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The energy loss inside a centrifugal pump has a significant effect on its performance characteristics. Based on the structural characteristics of the humpback pectoral fin, a new tongue was designed to improve the performance of the centrifugal pump. The influence of three sinusoidal tubercle volute tongues (STVT) and one original volute tongue (OVT) on energy dissipation using the enstrophy analysis method was investigated. To accomplish this, the pressure fluctuations and performances of four centrifugal pumps were analyzed. The results indicate that enstrophy is primarily distributed at the impeller outlet and near the tongue. The total enstrophy of the profiles of STVT was smaller than that of the profiles of OVT. This difference was more obvious near the tongue. The reductions in the total enstrophy of the pumps were 8% (STVT−1), 8.2% (STVT−2), and 9% (STVT−3). The pressure fluctuations of the STVT profiles also decreased to different degrees. The average pressure fluctuations at the monitoring points decreased by 20.6% (STVT−1), 21.7% (STVT−2), and 23.3% (STVT−3). The performances of the bionic retrofit pumps increased by 1.5% (STVT−1), 2% (STVT−2), and 2.45% (STVT−3) under the design flow rate. This study guides the structural optimization of pumps. [ABSTRACT FROM AUTHOR]

Although the energy change field in the centrifugal pump has been investigated under quasi-steady conditions (QSC), equivalent information is not yet known during the rapid starting period (RSP). A centrifugal pump loop system is constructed to investigate the energy change field in the centrifugal pump during RSP. The RSP is selected as a linear rotational speed from 0 rev/min to 2900 rev/min (design rotational speed) and a constant valve opening of 0.569. Results show that the flow rate lags behind the pump head value with the linear increase in rotational speed. The large values of partial derivations of mechanical energy in normal and tangential components are mainly concentrated at the impeller outlet, whose position is insensitive to rotational speed. The region of dominant energy loss is negatively correlated with rotational speed, and an opposite phenomenon is observed in the region of dominant energy increase. With the rotational speed increasing, the mean energy gradient function in the pump impeller and pump volute gradually increases, and the slope of the former is less than that of the latter. After reaching the design rotational speed, the energy change field gradually approaches that under quasi-steady conditions. [ABSTRACT FROM AUTHOR]

The current study numerically investigates the flow instability under several part-load conditions in a centrifugal pump with a straight inlet pipe to explore the underlying relationship between a positive slope phenomenon and internal flow using a partially averaged Navier–Stokes model. The model was validated by comparing the hydraulic performance and averaged flow in the impeller between the numerical results and experimental data of a tested pump. The internal flows in pumps have been intensively investigated based on Batchelor vortex family, Rayleigh–Taylor criterion, entropy generation rate, and energy equation to analyze the flow instability from different aspects. The simulation results using partially averaged Navier–Stokes model are acceptable due to the good agreement with the experimental data for the tested pump. No matter the geometry of the inlet pipe, the pre-swirling flows in the inlet pipe are in the convective instability region. Under the part-load condition of φ = 0.5 φ bep, the axial vorticity coefficient is affected by the geometry of the inlet pipe. However, under the part-load condition with rotating stall, e.g. φ = 0.78 φ bep, the flow in the inlet pipe is affected by the unstable flow in the pump impeller. For the pump with a straight inlet pipe, the vortex inside the blade-to-blade passage is in a stable state according to Rayleigh–Taylor criterion under the condition of φ = 0.5 φ bep. However, the vortex in the blade-to-blade passage is in an unstable state due to centrifugal instability under those operation conditions with rotating stall cells in the impeller, and the dominant oscillations are dependent on the propagation of rotating stall cells. Finally, head loss analysis based on energy equations elucidates that turbulent kinetic energy production term is predominant in the head loss in pump impeller. The present results are helpful for better understanding of the unstable flows and positive slope phenomenon for centrifugal pumps. [ABSTRACT FROM AUTHOR]

The objective of this study is to analyse the quantitative relationship between the local Euler head distribution and the internal flow in a centrifugal impeller and provide guidance for the design specifications of inverse design methods. The local Euler head at the inlet is mainly affected by the clockwise vortex on the blade suction side. At the outlet, it is affected by the relative motion of clockwise and counterclockwise vortexes. The effect of the two types of vortexes on the local Euler head makes the pump head almost constant under deep part-load conditions, proving that the impeller has an effective diameter. The mean local Euler head distribution along the impeller passage is closely interrelated with the flow pattern. The position in which the mean local Euler head increases fastest coincides with the radial position of the clockwise vortex centre. The position of its maximum value is consistent with the radial position of the end of the clockwise vortex. The position of its maximum value moves towards the inlet as the flow rate decreases, confirming the impeller has an extreme impeller diameter. The inflection points of the mean local Euler head ratio curve correspond to the appearance of vortex structures. • The distribution rules of local Euler head are investigated by PIV experiments. • The local Euler head distribution is related to the internal flow patterns. • The local Euler head distribution determines the hydraulic performance of pump. • The mean local Euler head ratio curve can reflect the position of vortex. [ABSTRACT FROM AUTHOR]

