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1、Flow-Induced Vibration流体引起的振动,Flow-Induced Vibration流体引起的振动,Unlike many of the other mechanical vibration problems such as unbalance, misalignment, resonance and so forth, flow-induced vibration is often very dependent upon operating conditions. That is, it can be very affected by load depending on
2、the type of machine and the work being performed by the machine. 与不平衡、不对中和共振等许多问题不同，流体引起的振动往往与设备的工艺运行状态密切相关。这就是说，依照设备类型的不同，设备的负荷以及设备承担的工艺角色对振动的影响会很大。,Flow Relevant Faults流体相关故障,Flow-induced vibration includes each of the following: Hydraulic and Aerodynamic Forces Cavitation and Starvation Recircula
3、tion Flow Turbulence Surge Choking 流体引起的振动包括以下几种情况： 流体动力 气蚀和抽空 回流 紊流 喘振 流体堵塞,Hydraulic and Aerodynamic Forces流体动力,Various types of machines including pumps, blowers, turbines, vacuum pumps and so forth inherently produce hydraulic or aerodynamic forces as their impellers impart work on the fluid (li
4、quid or gaseous) they are handling. In general, hydraulic and aerodynamic forces are generated as per the following equation: Blade (or Vane) Pass Frequency = BPF = #Vanes X Impeller RPM (CPM or Hz) 很多类别的设备，包括泵、风机、透平机、真空泵等等，均会不可避免地因为它们的叶片作用在输送的流体（液体或气体）上而产生流体动力。 一般，流体动力的产生遵从下面的等式： 叶片通过频率 BPF 叶片数 x 叶
5、轮转速 （cpm 或 Hz）,Blade & Vane Pass Freq 叶片通过频率,Hydraulic & aerodynamic force vibration流体动力振动的特点,1. Significant vibration both at blade pass frequency and blade pass harmonics will be generated if an impeller is not centrally located within its housing and properly aligned with diffusers. 若叶轮在机壳中偏心或相对于
6、蜗壳的位置不正确，会产生较大的BPF及其倍频的振动。 2. It is important to ensure that neither the blade pass frequency nor blade pass harmonics coincide with natural frequencies of the rotor or support structure. Excessive vibration can result if allowed to do so. 需要尽力避免BPF及其倍频与转子或支撑结构的固有频率临近，否则会引起较大的振动。,Hydraulic & aerodyn
7、amic force vibration流体动力振动的特点,3. A great increase in blade pass frequency will occur if welds securing diffuser vanes experience failure allowing the diffusers to shift position slightly relative to the impeller. 若导叶片的焊接处发生失效，使扩压器相对叶轮产生轻微位移，它会导致BPF频率处的振动大幅上升； 4. A great increase in blade pass vibrat
8、ion will be created if a pump impeller wear ring seizes to the shaft. 若泵口轮摩擦轴，会导致BPF频率振动的大幅上升； 5. Blade pass frequency in some particular fan types is particularly sensitive to damper settings. 对有些类型的风机，其叶片通过频率对阻尼设置情况非常敏感。,Hydraulic & aerodynamic force vibration流体动力振动的特点,6. Blade Rate Frequency (BRF
9、) has to do with the number of times and rate at which rotating and stationary vanes coincide with one another. When they do coincide, there can be a pronounced pulse due to compression of the fluid (gas or liquid) between the rotating and stationary vanes. BRF = (RPM)(#Impeller Vanes)(#Diffuser Van
10、es)/K K = Highest Common Factor of #Impeller Vanes and #Diffuser Vanes 叶片比频率 (BRF)按下式计算： BRF = (转速)(叶轮叶片数)(导叶叶片数)/K 其中：K叶轮叶片数和导叶叶片数的最大公约数 若两个叶片数不互质，则会产生较大的BRF频率的振动。,Cavitation and Starvation气蚀与抽空,Cavitation is a common problem with centrifugal pumps and can be quite destructive to internal pump comp
11、onents. Often, pumps subjected to continuing cavitation will have badly pitted and/or eroded impellers. In some cases, cavitation can completely erode away impeller vanes. Cavitation most often occurs when a pump is operating with excess capacity or low suction pressure. 气蚀是离心泵的常见问题，经常造成泵内部件的严重损坏。遭受
12、连续气蚀问题的泵叶轮会产生严重的点蚀，在一些案例中，气蚀会彻底蚕食掉叶轮叶片。 在泵输送量过大或入口压力偏低条件下，泵容易产生气蚀。,Typical Spectrum of Cavitation & Starvation典型的气蚀/抽空频谱,Cavitation Characteristics气蚀特点,1. Classic spectra indicating cavitation have random, broad band energy most often between approximately 20,000 CPM up through approximately 120,000
13、 CPM. 通常在300Hz至2,000Hz的频率范围内有随机宽带的振动。 2. When cavitation occurs it will increase ultrasonic measurements (spike energy, HFD, shock pulse, etc.). 气蚀会引起超声能量的上升，可用SKF加速度包络检测。,Cavitation Characteristics气蚀特点,3. Cavitation will most often generate unique noise. Milder cavitation normally sounds like sand
14、being pumped whereas more severe cavitation will actually sound as if gravel is being passed through the pump. 气蚀通常会产生很奇特的现场噪声。中等程度的气蚀产生的噪声象沙子在泵中流动，而严重的气蚀产生的噪声象小石子在泵中通过。 4. Starvation is the aerodynamic counterpart to cavitation. Like cavitation, it involves insufficient air flow relative to fan cap
