Best Efficiency Point Research Articles

Influence of Inlet Vane and Wrap Angles on Cavitation Behavior of a Centrifugal Pump

This comprehensive study focuses on the relationship between the inlet vane and wrap angles of a centrifugal pump impeller and its cavitation behavior. The objective is to propose a new design for cavitation performance enhancement of the pump by reducing the required net positive suction head (NPSHR). To render a detailed study, the variations of the mentioned angles were examined both at hub and shroud. A three-dimensional two-phase parametric computational fluid dynamics (CFD) study was conducted and variations of inlet blade and wrap angles at hub and shroud were investigated separately. After validating the experimental results with the pump model, the pump parameterization process was carried out, and pump geometry was re-defined with its geometrical properties. The characteristic curves of the parameterized pump and pump model were in agreement with each other. Numerical cavitation tests were performed and the NPSHR values of each design were calculated for four different operating conditions. Results showed that cavitation performance increase was achieved with angle variations at the best efficiency point (BEP) but, this situation led the pump to operate exposed to cavitation at high flows (HF) for some designs. Therefore, the design with the best cavitation performance increased at BEP and HF was proposed as a new design. During numerical simulations, shear stress transport (SST) turbulence model and Rayleigh–Plesset equation were used.

Effect of Blade Number on the Performance of a Centrifugal Pump Using Commercial Tool ANYS 91.2

Computational fluid dynamics (CFD) is frequently used in centrifugal pump design. The characteristics of the flow fields around turbomachinery can be simulated using tools for numerical computational fluid dynamics in three dimensions. Numerical simulation, which also provides significant information for the hydraulic design of the centrifugal pump, can be used to visualize the internal flow condition of a centrifugal pump. The purpose of this study was to examine the effect of blade number on the hydraulic performance curve using a commercial instrument. ANSYS 91.2. code commercial.The geometric model of the pump was built using CF turbo, and the flow domain was meshed using the commercial programme ICEM. The results demonstrated that an increase in the number of blades significantly improved the hydraulic performance of the centrifugal pump’s head. The findings also revealed that the area of the low-pressure zone at the blade’s input suction grew and that the static pressure distribution homogeneity in the diffusion section was significantly better than that in the spiral section. The design flow of 35 m3 per hour is where the best efficiency point (BEP) is located. At Z = 6 and Z = 7, the head values were 51.58 m and 53.13 m, respectively, while the efficiency values were 50.32% and 53.35%. The comparison of the H-Q curve for estimated head discharge indicates that all impeller efficiency curves share the same fundamental tendency.

Numerical and Theoretical Investigation of the Gap Flow in Centrifugal Fans for Design and Off-Design Conditions

Abstract Industrial turbomachines, such as fans and blowers for drying, venting, cooling or conveying tasks, are often used in industrial applications and frequently are large energy consumers. Thus, there is a need for further optimization and efficiency increase. For fans and blowers, gaps between moving parts are unavoidable due to manufacturing tolerances and possible thermal expansion. In this work, the radial gap and axial overlap between the inlet nozzle and the impeller and its impact on the performance characteristics have been investigated, because detailed knowledge of the losses due to the gap is important for the design of more efficient fans. The presented analysis was performed with the Navier–Stokes-solver ansyscfx. After a detailed grid study, the quantitative effect of the gaps on the performance of the centrifugal fan has been investigated by a variation of the radial gap and axial overlap. It was found, that at the best efficiency point (BEP) the efficiency drops between 1 and 6% depending on the gap width and at partial load it might drop fast also depending on the gap width, up to 50–60%. At overload the drop in efficiency is smaller than at partial load, dropping between 1 and 10%, depending on the gap width and the flowrate. In addition, a metamodel based on a dimensional and regression analysis was developed for partial and overload to predict the gap flowrate without additional computational fluid dynamics (CFD) simulations. The prediction accuracy between the CFD results and the dimensional analysis based metamodel is about 5–10%.

