小型高速离心风机噪音主要影响因素研究

通过实验和数值模拟方法,本文详细研究了影响小型高速离心风机噪音的主要因素。研究结果显示采用低转速、倾斜蜗舌、适当增加蜗壳出口张开度和增加蜗壳宽度能有效地降低噪音,其中以采用倾斜蜗舌降噪效果最为显著,且对风机气动性能影响不大。本文研究结果可为设计高速小型低噪离心风机提供参考。     

变工况下前弯离心风机宽带噪声的数值模拟及分析

为了解前弯离心风机不同工况下宽带噪声的变化规律及特性,本文以一款前弯高压离心风机为研究对象,针对带宽频特征的涡流噪声,运用基于Lighthill理论的FW-H方程和Proudman方程对前弯离心风机近场、远场噪声进行积分计算,通过三维非定常与定常数值模拟研究了其在设计流量,大流量与小流量三个运行工况下的噪声频谱特性,以及风机叶轮、蜗壳的宽带噪声分布特性,并将模拟结果与试验进行了对比验证。结果表明,该风机噪声宽频特性随流量增大变得明显。叶轮处宽带噪声声功率最高出现在离蜗舌最近的两个叶片上,蜗壳处宽带噪声最大声功率级主要出现在蜗舌处。     

贯流风机涡结构与噪声特性的数值研究

本文采用大涡模拟对空调室内机中贯流风机的内流进行了数值计算,结果显示了以偏心涡为代表的复杂非定常流动细节.计算结果表明,贯流风机气流两次进出叶轮,叶片尾缘、蜗舌处出现明显的脱落涡结构.叶轮周围监测点上出现了三个特征频率,分别对应叶片通过频率、叶片脱落涡频率以及蜗舌后缘的脱落涡频率,不同的特征点上表现出不同的频谱特性.另外,通过LEE方程中的声源项分布得到了贯流风机的主要噪声源区域,继而对蜗舌和叶轮等主要音源表面的远场辐射噪声频谱进行了分析,为后续的实验研究提供参考.     

改变蜗壳结构对离心风机性能及噪音的影响

利用Ansys Fluent软件进行数值模拟,通过分别改变蜗壳宽度和蜗舌倾角的方法,详细研究了改变蜗壳结构对离心风机气动性能及声功率级的影响。研究结果显示,在离心风机设计推荐范围内存在最佳蜗壳宽度,使得离心风机的声功率级最低;增加蜗壳宽度,离心风机的全压、效率略有下降,静压升高;固定离心风机蜗壳后盖板蜗舌半径R_1,增大蜗壳前盖板蜗舌半径R_2,能有效地降低离心风机的声功率级;在降噪效果上,改变蜗舌间隙优于改变蜗舌倾角.     

基于分组模型及仿生蜗舌的多翼离心风机设计

为提高多翼离心风机的流动效率,提出一种适合于该类型风机特点的分组设计模型,并借助于流场计算与试验设计相结合的分析方法,依次对多翼离心风机的叶轮、蜗壳和蜗舌进行分组设计。结果表明:具有更多设计自由度的双圆弧叶片气动性能明显优于单圆弧叶片;在保证蜗壳结构尺寸不变的前提下,采用等边基方法设计的蜗壳性能略优于三段圆弧设计出的蜗壳;基于长耳翼型前缘的仿生蜗舌能够有效减弱分离流动现象;利用本文方法改进后的多翼离心风机设计效率提高了4.33%,变工况性能明显改善。研究工作对深刻认识多翼离心风机内部复杂流动机理及发展优化设计方法具有学术意义和工程应用价值。     

贯流叶轮的旋转模态分析

应用旋转模态理论和CFD方法研究贯流叶轮的离散噪声特性,并分析贯流风机远场噪声主要呈现宽频的原因.设计了三种不同的蜗壳匹配方案,以控制贯流风机内主要的涡结构。通过采用CFD方法计算不同方案中贯流风机内部涡流动结构主要位置,确定出贯流叶轮上下游发生干涉的叶片数。根据模态分析理论,计算了不同蜗壳及蜗舌匹配方案中贯流叶轮的截止率。计算结果表明,由于叶轮内主流速度较低,使得贯流风机的离散噪声不明显。     

