Cavitation In Centrifugal Pump Research Articles

Numerical investigation of the effect of leakage flow on cavitation in centrifugal pump

Numerical studies on pumps emphasize mainly on modelling the interactions between the impeller and the volute to obtain an accurate understanding of the physics involved. However, the importance of modelling leakage paths, which is known to have a significant influence on the flow structure in the pump, necessitates an in-depth analysis. This activity is undertaken in this paper by investigating a specific case of a centrifugal pump. Numerical studies have been conducted on the pump modelled with and without leakages for the design condition. The sliding mesh method is used to obtain single phase pressure pulsations data at some important locations in the volute and the leakage path, and transient Multiple Reference Frame (MRF) modelling is utilized to conduct the cavitation analysis. It is observed that for the case under study, the pressure pulsations pattern and the cavitation behaviour varies significantly due to the inclusion of leakage paths in the analysis.

Analysis of vibration signals produced by the cavitation in centrifugal pumps using the Power Spectrum and Continuous Wavelet Transform

The cavitation phenomena cause noise, vibration and instability in centrifugal pumps. Furthermore, the cavitation usually generates wear and material erosion of the rotor blades which decreases the hydraulic performance and the pump life. In this work, it will be studied the vibration components produced by the centrifugal pumps cavitation using the signal processing and statistical analysis. For this purpose, the vibration signals were measured in three directions, x, y and z using accelerometers near to the rolling bearing of the pump with and without cavitation. In this way, an analysis of the power spectrum was applied in order to identify which direction would be more sensitive to the presence of the cavitation in the pump. Subsequently, the Continuous Wavelet Transform was applied to the vibration signals in the time domain for analyzing the vibration components caused by the cavitation. The results proved that this methodology can serve as a tool of analysis and identification of vibration components caused by the cavitation in centrifugal pumps.

Variations of Performance and Pressure Pulsation During Cavitation in Centrifugal Pumps with Entrained Air

Most of the research on the cavitation with entrained air has focused on the military direction, but it ,about centrifugal pumps, which is relevant to people's livelihood, is still relatively lacking. In order to study the basic law of the development of cavitation inside centrifugal pumps under aeration conditions, a test bench suitable for cavitation experiments with incoming flow containing gas was obtained. Furthermore, a single-stage single-suction 6-blade centrifugal pump was used as the research object to conduct pressure pulsation experiments under cavitation condition when the incoming flow was 1.0% air viod fraction at 2900r/min-50m3/h. The results showed that: After cavitation happened, the greater aeration content will deteriorate the pump's anti-cavitation performance, but the head curve is more gentle in falling down compared to natural cavitation. Hence aeration has a beneficial effect on the performance degradation of the pump under the cavitation condition. At the same time, before the cavitation number drops to the fracture cavitation number of the pump, aeration has improvement in the efficiency of the pump in different degrees , especially in the situation with the ventilated rate of 1.0%. The main frequency of pressure pulsation at the inlet and outlet of the test pump after aeration is dominated by the blade frequency. The shaft frequency signal at the outlet gradually decreases with the cavitation number lessened. Moreover the amplitude of the blade frequency grows slightly with the reduction of the cavitation number. But it tends to soar when the cavitation number is less than the fracture cavitation number.

Centrifugal Pump Cavitation Erosion and Its Countermeasures

Centrifugal Pump Cavitation Erosion and Its Countermeasures

Is there a "safe" suction pressure in the venous line of extracorporeal circulation system?

Successes of extracorporeal life support increased the use of centrifugal pumps. However, reports of hemolysis call for caution in using these pumps, especially in neonatology and in pediatric intensive care. Cavitation can be a cause of blood damage. The aim of our study was to obtain information about the cavitation conditions and to provide the safest operating range of centrifugal pumps. A series of tests were undertaken to determine the points at which pump performance decreases 3% and gas bubbles start to appear downstream of the pump. Two pumps were tested; pump R with a closed impeller and pump S with a semiopen impeller. The performance tests demonstrated that pump S has an optimal region narrower than pump R and it is shifted to the higher flows. When the pump performance started to decrease, the inlet pressure varies but close to −150 mmHg in the test with low gas content and higher than −100 mmHg in the tests with increased gas content. The same trend was observed at the points of development of massive gas emboli. Importantly, small packages of bubbles downstream of the pump were registered at relatively high inlet pressures. The gaseous cavitation in centrifugal pumps is a phenomenon that appears with decreasing inlet pump pressures. There are a few ways to increase inlet pump pressures: (1) positioning the pump as low as possible in relation to the patient; (2) selecting appropriate sized venous cannulas and their careful positioning; and (3) controlling patient’s volume status.

