scholarly journals Cavitating flow-induced unsteady pressure pulsations in a low specific speed centrifugal pump

2018 ◽  
Vol 5 (7) ◽  
pp. 180408 ◽  
Author(s):  
Ning Zhang ◽  
Bo Gao ◽  
Zhong Li ◽  
Qifeng Jiang
Keyword(s):  
Critical Point ◽  
Cavitation Bubble ◽  
Pressure Wave ◽  
High Energy ◽  
Cavitation Number ◽  
Centrifugal Pumps ◽  
Pressure Pulsations ◽  
Measuring Point ◽  
Number Range ◽  
Cavitation Region

With the development of cavitation, the high-energy pressure wave from a cavitation bubble collapsing is detrimental to the stable operation of centrifugal pumps. The present paper concentrates on pressure pulsations under cavitation conditions, and pressure amplitudes at the blade-passing frequency ( f BPF ) and RMS values in the 0–500 Hz frequency band are combined to investigate cavitation-induced pressure pulsations. The results show that components at f BPF always dominate the pressure spectrum even at the full cavitation stage. For points P1–P7 on the volute side wall, with a decreasing cavitation number, the pressure energy first remains unchanged and then it rises rapidly after the critical point. For point In1 in a volute suction pipe located close to the cavitation region, the pressure energy changes slightly at high cavitation numbers; then for a particular cavitation number range, the pressure energy decreases, and finally increases again. For different flow rates, the pressure energy at the critical point is much lower than the initial amplitude at the non-cavitation condition for In1. This demonstrates that the cavitation cloud in the typical stage is partially compressible, and the emitted pressure wave from a collapsing cavitation bubble is absorbed and attenuated significantly. Finally, this leads to the pressure energy decreasing rapidly for the measuring point In1 near the cavitation region.

scholarly journals Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Bo Gao ◽  
Pengming Guo ◽  
Ning Zhang ◽  
Zhong Li ◽  
Minguan Yang
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Local Maximum ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Vibration Characteristics ◽  
Vibration Energy ◽  
Stable Operation ◽  
Centrifugal Pumps ◽  
Number Range

Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.

scholarly journals Improvement of Intake Structures in a Two-Way Pumping Station with Experimental Analysis

2020 ◽  
Vol 10 (19) ◽  
pp. 6842
Author(s):  
Yanjun Li ◽  
Rong Lu ◽  
Huiyan Zhang ◽  
Fanjie Deng ◽  
Jianping Yuan
Keyword(s):  
Frequency Domain ◽  
Great Influence ◽  
Operating Conditions ◽  
Stable Operation ◽  
Pressure Pulsations ◽  
Pump Unit ◽  
Measuring Point ◽  
Time Frequency ◽  
Pumping Station ◽  
Bell Mouth

Pumping stations are important regulation facilities in a water distribution system. Intake structures can generally have a great influence on the operational state of the pumping station. To analyze the effects of the bell mouth height of the two-way intake on the performance characteristics and the pressure pulsations of a two-way pumping station, the laboratory-sized model pump units with three different intakes were experimentally investigated. To facilitate parameterized control, ellipse and straight lines were used to construct the profile of the bell mouth. The frequency domain and time-frequency domain of the pressure pulsations on the wall of intakes were analyzed by the Welch’s power spectral density estimate and the continuous wavelet transform (CWT) methods, respectively. The results showed that the bell mouth height (H) has significant influences on the uniformity of the impeller inflow and the operation stability of the pump unit. When H = 204 mm, the data fluctuated greatly throughout the test process and the performance curves are slightly lower than the other two schemes. As the bell mouth height gradually decreases, the average pressure difference of each measuring point began to decrease, more homogeneous velocity distribution of impeller inflow can be ensured. The amplitude of blade passing frequency is obvious in the spectrum. While when (H) is more than 164 mm, the main frequency of pressure pulsations at three points fluctuates with the rotation of the impeller. When H decreases to 142 mm, pressure pulsations will be independent of the operating conditions and positions which contributes to the long-term stable operation of the pump unit.

Cinematographic Analysis of Counter Jet Formation in a Single Cavitation Bubble Collapse Flow

2011 ◽  
Vol 27 (2) ◽  
pp. 253-266 ◽  
Author(s):  
S.-H. Yang ◽  
S.-Y. Jaw ◽  
K.-C. Yeh
Keyword(s):  
Flow Field ◽  
Cavitation Bubble ◽  
Pressure Wave ◽  
Bubble Surface ◽  
Bubble Collapse ◽  
Solid Boundary ◽  
Liquid Jet ◽  
Pressure Waves ◽  
Field Variation ◽  
Critical Position

