偏离工况下离心泵的压力脉动和振动分析

为分析偏离工况下离心泵压力脉动和振动情况,本文采用大涡模拟和滑移网格技术研究一离心泵在偏离工况下叶轮内部和叶轮与蜗壳动静干涉位置的压力脉动,并对其进行了频域分析。分析结果表明:离心泵内部流动产生的压力脉动主频多数情况下是其通过频率。在不同运行工况下,叶轮出口处的压力脉动幅值均最大,大流量偏离工况下离心泵内部各部分压力脉动特性与设计工况基本相同,只是脉动幅值略有增大;小流量偏离工况下,离心泵叶轮出口(叶轮和蜗壳动静干涉区域)压力脉动幅值有所增大,脉动主频不再是通过频率,而且其频谱宽度明显增大;当离心泵运行工况小于0.6Q时,压力脉动明显比设计工况剧烈。     

泵-管路系统振动噪声特性试验研究

泵-管路系统广泛应用于船舶均衡系统中，为研究不同工况下泵-管路系统振动特性，搭建了离心泵-管路系统的振动测试平台，通过采集不同工况下泵及管路的振动数据，分析了泵激振动、管路压力、辐射噪声与泵转速的关系，以及泵转速、阀门开度对管路振动的影响。试验结果表明，泵激振动、管路压力和辐射空气噪声均随着泵转速增加而增大，对于离心泵组的泵激振动并非在额定转速工况下振动最小，与泵的运行工况密切相关；管路压力在额定转速前已经建立，在保证泵功能性前提下，可根据使用工况适当降低转速实现降低噪声目标；泵转速、阀门开度均对管路振动有较大影响。     

离心泵多工况水力优化设计

目前的国家标准或者行业标准中,不管是对离心泵水力效率还是离心泵机组效率都是通过考核设计点的效率进行能耗评价。在大部分的实际应用中,离心泵都运行在不同的工况点,考虑多工况运行效率对离心泵能耗的考核更加全面,更接近离心泵运行实际情况。本文介绍了欧盟最低能效指标(MEI,Minimum Efficiency Index)的多工况能耗评价方法,通过实际案例对低比转速离心泵进行了多工况优化设计,并通过试验验证了离心泵多工况水力优化设计的有效性,为离心泵的节能优化设计提供参考。     

离心泵并联运行工况点的确定

分析了影响离心泵并联运行工况点的因素,研究了不同管路系统中离心泵并联运行工况点的确定方法,为离心泵的选型和操作提供了依据。     

离心泵变速工况叶片进口最低压力变化的模拟研究

针对离心泵在变速工况下抗汽蚀能力难以预测的情况,对某高比转速离心泵建立三维模型,并使用CFX软件对其在不同变速比例下内部流场的压力分布进行了模拟预测。模拟结果分析表明,可以较为准确地预测离心泵在不同变速工况下最低点压力变化,对实际使用中工况的选择运行具有积极的指导作用。     

离心泵进口基于高效区宽度的优化及影响分析

化工离心泵常常会在偏离最优工况的条件下运行，结合“双碳”政策，化工离心泵在工况变化时依然处于高效运行显得尤为重要。因此，如何拓宽高效区宽度成为一个重要的问题。以一台六叶片离心泵作为研究对象，进行了数值模拟，将离心泵部分叶片进口处型线调整为螺旋型并分析了其对离心泵外特性的影响。结果表明：设计工况下，调整两枚叶片离心泵的外特性高于调整三枚叶片；周向相位变化将导致离心泵外特性变化；调整后，离心泵高效区变宽，小流量工况下叶轮效率显著提高。     

递归定量分析在离心泵故障诊断中的运用

为了准确诊断离心泵的振动故障,针对振动信号的非平稳特征,提出了一种基于递归定量分析的离心泵振动故障诊断方法。采用递归定量分析(recurrence quantification analysis,简称RQA)方法提取离心泵振动信号的非线性特征参数,由这些特征参数构成特征向量,并以此作为改进Elman神经网络的输入,对神经网络进行训练,建立了离心泵运行状态分类器,用以诊断离心泵的不同状态。试验结果表明,递归定量分析与Elman神经网络相结合的方法可以准确诊断离心泵的振动故障。     

