(11):2714-22) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold and hot underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.     

Noise generation by instabilities in low Reynolds number supersonic jets

An experimental investigation of noise generation by instabilities in low Reynolds number supersonic air jets has been performed. Sound pressure levels, spectra and acoustic phase fronts were measured with a traversing condenser microphone in the acoustic field of axisymmetric, perfectly expanded, cold jets of Mach numbers 1·4, 2·1 and 2·5. Low Reynolds numbers in the range from Re = 3700 to Re = 8700 were obtained by exhausting the jets into an anechoic vacuum chamber test facility. This contrasts with Reynolds numbers of over 10⁶ for similar jets exhausting into atmospheric pressure. The flow fluctuations of the instability in all three jets have been measured with a hot-wire and the results are documented in a previous paper by Morrison and McLaughlin. Acoustic measurements show that the major portion of the sound radiated by all three jets is produced by the instability's rapid growth and decay that occurs near the end of the potential core. This takes place over a relatively short distance (less than two wavelengths of the instability) in the jet. In the lower two Mach number jets the instability has a phase velocity less than the ambient acoustic velocity. In the Mach number 2·5 jet the instability phase speed is 1·11 times the ambient acoustic velocity. In this case the acoustic phase fronts indicate the possibility of a Mach wave component. It was also determined that low level excitation at the dominant frequency of the instability actually decreased the radiated noise by suppressing the broad band component.     

On the sources of wayside noise generated by high-speed trains

A linear array of 14 microphones was used to measure radiated noise generated by a four-carriage electric train travelling at speeds between 160 and 250 km/h. Most of the results given in this paper pertain to apparent source locations of wheel/rail interaction noise, although preliminary data collected in a concurrent study of railway aerodynamic noise are briefly mentioned. An analysis of the measurements suggests that apparent sources of wheel/rail interaction noise are located (i) in the rail or substructure at low frequencies, (ii) on the wheel rim just below the axle at intermediate or peak frequencies, and (iii) on the lower part of the wheel and possibly in the rail at high frequencies.     

A visual study on elliptical jets in cross flow

Laser-induced fluorescence technique is used to study the near-field of an elliptical jet exiting normally into a cross flow, for elliptic jet having aspect ratio of 2 and 3. Results show that the non-uniform curvature of the elliptic geometry causes the leading-edge vortices at the interface between the jet and the cross flow to behave differently from that of a circular jet. In particular, when the major-axis is aligned with the cross flow there is an intense interaction between the leading-edge vortices which culminates in the pairing of adjacent vortices. The pairing is suppressed when the major axis is perpendicular to the cross flow.     

高层住宅阳台降噪量的计算分析

高层住宅中的阳台不仅具有居住及建筑上的功能,对道路交通噪声也有衰减作用。本文通过建立噪声传播模型计算高层住宅阳台的插入损失,并探讨了影响阳台降噪量的一些因素。同时对阳台内部吸声处理的效果进行了理论预测。     

On measurements of aerodynamic noise generated by a high-speed electric train

Noise measured above a high-speed railway train indicates that aerodynamically generated noise may be quite significant at high vehicle speeds. A comparison of experimental and predicted noise levels demonstrates the similarity between the levels of aerodynamic noise produced by aircraft (airframe noise) and railway vehicles.     

尾管中强脉动排气噪声辐射的特征线解

本文应用特征线法,对尾管中的强脉动流的传播问题进行了理论计算.尾管的强脉动排气,在流压超过临界值的情况下,在开口端处的流动将会阻塞,此时应取马赫数等于1代替流压等于大气压作为该处的边界条件.对于强脉动气流,流动的诸参数的起伏量可大于它们各自的时均值,本文将开口端向外的排气气流比作简源,令简源强度与排气气体的体积速度成正比,同时计及湍流噪声的贡献,这样得到的结果与实验可相比较.最后还计算了管长为一定时的噪声辐射与气室压力的关系,气压为一定时的噪声辐射和质量流通量与尾管长度的关系,以及不同气压下噪声辐射与尾管长度的关系,为指导气动声源和往复式发动机尾管的设计提供了计算方法.     