多翼风机新型斜蜗壳和常规直蜗壳的对比研究

本文采用Navier-Stokes方程和K-ε两方程模型对多翼风机分别采用新型斜蜗壳和常规直蜗壳的内流特性进行了三维数值模拟和实验研究。新型斜蜗壳的蜗舌间隙沿轴向从底盘到进风口由6％变化到4％,同时间隙位置沿圆周方向偏移15°。计算结果表明采用新型斜蜗壳可以改善多翼风机蜗舌间隙内的压力和速度分布,消除近底盘区域的出口旋涡。实验结果表明,采用新型斜蜗壳可以提高多翼风机的压力,降低叶片通过频率噪音并能改善音质。     

使用多孔蜗舌的贯流风机

将贯流风机的蜗舌替代为多孔板与容腔组合的结构,定性地研究其控制气动噪声的可行性。通过对气动特性和辐射声信号的实验测量,结合内部流场的非稳态雷诺平均数值模拟,分析了这种蜗舌改造对贯流风机的整体特性和内部流动特征的影响,结果表明多孔蜗舌对贯流风机的压力-流量曲线作用并不明显,但对风机的噪声有着重要的影响,改变蜗舌迎风面的穿孔率可以有效地控制贯流风机的噪声。     

多翼离心风机的三维数值分析

本文对一前弯多翼离心风机的内流场进行了三维数值分析。结果显示蜗壳内部的最大压力沿着轴线方向分布在不同的圆周位置,叶轮内部蜗舌上游区域存在着进口旋涡,蜗舌附近存在着明显的从叶片出口到进口的逆向回流,蜗舌间隙中存在着间隙涡,本文同时给出了一些典型位置上的速度和静压沿轴向的分布曲线,为验证本计算方法的可靠性,计算的流量和压力特性曲线和实验结果进行了比较,吻合良好。     

风机矩形蜗壳内部流动特性及其二次流的研究

—、前言 蜗壳作为离心风机的静止元件,其内部流动状况的好坏对风机性能有着很大的影响。相对运动部件叶轮而言,对蜗壳的研究较少,近年来的一些研究表明,蜗壳内的实际流动非常复杂,用流动解析方法求取蜗壳内的流动损失也并非易事。已有关于蜗壳舌部区域的实验研究大多也是定性的。本文利用单倾斜热线测试系统,在对后向离心风机矩形蜗壳内部流场进行测量的基础上,详细测量了蜗壳内的二次流动及舌部区域的流动状况,旨在为蜗壳的合理设计或数值研究提供基础性资料。     

Experimental study on the noise reduction of an industrial forward-curved blades centrifugal fan

Many previous researches have concentrated on the noise of backward-curved (BC) blades and forward-curved (FC) multi-blade centrifugal fans. In this paper, an experimental study has been carried out to study the noise reduction of an industrial FC blades centrifugal fan. First of all, the performance and noise characteristics of the FC centrifugal fan were tested to compare the similarities and differences from those of BC blades and FC multi-blade centrifugal fans. And then, some different volute geometric configurations were carried out in order to study the effects of inclined volute tongue, impeller blade-tongue clearance, hub-volute clearance and their coupling effect to the performance and noise of the FC blades centrifugal fan. The aim of many different experimental tests is to validate whether the effects of different modifications to fan performance and noise are additive and to find a good impeller-volute matching to reduce the centrifugal fan noise without reducing performance. The experimental results show that a good coupled modification not only could reduce the fan noise but also could advance the fan performance and extend the operating range.     

