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Journal ArticleDOI

Identification of Critical Net Positive Suction Head From Noise and Vibration in a Radial Flow Pump for Different Leading Edge Profiles of the Vane

01 Dec 2013-Journal of Fluids Engineering-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 135, Iss: 12, pp 121301

TL;DR: In this paper, experimental investigations concerning cavitation in radial flow pump for three different leading edge profiles of the vane were carried out in an open circuit system and the results revealed that the noise and vibration were better predictors of inception and development of cavitation.

AbstractExperimental investigations concerning cavitation in radial flow pump for three different leading edge profiles of the vane were carried out in an open circuit system. The operating condition of the radial flow pump under cavitating case was understood by measurement of noise and vibration along with the pump parameters for various speeds and flow rates. The outcome of the experimental results revealed that the noise and vibration were better predictors of inception and development of cavitation. Further observation inferred from critical net positive suction head (NPSH) curve of 3% head drop and critical NPSH value of noise and vibration are presented.

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Citations
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Journal ArticleDOI
Dazhuan Wu1, Peng Yan1, Xin Chen1, Peng Wu1, Shuai Yang1 
TL;DR: In this article, the effects of TE modification on the performance and internal flow of a mixed-flow pump are investigated through computational fluid dynamics (CFD) analysis, and the results show that TE modification significantly improves pump efficiency in the high flow rate region by more than 10%.
Abstract: Modern pumps are designed to guarantee a sufficiently large operating range or to satisfy the performance requirements relative to more than one operating point. This study applies trailing-edge (TE) modification method based on TE rounding in the suction surface to widen the operating range of a mixed-flow pump. The effects of TE modification on the performance and internal flow of the mixed-flow pump are investigated through computational fluid dynamics (CFD) analysis. Local Euler head distribution is introduced to reveal the pattern of energy growth along the blade-aligned (BA) streamwise location. A pump model with TE modification is tested, and numerical results agree well with experimental data. The results show that TE modification significantly improves pump efficiency in the high flow rate region by more than 10%. The best pattern of normalized local Euler head distribution (NLEHD) is a convex curve of nearly constant growth rate. The overall heads are also improved, and the flow near the exit of the impeller exhibits better uniformity. This finding demonstrates that a small change in the TE of the impeller can influence flow structure in most areas of impeller channels and that the local Euler head distribution is closely related to pump efficiency. TE modification can effectively improve the performance of the mixed-flow pump with high flow rate.

27 citations

Journal ArticleDOI
TL;DR: In this article, the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute was analyzed and it was proved that cavitation has a significant impact on low frequency signals.
Abstract: 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.

27 citations


Cites methods from "Identification of Critical Net Posi..."

  • ...Christopher and Kumaraswamy [6] used noise and vibration signals to identify critical net positive suction head in a radial flow pump....

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Journal ArticleDOI
TL;DR: In this article, a closed loop was established to investigate the pump cavitation phenomenon, the statistical parameters for PDF (Probability Density Function), Variance and RMS (Root Mean Square) were used to analyze the relationship between the cavitation performance and the suction pressure signals during the development of cavitation.
Abstract: Centrifugal pumps are often used in operating conditions where they can be susceptible to premature failure. The cavitation phenomenon is a common fault in centrifugal pumps and is associated with undesired effects. Among the numerous cavitation detection methods, the measurement of suction pressure fluctuation is one of the most used methods to detect or diagnose the degree of cavitation in a centrifugal pump. In this paper, a closed loop was established to investigate the pump cavitation phenomenon, the statistical parameters for PDF (Probability Density Function), Variance and RMS (Root Mean Square) were used to analyze the relationship between the cavitation performance and the suction pressure signals during the development of cavitation. It is found that the statistical parameters used in this research are able to capture critical cavitation condition and cavitation breakdown condition, whereas difficult for the detection of incipient cavitation in the pump. At part-load conditions, the pressure fluctuations at the impeller inlet show more complexity than the best efficiency point (BEP). Amplitude of PDF values of suction pressure increased steeply when the flow rate dropped to 40 m3/h (the design flow rate was 60 m3/h). One possible reason is that the flow structure in the impeller channel promotes an increase of the cavitation intensity when the flow rate is reduced to a certain degree. This shows that it is necessary to find the relationship between the cavitation instabilities and flow instabilities when centrifugal pumps operate under part-load flow rates.

18 citations

Journal ArticleDOI
TL;DR: 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) as discussed by the authors.
Abstract: 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.

17 citations

Journal ArticleDOI
Jiaxing Lu1, Shouqi Yuan1, Yin Luo1, Jianping Yuan1, Banglun Zhou1, Sun Hui1 
01 Jun 2016
TL;DR: The research reveals the occurrence and development of cavitation in the centrifugal pump which has been confirmed through experiments and numerical simulation, and the typical frequency of pump inlet pressure pulsation could be regarded as around 30 Hz in the severe cavitation conditions.
Abstract: Concerning the development of cavitation in a centrifugal pump, numerical simulations and experimental investigations have been carried out in a closed hydraulic test rig. The internal flow characteristics and pressure pulsation at pump inlet and outlet have been analyzed during the process of cavitation development. The results of the research reveal the occurrence and development of cavitation in the centrifugal pump which has been confirmed through experiments and numerical simulation. The degree of pump cavitation could be monitored through pump inlet and outlet pressure pulsation. Compared with pump outlet pressure pulsation, pump inlet pressure pulsation is more sensitive to the change of cavitation. According to the results of the investigation, the typical frequency of pump inlet pressure pulsation could be regarded as around 30 Hz in the severe cavitation conditions. Meanwhile, the pump head dropped by 0.77% from noncavitation conditions which could be regarded as a symbol of incipient cavitation.