ABSTRACTThis study utilized a U-shape platform device to generate a single cavitation bubble for the detail analysis of the flow field characteristics and the cause of the counter jet during the process of bubble collapse induced by pressure wave. A series of bubble collapse flows induced by pressure waves of different strengths are investigated by positioning the cavitation bubble at different stand-off distances to the solid boundary. It is found that the Kelvin-Helmholtz vortices are formed when the liquid jet induced by the pressure wave penetrates the bubble surface. If the bubble center to the solid boundary is within one to three times the bubble's radius, a stagnation ring will form on the boundary when impacted by the penetrated jet. The liquid inside the stagnation ring is squeezed toward the center of the ring to form a counter jet after the bubble collapses. At the critical position, where the bubble center from the solid boundary is about three times the bubble's radius, the bubble collapse flows will vary. Depending on the strengths of the pressure waves applied, either just the Kelvin-Helmholtz vortices form around the penetrated jet or the penetrated jet impacts the boundary directly to generate the stagnation ring and the counter jet flow. This phenomenon used the particle image velocimetry method can be clearly revealed the flow field variation of the counter jet. If the bubble surface is in contact with the solid boundary, the liquid jet can only splash radially without producing the stagnation ring and the counter jet. The complex phenomenon of cavitation bubble collapse flows are clearly manifested in this study.

scholarly journals THE NUMERICAL SIMULATION OF UNSTEADY CAVITATION EVOLUTION INDUCED BY PRESSURE WAVE

2014 ◽  
Vol 34 ◽  
pp. 1460374
Author(s):  
B.C. KHOO ◽  
J.G. ZHENG
Keyword(s):  
Numerical Simulation ◽  
Cavitation Bubble ◽  
Pressure Wave ◽  
External Perturbation ◽  
Compressible Liquid ◽  
Cavitating Flow ◽  
Bubble Collapse ◽  
Material Erosion ◽  
Noise Vibration ◽  
Compressibility Effects

The present study is focused on the numerical simulation of pressure wave propagation through the cavitating compressible liquid flow, its interaction with cavitation bubble and the resulting unsteady cavitation evolution. The compressibility effects of liquid water are taken into account and the cavitating flow is governed by one-fluid cavitation model which is based on the compressible Euler equations with the assumption that the cavitation is the homogeneous mixture of liquid and vapour which are locally under both kinetic and thermodynamic equilibrium. Several aspects of the method employed to solve the governing equations are outlined. The unsteady features of cavitating flow due to the external perturbation, such as the cavitation deformation and collapse and consequent pressure increase are resolved numerically and discussed in detail. It is observed that the cavitation bubble collapse is accompanied by the huge pressure surge of order of 100 bar, which is thought to be responsible for the material erosion, noise, vibration and loss of efficiency of operating underwater devices.

Reduction of Cavitation Damage in a High-Energy Water Injection Pump

2011 ◽  
Author(s):  
Paul Cooper ◽  
Ron Ungewitter ◽  
Rehan Farooqi ◽  
James McKenzie ◽  
Bruno Schiavello ◽  
...  
Keyword(s):  
Erosion Rate ◽  
Cavitation Erosion ◽  
Acoustic Analysis ◽  
Water Injection ◽  
High Energy ◽  
Cavitation Number ◽  
Two Phase ◽  
Cavitation Damage ◽  
Injection Pump ◽  
Unsteady Rans

The conventionally-designed first-stage impeller of a high-energy, two-stage 19MW seawater injection pump, running at 4950 rpm and generating 1500m of head at a flow rate of 1.05 m3/s was seriously damaged by cavitation erosion in the first two months of operation. The impeller was redesigned by reshaping the blades in the region near the leading edges so as to reduce the inception cavitation number. This impeller has been running for more than a year, and the cavitation erosion rate is predicted to be low enough for it to last 40,000 hours. However, a prominent tone at blade passing frequency appeared with the new impeller, which interacts more effectively with the distorted inflow from the side-suction approach passage. Acoustic analysis of both single- and two-phase unsteady RANS CFD solutions corroborate the presence of this tone, which had not been observed when the pump operated with the original, conventional impeller.

scholarly journals Numerical Research on Hydraulically Generated Vibration and Noise of a Centrifugal Pump Volute with Impeller Outlet Width Variation

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Houlin Liu ◽  
Jian Ding ◽  
Hanwei Dai ◽  
Minggao Tan ◽  
Xiaochen Tang
Keyword(s):  
Noise Level ◽  
Sound Radiation ◽  
Fem Analysis ◽  
Centrifugal Pumps ◽  
Pressure Pulsations ◽  
Performance Pressure ◽  
Impeller Outlet ◽  
Numerical Research ◽  
Structure Vibration ◽  
Vibration And Sound Radiation

The impeller outlet width of centrifugal pumps is of significant importance for numbers of effects. In the paper, these effects including the performance, pressure pulsations, hydraulically generated vibration, and noise level are investigated. For the purpose, two approaches were used to predict the vibration and sound radiation of the volute under fluid excitation force. One approach is the combined CFD/FEM analysis for structure vibration, and then the structure response obtained from the FEM analysis is treated as the boundary condition for BEM analysis for sound radiation. The other is the combined CFD/FEM/BEM coupling method. Before the numerical methods were used, the simulation results were validated by the vibration acceleration of the monitoring points on the volute. The vibration and noise were analyzed and compared at three flow conditions. The analysis of the results shows that the influences of the sound pressure of centrifugal pumps on the structure appear insignificant. The relative outlet widthb2*atnq(SI) = 26.7 in this paper should be less than 0.06, based on an overall consideration of the pump characteristics, pressure pulsations, vibration and noise level.

