Flow Induced Acoustic Resonance in In-line Tube Banks

In the present paper the attention is focused on the relation between vortex shedding phenomena andacoustic resonance which occurred in the two-dimensional model of boiler.There were tube bankswith in-line arrangement for small tube pitch ratio.We measured the sound pressure level,the phasedelay of acoustic pressures,the spectrum of velocity fluctuation and the gap velocity.As a result, wefound two peak frequencies of sound pressure level with different Strouhal numbers S_t,mainly about0.26 and 0.52.The noise of S_t=0.26 was the resonance of transverse mode and S_t=0.52 waslongitudinal mode.The vortex shedding of S_t=0.15 was generated inside the tube banks withoutacoustic resonance. As gap velocity increased, we observed that the peak level of spectrum was weakand broad-banded. The onset velocity of the acoustic resonance of longitudinal mode was lower thanthat of transverse mode.     

塔架对风轮旋转过程中声场及流场的影响探究

基于压力脉动与声压之间的关系,利用Fluent数值模拟平台对风力机旋转过程中整机和单转子的声场和流场进行分析。对比2种模型的最大声压级位置,发现由于塔架的介入,整个模型的声场落后于流场约30°。分析塔旁y轴负向测点处压力脉动与声压级第1个峰值对应的方位角,结果发现在y/R=0.14、y/R=0.42、y/R=0.71与y/R=1时声压级（SPL）分别落后于压力脉动22°、5°、9°与18°。分析风力机旋转过程中两种模型塔附近监测点的声压级与压力脉动的变化趋势,结果表明：声压级振幅沿展向先增大后减小,在y/R=0.71处达到最大值;同样,在y/R=0.71时压力波动幅度最大。     

基于BEM/FEM耦合技术的柴油机外声场模拟技术研究

采用BEM／FEM耦合技术对某高强化V6柴油机结构的声辐射情况进行了模拟，得到了整机辐射声功率、辐射效率、主要部件对声学结果的贡献以及近、远场声压(级)、整机外场声强矢量分布等声学结果，为该柴油机针对减振降噪的结构声学优化提供了详细信息与重要参考。在此基础上，重点对主要声辐射部件一下曲轴箱的结构进行了修改，并对修改方案的声辐射情况进行了重计算。主要声学量的对比结果表明，在所研究的频率域内，修改措施对改善低频域内整机外场声辐射情况具有较为明显的作用。     

基于SONAH的旋转风轮声源识别实验研究

在风洞开口实验段,针对不同风速及不同叶尖速比,应用Brükel&Kj?r公司60通道轮型声阵列及声信号采集系统对直径为1.4 m的S翼型风轮进行声场测试,并采用统计最优近场声全息(SONAH)技术进行旋转风轮低频噪声源识别及频域特征分析。实验结果表明:最大声强度是旋转叶片产生的基频噪声,其对应总声压级随风速增加呈函数f(x)=-0.0092x⁴+0.297x³-3.7403x²+23.186x+49.274增加,随叶尖速比增加呈函数f(x)=0.4467x⁴-10.273x³+87.728x²-328.75x+567.23增加;识别的噪声源最大能量中心集中于翼展位置约0.545 m,相对半径r/R=0.778处,且不随风速和尖速比的改变而改变。     

A computational investigation of airfoil aeroacoustics for structural health monitoring of wind turbine blades

A generalized computational methodology for reduced order acoustic‐structural coupled modeling of the aeroacoustics of a wind turbine blade is presented. This methodology is used to investigate the acoustic pressure distribution in and around airfoils to guide the development of a passive damage detection approach for structural health monitoring of wind turbine blades for the first time. The output of a k ? ε turbulence model computational fluid dynamics simulation is used to calculate simple acoustic sources on the basis of model tuning with published experimental data. The methodology is then applied to a computational case study of a 0.3048‐m chord NACA 0012 airfoil with two internal cavities, each with a microphone placed along the shear web. Five damage locations and four damage sizes are studied and compared with the healthy baseline case for three strategically selected acoustic frequencies: 1, 5, and 10 kHz. In 22 of the 36 cases in which the front cavity is damaged, the front cavity microphone measures an increase in sound pressure level (SPL) above 3 dB, while rear cavity damage only results in six out of 24 cases with a 3‐dB increase in the rear cavity. The 1‐ and 5‐kHz cases show a more consistent increase in SPL than the 10‐kHz case, illustrating the spectral dependency of the model. The case study shows how passive acoustic detection could be used to identify blade damage, while providing a template for application of the methodology to investigate the feasibility of passive detection for any specific turbine blade.     

Heat transfer and flow resistance in condensation of low pressure steam flowing through tube banks

This paper deals with an experiment performed on condensation, when saturated steam of low pressure flows through tube banks, crossing them horizontally. Simple expressions for heat transfer coefficients of steam side and pressure drops through tube banks are proposed, and resistance coefficients are represented graphically. At the same time, a comparison is made between the results for the two tube banks of in-line and staggered arrangement with 22/14 spacing-to-diameter ratio. Such results of observation as peripheral distribution of temperature on tube surface, accumulation of leaked air, breathing flow of steam etc. Are also reported.     

