【作者】 田杰；

【导师】 杜朝辉；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2009， 博士

【摘要】 含导风罩的部分管道式轴流风扇系统大量应用于民用和商用空调器中,其结构特点与全管道式以及全开式轴流风扇系统有很大的不同,为了提高空调室外机的性能以及降低噪声,对部分管道式轴流风扇系统的气动声学及其流动特点的研究已经成为室外机研究的主要方向之一。论文以分体式空调器室外机内部含导风罩的部分管道式轴流风扇系统为研究对象,采用先进的实验分析和CFD数值计算相结合的研究手段详细研究了均匀进气情况下部分管道式轴流风扇系统及复杂结构单转子和上下并联双转子室外机的气动-声学性能。分析了部分管道式轴流风扇内部复杂三维湍流流场,特别是叶顶区域叶尖涡的形成、发展,及其与导风罩干涉后的拉伸和破裂现象。提出了基于低速等熵流涡声理论和CFD数值计算方法相结合的部分管道式轴流风扇系统气动噪声源辨识方法,在此基础上发展了基于CFD的涡脱落噪声预测模型。采用近场CFD计算非定常脉动力和远场非齐次FW-H方程相结合的气动声学混合计算方法,分别在时域和频域对室外机轴流风扇离散频率噪声及其噪声谱进行了预测研究,并分别对时域预测模型和频域预测模型展开了讨论。本文的主要研究工作包括:1.建立了一套轴流风扇气动-声学实验装置。采用声强法对室外机噪声源分布进行了详细的测量,结合频谱分析手段分析了室外机主要噪声频谱特征。采用粒子图像测速仪(Particle imaging velocimetry, PIV)和热线风速仪(Hotwire Anemometer, HWA)对含导风罩的部分管道式轴流风扇系统内部流场进行了详细的测量。实验结果结合三维CFD数值模拟研究了部分管道式轴流风扇系统叶尖涡、尾缘涡特征,及其在室外机内部的流动变化。2.室外机中主要噪声来自于轴流风扇系统出口产生的气动噪声,噪声源表现为偶极源分布特征。室外机噪声频谱由宽频和离散频率噪声组成,宽频噪声起主导作用,离散频率噪声峰值在叶片通过频率及其谐波处。上下并联双转子室外机离散频率噪声峰值分别对应上下叶轮通过频率及其谐波处,室外机内部上下叶轮间流场干涉对室外机总声压级影响较小。3.含导风罩的部分管道式轴流风扇系统,在叶轮前缘由于吸力面和压力面压差产生叶尖涡,随叶轮旋转往下游和流道内部发展。当流经导风罩时,叶尖涡受导风罩挤压,涡结构发生拉伸和破裂现象从而辐射噪声。当轴流风扇置于室外机内部时,叶尖涡在子午面上的轨迹愈发向中部叶高方向发展。室外机不均匀进气导致室外机进出口流场表现出明显的不对称性,该不对称性使得叶轮旋转一周的脉动增大。室外机不同时刻叶片表面压力分布表明,叶尖涡与导风罩干涉是室外机中叶片表面非定常力脉动的主要原因,影响室外机离散频率噪声。对上下并联双转子室外机,进出口上下叶轮间流场干涉较小。4.采用叶尖涡涡心轨迹分析方法得到了不同安装角叶轮叶尖涡与导风罩干涉作用,建立了涡运动与声学辐射的关联。基于数值模拟的低速等熵流涡声理论分析表明,对于均匀进气的部分管道式轴流风扇系统,叶轮出口尾缘涡是噪声辐射的主要方面。对于室外机,除尾缘涡影响外,气流流经换热器产生湍流对轴流风扇进口湍流噪声有一定影响。热线测量表明,气流流经换热器产生湍流,经过与主流掺混作用,在到达叶片前缘时较小,产生的进气湍流噪声对低压轴流风扇的噪声辐射影响小。5.基于三维定常数值模拟的涡脱落噪声预测模型,计算得到空调室外机的宽频噪声及噪声总声压级。噪声预测与实验结果对比分析表明,在叶片下游5mm处提取尾迹流动参数,预测得到噪声较准确。单转子室外机误差在2 dBA,对于上下并联双转子室外机,不考虑干涉影响下,预测误差在3dBA以下,预测方法满足工程应用需要。基于FW-H方程和三维非定常数值模拟的混合方法,对室外机离散频率噪声进行时域和频域求解。通过精细的数值模拟计算,减少了时域噪声预测所需时间。对频域模型中Bessel函数的数值分析表明,对低马赫数的低压轴流风扇,仅二阶以下Bessel函数对离散频率噪声预测有影响,简化了频域预测模型。声学紧凑的分析及其与片条理论预测结果的对比,验证了旋转点源预测模型的准确性。时域和频域预测结果在叶片通过频率及其低阶谐波处吻合较好,且与实验结果相比误差小,说明了离散频率噪声预测模型在室外机应用中的准确性。更多还原