An adaptive Industrial Internet of things (IIOts) based technology for prediction and control of cavitation in centrifugal pumps

Cavitation is the phenomenon whereby the air bubbles implode on the impeller due to insufficient suction pressure at the inlet section thereby causing noise, vibration and in a long-term, corrosion of the impeller blades. However, the current devices and technologies used to address cavitation are inefficient. The use of intelligence gathered from telemetry data produced via cloud computing and IOT is becoming prevalent in the prediction and control of cavitation. The objective of this research is to simulate cavitation in industrial pumps using the IOT technology. Cavitation was simulated in both good and faulty centrifugal pumps using the Fast Fourier Transform Algorithm (FFT) integrated to an Arduino microcontroller. Subsequently, configuration of the sensors required to capture the data, ingestion into the cloud and numerical analysis of the data were executed using the Artificial Neural Network (ANN) as the machine learning algorithm. The results showed graphs as well as the tables of non-cavitation and cavitation patterns when the ball valve was fully opened (90º) respectively, at the suction of the centrifugal pump. For the non-cavitation patterns, the voltages lie from 0.5-0.75v and for the cavitation patterns, the voltages lie from 0.76-0.95v. Using this technique, the detection, analysis and accurate prediction of cavitation were established.

A Review of Experimental Detection Methods of Cavitation in Centrifugal Pumps and Inducers

An important flow mechanism that affects the performance and efficiency of centrifugal pumps is cavitation. In recent years, many researchers have studied the physics of cavitation in order to create appropriate detection methodologies. The aim of this paper is to review the various experimental tools that have been developed so far and enlighten the area of future research on the field of cavitation monitoring. According to the results, cavitation detection is possible, but a large number of sensors have to be used and permanent changes in the machine need to be made for increasing the results reliability. Therefore, future research steps are proposed towards the development of reliable, accurate but also easy to install and low cost experimental set ups.

Numerical study of cavitation in centrifugal pump conveying different liquid materials

Abstract A numerical study on cavitation in the centrifugal pump during the transportation of pure water and diesel is carried out. An improved cavitation model based on the Zwart–Gerber–Belamri Model is employed in the simulation. A Cash–Karp fourth–fifth order Runge–Kutta method was used to solve the original Rayleigh-Plesset equation to get the numerical solution. The effects from viscosity and surface tension on bubbles’ expansion and compression are taken into account in the improved model instead of the traditional simplification in which the bubble radius is just a function of pressure and density. The coefficients got by fitting the numerical solution are added to the constant pre-multiplier of the Zwart-Gerber-Belrami cavitation model and finally enhance the model. The vapor volume fraction was predicted to be larger in diesel compared to water. The distribution of pressure in diesel is more homogenous than that in pure water.

Prediction of flow blockages and impending cavitation in centrifugal pumps using Support Vector Machine (SVM) algorithms based on vibration measurements

The present work concentrates on the vibration based condition monitoring and fault diagnosis of centrifugal pumps. Two types of interrelated faults, i.e. flow blockages in the inlet pipe and impending bubble formation in the pump are considered. For the fault diagnosis and classification in the pump at varied speeds, a machine learning algorithm called, the Support Vector Machine (SVM) is utilized. Centrifugal pump is mounted on the Machine Fault Simulator (MFS™) set-up for the purpose of experimentation. Two tri-axial accelerometers, one on the pump casing and another on the bearing housing, are used to extract the vibration signals. Vibration signatures are taken at different flow blockages (0%, 16.7%, 33.3%, 50% and 66.6% of blockage) and at the start of bubble formation (inception of cavitation). Several statistical features are extracted from time domain vibration signal and fed to the SVM algorithm for training and testing. Standard deviation alone proves to be better than any other feature in this domain, and for this application. SVM parameters, including γ and C are optimally chosen. The ratio of training and testing data is also optimized. Binary fault classification offered better prediction accuracy for all blockage conditions over the multi-class fault classification. Moderately higher prediction accuracy in the multi-class fault classification (different level of blockages) has been found, when the training and the testing is done at higher rotational speeds. It has also been observed that the impending bubble formation could be very accurately predicted at higher rotational speeds.

An active method to control cavitation in a centrifugal pump by obstacles

In this article, we proposed an active method of obstacle attached on the blade to control cavitation in centrifugal pump. The modified shear stress transport k-ω model with a local density correct...