Effect of acoustic resonance phenomenon on fluid flow with light dust

In the present paper,the attention is focused on the characteristics of lightweight materials collection in the duct using acoustic resonance phenomena.The acoustic resonance was excited by using a controlled speaker at the middle of a test duct.We measured the sound pressure level,frequency response characteristics,acoustic damping ratio,mode shape,and lightweight materials response to acoustic resonance excited by a speaker.As a result,the acoustic damping ratio decreased as the mode number of acoustic re...     

联合循环发电机组的噪声测量与噪声源识别

通过对350Mw燃气-蒸汽联合循环发电机组厂房内各个机岛以及辅助设备的现场噪声测量,分析了厂房内的主要噪声源及其频谱特征。根据测量结果计算了各个机岛噪声的声功率和厂房内工作面的声压分布,验证表明计算结果与实测结果吻合较好。根据主要噪声源的频谱特性探讨了降低厂房噪声声压的吸声隔声措施。     

基于ATV的内燃机结构声辐射预测技术研究

基于声传递向量（ATV）的概念,研究探讨了ATV技术在内燃机结构辐射噪声仿真预测上的应用方法和途径。以某四缸柴油机为例,利用ATV技术,计算得到了整机结构辐射声功率、外场域点声压（级）、结构面板声学贡献、辐射效率等声学响应。在内燃机研制过程中,基于振动和声压域之间振一声关系的ATV技术,是快速进行振一声响应预测的一个有效方法。     

Statistical validation and an empirical model of hydrogen production enhancement found by utilizing a controlled acoustic field in the steam-reforming process

Preliminary studies have shown that a controlled sound field can produce enhancement of hydrogen production in a steam-reforming process. This paper expands on preliminary investigations to explain a statistical empirical model that was developed for space velocity parameters of reactor length and flow rate as well as for acoustic sound pressure level. The effects of these parameters are shown on the output of fuel conversion within a methanol-steam reformer. The experimental setup is discussed as well as the factorial method employed. Although the results of this model are particular to the experimental setup specified, this exercise statistically proves the validity of acoustic enhancement of steam reformation. The empirical model is derived and uncertainty analysis of the model takes place. Curvature was investigated for the model and was found significant for the parameter of reactor length. Linear model relationships were found adequate for sound pressure level and flow rate within the limits investigated. Preliminary results regarding the effect of frequency on the process are also discussed.     

摩托车加速噪声自动测试系统的实现及通过噪声特性分析

摩托车加速噪声自动测试系统是先进的车辆通过噪声测试手段,实现了对加速噪声相关数据准确完善地测量、存储及分析。本文经过大量分析加速噪声测试过程试验数据,确定发动机转速是影响摩托车噪声的最重要因素。通过建立加速噪声声学模型,深入分析加速噪声测试时传声器测点声压级变化规律,明确了确定加速噪声最大声压级对应车辆工况的方法及意义。     

考虑内部流体域的内燃机外声场模拟技术研究

采用体积有限元法模拟内燃机内部流体区域,结合整机结构辐射声场计算模型,建立了某V型六缸柴油机包含内部流体域的整机声学流体分析模型。在此基础上,以下曲轴箱润滑油域为例,进一步探讨了考虑内部流体域对整机结构辐射声场仿真结果的影响。对该柴油机整机结构辐射声场的计算对比结果表明,下曲轴箱润滑油域对整机结构辐射效率、外场声压分布等声学量在频率内的分布规律及幅值大小有着较为明显的影响,在内燃机整机结构辐射声场的计算中应该予以考虑。     

重型燃气轮机进气系统性能研究

针对某款重型燃气轮机进气系统辐射噪声超标问题,采用声学有限元法和计算流体力学方法对系统部件进行声学和流场计算,得出插入损失和压力损失,并与进气系统指标要求进行比较发现,进气系统噪声指标与限值余量较小,且压力损失远低于限值。在分析的基础上,选取片式消声器为研究对象,研究不同结构参数和形式对进气系统声学性能和空气动力学性能的影响。结果表明：片式消声器的厚度和数量对进气系统性能有明显的影响,当增加片式消声器厚度和数量时,压力损失略有增加,插入损失增大,进气口声压级减小;通过添加侧支共振器,进气口总声压级降低了3.1 dB(A),可以有效增大进气系统低频插入损失。     

燃烧超细颗粒声波团聚的谱分布数值模拟

在简要介绍声波团聚超细颗粒物的动力学机理的基础上,利用区域算法求解超细颗粒声波团聚的动力学方程(GDE),数值模拟了声波团聚前后的超细颗粒的谱分布变化,并同相关实验数据和数值算法进行了比较和分析．区域算法结果和实验数据以及数值解之间吻合较好,并且利用该算法研究了颗粒质量浓度、声波频率和声波强度对超细颗粒团聚效果的影响,结果表明颗粒质量浓度和声强的增加均有利于颗粒的团聚,而声波频率则存在一个最佳值．     