长输管道多工况输油泵国产化应用研究

根据长输管道下游炼厂的需求,本文论述的多工况高扬程单级双吸离心泵需满足1400、1100和650m3/h 3种运行工况。本文对其国产化应用进行了研究分析,着力解决了如下问题:国产泵组在偏离额定工况下的振动超标,泄漏、自润滑轴承温度高等问题。结果表明,该泵结构合理、流量范围宽,满足多工况工艺生产要求,振动、泄漏、温度等主要指标达到同类进口泵技术水平。该泵的成功应用,对提高长输管道输油泵国产化制造水平,优化离心泵的设计、选型、维护管理等有一定的借鉴意义。     

一种离心泵在小流量下振动异常的分析与处理

某食品加工厂用单级悬臂离心泵在出厂型式试验时,在额定流量工况下轴承箱体表面振动出现异常,超过ISO 5199标准规定的限值而无法出厂,影响生产进度和交货期。通过观察泵整机试验运行情况,分析试验台管路布置、泵结构和共同底座特点、泵组不同部位的振动监测及噪声测量,提出了针对性解决措施,通过后续试验验证其有效性深入分析了产生振动的根本原因,从而对同类型泵的设计、合理选型及确定最佳运行范围提供参考。     

3D测绘技术在离心泵改造中的应用

离心泵在运行过程中,叶轮、导叶、口环及轴套等会出现不同程度的磨损和腐蚀,离心泵会出现效率下降、流量扬程达不到要求、振动,甚至气蚀等情况,影响离心泵的运行。或是由于现场工艺参数的变化,原泵已经不再适合运行要求了。这时需要我们对离心泵进行改进,以便满足运行要求。而在进行离心泵水力改进时,最重要的是要知道原泵的叶轮、导叶等的水力模型,     

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.     

炼厂大型多级离心泵典型故障案例及分析

结合炼厂运行实际,对大型离心泵典型故障及其变化过程进行了论述,通过振动等状态监测以及数据分析,可以有效监测故障的发生。     

切片双谱分析在离心泵故障诊断中的应用

运用双谱及切片双谱分析技术对离心泵不同状态下的振动信号进行分析表明,离心泵在正常运行、地脚螺栓松动和空化状态下的双谱图的特征有着明显的差别,可以通过双谱对故障信号进行初步分类,且双谱的对角切片和反对角切片可以显著降低噪声干扰,进一步提取出故障特征频率,故可对离心泵的故障信号进行准确的分类和诊断。     

Rough set based rule learning and fuzzy classification of wavelet features for fault diagnosis of monoblock centrifugal pump

The fault diagnosis problem is conceived as a classification problem. In the present study, vibration signals are used for fault diagnosis of centrifugal pumps using wavelet analysis. Rough set theory is applied to generate the rules from the vibration signals. Based on the strength of the rules the faults are identified. The different faults considered for this study are: pump at good condition, cavitation, pump with faulty impeller, pump with faulty bearing and pump with both faulty bearing and impeller. However, the classification accuracy is based on the strength and number of rules generated using rough set theory. Wavelet features are computed using Discrete Wavelet Transform (DWT) from the vibration signals and rules are generated using rough sets and classified using fuzzy logic. The results are presented in the form of confusion matrix which shows the classification capability of wavelet features with rough set and fuzzy logic for fault diagnosis of monoblock centrifugal pump.     

