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.

Effect of Trailing-Edge Modification of a Mixed-Flow Pump

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

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.

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

With the increasing adoption of renewable energy sources globally, hydropower contributes significantly to energy generation through various schemes ranging from big to small-scale plants. In small-scale hydropower plants, the preference for reverse-operated pumps (known as pump as turbines or PATs) over small-scale hydroturbines has increased. However, apart from the associated economic advantages, PATs, like any other hydraulic machinery, are not free from common problems such as cavitation. Cavitation is a phenomenon in which air bubbles are formed within the fluid medium due to substantial local pressure drop and their eventual collapse causes material erosion and degrades the overall machine efficiency. Several studies have focused on PAT conventional operating mode, while its reverse mode just begun to gain research interest. Nevertheless, cavitation remains a common problem in PATs at various hydro-sites. Therefore, to analyze PAT cavitation performance and highlight the differences between its two operating modes in terms of their development mechanisms, this article presents a thorough review of PAT cavitation dynamics and influencing parameters, as well as the future research directions. It is found that PAT reverse mode is more prone to cavitation, but more damages would occur in the conventional mode. Nevertheless, modifying the PAT geometric design parameters can considerably improve its cavitation performance. However, this approach has not been sufficiently investigated for PAT reverse operating mode and hence requires further research. Note that the terms “PAT conventional mode,” “PAT pumping mode,” and “pump” are equally used throughout this paper. • Studies on cavitation performance in hydraulic pumps as turbines (PATs) are reviewed. • Both pump and turbine modes are considered in the review. • PATs are found to have gained importance due to their applicability in remote areas. • PAT reverse mode operations require high heads and flows; prone to cavitation. • Geometric design modification is widely used for PAT cavitation performance improvement. 

Pump as turbine cavitation performance for both conventional and reverse operating modes: A review

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.

Numerical and experimental investigation on the development of cavitation in a centrifugal pump

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. 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.

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

This paper aims to provide a possible link of noise and vibration readings to the condition of pump operation. For this purpose, the dimensions of a radial flow pump impeller were determined using a flow rate of 0.031 m3/s, total head of 25 m and speed of 1500 rpm as the design data. Performance tests were conducted for this test pump with/without cavitation for different speeds. Noise and vibration signals were obtained and the individual critical frequency/critical frequency band were identified. From the results, it was concluded that the noise and vibration signature from the pump have a relationship with the flow inside the pump.

Study of Noise and Vibration Signal for a Radial Flow Pump During Performance Test

The aim of this paper was to present a method to identify the extent of cavitation in pump using the photographic records of cavitation tests conducted on pumps having three different leading edge profiles of the vane. Based on the extent of cavitation in pump, the impeller with circular leading edge was found to be better in operation, followed by plain and ellipse2 leading edge impellers. The technique adapted here was useful to correlate the extent of cavitation with the head drop in pump.

S. Christopher

Papers

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

Study of Noise and Vibration Signal for a Radial Flow Pump During Performance Test

Flow Visualization Study on Radial Flow Pump under Cavitating Condition