立式双流道新风净化机CFD分析

对新风净化机的内部气流场和风道阻抗进行分析,可以为其滤芯及整机风道结构设计提供理论依据。依据新风净化机的功能要求,建立了整机内部流场及几何模型,以多空介质属性模拟定义了粗效滤网、活性炭滤芯、HEPA高效滤芯三种滤芯,通过流体分析软件模拟出了新风净化机的内部气流场,分析了进风口在不同风速下风道区域压力场和速度场的变化。分析结果表明:当进风口风速小于2m/s时,整机内部流场分布较均匀稳定,涡流现象较少,整机流道阻抗较小;尽可能增加进风口面积,可有效降低整机流道阻抗。     

一种基于AVR单片机的空气净化器控制系统

随着生活水平的提高,人们对自己日常生活和工作的室内空气环境质量的要求和期望也在不断提高.本文设计出一种新型的、利用紫外线杀菌消毒的空气净化器电路控制系统.该系统选择合适的ATmega128单片机,利用TGS800气体传感器与LHi878热释电红外传感器分别检测室内空气质量和移动人体红外信号,并将采集信号输出给单片机端口,单片机根据检测到的信号自动调整和控制空气净化器.该系统经过试运行和调试,效果明显,值得推广.     

Flow structure and flow-induced noise in an axisymmetric cavity with lids

Direct numerical simulations of incompressible turbulent flow through an axisymmetric cavity with or without lids were performed at Re_t,in = 186 to examine the hydrodynamic effects of the lids on the flow-induced noise. The strength of the recirculation in the downstream region was weakened by the installation of the lids. Comparison of the acoustic sources of the Lighthill equation indicated that the lid in the downstream region attenuated the flow-induced noise substantially. Frequency spectra and spatio-temporal correlations of pressure fluctuations revealed the most energetic mode and the convective nature of the flow over the cavity. It was evident from a detailed investigation of the instantaneous flow fields that the introduction of lids into the cavity significantly weakened the interaction between the separated shear layer and the trailing edge of the cavity. The present results clearly showed that the installation of lids is an effective means of reducing flow-induced noise.

     

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.     

Investigation study on the flow-induced noise by winglet and shroud shape of an axial flow fan at an outdoor unit of air conditioner

Journal of Mechanical Science and Technology - Axial flow fans of outdoor units are equipped with specially shaped winglets and shroud for reduction of the flow-induced noise. In this study, the...     

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.     

Investigation on the influence of number of blades on flow-induced noise optimization design of a centrifugal pump

Journal of Mechanical Science and Technology - Aiming at the quiet centrifugal pump design, the effect of number of blades on the flow-induced noise is explored. The results show that the sound...     

Characteristics of unsteady flow field and flow-induced noise for an axial cooling fan used in a rack mount server computer

The recent development of small and lightweight rack mount servers and computers has resulted in the decrease of the size of cooling fans. However, internal fans still need to achieve a high performance to release the heat generated from interior parts, and they should emit low noise. On the contrary, measurement data, such as flow properties and flow visualizations, cannot be obtained easily when cooling fans are small. Thus, a numerical analysis approach is necessary for the performance evaluation and noise reduction of small cooling fans. In this study, the noise of a small cooling fan used for computers or servers was measured and then compared with the aeroacoustic noise result based on a numerical analysis. Three-dimensional Navier-Stokes equations were solved to predict the unsteady flow field and surface pressure fluctuation according to the blades and casing surface used. The simplified Ffowcs Williams and Hawkings equation was used to predict aeroacoustic noise by assuming that a dipole is the major cause of fan noise. Results of the aeroacoustic noise analysis agreed well with that of the experiment, and a tonal noise whose frequency was lower than the first blade passing frequency could be identified in the noise spectrum. This phenomenon is caused by the shape of the bell mouth. A coherence analysis was performed to examine the correlation between the shape of the cooling fan and the noise.

     

空压机噪声信号的时频分析

为了提取空压机噪声信号中的周期成分,采用短时傅立叶变换在Matlab环境下分析了空压机噪声信号,提取了噪声信号中的主要周期分量.分析结果表明:利用短时傅立叶变换可以准确提取空压机噪声信号中的周期分量.时频分析方法是提取噪声信号中周期分量的有效方法.     

工业用油雾净化器的维护

分析了工业用油雾净化器的工作原理,提出了对其进行日常使用和维护的方法.     

风冷热泵机组噪声的治理

风冷热泵机组是中央空调的冷热源,但其噪声给周围环境带来严重污染,成为一个噪声源.如何治理噪声将是一个大问题,笔者通过工程实例,对如何有效、经济地治理风冷式热泵机组的噪声进行了探讨.     

Study on the reduction of flow-induced noise through the suppression of vortex shedding at rotating disk edge

We conducted a computational analysis to better understand the coherent flow structure that arises when the rotation of a disk drive generates flow-induced noise. We set the flow domain to be similar to the actual shape of the flow in Blu-ray disks and examined the phenomena of vortex generation and shedding at the disk edge, focusing on the source of the noise. Our results showed that disk edge vortex shedding was the primary cause of disk-drive-flow-induced noise; therefore, we investigated the technique of lowering the intensity of a disk edge vortex to reduce this noise. We attached concentric projections onto the cover of the disk to suppress the flow returning to the center of the disk through the gap between the disk and cover. Noise induced by disk rotation was reduced by 2.68 dB at the optimal setting: projections 0.002 m wide and 0.006 m width between the projections (and thus a ratio of 1: 3).     