Shock associated noise of supersonic jets from convergent-divergent nozzles

Results of experimental and theoretical studies of the characteristics of shock associated noise from imperfectly expanded supersonic jets over an extensive range of underexpanded and overexpanded operating conditions are described. This kind of broadband noise is believed to be generated by the weak but coherent interaction between the downstream propagating large scale turbulent flow structures in the mixing layer of the jet and the nearly periodic shock cell system. Theoretical reasoning based on this mechanism leads to the scaling formula that the intensity of shock associated noise varies as (M_j² ? M_d²)² where M_j and M_d are the fully expanded jet operating Mach number and nozzle design Mach number, respectively. This formula holds for underexpanded as well as overexpanded jet Mach numbers. In addition, a peak frequency formula is also derived from the same model. The noise intensity, directivity and spectra of supersonic jets from a convergent-divergent nozzle of design Mach number 1·67 were measured in an anechoic facility over the Mach number range of 1·1 to 2·0. The effect of jet temperature was investigated by operating the jet at three temperature conditions. These sets of data provide sufficient information for fully assessing the relative importance and characteristics of shock associated noise of supersonic jets from convergent-divergent nozzles. Comparisons between theoretical results and measurements show very favorable agreement.     

高速动车组气动噪声试验与仿真分析

通过风洞试验对某高速动车组整车、受电弓及转向架远场气动噪声特性进行分析.试验结果表明,高速动车组远场气动噪声是一宽频噪声,总声能随速度的6.6次方增加;由受电弓引起的远场气动噪声主要集中在中高频,噪声峰值频率随速度变化线性增加;由转向架引起的远场气动噪声主要集中在中低频,噪声峰值频率与速度无关.在此基础上,通过大涡模拟...     

A study of noise reduction by acoustic shock waves

I.IntroductionAcousticshockwavcs(ASW)isanimportantphcnomcnoninnonlinearacoustics.Experimentalrcsultshavcshownthatwhenanaircraftcngincinletopcratesneartheson-iccondition,vcrystrongnoisegcncratedbythcfanscanbcreduccdgreat1yowingtothcformationofASWatthcthroatofthcin1etll].ASWisadiscontinuityofacousticvaria-bles,whichisdifTcrcntfromthcshockwavesoccurringinhighspcedsteadyflowinducts.Theformer'sintensityismuch1cssthanthelattcr's.Furthcrmorc,thepositionandintensityofASWisalwayschangedwithtime.l…     

声激波降噪研究

本文数值研究了声激波产生的条件及其降噪效果,详细讨论了声源强度,频率,管道形状,喉部流动马赫数及多频声源对声激波降噪效果的影响。由于声激波降噪需要附加一段具有高速流动的缩放管道,它会附加流动噪声和压力损失,本文提供了这方面的一组实验数据,以说明应用声激波消声器的现实可能性。     

A theoretical study of spontaneous ignition of fuel jets in an oxidizing ambient with emphasis on hydrogen jets

An analysis was performed for the spontaneous ignition of a hydrogen (or other gaseous fuel) jet emanating from a slot into an oxidizing ambient (e.g., air). A similarity solution of the flow field was obtained. This was combined with the species and energy conservation equations, which were solved using activation energy asymptotics. Limits of spontaneous ignition were identified as functions of slot width, flow rate, and temperatures of the hydrogen jet and ambient gas. Two scenarios are examined: a cool jet flowing into a hot ambient and a hot jet flowing into a cool ambient. For both scenarios, ignition is favored with an increase of either the ambient temperature or the hydrogen supply temperature. Moreover, for the hot ambient scenario, a decrease in fuel Lewis number also promotes ignition. The Lewis number of the oxidizer only has a weak effect on ignition. Because spontaneous ignition is very sensitive to temperature, ignition is expected to occur near the edge of the jet if the hydrogen is cooler than the ambient gas and near the centerline if the hydrogen is hotter than the ambient gas.     

有源消声耳罩的研究

本文提出一种把闭环反馈式控制方式和开环前馈式控制方式结合在一起的复合式消声耳罩,并给出了原理式和具体的结构。理论和实验表明这种复合式结构具有有源消声频带宽、消声效果好的特点。     

A Dutch study on railroad traffic noise

This paper is about a Dutch study on the community response to noise. The set-up of the study is described broadly. Some details are given about the comprehensive sound level measurement programme. Some preliminary results from the social survey are given. A major finding is that annoyance is caused less by the sound of trains running through than by other sounds from the track.     

Shock associated noise of inverted-profile coannular jets,part II: Condition for minimum noise

An experimental and theoretical investigation of shock-associated noise of inverted-profile coannular jets is described. For a fixed fan-stream Mach number, it is observed that the shock-associated noise often drops suddenly to a minimum as the reservoir pressure of the primary jet increases. When this happens, the almost periodic shock cell structure of the fan stream is found to nearly completely disappear. In this paper, an analytical model of this phenomenon is constructed and studied. It is theoretically established that this sudden change in the shock structure and hence the decrease in shock associated noise would occur when the primary jet flow is just slightly supersonic regardless of the Mach number and temperature of the fan stream. This minimum shock associated noise condition is confirmed in several series of experiments.