An experimental investigation based on particle image velocimetry (PIV) technology was used to measure the internal flow in a low-specific-speed centrifugal pump impeller. The main purpose of this paper is to quantitatively study the influence of the internal flow patterns on the hydraulic performance and energy conversion characteristics through this visualization experiment. The PIV measuring region covers full impeller channels. Phase-averaged relative velocity distributions were calculated to investigate the evolution of internal flow pattern with the decrease in flow rate. The effect of flow pattern on pump head has also been investigated qualitatively. Results show that a clockwise vortex on the blade suction side and a counterclockwise vortex on the blade pressure side will appear in different impeller passages with the decrease in flow rate. The counterclockwise vortex moves towards the impeller outlet, but the clockwise vortex moves to the opposite side. Detailed studies show that the motion of the vortices considerably impacts pump hydraulic performance. The counterclockwise vortex will increase energy losses, whereas the clockwise vortex positively affects the pump head. Moreover, the blade loading distribution and its variation with flow rate are proposed to analyse the energy conversion mechanism in the centrifugal pump impeller. • A PIV experimental system which could measure full impeller channels was built. • The evolution of an impeller internal flow pattern was analysed. • The effect of flow pattern on a pump hydraulic performance was investigated. • The effect of flow pattern on a pump energy transfer characteristics was analysed. [ABSTRACT FROM AUTHOR]

In this study, a modified partially averaged Navier–Stokes (MPANS) model is applied to investigate the flow instability characteristics in a low specific centrifugal pump. In MPANS model, the unresolved-to-total ratio of kinetic energy f k is determined according to the local grid size and turbulence length scale. The numerical results by MPANS model are compared with that simulated by SST k-ω model and the available experimental data. It is noted that MPANS model shows better performance for investigating the unstable flow in the current pump under part-load operation conditions. The time-averaged internal flow and flow incidence in the pump impeller depicts that with the decreasing flow coefficient, flow separation develops in the impeller. Owing to the strong separation flow as well as vortex evolution, incidence angle is large and varies remarkably at the entrance of blade-to-blade passage in the pump impeller. The evolution dynamics of rotating stall is further discussed in detail based on vorticity transport equation. During the evolution of rotating stall, the vortex stretching term has an important effect on vorticity transport under the part-load conditions. The analysis of the pressure fluctuations excited by periodic evolution of rotating stall shows that the rotating stall cell propagates along the rotational direction, and identifies the rotating stall frequency (f stall), which is much lower than the rotational frequency of the impeller, f n (f stall = 8.76% f n). Finally, two-dimensional Lagrangian coherent structure (LCS) is used to reveal the separation flow in blade-to-blade passages of the pump by monitoring the trajectory of the particles. Both LCS and vortex structure by λ 2 can clearly demonstrates the passage blockage and flow separation under the part-load operation conditions, depicting that the separation flow occurs at blade suction side and develops from the leading edge to the main passage in the impeller. [ABSTRACT FROM AUTHOR]

Unstable or flat head-flow curves can cause problems in parallel operations or in flat systems. Despite the considerable efforts that have been devoted to the study of head-flow curve instability in single-stage centrifugal pumps with volute casing, the cause of such phenomenon is not sufficiently understood. In this study, we investigated the variation of hydraulic losses based on the relationship between velocity distribution and entropy generation fields. Steady-state and unsteady simulations were obtained for a pump with an impeller outlet diameter of 174 mm, and the unsteady results are more coincided with the experiments. Results showed that the losses mainly focused on the blade suction surface and volute tongue, as well as in the region of the volute discharge at high flow rates. The entropy generation rate of the pump casing at partial flow rates changed slightly with a decrease in flow rate, whereas the energy losses in the impeller increased steeply when the flow rate dropped to 35 m3/h (the design flow rate was 60 m3/h). The losses in the impeller were mainly concentrated on the region near the inlet and outlet and were lower near the impeller inlet than near the impeller outlet, where a counter-rotating vortex was developed near the blade trailing edge. The vortex caused a drastic increase in the entropy generation rate on the pressure surface and in the flow passage. Such increase was the main cause of the head-flow characteristic instability. [ABSTRACT FROM AUTHOR]

