离心泵空化判定及其流声特性研究

江苏大学硕士学位论文

ABSTRACT

This study is financial supported by the National Natural Science Fund of China (No.51509111,51779106).In order to meet the rapidly developing needs of the national security strategy equipment field,centrifugal pumps as an important energy conversion equipment,are gradually developing in the direction of high speed and high performance.While cavitation is the core issue that limits its further development.Mastering the generation mechanism of cavitation induced vibration and noise in centrifugal pumps,studying the effect of cavitation on the structure of unsteady flow field,proposing a reliable cavitation detection method,and establishing

a reasonable cavitation stage evaluation criteria,can not only provide a theoretical

basis and technical support for fault diagnosis of hydraulic machinery,but also can greatly increase the reliability of equipment operation and increase the service life.In this paper,the theoretical analysis,experimental and numerical investigation are used to study the variation law of cavitation signal in centrifugal pump and the characteristics of flow field and sound field distribution under cavitation conditions.

The aim is to establish a high-sensitivity and high-reliability method for detecting the cavitation of centrifugal pumps,to master the unsteady flow characteristics of centrifugal pumps under cavitation conditions,and to propose a reasonable cavitation noise prediction method.The main research contents of this dissertation are below:

1.The mechanism and main forms of cavitation and erosion is explained,the

research progress of numerical calculation of cavitation flow field and cavitation acoustic field is introduced,and the research status of judging method of cavitation in the centrifugal pump is summarized.

2.Taking a n s=117.3centrifugal pump as the research object,based on the

visualized closed test bench,the pump performance parameters,the distribution pattern of the bubbles and the vibration and noise signals are collected synchronously, and the variation law is studied.According to the results of high-speed photography

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离心泵空化判定及流声特性研究

experiments,different cavitation detection methods based on the total level values of liquid-borne noise,solid-loaded vibration,and air-borne noise are proposed.The results show that,the highest sensitivity of cavitation detection is based on high-speed photography;the cavitation thresholds based on the total level values of the liquid-borne noise,the solid-borne vibration,and the air-borne noise are0.5%,0.5%, and0.7%1bcb9c1d51e2524de518964bcf84b9d529ea2ccdpared to the solid-borne vibration and air-borne noise,the method based on total sound pressure level of liquid-borne noise has high sensitivity and is less affected by the environment.

3.On the basis of the traditional cavitation stage division method,taking the

relationship between the change of each signal quantity and the development of cavitation into account,a more elaborate cavitation stage division method is proposed.

Based on the distribution of cavitation coefficient corresponding to the maximum value of each signal magnitude curve,taking the relationship between cavitation development and energy loss into account,it is found that the cavitation based on extremum point of the solid-borne vibration is more severe comparable to the cavitation extremum point of the liquid-borne noise.The serious cavitation stage and over-serious caviattion stage is divided according to extremum point of the solid-borne vibration.Taking the3%drop in head as the critical point of cavitation, the developed cavitation stage and the serious cavitation stage is divided.The developed cavitation stage and onset cavitation stage is divided by a0.5%increase in the total sound pressure level of liquidborne noise.The non-cavitation stage and the onset cavitation stage is divided by the visible cavitation point.

4.Due to the restrictive nature of high-speed photography,in order to further

improve the accuracy of the cavitation judging method,by comparing the variation of the flow coefficient and the cavitation coefficient on the vibration and noise spectrum, acquired the frequency band for cavitation detection.And the3σprinciple is used to study the cavitation threshold values of vibration and noise signals.The method of wide-band sound pressure level of liquid-borne noise in the2000~3000Hz frequency

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江苏大学硕士学位论文

band increased by1%,the wide-band vibration acceleration level of solid-borne vibration in the10~50Hz frequency band increased by1%,the wide-band vibration acceleration level of solid-borne vibration in the1000~3000Hz frequency band increased by1.1%,have higher sensitivity to cavitation.

5.By means of an ultra-low specific-speed centrifugal pump with a specific

speed n s=25,further quantificational analysis the change rules of each signal.

Different cavitation judging methods are analyzed to verify the accuracy and reliability of the this methods.The rationality of the cavitation stage division method and the accuracy of the cavitation determination method based on the total semaphore values is verified.The cavitation spectrum interval is done statistics verifing the frequency band for cavitation detection,and the reliability of the cavitation thresholds for each frequency band.

6.In order to obtain the effect of cavitation on the internal flow field

characteristics of the pump,by selecting the appropriate turbulence model and cavitation model,the internal flow characteristics of centrifugal pump at different cavitation stages are simulated.The results show that:With the decrease of the cavitation coefficient,cavitation occurs first in the vicinity of the inlet edge of the suction surface of the blade,and gradually develops to the direction of the impeller outlet and pressure surface along with the blade suction surface.The high flow rate condition is more apt to cavitation than the low flow rate condition;the vortex cavitation is formed due to the inlet reflux,which results in the uneven distribution of the cavitation bubbles in the blades of the impeller.With the decrease of the cavitation coefficient,The main frequency of pressure pulsation gradually changes from blade passing frequency(BPF)to axial passing frequency(APF),the characteristic components at BPF and APF increase,while the high frequency pulsation decreases.

