流體引起的振動.ppt

1、Flow-Induced Vibration流體引起的振動,Flow-Induced Vibration流體引起的振動,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. 與不平衡、不對中和共振等許多問題不同，流體引起的振動往往與設備的工藝運行狀態(tài)密切相關。這就是說，依照設備類型的不同，設備的負荷以及設備承擔的工藝角色對振動的影響會很大。,Flow Relevant Faults流體相關故障,Flow-induced vibration includes each of the following: Hydraulic and Aerodynamic Forces Cavitation and Starvation Recircula

3、tion Flow Turbulence Surge Choking 流體引起的振動包括以下幾種情況： 流體動力 氣蝕和抽空 回流 紊流 喘振 流體堵塞,Hydraulic and Aerodynamic Forces流體動力,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) 很多類別的設備，包括泵、風機、透平機、真空泵等等，均會不可避免地因為它們的葉片作用在輸送的流體（液體或氣體）上而產生流體動力。 一般，流體動力的產生遵從下面的等式： 葉片通過頻率 BPF 葉片數 x 葉

5、輪轉速 （cpm 或 Hz）,Blade & Vane Pass Freq 葉片通過頻率,Hydraulic & aerodynamic force vibration流體動力振動的特點,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. 若葉輪在機殼中偏心或相對于

6、蝸殼的位置不正確，會產生較大的BPF及其倍頻的振動。 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. 需要盡力避免BPF及其倍頻與轉子或支撐結構的固有頻率臨近，否則會引起較大的振動。,Hydraulic & aerodyn

7、amic force vibration流體動力振動的特點,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. 若導葉片的焊接處發(fā)生失效，使擴壓器相對葉輪產生輕微位移，它會導致BPF頻率處的振動大幅上升； 4. A great increase in blade pass vibrat

8、ion will be created if a pump impeller wear ring seizes to the shaft. 若泵口輪摩擦軸，會導致BPF頻率振動的大幅上升； 5. Blade pass frequency in some particular fan types is particularly sensitive to damper settings. 對有些類型的風機，其葉片通過頻率對阻尼設置情況非常敏感。,Hydraulic & aerodynamic force vibration流體動力振動的特點,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 葉片比頻率 (BRF)按下式計算： BRF = (轉速)(葉輪葉片數)(導葉葉片數)/K 其中：K葉輪葉片數和導葉葉片數的最大公約數 若兩個葉片數不互質，則會產生較大的BRF頻率的振動。,Cavitation and Starvation氣蝕與抽空,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. 氣蝕是離心泵的常見問題，經常造成泵內部件的嚴重損壞。遭受

12、連續(xù)氣蝕問題的泵葉輪會產生嚴重的點蝕，在一些案例中，氣蝕會徹底蠶食掉葉輪葉片。 在泵輸送量過大或入口壓力偏低條件下，泵容易產生氣蝕。,Typical Spectrum of Cavitation & Starvation典型的氣蝕/抽空頻譜,Cavitation Characteristics氣蝕特點,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的頻率范圍內有隨機寬帶的振動。 2. When cavitation occurs it will increase ultrasonic measurements (spike energy, HFD, shock pulse, etc.). 氣蝕會引起超聲能量的上升，可用SKF加速度包絡檢測。,Cavitation Characteristics氣蝕特點,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. 氣蝕通常會產生很奇特的現(xiàn)場噪聲。中等程度的氣蝕產生的噪聲象沙子在泵中流動，而嚴重的氣蝕產生的噪聲象小石子在泵中通過。 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. 抽空與氣蝕差不多一樣，只不過它是風機的問題。典型的抽空頻譜與氣蝕頻譜幾乎完全一樣。,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. 對于泵來講，回流是與氣蝕相反的問題。泵輸送量太小或入口壓力太高時，泵會發(fā)生回流現(xiàn)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. 回流發(fā)生時，一部分流體會從出口回流到葉輪中，因為泵實際上在輸送過多的流體。這樣會引起反向的液流。兩個或多個反向的液流會引起噪聲和振動。,Recirculation Characteristics回流特點,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. 回流頻譜與氣蝕頻譜非常相似，也有隨機寬帶振動，有時還有葉片通過頻率。 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. 與氣蝕不同，回流不會產生

19、泵部件的腐蝕。然而，若回流引起的振動過高，會損壞軸承、磨損環(huán)、閥和其它相關部件。,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. 當有某種東西干擾或阻礙流體在泵、風機、壓縮機或真空泵中正常流動時，紊流就會發(fā)生。紊流可能是管道中的障礙物、直角彎角以及急劇的直徑改變等引起的。,Typical Spectrum of Flow Turbulence典型的紊流頻譜,Flow turbulence characteristics紊流特點,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 雖然紊流會產生隨機的較高頻率的振動，它通常產生在1xRPM以下頻率范圍內地隨機振動，大約在50CPM 至2000CPM。 2. Amplitudes and frequencies of flow turbulent vibration will be erratic, sometimes pulsating widely. 紊流引起的振動的幅值和頻率是不穩(wěn)定的，有時會在一個很寬的范

22、圍內波動。 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. 有時紊流引起的噪聲非常高而機器的振動卻相對較低，其原因是這時紊流發(fā)生在機器以外的管道中。,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. 對高速離心式和軸流壓縮機而言，危害更大的問題是喘振。發(fā)生喘振問題的壓縮機通常是工作在設計范圍以外。在特定的運轉速度下，當出口壓力太高或輸送介質的分子量較設計工況小時，壓縮機會遇到喘振問題。 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. 喘振發(fā)生時，壓縮機中的氣流會改變方向。當喘振問題輕微時，僅葉輪葉片邊界層附近的氣流會改變方向

26、。當喘振完全發(fā)生時，全部氣流都會改變方向，從出口流向入口。壓縮機的喘振問題必須得到排除，因為它會產生很大的破壞。,Surge Characteristics喘振特點,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. 輕微喘振僅在數秒的時間內使葉片通過頻率及其倍頻明顯上升。葉片通過頻率幅值會上升一倍或者甚至兩倍。 2. Fully developed surge will most often lif