Cavitation in centrifugal pump with rotating walls of axial inlet device

The article deals with the analysis of cavitation processes in the flowing part of the double entry centrifugal pump. The analysis is conducted using numerical modeling of the centrifugal pump operating process in the software environment ANSYS CFX. Two models of the axial inlet device is researched. It is shaped by a cylindrical section and diffuser section in front of the impeller, which includes fairing. The walls of the axial inlet device rotate with the same speed as the pump rotor. The numerical experiment is conducted under the condition of the flow rate change and absolute pressure at the inlet. The analysis shows that the pump has the average statistical cavitation performance. The occurrence of the cavitation in the axial inlet device is after narrowing the cross-section of flow channel and at the beginning of the diffuser section. Additional sudden expansion at the outlet of the axial inlet diffuser section does not affect the cavitation characteristics of the impeller, however, improves cavitation characteristics of the axial inlet device. For considered geometric parameters of the axial inlet device the cavitation in the impeller begins earlier than in the axial inlet device. That is, the considered design of the axial inlet device will not be subjected to destruction at the ensuring operation without cavitation in the impeller.

Optimization of centrifugal pump cavitation performance based on CFD

In order to further improve the cavitation performance of a centrifugal pump, slots on impeller blade near inlet were studied and six groups of hydraulic model were designed. Base on cavitating flow feature inside a centrifugal pump, bubble growth and implosion are calculated from the Rayleigh-Plesset equation which describes the dynamic behavior of spherical bubble and RNG κ-ϵ model was employed to simulate and analyze the internal two-phase flow of the model pump under the same conditions. The simulation results show that slots on blade near inlet could improve the cavitation performance and cavitation performance improvement of the second group was more obvious. Under the same conditions, the pressure on the back of blade near inlet was higher than the pressure on the back of unmodified blade near inlet, and energy distribution in the flow channel between the two blades was more uniform with a small change of head.

Vibration Characteristics Induced by Cavitation in a Centrifugal Pump with Slope Volute

Cavitation is one of the instability sources in centrifugal pump, which would cause some unexpected results. The goal of this paper was to analyze the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute. And special attention was paid to low frequency signals, which were often filtered in the reported researches. Results show that at noncavitation condition, vibration level is closely related to flow structure interior pump. At partial flow rates, especially low flow rates, vibration level increases rapidly with the onset of rotating stall. At cavitation condition, it is proved that cavitation process has a significant impact on low frequency signals. With cavitation number decreasing, vibration level first rises to a local maximum, then it drops to a local minimum, and finally it rises again. At different flow rates, vibration trends in variable frequency bands differ obviously. Critical point inferred from vibration level is much larger than that from 3% head drop, which indicates that cavitation occurs much earlier than that reflected in head curve. Also, it is noted that high frequency signals almost increase simultaneously with cavitation occurring, which can be used to detect cavitation in centrifugal pump.

Modelling of flow with cavitation in centrifugal pump

The paper concerns flow modelling in centrifugal pump with special consideration of cavitation phenomena. Cavitation occurs when local pressure drops below the saturation pressure according to the temperature of the flow. Vapour bubbles are created and then they flow through the areas with higher pressure. The bubbles collapse rapidly generating pressure wave, noise and vibration. Working under cavitation condition is very dangerous to a pump and can significantly shorten its lifetime. The investigated centrifugal pump consists of three two-flow rotors and stators working on a single shaft. The modelling process started with grid independence study. When the grid was chosen, the pump performance curve was obtained using the single phase fluid model. Next, using the results from pump performance curve calculations, the cavitation characteristic was obtained. The constant capacity was held when the pressure at the inlet was reduced. The two – phase model was used with Zwart cavitation model. The results indicate that the pump work in safe range of parameters. The analysis also provides wide range of information about the areas of vapour appearance. The most endangered regions are leading edges of rotor. When pressure at the inlet drops to about one third of pressure that calculations started from the cavitation cloud appears in whole rotor. The intense of vapour bubbles creation is greater near the shroud of the pump, rather than near the hub. As cavitation is strongly unsteady phenomena, the transient calculations were performed to check if the results are close to those obtained using the steady state type. The differences are not significant.