不同叶片冲角离心泵内流诱导振动噪声研究

基于离心泵流动诱导振动噪声的试验测试系统,测量了不同叶片进口冲角模型泵在全流量范围内的振动和噪声信号并对其进行了处理和分析。研究结果表明:叶片进口冲角存在一个最优值,使离心泵的性能最佳;模型泵内部流动诱导的振动对泵体的影响最大,随着叶片进口冲角的增加,在各流量下模型泵噪声信号的轴频和叶频能量峰值均没有明显变化规律,但当叶片进口冲角为9°时,在1750～2250Hz频段内的噪声信号消失。     

An experimental study on the cavitation vibration characteristics of a centrifugal pump at normal flow rate

Cavitation is a challenging flow abnormality that leads to undesirable effects on the energy performance of the centrifugal pump and the reliable operation of the pump system. The onset and mechanism of a phenomenon that results in unsteady cavitation must be realised to ensure a reliable operation of pumps under the cavitation state. This study focuses on cavitation instability at normal flow rate, at which point the unsteady cavitation occurs as the available net positive suction head (NPSHa) falls below 5.61 m for the researched pump. An ameliorative algorithm–united algorithm for cavitation vibration analysis is proposed on the basis of short time Fourier transform (STFT) and Wigner–Ville distribution (WVD). The STFT–WVD method is then tested using vibration data measured from the centrifugal pump. The relationship between vibration and suction performance indicates that the inception and development of cavitation can be effectively detected by the distribution and intensity of the united algorithm at the testing points. Intermediate frequency components at approximately 6 kHz fluctuate initially with the development of cavitation. A time–frequency characteristic is found to be conducive to monitoring the cavitation performance of centrifugal pumps.     

DETECTION OF CAVITATION PHENOMENON IN A CENTRIFUGAL PUMP USING AUDIBLE SOUND

One of the sources of instability in a centrifugal pump is cavitation phenomenon. Cavitation within a centrifugal pump can cause more undesirable effects, such as deterioration of the hydraulic performance (drop in head-capacity and efficiency curves), damage of the pump by pitting and erosion and structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore it must, by all means, be prevented. To prevent the onset of the cavitation, we have to know the beginning of cavitation phenomenon in the pump. To detect the beginning of the cavitation process, the emitted noise can also be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, at 147 Hz or BPF/2, which is strongly dependent on the cavitation process and its development. Therefore, the discrete frequency tone at 147 Hz was separated from the noise spectra of cavitating pumps and then used to detect the incipient of cavitation and its development. It was also used to determine the net positive suction head required or the critical value, as well as to prevent cavitation in the pump by means of initiating an alarm, shutdown or control signal via an electrical control system.     

Investigation on Reduction of Pressure Fluctuation for a Double-Suction Centrifugal Pump

Double-suction centrifugal pumps have been applied extensively in many areas,and the significance of pressure fluctuations inside these pumps with large power is becoming increasingly important.In this study,a double-suction centrifugal pump with a high-demand for vibration and noise was redesigned by increasing the flow uniformity at the impeller discharge,implemented by combinations of more than two parameters.First,increasing the number of the impeller blades was intended to enhance the bounding effect that the blades imposed on the fluid.Subsequently,increasing the radial gap between the impeller and volute was applied to reduce the rotor-stator interaction.Finally,the staggered arrangement was optimized to weaken the efficacy of the interference superposition.Based on numerical simulation,the steady and unsteady characteristics of the pump models were calculated.From the fluctuation analysis in the frequency domain,the dimensionless pressure fluctuation amplitude at the blade passing frequency and its harmonics,located on the monitoring points in the redesigned pumps(both with larger radial gap)are reduced a lot.Further,in the volute of the model with new impellers staggered at 12°,the average value for the dimensionless pressure fluctuation amplitude decreases to 6% of that in prototype pump.The dimensionless rootmean-square pressure contour on the mid-span of the impeller tends to be more uniform in the redesigned models(both with larger radial gap);similarly,the pressure contour on the mid-section of the volute presents good uniformity in these models,which in turn demonstrating a reduction in the pressure fluctuation intensity.The results reveal the mechanism of pressure fluctuation reduction in a double-suction centrifugal pump,and the results of this study could provide a reference for pressure fluctuation reduction and vibration performance reinforcement of doublesuction centrifugal pumps and other pumps.     

Design principles for low-noise multistage centrifugal pumps in power plants

Basic design principles for centrifugal pumps with low vibrational activity are considered. Increase in pump vibration is due not so much to residual rotor imbalance as to design and technological factors, some of which are intrinsic to multistage pumps and cannot be eliminated by any means.