Particle image velocimetry in a centrifugal pump: Details of the fluid flow at different operation conditions

Centrifugal pumps are present in the daily life of human beings. They are essential to several industrial processes that transport single- and multi-phase flows with the presence of water, gases, and emulsions, for example. When pumping low-viscous liquids, the flow behavior in impellers and diffusers may affect the centrifugal pump performance. For these flows, complex structures promote instabilities and inefficiencies that may represent a waste of energetic and financial resources. In this context, this paper aims at characterizing single-phase water flows in one complete stage of a centrifugal pump to improve our understanding of the relationship between flow behavior and pump performance. For that, a transparent pump prototype was designed, manufactured and installed in a test facility, and experiments using particle image velocimetry (PIV) were conducted at different conditions. The acquired images were then processed to obtain instantaneous flow fields, from which the flow characteristics were determined. Our results indicate that the flow morphology depends on the rotational speed of the impeller and water flow rate: (i) the flow is uniform when the pump works at the best efficiency point (BEP), with streamlines aligned with the blades, and low vorticity and turbulence in the impeller; (ii) the velocity field becomes complex as the pump begins to operate at off-design conditions, away from BEP. In this case, velocity fluctuations and energy losses due to turbulence increase to higher numbers. Those results bring new insights into the problem, helping validate numerical simulations, propose mathematical models, and improve the design of new impellers.

Influence Mechanism of Trimming Impeller Diameter in a Centrifugal Pump by Computational Fluid Dynamics Investigation

Abstract Trimming the impeller diameter of a centrifugal pump is the easiest and most economical way to adjust its efficient operating range based on its original performance. Three impellers obtained by trimming the diameter are investigated. Energy performance, internal flow field, and entropy production analysis have been discussed in different cases. The results show that trimming the impeller diameter causes a great change in the energy performance of centrifugal pumps. The turbulent kinetic energy (TKE) distribution and entropy production also change significantly. The best efficiency point (BEP) shifts to low flowrate with trimming impeller diameter. The BEP shift rate was 6.67% and 20% for trimming amounts of 5.15% and 10.29%, respectively. As the impeller diameter decreases, the backflow phenomenon that occurs at the diffuser inlet at low flowrate improves. The ratio of mechanical energy to kinetic energy and pressure energy is not constant for pumps with different impeller diameters. The energy performance changes are mainly caused by flow changes inside the impeller, chamber, and diffuser. The results could be referred to as the design and selection of centrifugal pumps.

Pumps-as-Turbines’ (PaTs) performance prediction improvement using evolutionary artificial neural networks

Energy production from clean sources is mandatory to reduce pollutant emissions. Among different options for hidden hydropower potential exploitation, Pump-as-Turbine (PaT) represents a viable solution in pico- and micro-hydropower applications for its flexibility and low-cost. Pumps are widely available in the global market in terms of both sizes and spare parts. To date, there are several PaTs’ performance prediction models in the literature, but very few of them use optimization algorithms and only for specific and limited prediction goals. The present work proposes evolutionary Artificial Neural Networks (ANNs) based on JADE, which is a typology of differential evolution algorithm, to forecast Best Efficiency Point (BEP) and performance curves of a PaT starting from the pump operational data. In this model, JADE is employed as optimizer of basic ANNs to upgrade parameter values of the learning rate, weights, and biases. The accuracy of the proposed model is evaluated through experimental data available from the literature and compared to a basic ANN and two versions of the differential evolution algorithm. Results are also validated with experiments on a PaT showing that the proposed method can achieve an average R2-value of 0.97, which is 5% higher than the one obtained with a basic ANN.

Software for Monitoring the In-Service Efficiency of Hydraulic Pumps

The present paper introduces the creation of an algorithm and the software used to determine the energetic performance and monitor the efficiency of hydraulic pumps working in various industrial applications, such as water supply systems, water treatment processes, and irrigation systems, particularly in the cases where there is no permanent monitoring. Our field investigations and the surveyed literature show that the only parameter that is neither monitored nor computed is the efficiency of the pumps. The software implementation allows for determining the in-service efficiency of the pumps and comparing it to the value associated with the best efficiency point (BEP). The solution is user-friendly and can be easily installed on any computer or smartphone. The software has been applied and tested in the Hydraulic Machines Laboratory at the “Politehnica” University Timişoara and at the AQUATIM S.A. regional water supply company. The software module monitors the operating regimes of the pumps and supports the deployment of predictive maintenance and servicing.

