The physical mechanism of flow unsteadiness is one of the key problems in cavitating flow. Significant efforts have been exerted to explain the cavitation-vortex interaction mechanism. As well, the process of kinetic energy transport during the evolution of unsteady cavitating flow must be elucidated. In this work, 2D calculations of cavitating flow around a NACA66 hydrofoil were performed based on the open source software OpenFOAM. The modified shear stress transport k-ω turbulence model, which considers curvature and turbulent eddy viscosity corrections, was employed to close the governing equations. The Schnerr-Sauer cavitation model was adopted to capture the cavitation phase change process. Numerical results showed reasonable consistency with the results of the experiments conducted by Leroux et al. (2004). The results showed that cavitation promotes turbulence intensity and flow unsteadiness around the hydrofoil. During the attached sheet cavity growth stage, high-value regions of turbulent kinetic energy are located substantially at the interface of the cavity, particularly at the rear portion of the cavity region. During the cloud cavity shed-off stage, the cavity begins to break off and the maximum value of turbulent kinetic energy is observed inside the shed cavity. Finally, the influence of cavitation on the turbulence intensity is illustrated using the turbulent kinetic energy transport equation, which shows that the pressure diffusion and turbulent transport terms dominate as cavitation occurs. In addition, cavitation promotes turbulence production and increases dissipation with fluid viscosity and flow unsteadiness. The viscous transport term only acts in the cavitation shedding stage under large-scale vortex shedding. Overall, these findings are of considerable interest in engineering applications.

Calculation of cavitation evolution and associated turbulent kinetic energy transport around a NACA66 hydrofoil

Vibration signatures have been studied for monitoring the condition of centrifugal pumps by many researchers, however, there is limited published information on the application of vibration analysis to incipient pump cavitation. The paper will review the state of the art in the field and develops an effective signal processing approach based on envelope spectral analysis to close this gap. A purpose-built test rig was employed for recording vibration signals from a centrifugal pump at a wide range of operating conditions. The collected data was then processed using time domain and frequency domain analysis methods. The study has shown that the vibration energy concentrated mainly in the frequency range between 8-15 kHz. At the flow rates less than 300(l/min), i.e. in design flow rate range, the vibration amplitudes remain constant and does not show a notable change by the flow rate increase. However, a notable increase in the vibration level is evident when the flow rate exceeds 300 (l/min). Analysis the result of filtered vibration signatures has revealed that vibration signal parameters: peak value, root mean squared (RMS), crest factor along with vibration spectrum allow development of cavitation (for the flow rates higher than 300 (l/min)) to be diagnosed reliably. However, conventional signal processing methods may not produce a clear separation of the incipient cavitation from the healthy baseline. Therefore, envelope spectrum analysis has been carried out on recorded vibration signatures to detect the onset of cavitation from the baseline and satisfactory results have been perceived.

https://jafmonline.net/JournalArchive/download?file_ID=50352&issue_ID=1003

An Experimental Study on Vibration Signatures for Detecting Incipient Cavitation in Centrifugal Pumps Based on Envelope Spectrum Analysis

This review mainly summarizes the latest developments in the internal flow field and external characteristics of centrifugal pumps. In particular, the latest findings of centrifugal pumps focused on turbulence and cavitation models, flow visualization methods, and fault detection based on noise and vibration. The external characteristics, cavitation, and vibration of the centrifugal pump were extensively discussed. In addition, advanced multi-objective optimization methods for improving impeller’s efficiency and reducing net positive suction head (NPSH) were briefed. Although some progress was made in this field, there remain many unsolved problems, such as monitoring and modeling of cavitation, rotational stall phenomenon, and discrepancies between simulation and measurement. In the future, researchers are encouraged to employ multi-dimensional flow visualization technologies and high-performance computing facilities to advance existing understandings on these issues and create new research directions.

Internal flow structure, fault detection, and performance optimization of centrifugal pumps

Flow-induced noise is a significant concern for the design and operation of centrifugal pumps. The negative impacts of flow-induced noise on operating stability, human health and the environment have been shown in many cases. This paper presents a comprehensive review of the flow-induced noise study for centrifugal pumps to synthesize the current study status. First, the generation mechanism and propagation route of flow-induced noise are discussed. Then, three kinds of study methodologies, including the theoretical study of hydrodynamic noise, numerical simulation and experimental measurement study, are summarized. Subsequently, the application of the three study methodologies to the analysis of the distribution characteristics of flow-induced noise is analyzed from aspects of the noise source identification and comparison, the frequency response analysis, the directivity characteristics of sound field and the noise changing characteristics under various operating conditions. After that, the analysis of the noise optimization design of centrifugal pumps is summarized. Finally, based on previous study results, this paper puts forward the unsolved problems and implications for future study. In conclusion, the information collected in this review paper could guide further study of the flow-induced noise of centrifugal pumps.

