Numerical simulation for fan broadband noise prediction

In order to elucidate the broadband noise of fan,the numerical simulation of fan operating at two different rotational speeds is carried out using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations.The computed results are compared to experiment to estimate its accuracy and are found to show good agreement with experiment.A method is proposed to evaluate the turbulent kinetic energy in the framework of the Spalart-Allmaras one equation turbulence model.From the calculation results,the turbulent kinetic energy is visualized as the turbulence of the flow which leads to generate the broadband noise,and its noise sources are identified.     

Influence of diffuser on aerodynamic noise of a forward curved fan

In order to clarify the influence of a diffuser on the characteristics of a forward curved fan,the influence of the bare ratio and the outlet angle on the characteristics of the fan were measured through an experiment performed with an actual fan as well as through a numerical simulation,respectively.The mechanism of the discrete frequency noise generated by the separated flow of the diffuser was analyzed.The optimized bare ratio was approximately 17%.The flow separated inside of the diffuser generated discrete frequency noise owing to the interaction between the reversed flow from the diffuser and the impeller rotating at the blade passing frequency.The diffuser outlet angle influenced the pressure ratio more than that by the bare ratio.Furthermore,it was confirmed that restraining the separation in the diffuser effectively decreases the fan noise.     

Prediction of aerodynamic noise in a ring fan based on wake characteristics

A ring fan is a propeller fan that applies an axial-flow impeller with a ring-shaped shroud on the blade tip side. In this study, the entire flow field of the ring fan is simulated using computational fluid dynamics (CFD); the accuracy of the CFD is verified through a comparison with the aerodynamic characteristics of a propeller fan of current model. Moreover, the aerodynamic noise generated by the fan is predicted on the basis of the wake characteristics. The aerodynamic characteristic of the ring fan based on CFD can represent qualitatively the variation in the measured value. The main flow domain of the ring fan is formed at the tip side of the blade because blade tip vortex is not formed at that location. Therefore, the relative velocity of the ring fan is increased by the circumferential velocity. The sound pressure levels of the ring fan within the frequency band of less than 200 Hz are larger than that of the propeller fan. In the analysis of the wake characteristics, it revealed that Karman vortex shedding occurred in the main flow domain in the frequency domain lower than 200 Hz; the aerodynamic noise of the ring fan in the vortex shedding frequency enlarges due to increase in the relative velocity and the velocity fluctuation.     

发动机排气噪声自适应有源消声系统的设计与试验研究

针对发动机排气噪声的特点,选取与噪声基频相关的振动和点火信号作为控制器参考信号,以Filtered—X LMS算法作为调节自适应滤波器各权系数的基本依据,并采用外加抖动信号的次级通道在线自适应建模方式,建造并实现了相应的试验系统。在所设计的有源消声试验台架上,对SUZUKI AX-100摩托车发动机排气噪声进行了有源消声试验,在400Hz以下取得了30dB以上的降噪效果。     

基于模拟电子技术的有源消声实验研究

为了提高发动机的动力性、经济性指标,同时改善其排放性能,根据发动机排气噪声的频谱特征,结合有源消声技术的特点,提出并设计了一种基于模拟电子技术的有源消声系统,并对该系统的消声机理进行了理论研究。实验系统的结果表明,取得了明显的降噪效果。     

金隆转炉风机防喘振控制系统

转炉风机防喘振控制是全厂自控系统中较复杂类型的一项，系统投运获得成功，为转炉安全、稳定、高效的生产起到了重要作用。     

提高发动机排气有源消声系统中次级通道辨识精度的方法与实验研究

在发动机排气自适应有源消声系统中的次级通道的辨识环节引入自适应线性增强器（ALE）,通过理论分析和计算机仿真考察ALE对次级通道辨识精度及系统性能的影响,改进了次级通道辨识算法,并编制了相应的控制系统程序.在自行研制的实验台上进行了自适应离线、抖动信号自适应在线、以及使用ALE的抖动信号自适应在线3种次级通道辨识方法的对比实验,结果表明：应用改进后的辨识算法,能够减小次级通道传递函数估计的失真,提高次级通道的辨识精度,加快系统的收敛速度,并降低系统对外加抖动信号的功率要求.通过对铃木AX-100摩托车发动机排气噪声的有源消声实验表明,提出的发动机排气有源消声系统能够有效消除噪声源中的窄带成分,提高系统整体降噪效果.     