scholarly journals On optimization of flow passages of impellers of centrifugal pumps

2019 ◽  
Vol 11 (4) ◽  
pp. 311-318
Author(s):  
A. V. Volkov ◽  
A. G. Parygin ◽  
A. A. Vikhlyantsev ◽  
A. A. Druzhinin
Keyword(s):  
High Efficiency ◽  
Modular Design ◽  
Energy Performance ◽  
High Energy ◽  
Experiment Planning ◽  
Centrifugal Pumps ◽  
Hydraulic Machines ◽  
Specific Speed ◽  
Conventional Solution ◽  
Turbine Mode

The conventional solution for HAPPs is the use of reversible hydraulic machines operating both in the pump mode as well as in the turbine mode. At the same time, for example, a blade system of a hydraulic machine designed for the pumping mode has a high efficiency. However, in the turbine mode, the energy characteristics of such machine are far from optimal. Considering different patterns of micro- and mini-HAPPs (up to 100 kW) of modular design, it is most appropriate to use a pump and a turbine separately, since the efficiency of hydraulic machines is very important in the case of such low power. To date, approaches to the design of hydraulic turbines are quite developed and allow to achieve high energy performance [1, 2]. According to different data sources the level of axial turbine efficiency with power less than 100 kW is about 80÷91%. At the same time, for centrifugal pumps, especially those of low specific speed, the problem of increasing energy efficiency is very urgent. E.g., for pumps with a specific speed ns< 80 the efficiency level is usually 40 to 65%. The aim of the presented research is the development of methods of synthesis and optimization of the flow passages of centrifugal pumps using the approaches of the theory of optimal control and increasing energy performance of hydraulic machines. Various ways of local correction of geometry of flow passages are presented in the paper. As an alternative to empirical approaches, methods based on the control of the circulation distribution are considered in detail. Various mathematical dependences of the flow circulation on the coordinate of the point lying on the surface of the blade are analyzed. Possibilities of application of the theory of experiment planning in relation to the problems to be solved are considered.

Computational Study of Pressure Pulsation in a Medium Specific Speed Pump

2005 ◽  
Author(s):  
Serguei Timouchev
Keyword(s):  
Complex Geometry ◽  
Computational Study ◽  
Spectral Component ◽  
Axial Component ◽  
Centrifugal Pumps ◽  
Pressure Pulsations ◽  
3 Dimensional ◽  
Order Of Magnitude ◽  
Specific Speed ◽  
In The Beginning

The centrifugal pump of high specific speed with a diagonal type of impeller flow is studied experimentally and numerically. Both 2D and 3D numerical methods are used by applying acoustics–vortex equations. Increasing energetic parameters of centrifugal pumps requires a more complex geometry of the impeller and volute as one needs to raise the specific speed of the pump to provide a higher efficiency value. The pump of higher specific speed has an impeller with curved blades and diagonal meridional section. The flow outgoing the impeller has an essential axial component of velocity. Thus the two dimensional approach will not give the accurate prediction of pressure pulsations in the volute casing. This is why the new 3-dimensional method has been elaborated for this task. The 3D computational results of pressure pulsations are compared with those obtained by 2D-computation Measurements show that in the beginning of volute, in the pseudo-sound zone, amplitude of Blade Passing Frequency (BPF) spectral component is higher than that at the pump outlet by an order of magnitude. The 3-Dimensional analysis gives a good agreement with experimental data while the 2D prediction underestimates the BPF amplitude in the beginning of volute.

Pathophysiology of ballistic trauma

2016 ◽  
Author(s):  
Michael C. Reade ◽  
Peter D. Thomas
Keyword(s):  
Energy Transfer ◽  
Kinetic Energy ◽  
Pressure Wave ◽  
Mass Movement ◽  
High Energy ◽  
Low Energy ◽  
Wound Contamination ◽  
Blast Fragmentation ◽  
Low Energy Transfer ◽  
Ballistic Trauma

Bullets and other projectiles cause ballistic trauma. Explosions wound by the effect of a blast pressure wave, penetrating fragments propelled by the explosion, the mass movement of gas interacting with the casualty or the environment, and miscellaneous effects. Most blast casualties surviving to hospital care will not have significant pressure wave injury, but some will. Blast fragmentation most commonly resembles other types of low energy transfer ballistic trauma.. The effect of bullets depends on the kinetic energy transferred and the nature of the tissues struck, with energy transfer partly determined by bullet design. Low energy transfer bullets wound by crushing and laceration, limited to the tissues struck. High energy bullets may impart kinetic energy to surrounding tissues, causing a temporary cavity which sucks in debris and damages tissues sometimes well beyond the bullet track. Predicting the extent of devitalization can be difficult at the time of initial inspection. Wound contamination, particularly with soil, may modify the usual conservative approach to initial debridement.

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