15、acity. Typical starvation spectra are almost identical to those of cavitation. 抽空与气蚀差不多一样，只不过它是风机的问题。典型的抽空频谱与气蚀频谱几乎完全一样。,Recirculation回流,In the case of a pump, recirculation is just the opposite of cavitation. Recirculation can occur when a pump is operated at too low a capacity or too high suction
16、pressure. 对于泵来讲，回流是与气蚀相反的问题。泵输送量太小或入口压力太高时，泵会发生回流现象。 When it occurs, a portion of the fluid returns from the discharge to the impeller as the pump attempts to move an excessive amount of fluid through the pump. This brings about a reverse flow and results in 2 or more fluids moving in opposite direc
17、tions causing noise and vibration. 回流发生时，一部分流体会从出口回流到叶轮中，因为泵实际上在输送过多的流体。这样会引起反向的液流。两个或多个反向的液流会引起噪声和振动。,Recirculation Characteristics回流特点,1. Recirculation generates vibration spectra very similar to those caused by cavitation. That is, it will often have random, higher frequency vibration, sometimes
18、superimposed with vane pass frequencies. 回流频谱与气蚀频谱非常相似，也有随机宽带振动，有时还有叶片通过频率。 2. Unlike cavitation, recirculation will not likely cause wear or erosion of pump components. However, if the vibration becomes excessive, it can damage bearings, wear rings, valves and other related components. 与气蚀不同，回流不会产生
19、泵部件的腐蚀。然而，若回流引起的振动过高，会损坏轴承、磨损环、阀和其它相关部件。,Flow Turbulence紊流,Flow turbulence occurs when something interferes with or resists the normal flow of liquids or gases through pumps, fans, compressors or vacuum pumps. Such flow disturbances might be caused by obstructions in the duct or pipe, sharp right an
20、gle turns, abrupt changes in diameter, etc. 当有某种东西干扰或阻碍流体在泵、风机、压缩机或真空泵中正常流动时，紊流就会发生。紊流可能是管道中的障碍物、直角弯角以及急剧的直径改变等引起的。,Typical Spectrum of Flow Turbulence典型的紊流频谱,Flow turbulence characteristics紊流特点,1. Although flow turbulence can generate random, higher frequency vibration, it normally will cause rando
21、m, lower frequency vibration below 1X RPM concentrated in a range from approximately 50 CPM up to 2000 CPM 虽然紊流会产生随机的较高频率的振动，它通常产生在1xRPM以下频率范围内地随机振动，大约在50CPM 至2000CPM。 2. Amplitudes and frequencies of flow turbulent vibration will be erratic, sometimes pulsating widely. 紊流引起的振动的幅值和频率是不稳定的，有时会在一个很宽的范
22、围内波动。 3. Sometimes noise produced by flow turbulence will be very high although the vibration accompanying it will be relatively low on the machine itself. The reason for this is that the turbulence condition itself exists outside the machine. 有时紊流引起的噪声非常高而机器的振动却相对较低，其原因是这时紊流发生在机器以外的管道中。,Surge 喘振,On
23、e of the more important problems plaguing high speed centrifugal and axial-flow compressors is surge. Typically a compressor experiencing surge is operating outside design limits. Surge occurs when the discharge pressure is too high or if the volumetric mass flow rate is too low relative to design c
24、onditions for a particular operating speed. 对高速离心式和轴流压缩机而言，危害更大的问题是喘振。发生喘振问题的压缩机通常是工作在设计范围以外。在特定的运转速度下，当出口压力太高或输送介质的分子量较设计工况小时，压缩机会遇到喘振问题。 When this occurs, the gas flow will actually reverse directions in the compressors. When the surge is only minor, this flow reversal may occur only at the bounda
25、ry layers of the impeller blades. However, when full surge develops, the entire fluid flow will reverse directions and will flow from the discharge to the inlet. Surge must be prevented in a compressor due to the fact that it can wreak extensive damage. 喘振发生时，压缩机中的气流会改变方向。当喘振问题轻微时，仅叶轮叶片边界层附近的气流会改变方向
26、。当喘振完全发生时，全部气流都会改变方向，从出口流向入口。压缩机的喘振问题必须得到排除，因为它会产生很大的破坏。,Surge Characteristics喘振特点,1. Minor surge causes a noticeable increase at blade pass frequency and harmonics within only a time period of seconds. Such blade pass frequencies may double or even triple in amplitude. 轻微喘振仅在数秒的时间内使叶片通过频率及其倍频明显上升。叶
27、片通过频率幅值会上升一倍或者甚至两倍。 2. Fully developed surge will most often lift up the entire spectrum. That is, the entire “noise floor” of the spectrum will be lifted, creating high amplitude, random response covering a broad frequency range. 完全的喘振会提高整个频谱的底脚，即引起宽频段、大幅值的随机响应。 3. Left uncorrected, surge can wreck
28、 a compressor within a short period of time. 若不加以校正，喘振能在短时间你损坏压缩机。,Choking流体堵塞,Choking (sometimes called “stone walling”) is essentially the opposite of surging in a compressor. Choking occurs when discharge pressures are too low creating high velocities in the diffuser section. 流体堵塞本质上来说是与喘振相反的故障。当
29、出口压力太低导致流体速度太高时，压缩机会发生流体堵塞问题。 Vibration spectral characteristics of choking will be essentially identical to those of surging. Therefore, one will have to check other operating parameters such as pressure, mass flow, and so forth in order to differentiate which problem is occurring. 流体堵塞频谱与喘振频谱相同。因此故障分析人员必须监测其它工艺参数如压力、流量等，以确认发生的是哪种问题。,