The radial force of the impeller decreases,and its distribution regularity deteriorates.

7.In order to study the effect of cavitation on the acoustic field distribution of

pumps,a cavitation-induced noise calculation model is constructed.For the

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离心泵空化判定及流声特性研究

liquid-borne noise,the far-field and near-field noise distributions in different cavitation stages are calculated based on the boundary element method and the Proudman semi-empirical model method respectively.For air-borne noise,the flow noise and flow-induced noise analysis models under different sound sources are established,and the sound pressure distribution and contribution of different nature noise sources are analyzed.The results show that:After cavitation occurs,the turbulent kinetic energy,turbulent kinetic energy dissipation rate and near-field acoustic power of liquid-borne noise gradually increase,with the decrease of the cavitation coefficient.The sound pressure level at characteristic frequencies of the liquid-borne noise and the air-borne noise shows a law of decreasing first and then increasing.The sound pressure level at outlet monitoring point is larger than the inlet monitoring point.The sound pressure distribution of air-borne noise is different under different acoustic sources.The sound pressure directional distribution of flow-induced noise and flow induced structure noise of air-borne noise under the same acoustic source are not the same.The radiated energy of flow-induced structure noise provides

a major contributor to air-borne noise.

Keywords：Centrifugal pump;Cavitation;Vibration and noise;Interior flow field characteristics;Experimental research

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目录

第一章绪论 (1)

1.1引言 (1)

1.2国内外研究现状 (2)

1.2.1空化产生及空蚀机理研究现状 (2)

1.2.2空化数值模拟研究进展 (4)

1.2.3空化判定研究现状 (8)

1.3本文的研究工作 (11)

第二章离心泵空化判定及阶段划分方法 (12)

2.1试验对象及试验测试系统 (12)

2.1.1试验装置 (13)

2.1.2试验对象 (14)

2.1.3数据采集系统 (15)

2.1.4高速摄影系统 (18)

2.1.5外特性测试系统 (19)

2.2试验方案及试验步骤 (20)

2.2.1试验方案 (20)

2.2.2试验步骤 (21)

2.3空化初生点的判定 (22)

2.3.1传统空化判定方法 (22)

2.3.2基于高速摄影的空化判定方法 (23)

2.3.3基于液载噪声的空化判定方法 (26)

2.3.4基于固载振动的空化判定方法 (27)

2.3.5基于气载噪声的空化判定方法 (29)

2.3.6各空化判定方法的比较 (30)

2.4空化极值点的判定 (32)

2.5空化阶段判定方法提出 (33)

2.6不同空化阶段空化信号频谱分析 (35)

2.6.1空化对液载噪声频谱影响 (35)

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2.6.2空化对固载振动频谱影响 (38)

2.7基于频段量化的空化判定 (41)

2.7.1基于液载噪声频段量化的空化判定 (42)

2.7.2基于固载振动频段量化的空化判定 (43)

2.8不同空化判定方法的灵敏度对比 (45)

2.9本章小结 (46)

第三章空化判定方法分析及验证 (48)

3.1试验对象及试验测试系统 (48)

3.1.1试验对象 (48)

3.1.2试验测试系统 (49)

3.1.3试验方案及试验步骤 (50)

3.2空化性能曲线验证 (50)

3.3基于液载噪声的空化判定方法验证 (51)

3.3.1基于液载噪声总声压级的空化判定方法验证 (51)

3.3.2基于液载噪声频谱变化的空化判定方法验证 (53)

3.4基于固载振动的空化判定方法验证 (54)

3.4.1基于固载振动总振级的空化判定方法验证 (54)

3.4.2基于固载振动频谱变化的空化判定方法验证 (55)

3.5不同空化信号频段阈值验证 (57)

3.5.1基于液载噪声空化信号的阈值验证 (57)

3.5.2基于固载振动空化信号的阈值验证 (58)

3.6本章小结 (60)

第四章离心泵不同空化阶段不稳定流动规律研究 (61)

4.1数值模拟计算方法 (61)

4.1.1计算模型及网格划分 (61)

4.1.2数值计算前处理 (62)

4.1.3计算模型选择 (64)

4.2空化对内流场的影响 (65)

4.2.1空化对叶片间空泡分布的影响 (65)

4.2.2空化对空化流场的影响 (67)

4.2.3空化对涡结构的影响 (68)