English

Centrifugal pumps are a most commonly used in different fields like industries, agriculture and domestic applications. Computational Fluid Dynamics is most commonly used tool for simulation and analysis. 3-D numerical CFD tool is used for simulation of the flow field characteristics inside the turbo machinery. CFD simulation makes it possible to visualize the flow condition inside centrifugal pump. The present paper describes the head, power, efficiency and to evaluate the pump performance using the ANSYS CFX-14, a computational fluid dynamics simulation tool. These simulations of centrifugal pumps are strongly related to cavitation flow phenomena, which may occur in either the rotating runner-impeller or the stationary parts of the centrifugal pumps. The numerical simulation can be used to detect the cavitation in centrifugal pump and to get safe range of operating at different flow rate and rotating speed

Incipient Detection of Cavitation Phenomenon in Centrifugal Pumps

The aim of this paper is to present a computer-based tool to aid in the process of detecting cavitation in centrifugal pumps. The method proposed in this paper, namely, the Load Torque Signature Analysis, employs electrical signals from the motor to estimate the torque developed by the pump and determines the occurrence and intensity of the phenomenon through its frequency spectrum information.

Acoustic Based Cavitation Detection of Centrifugal Pump by Neural Network

A neural network simulator built for prediction of cavitation in centrifugal pump is discussed. A back propagation learning algorithm and a multi-layer network have been employed. The layers are constituted of nonlinear neurons and an input vector normalization scheme has been built into the simulator. This paper concentrates on a procedure for prediction of cavitation using acoustic signals and multi-layer perceptron neural network. Acoustic signals carry rich information about the condition of the system. Fast Fourier transform, proved itself a fast and strong technique for frequency analysis in the steady conditions and constant speed such as this work. Two classes were defined, namely i) healthy ii) cavitation. The extracted features were employed to feed the ANN classifier for cavitation detection. In developing the ANN models, different ANN architectures, each having different numbers of neurons in hidden layer, were evaluated. The optimal model was selected after several evaluations based on minimizing of mean square error (MSE) and correct classification rate (CCR). The network structure with 11 neurons in hidden layer and 11-11-2 structure is the best network. The mean square error achieved during training is 8.7204*10 -8 . Correct classification rate in system was 98.57%.

Experimental investigation and numerical analysis of unsteady attached sheet cavitating flows in a centrifugal pump

This paper studies the attached sheet cavitation in centrifugal pumps. A pump casted from Perspex is used as the test subject. The cavitation bubbles were observed in the entrance of the impeller and the drops of the head coefficients were measured under different operating conditions. A Filter-Based Model (FBM), derived from the RNG k – ɛ model, and a modified Zwart model are adopted in the numerical predictions of the unsteady cavitating flows in the pump. The simulations are carried out and the results are compared with experimental results for 3 different flow coefficients, from 0.077 to 0.114. Under four operating conditions, qualitative comparisons are made between experimental and numerical cavitation patterns, as visualized by a high-speed camera and described as isosurfaces of the vapour volume fraction αv = 0.1. It is shown that the simulation can truly represent the development of the attached sheet cavitation in the impeller. At the same time, the curves for the drops of the head coefficients obtained from experiments and calculations are also quantitatively compared, which shows that the decline of the head coefficients at every flow coefficient is correctly captured, and the prediction accuracy is high. In addition, the detailed analysis is made on the vapour volume fraction contours on the plane of span is 0.5 and the loading distributions around the blade section at the midspan. It is shown that the FBM model and the modified Zwart model are effective for the numerical simulation of the cavitating flow in centrifugal pumps. The analysis results can also be used as the basis for the further research of the attached sheet cavitation and the improvement of centrifugal pumps.

원심펌프의 캐비테이션에 대한 수치해석

As the operating range of centrifugal pump is expanded recently, the various suction conditions are demanded . The most important problem in the suction conditions is cavitation. In this study, to analyze the characteristics for such the cavitation, first the validity of the numerical analysis was certified through comparison with the experimental result of performance curve according to flow rate for the industrial centrifugal pump. At this time, the transient numerical analysis for the full type model of the centrifugal pump was performed to get more accurate results. The numerical analysis on the cavitation of centrifugal pump were conducted on the two-phase flow as the same method of one-phased flow.

Cavitating flow investigation inside centrifugal impellers for a condensate pump

In order to investigate the effect of blade inlet angle on centrifugal pump cavitation performance, numerical simulation of cavitating turbulent flow is conducted for a condensate pump with different impellers based on SST k−ω turbulence model and a mixture cavitation model. The results indicate that for a condensate pump having meridional section with larger area at blade leading edge compared with conventional pumps, the reverse flows inside the blade-to-blade channels are not negligible. It is noted that large incidence at blade leading edge is helpful to improve the cavitation performance for the pump. The possible reason may be the growth of cavities inside the impeller has less influence on the flow in the channel between two neighboring blades. Further, uniform incidence angle along the blade leading edge is preferable for the improvement of cavitation performance.