Numerical and experimental investigations of the unsteady aerodynamics and aero-acoustics characteristics of a backward curved blade centrifugal fan

A numerical study of the aerodynamic and aeroacoustic behaviors of a backward curved blade centrifugal fan was conducted under two important flow conditions: BEP and 1.3 × BEP. Three-dimensional numerical simulations of the complete unsteady flow field for the whole impeller-volute configuration were used to determine the aeroacoustic sources. To locate the unsteady flow and perturbations, the near field wall pressure fluctuations at different strategic points on the volute were computed using the URANS approach. Thus the intensities and positions of the aeroacoustic sources were identified by analyzing frequency spectra. The aeroacoustic sources caused by fluctuations in the interactions of the flows leaving the impeller and volute were close to the volute tongue, and the most effective noise sources related to the flow rate were near the impeller shrouds. In addition, the unsteady flow variables provided by CFD calculations were used as inputs in the Ffowcs Williams-Hawkings equation to estimate the noise tones of the fan. The aeroacoustic calculation results showed that the volute noise was much larger than the blade noise, and the noise mainly propagated from the outlet duct of the fan. Moreover, to account for the noise propagation, three calculation methods were used by applying different solid boundaries. Compared with the other methods, the FEM method, which accounted for the complex solid boundaries, produced good agreement and showed that the complex solid boundaries cannot be neglected in aeroacoustic predictions. The calculation results showed good agreement with the experimental results.     

A numerical optimization on the vibroacoustics of a centrifugal fan volute

A numerical optimization is presented to reduce the vibration and noise of a centrifugal fan volute. Minimal vibration was considered as the aim of the optimization, and the calculation of sound field induced by the vibration of the volute was only based on the final results of the optimization. After the three-dimensional unsteady flow simulation of a centrifugal fan, the parametric finite element model of the volute was created using the pressure fluctuations at blade passing frequency on the volute as external excitation forces. To validate the finite element model of the volute, natural frequencies and amplitudes of the normal velocities of the volute at blade passing frequency were measured. A good agreement was found between the numerical and the experimental results. Then, random method and first-order optimization method were applied in the optimization process. The numerical optimization of the volute was carried out using the local thickness of the volute as design variables and the quadratic sum of the nodal velocities as an objective function. Numerical optimization results show that the volute vibration is reduced by the optimization method. Finally, vibroacoustics of the volute before and after the optimization were calculated by direct boundary element method. The results show that the radiated power of the vibroacoustics of the volute is reduced significantly as well as the vibration of the volute after the optimization.This numerical optimization process provides a useful reference for vibroacoustic reduction of centrifugal compressors and centrifugal fans whose fluids should be kept strictly in a system without leakage.     

基于两级通流模式的贯流风扇气动噪声模型

贯流风扇独特的流动形态导致主流并非发生于部分流道,根据其内流特点,本文提出了两级通流模式。在离心风扇及轴流风扇气动噪声模型基础之上,同时考虑风扇的具体几何尺寸,运行情况,及蜗壳的存在对噪声传播的影响,提出了贯流风扇叶轮气动噪声的预估模型。试验结果验证了该模型的可靠性,在低转速1100r/min以下时可以较好地预测贯流风扇的气动噪声总声压级,在较高转速时,存在一定的误差。     

A simple acoustic model to characterize the internal low frequency sound field in centrifugal pumps

Conventional centrifugal pumps with volute casing generate fluid-dynamic noise particularly at the so-called blade-passing frequency, which is attributed to the interaction of the flow exiting the pump impeller with the volute tongue. Following previous work by the authors to characterize the effect of that blade–tongue interaction on the tonal sound produced, this paper presents a simple acoustic model for centrifugal pumps that considers ideal sound sources of arbitrary position and properties. The model is to be implemented in a software code that applies it systematically to a pump previously tested at laboratory, until identifying the set of ideal sources that best reproduce the pressure fluctuation measurements. In this model, the ideal sources are assumed to radiate plane sound waves along the impeller channels, volute, and outlet diffuser. The volute was considered to be composed by a succession of slices, each of them equivalent to a linear 3-port acoustic system with individual sound transmission and reflection coefficients. A series of tests was conducted to check the validity of the acoustic model, by applying an external acoustic load onto the pump outlet duct and measuring the noise reflected. The resulting reflection coefficient was in good agreement with the predictions of the acoustic model. Finally, the model was used to investigate the pump internal sound field at the blade-passing frequency when operating at 70% of nominal flow rate. It was concluded that the sound field can be characterized reasonably by a dipole-like source located at the tongue region.     