The objective of this study is to explore a method that can describe the loss distribution trend of flow field directly through the PIV experiment. Three main concepts, namely Local pressure head increase (H pr), Local velocity head increase (H vr) and Local pump degree of reaction (λ), are proposed to characterise the energy distribution in the impeller. Results show the distribution of H pr is affected mainly by the inlet flow field of the impeller passage, while the maximum value region of H vr along the radial direction is located at the downstream of the unstable region on the blade suction side and in the center of the unstable region in the pressure side. These distributions are due to the local increase of absolute velocity (C) caused by vortex motion. The large vortex is dispersed along the suction side of the impeller blade, causing the energy losses to become more obvious than in the pressure side. The developing trends of the pump efficiency and passage-averaged λ as the flow rate increased are consistent. Consequently, the distribution of loss intensity in the flow field can be quantitatively reflected by λ. • Three concepts are proposed to characterise the energy distribution in the impeller. • The distribution of H pr is determined by the flow pattern at impeller entrance. • The distribution of H vr is affected by the vortexes in the impeller passage. • Losses caused by vortices along the blade suction side is more obvious than that on the pressure side. • The distribution of loss intensity is quantitatively reflected by the λ. [ABSTRACT FROM AUTHOR]

The purpose of the study is to investigate the flow structure and energy dissipation mechanism within centrifugal pump impellers. The velocity fields at the mid-sections of the flow passages of 4- and 5-blade impellers were measured under various flow rates using the Time-resolved Particle Image Velocimetry (TR-PIV) technique; the proper orthogonal decomposition (POD) analysis was performed to extract flow structures with different scales; the dissipation rate was estimated using the large-eddy PIV method; the correlation between turbulent kinetic energy (TKE) and dissipation rate was measured using the cross-correlation analysis. The findings are as follows: impeller with more uniform and stable flow, the scale and energy contribution of large-scale structures in lower order modes are smaller, leading to higher impeller efficiency; large-scale structures identified in the low-order modes correspond to locations of high TKE and dissipation areas; the high velocity gradients within the impeller passage and the interactions between large-scale flow structures encourage the breakup of large-scale turbulent structures into dissipative-scale structures; the correlation between TKE and dissipation rate reflects the extent to which large-scale flow structures within the impeller passage break up into dissipative scales. • The fluid in the impeller passages will be more uniform and stable the greater the fluid's capacity to follow the blades. • The "jet-wake" region is the primary dissipation zone in the impeller passages. • High-velocity gradients and the interaction of large-scale structures enhance the decomposition of turbulent structures. • The correlation of TKE and dissipation rate reflects the degree of large-scale structures break up into dissipation scales. [ABSTRACT FROM AUTHOR]

By studying the flow-field structures, turbulent kinetic energy (TKE), flow angle distribution, and pump performance of centrifugal pump impellers under different flow conditions, the influence mechanisms of the blade leading-edge geometry (elliptical, arc-shaped and circular) on energy loss in centrifugal pump impellers were studied. At large flow rate condition, the negative velocity gradient at the inlet caused by the squeezing effect is the main factor causing energy loss. The blunter the blade inlet shape, the greater the squeezing effect, and the closer the negative velocity gradient region is to the inlet, resulting in greater energy loss. For the low flow rate conditions, the large-scale vortex structures at the channel outlet are the flow structures that contributed most to the energy loss. The effect of the blade leading-edge geometry on the fluid increases gradually as it moves from inlet to outlet, and the sharper the blade inlet shape, the slower the fluid deviates from the blade in its subsequent development, suppressing the early formation of large-scale vortex structures, making their strength more dispersed at the channel outlet, and closer to the suction side, a lower vortex intensity, resulting in smaller energy loss of the impeller. • The influence mechanism of the impeller blade leading-edge geometry on centrifugal pump performance was revealed. • The squeezing effect at the channel inlet at large flow rates was the main cause of low pump efficiency. • The energy loss at low flow rates is mostly driven by the vortex structure at the outlet of the flow channel. • The influence of blade leading edge geometry on flow field gradually increases as the fluid moves from inlet to outlet. • The stronger the outlet vortex structure, the more severe the "jet-wake" phenomenon. [ABSTRACT FROM AUTHOR]

Pressure pulsations may cause high-amplitude vibrations during the process of a centrifugal pump. The trailing edge shape of the blade has a critical influence on the pump's pressure fluctuation and hydraulic characterization. In this paper, inspired by the humpback whale flipper, the authors research the impact of applying the sinusoidal tubercles to the blade suction side of the trailing edge. Numerical calculation and experiments are carried out to investigate the impact of the trailing edge shape on the pressure pulsations and performance of a centrifugal pump with low specific speed. Two designed impellers are tested, one is a sinusoidal tubercle trailing edge (STTE) impeller and the other is the original trailing edge (OTE) prototype. The detailed study indicates that the sinusoidal tubercle trailing edge (STTE) reduces pressure pulsation and enhances hydraulic performance. In the volute tongue region, the pressure pulsation amplitudes of STTE at fBPF decrease significantly. The STTE impeller also effectively changes the vortex structure and intensity in the blade trailing edge area. This investigation will be of great benefit to the optimal design of pumps. [ABSTRACT FROM AUTHOR]