Discharge flow measurements of a centrifugal turbomachinery

The objective of this research is to obtain a better insight into the flowfield in a centrifugal turbomachinery. To investigate this turbomachinery flowfield, measurements have been made with hot-wire sensors at the exit of a centrifugal impeller. The measured data at the discharge show a jet-wake type of flow pattern which results in a strong vorticity field. The flow with high velocity found on the pressure side tends to move to the low pressure region present at the suction side of an impeller blade as a form of roll-up around the blade trailing edge. This flow motion is believed to cause an unsteady flow separation at the suction side of the blade and consequently to disturb the flow in the adjacent passage.     

Wheel-rail noise generation

Wheel-rail noise is probably the least tractable problem of railway acoustics. Wheel and rail roughness are both known to be responsible to a substantial degree for the observed effects. When wheels and rails have been made as smooth as possible, there may well be more subtle effects within the contact patch responsible for the still substantial level of noise generated.     

Aerodynamic noise numerical simulation and noise reduction study on automobile alternator

Aerodynamic noise is the predominant component of automobile alternator noise at high speed, which directly affects the noise characteristic and noise control of alternator. Based on Lighthill acoustic theory, the aerodynamic noise of an automobile alternator was simulated with three-dimensional, Large eddy simulation (LES) and Ffowcs Williams-Hawkings (FW-H) acoustic model, and the aerodynamic noise reduction research was conducted through optimizing the front fan blade spacing angle of alternator with vector composition method while considering high fan flow and optimal noise frequency components for reduced harmonic rotating noise of alternator. The results show that the sound pressure amplitude of the primary aerodynamic noise components simulated with LES are in good agreement with experimental ones, and the dominant harmonic frequency components of aerodynamic noise are in the 4th, 6th, 8th, 10th, 12th and 18th orders and the A-weighted sound pressure level of one-third octave mainly concentrates in 1120-7000 Hz. The average total noise level of alternator noise is decreased by 2.58 dB, and the mass flow of monitoring surface of fan blade is increased by 1.36 g/s with 5.80 dB decrease in the sound level of the 12th and 18th harmonic orders on average with optimized front fan blade spacing angles, which verifies the effectiveness of the noise reduction method proposed in this paper.     

Rubber tyre noise generation

The noise generated by the action of lorry tyres rolling on road surfaces has been studied at the Transport and Road Research Laboratory by examining the various parameters affecting noise and the sources and the mechanisms of noise generation. It is concluded that lorry tyre noise is caused mainly by vibration of the tyre surface which is controlled by the slip of the tread elements in the contact zone.     

雷达天线系统离心风机气动噪声研究

基于FW-H方程,对离心风机进行气动声学理论分析,结合噪声测试方法,对某雷达天线系统进行噪声试验研究分析.测试数据表明,噪声和振动加速度频谱图分布较为接近,噪声振动能量峰值频率均为离心风机叶片基频的倍频,即雷达天线系统噪声主要来源于离心风机的气动噪声.通过改变均热板上翅片与风机叶片边缘的间距和调节风机转速,对单个离心风...     

离心式通风机降噪设计研究

探讨了离心式通风机噪声产生的机理,并详细分析了离心式通风机在设计中常用的降噪设计的方法、思路以及每种设计方法的适用范围.可为解决离心风机降噪问题提供科学的指导.     

Numerical and experimental study on flow-induced noise at blade-passing frequency in centrifugal pumps

With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics （CFD） with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem＇s assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency （BPF） noise, and the sound pressure level （SPL） reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point （BEP）; it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.     

Rotor-bearing dynamics of modern turbomachinery

High speed, high power-density machinery is subject to a number of vibration-producing forces. The fuel pump for the space shuttle is an example of such an advanced technology turbomachine. The low viscosity of the working fluid (liquid hydrogen) dictated novel solutions to the vibration problems which arose in the development of this pump     

Experimental and theoretical analysis of stresses, noise and flow in centrifugal fan impeller

Stress analysis of fan impeller by experimental and finite element method has shown that, the stress pattern in impeller components is highly complex. The stresses in the impeller components can be reduced, by using the stiffening rings on the blades. In this paper, experimental and finite element approaches have been discussed to study the stresses in centrifugal fan impeller. The flow of centrifugal fan has been also determined by using the set-up as per AMCA and NAFM guidelines. The effect of the stiffening rings on the stresses, noise and fluid flow has been also investigated and discussed.     