四类螺旋翅片管束热力特性数值研究

对气流横掠螺旋翅片管错列管束的流动与换热特性进行了数值研究,在雷诺数Re=10 000～40 000范围比较了四类(连续型、平齿I型、平齿L型和扭齿型)螺旋翅片管束的换热、阻力及热力综合性能。结果表明:与常规的连续型管束相比,在相同Re下,平齿I型、平齿L型和扭齿型管束的努塞尔数Nu分别提高约24%、32%和38%,欧拉数Eu分别增大约24%、85%和90%;在相同的换热量、流体输运功耗和翅片管结构参数下,平齿I型、平齿L型和扭齿型管束所需的换热面积较之连续型管束所需的分别减小约9%、6%和12%,扭齿型表现最佳;在管束紧凑性方面,连续型、平齿I型和扭齿型管束无明显差别,但选用平齿L型会使管束体积相对增大约18%。     

Prediction of acoustic absorption performance of a perforated plate with air jets

The present study focuses on the prediction of acoustic absorption performance of a perforated plate with air jets by theoretical calculations.In addition,we experimentally measured the flow rate,internal pressure,acoustic pressure,and transfer function using an acoustic impedance tube.The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods.We investigated the influences of background air space,flow velocity,thickness,aperture rate,and aperture diameter of a perforated plate on the acoustic absorption characteristics.The frequency characteristics of the acoustic absorption coefficient showed a maximum value at a local frequency.As the background air space increased,the peak frequency of acoustic absorption characteristics decreased.As the flow velocity passing through the apertures increased,the peak level of the acoustic absorption coefficient also increased.The theoretical results agreed well with the experimental ones qualitatively.     

前缘改形对翼型气动噪声特性影响

为得到高气动性能、低噪声的风力机专用翼型,基于参数化建模翼型,研究前缘外形对风力机翼型气动性能及气动噪声的影响规律。通过分离涡模拟方法和声学类比方程建立噪声预测方法。针对非对称翼型S809通过样条函数参数化处理前缘改形进行气动噪声计算。结果表明:翼型压力面前缘加厚,对翼型升阻力系数无明显影响,但大攻角时翼型周围压力分布均匀,流动相对稳定,且气动噪声声压级低于原始翼型,随压力面厚度增加气动噪声越大;吸力面加厚使得翼型升力系数增大,阻力系数减小,能抑制翼型失速时尾缘涡与前缘涡的生成,变形量越大气动噪声越小;翼型前缘上弯,翼型在失速区升力系数减小,阻力系数增大,流动越加不稳定,声压级随着攻角的增加呈递增趋势;翼型前缘下弯,翼型处于失速区升力系数增大,阻力系数减小,能抑制流动分离,未生成前缘涡和尾缘涡,当前缘下弯不变时,随加厚厚度增加翼型声压级呈减小趋势,且前缘下弯翼型声压级小于前缘上弯。     

Local Convective Heat Transfer from a Horizontal Tube in an Acoustic Cavitation Field

An experiment has been carried out to investigate the local convective heat transfer from a horizontal circular copper tube in an acoustic cavitation field. The effects of acoustical parameters (including sound source intensity, the vibrator location and sound distance), fluid temperature and thermophysical properties of working fluid on heat transfer enhancement were studied, as well as the variation of heat transfer rate with sound source intensity at constant heat flux. Results show that convection heat transfer was remarkably enhanced due to disturbance and impingement by cavitation bubble. Among these cases tested, the maximum augmentation ratio of 3.95 was reached for acetone with a cluster of cavitation bubbles impinging perpendicularly on the tube surface.     

基于声发射技术的高压加热器漏泄监测的研究

介绍了高压给水加热器发生管束漏泄时所产生的声发射信号的特征,据此研制了在线监测系统。经实践证明,采用声发射技术监测加漏率,具有及时,准确的优点,进行实时在在线监测,不仅能准确及时确定出漏泄部位和漏泄时间,而且可为检修提供依据。     

Heat Transfer Characteristics of Nanofluids in an Acoustic Cavitation Field

Heat transfer characteristics of nanofluids in an acoustic cavitation field have been investigated experimentally. The effects of acoustical parameters, nanofluids concentration, and fluid subcooling on heat transfer are determined in detail. Results show that acoustic cavitation and nanometer particles have a profound influence on single-phase convection and boiling heat transfer of a horizontal circular copper tube. The former is mainly ascribed to the impingement and disturbance of cavitation bubbles and anticipatory activation of smaller vapor embryos within the cavities, while the latter is caused by roughness modification of the tube surface. The above mechanisms are given based on the Schlieren photographs and optical observation. Acoustic cavitation has been shown to be a good way to reduce or eliminate boiling hysteresis.