/pdf/a-review-of-the-flow-induced-noise-study-for-centrifugal-5bwus0qrs9.pdf

A Review of the Flow-Induced Noise Study for Centrifugal Pumps

In fluid transportation industries, long straight transition pipelines upstream of flowmeters are required to eliminate the influence of disturbed inflow on flow metering accuracy. To ensure an accurate flow measurement, the straight transition pipeline, which is often lengthy, can be shortened, particularly when the installation space is limited. However, the characteristics of disturbed flow (mainly characterized by vortex inflow) evolving along the straight transition pipeline to affect the metrological performance must be investigated for optimizing the pipeline length. The objective of this study was to investigate the metrological performance of a swirl flowmeter affected by the vortex inflow caused by flow regulation with a sleeve valve. The effect of a straight transition pipeline length upstream of a swirl flowmeter on the evolving characteristics of the vortex inflow was investigated experimentally and by conducting a numerical simulation under flow regulation parameters, including valve openings and flow velocities. The flow coefficients for different straight transition pipeline lengths were investigated to verify the flow simulation. The periodic pressure variation in the swirl flowmeter was monitored and its corresponding characteristic frequency was analyzed. It was found that the metrological characteristics of the swirl flowmeter were extremely affected by a smaller valve opening, which can be improved by lengthening the straight transition pipeline. By analyzing the velocity vector and vorticity in the internal flow field, the vortex inflow was found to be vulnerable to dissipation within a longer straight transition pipeline. The average vorticity at the cross-section of the entrance to the swirl flowmeter was adopted to evaluate the inflow vortex intensity. Additionally, a power curve model was established to assess the critical characteristic frequency determined by the maximum unaffected inflow vorticity for different straight transition pipeline lengths. This study can provide helpful insights to the metrological performance and pipeline arrangement in the field of fluid transportation engineering.

Metrological performance investigation of swirl flowmeter affected by vortex inflow

Cavitation is a challenging flow abnormality that leads to undesirable effects on the energy performance of the centrifugal pump and the reliable operation of the pump system. The onset and mechanism of a phenomenon that results in unsteady cavitation must be realised to ensure a reliable operation of pumps under the cavitation state. This study focuses on cavitation instability at normal flow rate, at which point the unsteady cavitation occurs as the available net positive suction head (NPSHa) falls below 5.61 m for the researched pump. An ameliorative algorithm–united algorithm for cavitation vibration analysis is proposed on the basis of short time Fourier transform (STFT) and Wigner–Ville distribution (WVD). The STFT–WVD method is then tested using vibration data measured from the centrifugal pump. The relationship between vibration and suction performance indicates that the inception and development of cavitation can be effectively detected by the distribution and intensity of the united algorithm at the testing points. Intermediate frequency components at approximately 6 kHz fluctuate initially with the development of cavitation. A time–frequency characteristic is found to be conducive to monitoring the cavitation performance of centrifugal pumps.

An experimental study on the cavitation vibration characteristics of a centrifugal pump at normal flow rate

The invention discloses a centrifugal pump cavitation monitoring device which comprises a plurality of cavitation monitoring units, an amplifier, an A/D converter, a microprocessor and an output unit. The cavitation monitoring units are ultrasonic transducers; and each ultrasonic transducer comprises a transmitting terminal with the power smaller than 10w, and a receiving terminal matched with the transmitting terminal, wherein the receiving terminal is used for receiving ultrasonic signals from the transmitting terminal and converting the received ultrasonic signals into sonic analog signals. The amplifier is used for receiving and amplifying the sonic analog signals. The A/D converter is used for converting the amplified primary analog signals into sonic digital signals. The microprocessor is used for receiving and judging the sonic digital signals from the A/D converter, and outputting corresponding feedback signals. The output unit is controlled by the microprocessor and displays the received feedback signals. By adoption of the centrifugal pump cavitation monitoring device, cavitation inception can be better predicted, the whole cavitation process can be monitored in real time, the device can automatically adapt to signal variation caused by factors including environment temperatures, installing differences and the like, and misdeclaration is avoided.

Centrifugal pump cavitation monitoring device

The utility model discloses a centrifugal pump cavitation monitoring devices, include: a plurality of cavitation monitor cell, this cavitation monitor cell are ultrasonic transducer, this ultrasonic transducer including power be less than 10w the transmitting terminal, and with transmitting terminal matched with receiving terminal, this receiving terminal is used for receiving the ultrasonic signal that comes from the transmitting terminal direction, just turns into sound wave analog signal with received ultrasonic signal, the amplifier for receive and enlarge sound wave analog signal, the AD converter for elementary analog signal transition after will enlargeing becomes sound wave data signal, microprocessor for it comes from the sound wave data signal of AD converter and exports corresponding feedback signal to receive the judgement, output unit is controlled by microprocessor and shows received feedback signal. The utility model discloses the better prediction cavitation inception of ability carries out whole real -time supervision to the cavitation process, can automatic adapt to the signal change that factors such as ambient temperature, installation difference lead to, avoids reporting by mistake.

Feng Guangwei

Papers

An experimental study on the cavitation vibration characteristics of a centrifugal pump at normal flow rate

Centrifugal pump cavitation monitoring device

Centrifugal pump cavitation monitoring devices