【作者】 刘敏；

【导师】 吴克启；

【作者基本信息】 华中科技大学 ， 流体机械及工程， 2009， 博士

【摘要】 空调室内机的气动噪声问题引起了越来越多的关注，降低气动噪声在目前正变得越来越重要。本文针对空调室内机贯流风扇的气动流场及气动噪声展开研究。结合数值模拟及实验测量对样机在三档不同转速下的内流特征及噪声特性进行了模拟，实验及分析，总结了其内流特征，分析了气动噪声源产生的位置及机制，其气动噪声远场传播特点，最后给出了贯流风扇气动噪声的一个预测模型，并进行了验证。内流场的研究是进行气动噪声研究的基础。本文首先采用CFD技术对贯流风扇模型内流进行了模拟。采用二维及三维计算模型，在定常及非定常条件下对贯流风扇运行于三档不同转速(800rpm，1000rpm，1200rpm)时的内流情况进行了详细的分析及总结。这为进行气动噪声模拟及噪声模型的提出奠定了基础。结合CFD计算结果，对贯流风扇气动噪声产生机理进行了分析。采用Lighthill声学类比方法，线性欧拉方程中声源项分析，Lilly方程中声源项分析，Powell涡声方程中的声源项分析对其气动噪声源进行了定位及源特征总结。在频率域内采用“两步法”对噪声传播进行了数值模拟。模拟分别基于Ffowcs Williams-Hawkings方程积分求解方法及有限元模拟方法进行。比较了不同转速条件下的频谱特征，声压指向性，声压云图分布等，特别分析了基于有限元波动方程解法结合Lighthill声源项模拟了蜗壳的存在对噪声传播的影响。在时域内分别采用“两步法”及计算气动声学方法对气动噪声的产生及传播进行了数值模拟。基于CE／SE算法发展了计算流体力学及计算气动声学软件CFDCA。针对贯流风扇气动噪声传播特性，采用基于非结构网格的CE／SE算法对其气动流场进行数值模拟，并模拟了气动噪声的传播。湍流模拟采用大涡模型，搭接式滑移网格模型处理动静干涉。噪声传播采用完全欧拉方程作为控制方程，远场采用无反射边界条件。通过该软件对贯流风扇的模拟结果分析，总结了其时域模拟的特点。为了验证数值模拟的正确性，采用实验的手段研究了贯流风扇的气动噪声源特性。实验在本底噪声为19dB(A)的静音室中进行，采用高精度，高频响的声压传感器分别测量了室内机进口，蜗舌壁面，近叶轮出口，远场等位置的声压波动。对得到的原始压力脉动数据进行了快速傅里叶变换，基于FFT变换的联合时频分析，基于连续小波变换的联合时频分析。分别在时间域和频率域进行了不同测量点及不同运转条件下的对比分析。采用性能实验台测量了贯流风扇的外特性，并将流动及噪声数据与数值模拟结果进行了比较，检验并评判了数值模拟结果的准确性。基于贯流风扇内流场特点，本文提出了两级通流的模式来描述其内流特点；基于贯流风扇内流及气动噪声特点，参考离心风扇及轴流风扇气动噪声模型，根据已有的结论，本文提出了一种贯流风机气动噪声模型。模型采用本文实验结果进行参数确定，为了验证模型的适用性，本文对文献[165，166]中的实验风扇采用本文提出的模型进行了计算并与实验结果进行了比较，表明了本文模型的正确性。更多还原

【Abstract】 The aeroacoustic noise reduction of an indoor unit in an air-conditioner has become an important issue and caused more attention at the present time.The purpose of this dissertation is to research the aerodynamic characteristics and aeroacoustics of an indoor unit in an air-conditioner, especially the cross-flow fans. For this purpose, both CFD simulation and experimental investigation are performed on the prototype fan under three different rotational speeds. The flow characteristics are summerized and the analysis of aerodynamic noise includes location of the source and mechanism of source generated and the characteristics of noise propagation. Finally a model for cross-flow fan aerodynamic noise prediction is put forward and verified eventually.The CFD technology is empoyed to simulate the internal aerodynamic flow in a cross-flow fan model. Both two-dimensional and three-dimensional calculation model are used under steady and unsteady condition at three different rotational speeds (800rpm, 1000rpm, 1200rpm). A detailed analysis and summary to the internal flow field are carried out.Such work lays the foundation of aerodynamic noise simulation and noise model.Combined with results of CFD simulation, noise mechanism of the cross-flow fan is analyzed. Using Lighthill’s acoustic analogy method and the sound source item analysis in the linear Euler equations, Lilly equation and Powell vortex sound equations, the location of aerodynamic noise source and source characteristics are summerized.The simulation based on the Ffowcs Williams-Hawkings integral equation method and finite element simulate seperately, is carried out in the frequency domain by two-step method. The characteristics of the spectrum, directivity of sound pressure and contours of sound pressure are simulated and analysed at different rotational speed particularly; the sound propagation with the influence of volute is analysised using wave equation finite element method combined with Lighthill’s acoustic source terms.In the time domain, generation and propagation of aerodynamic noise are simulated using the two-step method and CAA respectively .Based on the CE/SE method, a computational fluid dynamics and computational aeroacoustics software CFDCA is developed. In response to the characteristics in the cross-flow fan, both the flow and noise propagation are simulated based on the unstructured mesh CE/SE scheme. Using the Navier-Stokes equations as the governing equations, the large eddy simulation (LES) model and sliding mesh model are used in the simulation. By solving Euler equations and no-reflection boundary condition in the far field, the results of aeroacoustics field is obtained. Through analysis, the time-domain noise characteristics of the cross-flow fans are summerized.Experiment is carried out to study the characteristic of aeroacoustics source and propagation of noise caused by cross-flow fan. Pressure fluctuations near the inlet, stabilizer, outlet of rotor and sound-far field are measured with high precision microphones in an anechoic chamber with the blackground noise of 19dB (A). The FFT, time-frequency transform based on FFT and wavelet are performed in order to analize the results at time domain and frequency domain. The aerodynamic characteristic of the cross-flow fans is measured on the own-designed automatic testing instrument according to GB 1236-2000 standards.The calculated charactertics of flux-rotational speed and noise are compared with the results of experiments. Some agreementes and variances are detected and discussed.Based on the characteristics of the flow field in cross flow fan, this paper presents a "two stages through-flow model" to describe the characteristics of its influx. Given on the characteristics of internal flow and aerodynamic noise of the cross flow fans and consulting to centrifugal fans and axial fan aerodynamic noise model, an aeroacoustics model of cross-flow fan is presented. On the basis of the conclusions of this paper, the parameteres of the model are determined according to experimental data of this paper. In order to verify the applicability of the model, a corss flow fan on the reference [165,166] is computed using this model, the comparision between the experimental results and the simulated results show that the model is correct.更多还原