Suitability analysis of advanced diesel combustion concepts for emissions and noise control

During the last years, the preservation of the atmospheric environment has played an increasingly important role in society. The Diesel engine can be considered an environmentally friendly engine because of its low consumption and the subsequent carbon dioxide (CO₂) emissions reduction. However, in the near future it will face strong restrictive emission standards, which demand that the current nitrogen oxides (NO_x) and soot emissions are halved. To comply with these restrictions new combustion concepts are emerging, such as PCCI (premixed charge compression ignition), in which the fuel burns in premixed conditions. Combustion noise is thus deteriorated and consequently end-users could be reluctant to drive vehicles powered with Diesel engines and their potential for environment preservation could be missed. In this paper, Diesel combustion is addressed through the analysis of performance, emissions and combustion noise in order to evaluate the suitability of PCCI engines for automotive applications. The results show that PCCI combustion offers great possibilities to fulfill future emission restrictions, but the engine noise is strongly deteriorated. The great sensitivity of users to this factor requires vehicle manufacturers to focus their efforts on the optimization of passive solutions for implementing the PCCI concept in passenger car and light-duty engines, even with the subsequent increase in the cost of vehicle. This aspect is less restrictive in heavy-duty engines, since the great benefits in emissions reduction compensate the deterioration of engine noise.     

Performances and acoustic noise of micro multi-blade fan

In this paper, the performances and the acoustic noise of the traditional type micro multi-blade fan were investi- gated experimentally and numerically, to optimize the specifications of the fan for the resident circumstances. The acoustic noise level decreases but the efficiency deteriorates slightly with the increase of the blade number of the impeller. Besides, the acoustic noise decreases with the increase of the distance between the impeller outlet and the volute tongue, in accompanying with the increase of the input and the deterioration of the fan efficiency.     

基于BP神经网络的温度控制系统

文中介绍了基于BP(Back Pmpagation)的神经网络气化炉温度控制系统。对BP神经网络控制算法作了详细的介绍，运用模糊逻辑控制概念赋予隐层含义，并决定其节点数，同时用高斯核函数作为节点激励函数，并做了仿真研究，叙述了系统的硬件与软件构成，试验表明所设计的系统操作方便、安全可靠，所选择的控制算法适应性强，控制效果良好。     

Designing and modelling of the asymptotic perturbed extremum seeking control scheme for tracking the global extreme

This paper presents the designing and modeling of the Asymptotic Perturbed Extremum Seeking Control (aPESC) scheme that is capable to locate and track the Global Extremes on the multimodal patterns. The multimodal patterns may appear on power generated by a photovoltaic (PV) array under Partial Shading Conditions (PSCs), but also on net power generated by a Fuel Cell (FC) system. The proposed aPESC scheme uses a scanning technique to determine the GMPP on different multimodal patterns based on two components of the searching signal: (1) the scanning signal locates the LMPP by sweeping the PV pattern based on a asymptotic dither modulated by the first harmonic of the PV power and controlled by the dither gain (k₂); (2) the tracking signal finds and tracks accurately the GMPP based on similar loop used in PESC schemes proposed in the literature that is controlled by the loop gain (k₁). These tuning parameters are designed based on the averaged model of this aPESC scheme. Also, the averaged scheme and local averaged loop of the aPESCH1 scheme are used to estimate the searching gradient and analyze the closed ESC loop stability. The design methodology is tested on generic multimodal patterns and then is validated considering a PV system and a FC system.     

Influence of tip end-plate on noise of small axial fan

In this work, tip end-plate is used to improve the noise performance of small axial fans. Both numerical simulations and experimental methods were adopted to study the fluid flow and noise level of axial fans. Four modified models and the prototype are simulated. Influences of tip end-plate on static characteristics, internal flow field and noise of small axial fans are analyzed. The results show that on basis of the prototype, the model with the tip end-plate of 2 mm width and changed length achieved best noise performance. The overall sound pressure level of the model with the tip end-plate of 2 mm width and changed length is 2.4 dB less than that of the prototype at the monitoring point in specified far field. It is found that the mechanism of noise reduction is due to the decrease of vorticity variation on the surface of blades caused by the tip end-plate. Compared with the prototype, the static pressure of the model with the tip end-plate of 2 mm width and changed length at design flow rate decreases by 2 Pa and the efficiency decreases by 0.8%. It is concluded that the method of adding tip end-plate to impeller blades has a positive influence on reducing noise, but it may diminish the static characteristics of small axial fan to some extent.     

