水平轴风力机叶片气动噪声源分布特性的试验研究

为寻找水平轴风力机额定来流风速不同转速工况时叶片气动噪声源分布特性的规律,利用30通道切片轮式阵列采用近场声全息法和远场波束形成法对水平轴风力机近尾迹区域进行噪声数据采集和声源成像分析。其试验结果表明：风力机气动噪声源在不同噪声频段下声压级随风力机转速的升高而增大,且气动噪声源位置未发生变化;在额定来流风速和额定转速下,随着气动噪声源频率由低频段向高频段过渡,其叶片气动噪声源位置由叶片中部沿叶片展向朝叶尖处规律移动,该结论可为风力机的降噪研究提供参考。     

可调导叶对气悬浮离心压缩机及系统性能影响研究

离心压缩机作为离心式冷水机组的核心设备,被广泛应用于大型制冷空调系统、工业制冷等领域。由于气悬浮轴承具有成本低、无需主动控制等优点,使气悬浮离心式制冷压缩机成为近年研究热点及重要发展方向。针对气悬浮双级压缩制冷系统,建立了离心压缩机模型,且在第一级压缩机进口安装可调导叶,通过CFD的方法,模拟了变导叶开度下压缩机及系统性能。结果表明,采用可调进口导叶能够改善压缩机内部流场,导叶开度为正时,压缩机的喘振流量以及最高效率点的流量向小流量方向偏移,反之则向大流量工况偏移。蒸发温度相同、压缩机出口流量固定时,不同导叶开度下系统的COP随中间补气量的增加而降低,导叶开度改变了压缩机工作压比,进而间接影响系统工况及COP。不同导叶开度下系统的COP随工作压比的增加而降低,当工作压比小于2.4时,导叶开度为20°时系统的COP最高。     

离心式压缩机喘振原因及其预防对策

离心压缩机是用高于0.015兆帕的排气来输送空气和其他各种混合气体的径流压缩机,这些空气、工艺气体和混合气体沿着规定的径向流动。喘振是离心式压缩机在流量减少到一定程度时所发生的一种非正常情况下的振动。当离心压缩机系统内的压力过高或者流量吸入不够等都会引发喘振现象,喘振对离心压缩机有着极大的危害,会破坏工艺系统的稳定性运行,烧毁轴承,缩短压缩机的使用寿命。我们可以通过采用固定极限流量的防喘振系统或者在压缩机的出口管线上设置防喘振控制阀等方法防止离心压缩机产生喘振。本文主要分析了离心式压缩机发生喘振的原因和危害,探讨了针对离心式压缩机发生喘振的预防对策。     

电子膨胀阀内啸叫噪声特性及发声规律的实验研究

空调系统中电子膨胀阀节流时出现的尖锐啸叫噪声严重影响用户使用舒适性,了解制冷剂流经电子膨胀阀时的啸叫噪声产生机理及其发声规律是解决上述噪声问题的关键。本文设计了可以对阀前后制冷剂状态进行调节控制并对产生的啸叫噪声进行测量分析的实验系统,得到不同工况及阀开度下的啸叫噪声发声规律。研究表明：啸叫噪声来源于阀内流体高频压力脉动引起的流体周期性振荡,其发声特性是阀内环锥形节流通道与阀腔构成的亥姆霍兹共振腔结构对共振频率附近的噪声源信号选择性放大的结果。啸叫噪声声压级主要与阀内制冷剂流速及阀开度有关,阀开度为700 pls下制冷剂速度由2.5 m/s增至3 m/s时,噪声声压级提高了21%;阀内制冷剂流速决定了流体振荡频率,阀开度决定了阀内声腔共振频率;通过改变阀腔结构以增大共振频率,使常见空调工况下阀内制冷剂冲击引起的振荡频率低于共振频率,可以有效避免啸叫噪声产生。     

河南众力160000m~3/h大型离心空气压缩机组项目被列入国家火炬计划

<正>河南众力空分设备有限公司(以下简称:河南众力)160000 m3/h大型离心空气压缩机组项目被列入2010年度国家火炬计划项目名单。与此同时,该机组上采用的带可调进口导叶和可转动叶片扩压器的离心压缩机技术获得国家专利证书。该项目通过良好的气动设计,使机组具有先进的气动     