Experimental investigation on the flow-induced noise under variable conditions for centrifugal pumps

With extensively using of centrifugal pumps,noise generation in these pumps is increasingly receiving research attention in recent years.The noise sources in centrifugal pumps are mainly composed of mechanical noise and flow-induced noise.And the study of flow-induced noise has become a hotspot and important domain in the field.The flow-induced noise closely related to the inner pressure pulses and vibration of volute in pumps,therefore,it is necessary to research the interaction and mechanism among them.To investigate the relationships,a test system is designed which includes a test loop and a measurement system.The hydrophones and pressure sensors are installed on the outlet of the pump and vibration acceleration sensors are disposed on the pump body.Via these instruments,the signals of noise,pressure pulses and vibration are collected and analyzed.The results show that the level of flow-induced noise becomes smaller as the flow increment during low flow rate operations,and it is steadily close to the design point,then it increases with the growing of flow rate in high flow rate conditions.Furthermore,there are some similar peak points in the power spectrum charts of noise,pressure pulses and vibration.The broadband noise at low flow rate is mostly focused on the region of 0-40 times shaft frequency,which is mostly made by rotating stall and vortex;while the noise at high flow rate conditions is focused on the region of 60-100 times shaft frequency,which may be mostly made by cavitations.The proposed research is of practical and academic significance to the study of noise reduction for centrifugal pumps.     

机械噪声的产生及其控制方法

对设备产生机械噪声的原因以及噪声的传播与辐射形式作了简要的说明和分析。例举了机械设备中常见的几种噪声源,并对其传播形式作了扼要叙述,同时针对噪声源的控制原则与步骤进行了较详细的介绍。     

Streaming current noise generation in electromagnetic flowmeters measuring conducting fluids

This paper provides a model of streaming current noise generated by the interaction of turbulence with the charge distribution which occurs in the liquid, close to the surface of the insulating liner of an electromagnetic flowmeter, as a consequence of charge species being absorbed by the lining material itself. Such noise is present whether the electromagnetic field of the flowmeter is excited or not. It is shown in this paper that this noise can be detected in potable water at a conductivity of order 5 mS/m, although at such levels it is often masked by the first stage amplifier noise, but that it becomes more significant when measurements are made in de-ionised water where the conductivity may be as low as 5 μS/m. The predicted spectral characteristic of the noise and the dependencies of the noise on the conductivity of the fluid, the pipe size and flow velocity provided by the model are all shown to be in good agreement with experimental data. The model is valid for clean aqueous fluids, where there is no noise generated by particle impact or significant electrochemical reaction between the fluid and the sensing electrodes. It can be used to predict the signal to noise ratios in electromagnetic flowmeters using different excitation waveforms and frequencies or different electrode structures.     

Aeroacoustic characteristics and noise reduction of a centrifugal fan for a vacuum cleaner

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 3000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB(A) and the 2^nd BPF is reduced about 20 dB(A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.     

A study of the Newkirk effect in turbomachinery

An analytical and experimental study was undertaken on the Newkirk Effect as applied to turbomachinery which is the vibration change produced when a high speed rotor rubs on stationary components due to the uneven distribution of the produced heat around the rotor. The analysis predicted three possible modes of the Newkirk Effect: spiralling, oscillatory and constant modes. The first is associated with very high vibration amplitudes and the latter two with low amplitudes, even vibration suppression and may be considered as stable modes.To support and verify analysis, an experimental rig was constructed and a limited number of tests conducted. The test results verified both quantitatively and qualitatively the analytical findings for the modes of the Newkirk Effect. The parameter study indicated that stability of the system does not depend explicitly on whether the running speed is below or above the critical speed, but rather on the phase angle between static and dynamic bow. This is a dynamic property of the system unrelated to the friction characteristics. It depends, to a lesser extent, upon the amount of generated heat and the other characteristics of the system. The clearance was found to be a very important factor. The existence of a threshold value of the clearance was demonstrated.     