Numerical analysis of aerodynamic noise radiated from cross flow fan

The flow field in a cross flow fan was simulated by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations. The calculated pressure fluctuations of the blades, the vortex wall, and the rear wall were then used as noise sources to calculate the sound field. The Ffowcs Williams-Hawkings (FW-H) equation was employed to predict the noise field caused by these sources. The predictions show that the rear wall and the vortex wall sources contribute significantly to the total noise and that both the predicted aerodynamic performance and noise agree well with the experimental results. __________ Translated from J Tsinghua Univ (Sci & Tech), 2007, 47(2): 236–239 [译自: 清华大学学报(自然科学版)]     

Numerical analysis of aerodynamic noise radiated from cross flow fan

The flow field in a cross flow fan was simulated by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations. The calculated pressure fluctuations of the blades, the vortex wall, and the rear wall were then used as noise sources to calculate the sound field. The Ffowcs Williams-Hawkings (FW-H) equation was employed to predict the noise field caused by these sources. The predictions show that the rear wall and the vortex wall sources contribute significantly to the total noise and that both the predicted aerodynamic performance and noise agree well with the experimental results.     

降低柴油机噪声技术研究

本文论述了柴油机的噪声控制措施,对柴油机噪声进行了分类,并分别从燃烧噪声、机械噪声、进排气噪声和风扇噪声等方面进行了分析并提出了具体的解决措施。     

降低柴油机噪声技术研究

本文论述了柴油机的噪声控制措施,对柴油机噪声进行了分类,并分别从燃烧噪声、机械噪声、进排气噪声和风扇噪声等方面进行了分析并提出了具体的解决措施。     

Active fault tolerance control system of fuel cell hybrid city bus

With ever growing concerns on energy crises and environmental issues, Proton Exchange Membrane Fuel Cell is favored in automotive applications because it is clean, efficient and low noise. A fuel cell hybrid powertrain is composed of a fuel cell system as the primary power source, a battery as the secondary power source and an electric motor. In order to improve the reliability, a distributed control system that can be preserved even under faulty cases is necessary. This paper presents an active fault tolerance control system (AFTCS) for a fuel cell/battery hybrid powertrain applied to a city bus. The AFTCS consists of a system for fault detection and diagnose and a reconfigurable controller. Algorithms to detect and isolated three kinds of important faults are introduced. The real-time applicable reconfigurable controller is exploited to recover the pre-fault system performance as much as possible. Experimental results show the effectiveness of the proposed system.     

Power variation control of a wind generator by using feed forward control

The pitch control of wind generators is usually made by a feed back control concept. However, under the conditions where a wind speed changes very frequently due to geographic reasons of the site and the target system has large rotor inertia, the feed back signal which is applied to the control system to compensate disturbance such as wind speed variations is delayed, and consequently the control strategy to keep the generated power at a constant value does not work well. If the wind speed shows too much variation, this will cause a violent variation of power and result in step out operation of the generator from the power system due to magnetic saturation. This paper proposes a control strategy to reduce the power variations by introducing feed forward control combining with the conventional feed back control.     

矿井节能风机控制系统的研制

针对矿井风量的非线性、时变及滞后的特点,介绍一种适用于PLC的模糊控制系统,通过PLC查表方式实现模糊控制的设计方法。给出了PLC程序设计的算法流程及输入量量化程序、模糊控制表查询程序等关键步骤的梯形图。     

Acoustics of weirs: Potential implications for micro-hydropower noise

There is great potential for the expansion of the small or micro scale hydropower network. Of the 43 thousand weirs in the UK there are only 500 consented hydro schemes. Planning applications for such schemes require a noise assessment. Noise evaluation of a proposed renewable scheme is often complicated by the turbine sites having distinct noise characteristics in the first instance, which are often caused by the weirs themselves. Three types of weir were studied: Broad Crest weirs were studied in detail; this is complimented by further studies in Flat V and Crump weirs. Flow data was collected for ten sites from the Environment Agency and the National Rivers Flow Archive to assess the collected Sound Pressure Level (SPL) and calculated Sound poWer Level (SWL) in relation to various river flows. Weir head height, width and meteorological data were also collected. It has been shown that the SPL data collection method used was the right choice, as the greatest amplitudes at the water impact interface at all weir types was recorded. SPL and SWL were found to be within a 36–82 dBz and 45–86 dBz range respectively for all weir types. These values can be used in computer simulations of sound propagation. The mean SPL and SWL difference between the weir types are 6.1 dBz and 6.3 dBz. Head height has the greatest effect on SPLs. Attenuation with distance was found to be similar to that of a free field line source in general.