Numerical study on effect of operating condition and solid concentration on hydro-abrasive erosion of high head Francis turbine

The powerplants in the Himalayan region are generally subjected to hydro-abrasive erosion. The deterioration of components due to erosion causes reduction in performance, changes the fluid flow pattern and even the breakdown of the turbine. In the present work, the Bhilangana-III powerplant Francis turbine is considered a reference turbine for numerical investigation using the computational fluid dynamics (CFD) tool. The study presented an evaluation of hydro-abrasive erosion of high head Francis turbine for the different operating conditions and sediment concentrations. The modified Grant and Tabakoff erosion model is used for the erosion rate calculation. To investigate the effect of various operating conditions, the study is conducted at part load, best efficiency point (BEP) and high load. Also, to examine the impact of suspended sediment on the erosion of turbine components, the solid concentration varies from 500, 1200, 2000, 3000 and 4000 ppm. The observed erosion pattern is similar at all operating conditions for the stay vane, guide vane and runner, but the density of erosion is different. The observed deterioration density due to erosion is higher for part and full load than in the BEP condition. The guide vanes and runner vanes are highly susceptible to erosion due to higher absolute velocity and relative velocity at guide vane and runner vane, respectively. The observed erosion rate variation is qualitatively in-line with the on-field turbine erosion condition. It is also found that the increase in erosion rate with the sediment concentration is almost linear but more than 90% and 79% higher for the runner than stay vane and guide vane, respectively.

Proper Orthogonal Decomposition Of The Turbulent Flow In An Impeller Of A Centrifugal Pump

The flow field in the channels of a centrifugal pump impeller contains eddy motions of a wide range of time and length scales and identifying coherent structures and their dynamic behavior is not a trivial task. Thus, modal decomposition techniques have been used in order to improve the knowledge on turbulence and coherent structures. In this work, the proper orthogonal decomposition (POD) method is employed to identify the occurrence and development of the dominant unsteady flow structures in a centrifugal pump impeller. For this, experiments using a time-resolved PIV system for different operating conditions of pump impeller were carried out. The results show that in the range of the pump's best efficiency point (BEP) there is no significant flow separation. As the flow rate starts to decrease from the BEP flow rate, unstable flow phenomenon begin to appear and develop in the impeller. The POD analysis reveals that for low flow rates, the flow is dominated by large-scale structures with higher energy, while for the BEP and high flow rates, the flow is dominated by smaller-scale structures.

An Operative Framework for the Optimal Selection of Centrifugal Pumps As Turbines (PATs) in Water Distribution Networks (WDNs)

The current significant increase in energy consumption has resulted in the need to develop and implement effective approaches for defining alternative and sustainable solutions to couple primary resources with supporting methods of energy generation. In the field of effective water distribution network (WDN) management, the suitability of combining pressure regulation with small-scale hydropower generation is attracting even more interest, given that it can possibly reduce water leakages, as well as produce attractive rates of renewable energy. Specifically, pumps as turbines (PATs) are widely considered a viable solution because they combine hydraulic benefits with affordable investment and management costs. Nevertheless, despite several approaches available in the literature for the optimal selection and management of PATs, choosing the most suitable device to be installed in the network is still a challenge, especially when electrical regulation is arranged to modulate the PAT rotational speed and optimize the produced energy. Several approaches in the literature provide interesting solutions for assessing the effectiveness of electrical regulation when a PAT is installed within a water network. However, most of them require specific knowledge of the PAT mechanical features or huge computational efforts and do not support swift PAT selection. To overcome this lack of tools, in this work, an operative framework for the preliminary assessment of the main features (the head drop and the produced power at the best efficiency point (BEP), the impeller diameter and the rotational speed) of a PAT is proposed, aimed at both maximizing the daily produced energy and performing challenging economic selection. Then, it is assessed by estimations of the corresponding payback period (PP) and the net present value (NPV).

Modal Decomposition of the Precessing Vortex Core in a Hydro Turbine Model

We report on the experimental study of a precessing vortex core (PVC) in an air model of a Francis turbine. The focus is placed on the modal decomposition of the PVC that occurs in the draft tube of the model turbine for a range of operation conditions. The turbulent flow fluctuations in the draft tube are assessed using stereo particle image velocimetry (PIV) measurements. Proper orthogonal decomposition (POD) is applied to the antisymmetric and symmetric components of the velocity fields to distinguish the dynamics of the azimuthal instabilities. The pressure pulsations induced by the PVC are measured by four pressure sensors mounted on the wall of the hydro turbine draft tube. Spatial Fourier decomposition is applied to the signals of the pressure sensors to identify the contributions of azimuthal modes, m=1 and m=2, to the total pressure fluctuations. The analysis based on velocity and pressure data shows similar results regarding the identification of the PVC. The contribution of the m=2 mode to the overall turbulent kinetic energy is significant for the part load regimes, where the flow rates are twice as low as at the best efficiency point (BEP). It is also shown that this mode is not the higher harmonic of the PVC, suggesting that it is driven by a different instability. Finally, we show a linear fit of the saturation amplitudes of the m=1 and m=2 oscillations to determine the critical bifurcation points of these modes. This yields critical swirl numbers of Scr=0.47 and 0.61, respectively. The fact that the PVC dynamics in hydro turbines are driven by two individual instabilities is relevant for the development of tailored active flow control of the PVC.