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江苏大学硕士学位论文

4.2.4空化对叶片表面载荷分布的影响 (71)

4.3空化对离心泵非定常力的影响 (73)

4.3.1空化对压力脉动的影响 (73)

4.3.2空化对径向力的影响 (79)

4.4本章小结 (80)

第五章离心泵空化诱导噪声数值模拟 (82)

5.1离心泵噪声计算理论及方法 (82)

5.1.1基于声类比的噪声计算 (82)

5.1.2基于半经验模型的噪声计算 (84)

5.2不同空化数下离心泵液载远场噪声计算 (84)

5.2.1基于叶轮扇声源的内声场计算 (85)

5.2.2基于蜗壳固定声源的内声场计算 (88)

5.3不同空化数下离心泵液载近场噪声计算 (91)

5.4不同空化数下离心泵气载噪声计算 (95)

5.4.1结构模态响应 (96)

5.4.2叶轮扇声源作用下的气载流动噪声 (98)

5.4.3蜗壳固定声源作用下的气载流动噪声 (100)

5.4.4蜗壳固定声源作用下的气载流激噪声 (102)

5.5本章小结 (105)

第六章总结与展望 (106)

6.1研究总结 (106)

6.2研究展望 (108)

参考文献 (109)

致谢 (117)

作者在攻读硕士学位期间取得的科研成果 (118)

一、发表学术论文 (118)

二、专利申请 (119)

三、参与科研项目 (119)

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离心泵空化判定及流声特性研究

主要符号说明

符号物理意义单位符号物理意义单位

u速度分量m/s F叶轮径向力N

p流体热力学压强PaΨ扬程系数

ρ密度kg/m3σ空化数

t时间sφ流量系数

υ运动粘度m2/s u2叶轮出口圆周速度m/s

k湍动能m2/s2p v饱和蒸气压值Pa

ε湍动能耗散率m2/s3σc临界空化数

ν速度m/sσp可视空化初生数

c声速m/sσio液载声学空化初生数

f频率Hzσso固载振动空化初生数

τ应力张量σeo气载噪声空化初生数

Q流量m3/hσie液载噪声空化极值数

H扬程mσse固载振动空化极值数

n转速r/minσee气载噪声空化极值数

n s比转速R相间质量传输率

η效率R e蒸汽生成率

D1进口直径mm R c蒸汽凝结率

D2出口直径mm C p压力脉动系数

φ叶片包角(°)L pa宽频噪声声压级dB

b2叶轮出口宽度mm L aa宽频振动加速度级dB

D3基圆直径mm L a总振动加速度级dB

b3蜗室进口宽度mm L p总声压级dB 注：文中对符号有注释的优先；多于一个含义的符号在文中另作说明

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第一章绪论

1.1引言

泵是一种广泛应用于国防、工农业、排水消防等领域的通用机械，是液体输送系统的“心脏”，其中离心泵占泵产品总量的70％左右[1]。在国家提倡节能减排、建设节约型社会以及提升国民经济的需求下，离心泵正逐渐朝向大型化、高速化、大功率、高性能方向发展，因而对其效率、稳定性及空化性能等重要的性能指标提出了越来越高的要求[2-3]。效率关系能量的利用率，稳定性关系设备能否安全、正常运行，而空化不仅关系到设备运行稳定性及可靠性，还会对一些国防设备的声隐性能造成影响[4]。虽然通过合理的过流部件设计、进口增压等方法能抑制空化的产生，但都无法从根本上消除空化。因此空化问题是目前工程应用领域亟待解决的技术难题。

对于离心泵空化的研究，有几个亟需解决的问题。一是提出离心泵空化监测及状态评估方法。传统的能量法是以离心泵扬程下降3%作为空化初生的判断依据，但该方法存在极大的滞后性；而其他空化判定方法，由于灵敏度较低，普适性较差，因此无法真正的指导工程应用。二是构建高精度瞬态空化流动数值计算方法。由于离心泵空化涵盖了多尺度湍流、相变、非定常汽液多相等复杂流动问题，通过稳态空化计算虽能实现对离心泵空化状态下水力性能的预测，但难以捕捉其内部非定常流动特性，而高精度的瞬态空化计算需依靠合适的空化模型选择及针对性优化。三是解决空化诱导噪声精确数值预测问题。某些场合客观因素的限制，试验测量空化噪声无法实现；而空化噪声数值预测计算量大，涉及理论复杂。目前针对离心泵噪声数值计算研究主要集中于非空化状态下的声场研究，缺乏空化状态下声场预测理论及方法。

因此，针对离心泵空化判定和流声变化规律的研究，不仅能够促进离心泵空化监测及状态评估系统的构建，还能为其他水力机械内部空化非定常流声特性变化机理研究提供理论参考和技术支撑，具有重要的学术价值和工程意义。

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