压缩机吸气消声器气动噪声辐射特性研究

以某变频压缩机吸气消声器为研究对象,在不同压缩机转速下,研究消声器内流场气动噪声辐射特性。通过仿真分析消声器内部流场和声场,采用FW-H声学模型计算其声场参数,获得噪声源数据,计算气动噪声辐射特性,并与整机测试结果进行对比分析。结果表明,吸气消声器噪声源强度从入口至出口沿气流方向逐渐增大,主要噪声源位于出口附近;随转速增加,噪声源强度逐渐增大;出口和入口的声压级都随转速上升而增大,且声压级的最大值所在频段随转速上升逐渐向高频移动;相同转速下,出口处的声压级高于入口处;消声器气动噪声表现为一种宽频噪声,主要集中于400 Hz至6 000 Hz频段内,吸气消声器气动噪声对压缩机整机噪声影响较大。     

双吸离心泵正反转工况流致振动噪声研究

为深入了解双吸离心泵运行的振动噪声规律,以某一双吸式离心泵为研究对象,基于声学间接边界元法(IBEM),采用LMS Virtual-Lab分析计算平台,进行基于泵壳模态的强迫振动响应计算。然后根据泵壳模态强迫振动响应计算与声学间接边界元的声学波动方程求解耦合方程,得到双吸泵在液力透平工况和泵工况下外辐射声场的声压级指向分布和声压级分布。结果表明:偶极子声源是流体噪声的主要声源;在蜗壳隔舌处非定常脉动力是主要的噪声源;叶频及其倍频是双吸泵外辐射声场噪声的主要诱导频率;泵壳发生了共振,所以声振耦合的作用不可忽略。研究揭示了双吸泵作液力透平及泵工况内部流动诱发的外辐射声场的声振耦合计算规律,为后续减振降噪研究提供了理论基础。     

多翼离心风机气动噪声的降噪

针对多翼离心风机气动噪声的主要噪声源提出降噪方案。首先,对于多翼离心风机涡流噪声的降噪,主要通过优化叶轮、蜗壳的结构几何参数和在叶轮出口加装旋转扩压器等方式进行。其次,对于多翼离心风机旋转噪声的降噪,主要通过改变蜗舌形式进行。最后对优化进出口安装角的叶轮和在叶轮出口加装旋转扩压器这两种降噪措施进行试验验证。结果表明,改进后的风机与原型相比达到显著的降噪效果。     

多翼离心风机气动噪声的降噪与实验研究

本文针对多翼离心风机气动噪声的主要噪声源提出了降噪方案。首先,对于多翼离心风机涡流噪声的降噪,主要通过优化叶轮、蜗壳的结构几何参数和在叶轮出口加装旋转扩压器等方式进行。其次,对于多翼离心风机旋转噪声的降噪,主要通过改变蜗舌形式进行。最后对优化进出口安装角的叶轮和在叶轮出口加装旋转扩压器这两种降噪措施进行了试验验证。结果表明,改进后的风机与原型相比达到了显著的降噪效果。     

数值方法在轴流式风机气动噪声识别中的应用

采用非定常流场计算和基于FWH方程的声学类比方法对小型轴流式风机的气动噪声进行数值仿真研究,并在消声室中建立轴流式风机的测试装置研究其噪声特征。数值模拟中的虚拟消声室的大小与实物大小相同,选取最优计算工况为LES模型、2 300万网格及时间步长为叶轮转过1°所需时间,通过与试验对比,在噪声频率200～1 000 Hz范围内,计算结果与试验结果有较好的吻合。在此基础上,对分离作用、旋转叶片和分离流的相互作用、叶尖处涡流等叶片噪声源进行分析,发现噪声源主要来自叶片前缘的顶部位置、叶尖位置以及叶片中心区域,这3个区域产生的噪声频率分别在200～500 Hz,500～1 100 Hz以及800 Hz左右。     

Calculation of a transient in a two-pole network with a thermistor

An analytical expression is derived which describes the variation of the thermistor temperature during a relay-effect transient process following an instantaneous change in the supply voltage in an R — R_T two-pole network.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 3, pp. 465–472, March, 1980.     