Challenges in the Numerical Analysis of Centrifugal Pumps¨: Energetic, Cavitation and Dynamic Characteristics

Pumps are energetic devices that are present in a wide range of industries. Their installed power varies from a few tens of watts up to hundreds of megawatts. As the energy consumption is connected with global warming and climate change, the development of pumps that have good characteristics is very important. Theoretical and experimental methods have long been utilized in the development of pumps, but recently much research has been carried out with the help of Computational Fluid Dynamics (CFD) analysis. Certain numerical analyses can be of high quality and accurate, but special operational phenomena still occur, where special attention is required when performing analysis. This category includes operating regimes outside the Best Efficiency Point (BEP), the formation of inlet recirculation, cavitation, and the influence of wall roughness on all the above characteristics. The current paper presents the main problems that developers face when numerically analyzing the above-mentioned special operating regimes. Both numerical and experimental results are considered.

Analytical Implementation and Prediction of Hydraulic Characteristics for a Francis Turbine Runner Operated at BEP

The extensive investigation and profound understanding of the hydraulic characteristics of the Francis turbine are crucial to ensure a safe and stable hydraulic system. Especially, predicting the runner’s hydraulic efficiency with high fidelity is mandatory at the early stage of a new hydropower project. For these purposes, the current technologies mainly include experimentation and CFD simulation. Both methods generally have the demerits of a long period, massive investment and high requirements for supercomputers. In this work, an analytical solution is therefore introduced in order to predict the internal flow field and working performance of the runner while the Francis turbine operates at the best efficiency point (BEP). This approach, based on differential-geometry theory and the kinematics of ideal fluid, discretizes the blade channel by several spatial streamlines. Then, the dynamic parameters of these streamlines are determined in a curved-surface coordinate system, including velocity components, flow angles, Eulerian energy and pressure differences across the blade. Additionally, velocity components are converted from the spatial-velocity triangle to the Cartesian coordinate system, and the absolute-velocity vectors as well as the streamlines are subsequently derived. A validation of this approach is then presented. The analytical solution of hydraulic efficiency shows good agreement with the experimental value and simulation result. Additionally, the distributions of pressure differences over the blade, velocity and Eulerian energy are well predicted with respect to the CFD results. Finally, the discrepancy and distribution of the dynamic parameters are discussed.

Optimization of Centrifugal Pump Based on Impeller-Volute Interactions

The design and off-design performance of a centrifugal pump largely depends on geomechanical parameters. This study aims at enhancing the performance by optimizing three geomechanical parameters of impeller-volute interactions. The present optimization is carried out using the Taguchi method combined with a numerical approach. A comparison between the base and optimized pumps is presented under the design and off-design conditions based on numerical and experimental analyses. The numerical results reveal that, compared to the base pump, the optimized pump shows the improved performance through uniform pressure distribution in the impeller, the reduced low-pressure region towards a blade’s leading edge, and the stable total pressure at the impeller-volute interaction zone. The experimental results suggest that the optimized pump covers a wider range of operation, and its best efficiency point (BEP) is 10%, 5%, and 12% higher in flow rate, head, and efficiency, as compared to the base one.

Coherent structures decomposition of the flow field in Francis turbine runner under different working conditions

The dynamic mode decomposition (DMD) method is adopted to do flow field decomposition in the runner of Francis turbine. The coherent structures corresponding to main frequency components in runner passage under different working conditions are extracted, and the relative error of the reconstructed flow field and the predicted flow field are analyzed. The results show that the DMD method successfully decomposes the position and shape of the coherent structure corresponding to a single frequency in the unsteady flow, and its temporal and spatial evolution. Under part load (PL), best efficiency point (BEP), and high load (HL) working conditions, the coherent structures with high frequency induced by rotor-stator interaction (RSI) are the most stable, which located at the entrance of the runner passage. The low-frequency coherent structures mostly appear inside the runner passage, which is mainly caused by the short blade wake and flow separation under off-design conditions. The averaged flow field contains the most flow energy (larger than 90%), and unsteady coherent structures consume or transport less energy. The flow field in runner passage predicted by the DMD method is consistent with the computational flow field, which relative error is stable at 10−2. The study of coherent structures in runner passage of Francis turbine is beneficial to achieve a better design of runner and more stable operation of power plants.