Reduction of motor fan noise using CFD and CAA simulations

Motor fans used for cooling electric motors have long been recognized as one of the major noise sources. Current paper focuses on design of motor fan for electric motors that are used in submarines for pumping sea water. Noise reduction at source is very important and the critical task, for under water applications. An attempt has been made for reduction of motor fan noise by modification of noise sources. For this purpose computational fluid dynamics and computational aeroacoustics code FLUENT package is used to identify the noise sources and to know the overall sound pressure level of motor fan. From these results it is observed that aerodynamic noise is the dominate fan noise source. Aerodynamic noise of motor fan can be reduced by modifying fan geometry. The aerodynamic noise level of motor fan has been reduced by replacing the straight blades with various digits of NACA (National Advisory Committee for Aeronautics) 65 series airfoil sections. From the numerical results it is observed that the minimum sound pressure level for NACA 65-010 is 65.4 dB(A). These numerical results are compared with measurements in a semi-anechoic chamber. It is found that there is good agreement between numerical and experimental results.     

A numerical study on the flow and sound fields of centrifugal impeller located near a wedge

Centrifugal fans are widely used and the noise generated by these machines causes one of the serious problems. In general, the centrifugal fan noise is often dominated by tones at blade passage frequency and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cut-off in the casing. However, only a few researches have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and considering the scattering effect of the casing. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of the centrifugal impeller. A discrete vortex method is used to model the centrifugal impeller and a wedge and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. In order to consider the scattering and diffraction effects of the casing, Kirchhoff-Helmholtz boundary element method (BEM) is developed. The source of Kirchhoff-Helmholtz BEM is newly developed, so the sound field of the centrifugal fan can be obtained. A centrifugal impeller and wedge are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal sound. The radiated acoustic field shows the diffraction and scattering effect of the wedge.     

Relationship between volute pressure fluctuation pattern and tonal noise generation in a squirrel-cage fan

In this work, the pressure fluctuation pattern in the volute of a squirrel-cage fan is analyzed. Also studied is how this pattern is modified when a slight geometry change is introduced in the volute tongue. The study has been carried out on a commercial machine, used in automotive air conditioning units. A three-dimensional and unsteady numerical simulation of the flow in the complete machine has been carried out using the commercial code FLUENT. In this way, the pressure fluctuations in some locations near the volute wall have been obtained. The results of this numerical simulation have been compared to the sound pressure level spectra radiated by the fan, measured in a ducted test installation at the laboratory. The tendencies of the sound pressure levels measured at the blade passing frequency show a good correlation with the amplitudes of pressure fluctuations obtained numerically near the volute wall.     

Reduction of the aerodynamic tonal noise of a forward-curved centrifugal fan by modification of the volute tongue geometry

In this work, an experimental study about the influence of some geometric features on the aeroacoustic behaviour of a squirrel-cage fan, used in automotive air conditioning units, has been carried out. The study focused on the effect of both the shape and the position of the volute tongue on the noise generated by the fan. Different geometric configurations were tested in order to compare the results. First of all, the performance curves were measured in a standardized test facility. Then, the acoustic behaviour of the fan was characterized by means of acoustic pressure measurements near the fan inlet. The comparison of the test results indicated a great dependence of both the shape and the position of the volute tongue and the noise generation. In particular, some geometric configurations of the volute tongue were able to reduce the fan noise generation without reducing the fan operating range.     

不同叶轮形式下离心泵噪声特性对比研究

针对具有无短叶片和有短叶片两种叶轮形式的离心泵,对设计状态下离心泵内部流场进行了全三维、非定常数值模拟,对比分析了其非定常流场特性和噪声辐射特性。流场分析表明:叶轮叶片和蜗舌的相互作用造成了叶片表面强烈的压力脉动,对长短叶片的叶轮形式,在局部增加长叶片表面压力脉动的同时,短叶片表面的压力脉动保持较低水平;同时能够有效降低泵体进口压力脉动,但出口压力脉动有所增强。以叶轮叶片表面作为声源辐射面,对比分析了两种叶轮的偶极子噪声辐射特性,结果表明:长短叶片结构通过改变声能在频域上的分布,从而能有效降低总声压级。