【Abstract】 Partly-ducted axial flow fans with bellmouth are widely used in civil and commercial air conditioners, which are different from full-ducted and open axial flow fans in structure. In order to improve aerodynamic performance and reduce noise, it is important to study aeroacoustics and flow characteristics of partly-ducted axial flow fans, which has already been one of major problems of research in outdoor units.In this paper partly-ducted axial flow fan system with bellmouth, which are included in split-type outdoor units of air conditioner, are investigated. With help of advanced experiment and CFD simulation, aerodynamic and aeroacoustic performances of partly-ducted axial flow fan with uniform inflow and complex structure of single and collateral axial flow fan inside outdoor units are first studied. Then, complex three-dimensional turbulent flow field inside flow passage of partly-ducted axial flow fan are analyzed, characteristics of tip vortex with its formation, development, stretched and broken down by the interaction with bellmouth are discussed. Next, the methods used to identify noise source of partly-ducted axial flow fan are introduced, which is based on vortex sound theory of low Mach number and homentropic flow together with CFD simulation. Furthermore, vortex shedding noise prediction model based on CFD simulation is developed. In the end, a hybrid method coupling near-field CFD calculation plus the application of an integral nonhomogeneous FW-H function for the far-field is adopted to predict the discrete frequency noise and spectrum of outdoor units in time and frequency domain. At the same time prediction models in time and frequency-domain are discussed, respectively.Main research contents and results of this paper are as follows:1. Set up experimental equipment suitable for aerodynamic-aeroacoustic measurement of axial flow fan. Noise source of outdoor units is obtained by sound intensity method and characteristic of noise spectrum of outdoor units is investigated by spectrum analysis. Flow field of partly-duct axial flow fan system is measured in detail by Particle Imaging Velocimetry (PIV) and Hotwire Anemometer (HWA). With help of experiment and CFD simulations, character of tip vortex and trailing edge vortex of partly-ducted axial flow fan is studied, with flow change in outdoor units also analyzed.2. Major noise source radiated from outlet of axial flow fan in outdoor units is aerodynamic noise, which is acted as dipole noise. Noise spectrum of outdoor units is composed of broadband and discrete frequency noise. Effect of broadband noise is crucial and discrete frequency noise is located at Blade Passing Frequency (BPF) and its harmonics. To collateral axial flow fan inside outdoor unit discrete frequency noise is located at BPF and its harmonics of upside and downside rotor, respectively. Interaction of flow field generated by upside and downside rotor has little effect on total sound pressure level of outdoor units.3. In partly-ducted axial flow fan system with bellmouth, blade tip vortex formed at blade leading edge is generated by pressure gradient between suction side and pressure side, it develops downstream and into flow passages as blades rotate. When blade tip vortex passes by bellmouth, it is extruded by bellmouth, and its structure is stretched and broken down, and noise is radiated. When axial flow fan is included in outdoor units, blade tip vortex further develops mid span at meridional plane. Uneven inflow in outdoor units will induce asymmetry flow field at inlet and outlet, which will increase fluctuation at one blade rotating period. According to distribution of pressure of blade surface at different time of outdoor units, it is shown that interaction between tip vortex and bellmouth is the major factor of unsteady fluctuation of blade surface and has large effect on discrete frequency noise of outdoor units. To collateral axial flow fan system inside outdoor units, the interaction of flow field between upside and downside rotor is weak.4. Vortex line analysis based on trail of tip vortex core of rotor with different setting angles is used to illustrate the interaction between tip vortex and bellmouth and set up the relationship between vortex movement and noise radiation. Based on vortex-sound theory of low Mach number and homentropic flow together with CFD simulation, it is shown that trailing edge vortex is the major noise source of partly-ducted axial flow fan with uniform inflow. To outdoor units, besides effect of trailing edge vortex, inlet turbulence generated by heat exchanger has a little effect on inlet turbulent noise of axial flow fan. On the other hand it is shown by HWA measurement that turbulence generated by heat exchanger will be weakened by mixture of main flow, and turbulence intensity will be little at blade leading edge, and then inlet turbulent noise of outdoor units will be little and has weak effect on total sound pressure of outdoor units.5. Broadband noise and total sound pressure level of outdoor units is predicted by vortex shedding noise prediction model based on three-dimensional steady CFD simulation. It is shown that wake parameter at 5mm downstream of blade is accurate. Error of total sound pressure level of single and collateral axial flow fan system inside outdoor units is 2 and 3 dBA, respectively. That is to say this prediction method is suitable for engineering demand. Discrete frequency noise of outdoor units is predicted in frequency and time domains based on a hybrid method coupling FW-H equation and three dimensional unsteady CFD simulations. With careful CFD simulation, time consumption of time-domain noise prediction is reduced. By numerical analysis of Bessel function in frequency-domain noise prediction model, it is shown that only Bessel function below second order has effect on discrete frequency noise of axial flow fan system with low pressure and low Mach number, which can be used to simplify frequency-domain noise prediction model. By contrast of noise prediction based on compact noise source assumption and stripe theory, it is justified that prediction model based on rotating point source is accurate. Results of time and frequency-domain noise prediction are both consistent with experimental one at BPF and its low order harmonics, which attests that this noise prediction model is accurate in discrete frequency noise prediction of outdoor units.更多还原