Friction-induced vibration and noise generation of instrument panel material pairs

This study investigated the effect of various parameters of the friction–velocity relationship on the friction-induced vibration of simulated instrument panel components. The effect of subsystem stiffness and damping on the system response was also studied. A simple discretized model was utilized with subsystem properties that were intended to realistically model values of low, medium, and high stiffness components. Specifically, the metric of mean squared velocity was used as an indicator of the noise generated during the stick–slip process. It was found that the difference between the static and the asymptotic kinetic value of friction was the most important friction parameter in determining the resulting behavior. As stiffness and damping are increased, the mean squared velocity decreases. Additionally, results from single excursion tests on a variety of instrument panel material pairs showed good correlation between mean squared velocity and the difference in static and kinetic friction.     

Numerical simulation and analysis of the aerodynamic noise of a nautilus-inspired bionic multiblade centrifugal fan

Journal of Mechanical Science and Technology - This paper proposes a nautilus-inspired bionic volute for a multiblade centrifugal fan. Analysis of the noises generated by the fan is presented. This...     

Fast-response total pressure probe for turbomachinery application

To evaluate the accurate performance and characteristics of turbomachinery, it is important to measure the unsteady flow phenomena downstream of the rotating blades. This paper presents the development of a fast-response total pressure probe for the measurement of the total pressure field at the exit of blades. The result of measurement in a one-stage axial turbine is also presented. The fast-response total pressure probe is fabricated by installing a fast-response pressure sensor in the cylindrical head of the probe. In terms of simplicity of the measurement system and data reduction method, this method is more competitive over established methods that use more than four sensors. The probe is applied to the one-stage axial turbine in order to measure the instantaneous total pressure downstream of rotor blades. The measured instantaneous signal is decomposed to obtain the blade-to-blade pressure distribution. The pressure distribution due to blade passing is clearly captured. Due to the loss generation in the casing region, the total pressure and its amplitude of fluctuation by the blade passing are lower in the shroud and hub region than in mid-span. The total pressure distribution at the exit of the rotor blade is found to be slightly different from blade to blade due to the geometric difference and the different relative positions of the rotor blades and stator vanes. The developed probe successfully measures the accurate total pressure distribution at the rotor exit, and allows the evaluation of the loss distribution and the accurate performance of turbomachinery.     

扭曲叶轮对多翼离心风机内流及噪声特性的影响分析

针对扭曲叶轮多翼工频离心风机内流及声学特性的探究问题,研究了不同叶轮扭曲度对多翼离心风机的气动性能的影响。首先,建立了离心风机CFD计算模型,进行了离心风机流量-全压效率性能曲线验证试验;然后,利用Fluent计算得到了不同扭曲参数的风机性能数据,速度流线图和A、B处回流涡涡量;最后,基于FW-H方程分析了不同叶轮扭曲度声压频谱图,并分析了不同叶轮扭曲度离心风机的1/3倍频程频谱图。研究结果表明：扭曲叶轮风机较直叶轮风机全压效率下降了7.75%～8.07%,且存在去偏心涡的现象;扭曲叶轮可减少涡流的形成,有效降低风机噪声,在基频1 300 Hz处,3°,6°和9°扭曲叶轮风机噪声分别降低了0.06 dB、1.15 dB和8.35 dB,可见扭曲叶轮可应用于多翼离心风机的降噪设计。     

叶轮机械气动特性的设计计算

本文的工作主要是借助于现代计算流体动力学（ＣＦＤ）技术的高速发展，讨论应用数值方法来模拟叶轮机械内部的实际流动，以期获取大量真实可靠的流动信息。据此，可以为现代叶轮机械的设计提供一种快速可靠的工具。本文提出了二阶精度隐式矢量单步差分格式并用来求解叶栅的跨音流场，数值试验表明：该方法具有精度高、稳定性好、计算量少、收敛快等优点。