Interaction between a liquid and a cylindrical body touching a wall

An exact solution is obtained for the problem of interaction between the ideal liquid homogeneously moving at infinity and streamlining a round cylinder touching a solid wall.     

Stress analysis of a strip with a step and a crack

Stress analysis for a strip of which widths are different at the right and left handsides is carried out for before and after occurrence of a crack at a corner of a step. The strip is analyzed as a thin plate bending problem subject to transverse bending and torsion, and as a plane eleastic problem subject to bending in the plane and uniaxial tension. The rational mapping function of a sum of fractional expressions and complex variable method are used. Stress distribution and stress intensity factors are obtained.     

Imaging a point to a line with a single spherical mirror

Methods for imaging a single point source to a line image are discussed, and a design study of single spherical mirror systems that form aberration-free line images is presented. An expression forthe ray density along the line image is derived for such systems in the cases of (i) uniform beam profiles and (ii) Gaussian beam profiles. The resulting ray density profiles are illustrated for single spherical mirror systems over a wide range of design parameters.     

Influence lines for bending under a ring load of a free shell,a shell embedded in a soft medium and a shell containing a soft core

Summary Theoretical expressions for stresses and displacements have been derived for bending under a ring load of a free shell, a shell embedded in a soft medium, and a shell containing a soft core. Numerical work has been done for typical cases with anElliot 803 Digital Computer and influence lines are drawn therefrom.

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Einflußlinien für die Biegung einer freien Schale, einer Schale in einer weichen Bettung und einer Schale mit weichem Kern

Zusammenfassung Für die Biegung einer freien Schale, einer weich gebetteten Schale und einer Schale mit weichem Kern unter einer Ringlast werden Ausdrücke für die Spannungen und Verschiebungen hergeleitet. Die Ergebnisse wurden für einige typische Fälle mit einem DigitalrechnerElliot 803 numerisch ausgewertet. Die sich ergebenden Einflußlinien wurden graphisch dargestellt.

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Nomenclature A (),B () Functions of - a, t Mean radius and thickness of the shell - E _S , _S Young's modulus andPoisson's ratio of the shell - G _c , _c Shear modulus andPoisson's ratio of the casting or core - I ₀ (r),I ₁ (r) ModifiedBessel functions of the first kind and order zero and one respectively - K ₀ (r),K ₁ (r) ModifiedBessel functions of the second kind and order zero and one respectively - p Ring load, lb/in - U, W Displacement components in the casing or core in thez andr direction - u, w Displacement components of a middle surface point in the shell - _r , _rz Radial and shearing stress components - Independent variable of infinite integrals - k [3(1–S ²)a ²/t ²]^1/4 With 13 Figures     

Linear heat transfer in a flow around a cylinder or a sphere

It is shown that the relation between the Nusselt and Reynolds numbers determined by the Reynolds analogy is linear with self-similarity of the hydrodynamic resistance coefficient.Special Design and Technology Office Element, Odessa, Ukraine. translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, May–June, pp. 395–396, 1995.     

Interaction between a cylindrical shell in a fluid and a pulsating bubble

The dynamic behavior of a cylindrical fluid-immersed shell in a pressure wave initiated by a pulsating vapor-gas bubble that develops as a result of the action of laser radiation on the absorbing medium (metal) is examined experimentally and theoretically. The results of the experiments suggest that the amplitude of the shock wave that develops as a result of complete or partial vaporization of the absorbing medium is appreciably smaller than the amplitude of the waves due to pulsations of the bubble that is formed. Experimental data on the pattern of structural deformation are confirmed by calculations. The effect of load simulation on the behavior of the shell is established according to computational data.Translated from Problemy Prochnosti, No. 6, pp. 116–120, June, 1990.     

Resistance of a sphere in a slow flow of a viscoelastic fluid

The authors have obtained an approximate solution of the problem of the resistance of a rigid sphere in a slow flow of a Maxwell viscoelastic fluid that is in good agreement with experimental data [1] for Weissenberg numbers We ≤ 0.7. It is shown that the effect of a decrease in the coefficient of resistance of a sphere in the interval 0.1 ≤ We ≤ 0.7 established experimentally is determined in full measure by the linear viscoelastic properties of the Maxwell fluid. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1138–1140, November–December, 1998.