活塞空压机站房的噪声控制探讨

分析了活塞式空压机站房噪声产生机理,并提出了相应的噪声控制措施和对策。     

Effect of rounding on flow-induced forces on a square cylinder

A numerical study has been carried out to elucidate the effects of rounding the sharp edges on flow-induced forces on a square cylinder immersed in a laminar cross flow. Rounding reduces both the upstream stagnation pressure and the downstream base pressure. Consequently, competition between these two pressure reductions yields the minimum drag on the cylinder when its edges are partially rounded. It was also found that the leading-edge rounding is mainly responsible for the topological change thus the drag reduction, while the trailing- edge rounding alone just enhances lift fluctuation. However, trailing-edge rounding plays a role of stabilizing the flow when all of the four edges are rounded.

     

空压机储气罐噪声测量与降噪的研究

从某厂的空气压缩机储气罐噪声的现场测试入手，摸索出一种测量储气罐噪声的方法。把测试数据放在频谱仪上进行分析，得出了管道振动和噪多是由管道内脉动气流所引起的结论，并对空气压缩机储气罐噪声的治理方法进行了探讨。     

Parametric noise squeezing and parametric resonance of microcantilevers in air and liquid environments

In this work, parametric noise squeezing and parametric resonance are realized through the use of an electronic feedback circuit to excite a microcantilever with a signal proportional to the product of the microcantilever's displacement and a harmonic signal. The cantilever's displacement is monitored using an optical lever technique. By adjusting the gain of an amplifier in the feedback circuit, regimes of parametric noise squeezing/amplification and the principal and secondary parametric resonances of fundamental and higher order eigenmodes can be easily accessed. The exceptionally symmetric amplitude response of the microcantilever in the narrow frequency bandwidth is traced to a nonlinear parametric excitation term that arises due to the cubic nonlinearity in the output of the position-sensitive photodiode. The feedback circuit, working in both the regimes of parametric resonance and noise squeezing, allows an enhancement of the microcantilever's effective quality-factor (Q-factor) by two orders of magnitude under ambient conditions, extending the mass sensing capabilities of a conventional microcantilever into the sub-picogram regime. Likewise, experiments designed to parametrically oscillate a microcantilever in water using electronic feedback also show an increase in the microcantilever's effective Q-factor by two orders of magnitude, opening the field to high-sensitivity mass sensing in liquid environments.     

Suppression of flow-induced vibration of a circular cylinder by means of a flexible sheet

In this study, the suppression of flow-induced vibration of an elastically supported circular cylinder by attachment of a flexible sheet was investigated experimentally. In particular, the dependence of flow-induced vibration characteristics of the circular cylinder upon the flow velocity was investigated in detail by axially attaching the flexible poly-ethylene sheet to the cylinder surface. The characteristics of the flow-induced vibration of the cylinder were investigated by changing the attachment angle ?? and the length l of the flexible sheet (rectangular type) as experimental parameters in various combinations. The angle ?? was set at five different angles, 90°, 45°, 0°, ?45° and ?90°. The angle??s base point was the back side stagnation point of the cylinder. The length l of the flexible sheet varied from 0.5 to 3.0 times of the cylinder??s diameter at the interval of 0.5 times. The width T of the flexible sheet along the span of the cylinder also varied in 7 cases from 1.0L to 0.4L (L is the length of the cylinder) in order to discover the minimum width of the sheet necessary to effectively suppress the flow-induced vibration of the cylinder. Furthermore, the flexible sheet of the minimum width was split into 2 to 5 pieces and attached to the cylinder, and changes in the flow-induced vibration characteristics were investigated. Also, vibration characteristics were investigated for a flexible sheet in the shape of an isosceles triangle. As a result, the optimal length l and minimum width T of the flexible rectangular sheet were found to be 2??2.5D and 0.7L, respectively, to suppress the flow-induced vibration of the cylinder. Most importantly, it was found that the sheet located at the back side stagnation point can suppress the flow-induced vibration generated by any directional flow to strike the front surface of the cylinder.     

Suppression characteristics of flow-induced vibration in a test cylinder with varying locations of a control cylinder

This study was designed to identify the suppression characteristics and mechanisms of flow-induced vibration occurring in a test cylinder installed on an elastic support by placing a control cylinder with a smaller diameter behind the test cylinder. To identify the effects of this installation, the diameter and location of the control cylinder were varied systematically to examine the characteristics of flowinduced vibration occurring in the test cylinder. Furthermore, the fluctuating streamwise velocity of the wake flow of the test cylinder was examined as it varied with the installation of the control cylinder. Subsequently, the peripheral flow of the test cylinder installed in front of the control cylinder was examined via a flow visualization test that used a water channel. Results obtained from the experiments are summarized as follows. i) Flow-induced vibrations in the test cylinder, which occur and are varied by the installation of the control cylinder behind the test cylinder, have four types that change according to the different diameters and locations of the control cylinder. ii) The domain of the positions of the control cylinder, which can suppress flow-induced vibration in the test cylinder, increases in proportion with the diameter of the control cylinder. iii) Flow-induced vibration that will be generated in the test cylinder is predicted by examining the distribution of the flow velocity of the wake flow and the intensity of the fluctuating streamwise velocity at the lower flow velocity level before it reaches a flow velocity that can create flow-induced vibration in the test cylinder.     

基于T-S模糊故障树的家用空调可靠性分析

为降低家用空调运行故障率以提高用户体验度和减小家用空调高空维修作业风险,提出应用T-S模糊故障树分析法分析家用空调的可靠性.用T-S模糊门描述空调系统各事件间的联系,用模糊数描述部件的故障程度.根据建立的空调系统T-S模糊故障树模型,计算出顶事件不同状态下的模糊失效可能性,分析顶事件不同状态下各部件的重要度,找出影响整...