17 citations


Cites background or methods from "Identification of Critical Net Posi..."

  • ...The most common method used to identify the presence of cavitation was based on the observations of the drop in head and 3% head drop from noncavitation was regarded as the critical cavitation.(1) In addition, other techniques for pump fault diagnosis including cavitation monitoring were well established....

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  • ...Cavitation is one of the most important problems which should be considered in designing and operating a pump, especially when the rotating speed of pump increases.(1) Severe damage could be caused on the surface of flow channels and stability of system could be affected by cavitation....

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References
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Book
01 Oct 2013
TL;DR: In this paper, the fundamental physical processes involved in bubble dynamics and the phenomenon of cavitation are described and explained, and a review of the free streamline methods used to treat separated cavity flows with large attached cavities is provided.
Abstract: This book describes and explains the fundamental physical processes involved in bubble dynamics and the phenomenon of cavitation. It is intended as a combination of a reference book for those scientists and engineers who work with cavitation or bubble dynamics and as a monograph for advanced students interested in some of the basic problems associated with this category of multiphase flows. A basic knowledge of fluid flow and heat transfer is assumed but otherwise the analytical methods presented are developed from basic principles. The book begins with a chapter on nucleation and describes both the theory and observations of nucleation in flowing and non-flowing systems. The following three chapters provide a systematic treatment of the dynamics of the growth, collapse or oscillation of individual bubbles in otherwise quiescent liquids. Chapter 4 summarizes the state of knowledge of the motion of bubbles in liquids. Chapter 5 describes some of the phenomena which occur in homogeneous bubbly flows with particular emphasis on cloud cavitation and this is followed by a chapter summarizing some of the experiemntal observations of cavitating flows. The last chapter provides a review of the free streamline methods used to treat separated cavity flows with large attached cavities.

2,835 citations

Book
01 Jan 1976
TL;DR: The basic mechanisms by which acoustic noise is generated, transmitted by structures, and radiated into the underwater environment are explained.
Abstract: : The basic mechanisms by which acoustic noise is generated, transmitted by structures, and radiated into the underwater environment are explained. Dominant mechanisms which have practical application are emphasized.

510 citations

Journal ArticleDOI
TL;DR: In this article, the growth and collapse of cavitation bubbles generated by axisymmetric headforms were investigated using a surface electrode probe and the results were compared with relevant theoretical and emperical predictions.
Abstract: Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles, almost all of which were quasi-spherical caps moving close to the headform surface, were studied photographically. Although the growth patterns for the two headforms were similar, the collapse mechanisms were quite different. These differences were related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse were analyzed and found to correlate with the maximum volume of the bubble for each headform. Numerical solutions of the Rayleigh-Plesset equation were generated for the same flows and compared with the experimental data. The experiments revealed that for smaller bubbles the impulse-volume relationship is determinate, but for larger bubbles the impulse becomes more uncertain. The theoretical impulse was at least a factor of two greater than the measured impulse, and the impulse-volume relationship was related to the details of the collapse mechanism. Acoustic emission of individual cavitation events was spectrally analyzed and the results were compared with relevant theoretical and emperical predictions. Finally, the cavitation nuclei flux was measured and compared to the cavitation event rate and the bubble maximum size distribution through the use of a simple model. The nuclei number distribution was found to vary substantially with tunnel operating conditions, and changes in the nuclei number distribution significantly influenced the cavitation event rate and bubble maximum size distribution. The model estimated the cavitation event rate but failed to predict the bubble maximum size distribution. With the above theoretical and experimental results, the cavitation rate and resulting noise production may be estimated from a knowledge of the non-cavitating flow and the free stream nuclei number distribution.

134 citations

Journal ArticleDOI
TL;DR: In this article, the authors have shown that there is a discrete frequency tone within the audible noise spectra, at 147 Hz or BPF/2, which is strongly dependent on the cavitation process and its development.
Abstract: One of the sources of instability in a centrifugal pump is cavitation phenomenon. Cavitation within a centrifugal pump can cause more undesirable effects, such as deterioration of the hydraulic performance (drop in head-capacity and efficiency curves), damage of the pump by pitting and erosion and structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore it must, by all means, be prevented. To prevent the onset of the cavitation, we have to know the beginning of cavitation phenomenon in the pump. To detect the beginning of the cavitation process, the emitted noise can also be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, at 147 Hz or BPF/2, which is strongly dependent on the cavitation process and its development. Therefore, the discrete frequency tone at 147 Hz was separated from the noise spectra of cavitating pumps and then used to detect the incipient of cavitation and its development. It was also used to determine the net positive suction head required or the critical value, as well as to prevent cavitation in the pump by means of initiating an alarm, shutdown or control signal via an electrical control system.

126 citations