Performance Prediction and Geometry Optimization for Application of Pump as Turbine: A Review

Pump as Turbine (PAT) is a technically and economically effective technology to utilize small/mini/micro/pico hydropower, especially in rural areas. There are two main subjects that influence the selection and application of PAT. On the one hand, manufacturers of pumps will not provide their characteristics under the turbine mode, which requires performance prediction methods. On the other hand, PAT efficiency is always slightly lower than that of pump, which requires further geometry optimization. This literature review summarized published research studies related to performance prediction and geometry optimization, aimed at guiding for selection and optimization of PAT. Currently, there exist four categories of performance prediction methods, namely, using BEP (Best Efficiency Point), using specific speed, loss modeling, and polynomial fitting. The using BEP and loss modeling methods are based on theoretical analysis, while using specific speed and polynomial fitting methods require statistical fitting. The prediction errors of published methods are within ±10% mostly. For geometry optimization, investigations mainly focus on impeller diameter and blade geometry. The influence of impeller trimming, blade rounding, blade wrap angle, blade profile, blade number, blade trailing edge position, and guide vane number has been studied. Among published methods, the blade rounding and forward-curved impellers are the most effective and feasible techniques.

Effect of Impeller Size on the Performance of a Single Blade Pump

Changing the impeller diameter is a frequently used method for adjusting pump performance parameters. In the case of conventional multi-blade impellers, this is done by reducing the diameter on the machine tool to the prescribed shape. The other dimensions of the pump (diffuser, inlet) remain unchanged. This method is called trimming. The article deals with the diameter reduction and subsequent modification of the performance parameters of a single blade pump. These pumps are characterized by certain specific features. First of all, it is an unsymmetrical impeller that must be both statically and dynamically balanced. This plays an essential role in the whole modification process. Research results obtained on a pump with an impeller diameter of 138 mm are presented. The change in diameter was monitored on a total of 3 impellers. Experiments were carried out in the laboratory of hydraulic machinery. The results were verified by CFD calculations. Research background: The article concerns the modification of impellers of single blade pumps. The effects of diameter modifications on multi-blade pumps are currently known. However, these have symmetrical impellers and can therefore be changed without restriction. For asymmetric (single blade) impellers, the problem is more complex as additional mass must be added to provide static and dynamic balance. Purpose of the article: The aim is to determine the nature of the change in performance parameters when the output diameter is changed. The results of the research can be applied in the prediction of the change in the operating point and the creation of tombstone charts. Methods: Two kinds of methods were used in the research: experiment and CFD calculation. A total of 4 impeller sizes were investigated. Findings & Value added: The results of the paper can be divided into two areas. In the experimental area, a device was designed to measure the characteristics of single blade pumps. Four impellers were manufactured and tested. In the area of CFD calculations, simulations of the hydraulic parameters around the best efficiency point (BEP) were performed. The calculation results were verified by experiment. The nature of the change of the BEP when the diameter of the impeller changes up to 87.9 % was found.

Optimization of the centrifugal slurry pump through the splitter blades position

Optimal transfer of two-phase solid-liquid flow (slurry flow) has long been a major industrial challenge. Slurry pumps are among the most common types of centrifugal pumps used to deal with this transfer issue. The approach of improving slurry pumps and consequently increasing the efficiency of a flow transmission system requires overcoming the effects of slurry flow such as the reduction in head, efficiency, and wear. This study attempts to investigate the changes in the pump head by modifying the slip factor distribution in the impeller channel. For this purpose, the effect of splitter blades on slip factor distribution to improve the pump head was investigated using numerical simulation tools and validated based on experimental test data. Next, an optimization process was used to determine the characteristics of the splitter (i.e., length, number, and environmental position of the splitter) based on a combination of experimental design methods, surface response, and genetic algorithm. The optimization results indicate that the splitters were in a relative circumferential position of 67.2% to the suction surface of the main blade. Also, the optimal number and length of splitter blades were 6 and 62.8% of the length of the main blades, respectively. Because of adding splitter blades and the reduction in the flow passage, the best efficiency point (BEP) of the slurry pump moved toward lower flow rates. The result of splitter optimization was the increase in pump head from 29.7 m to 31.7 m and the upkeep of efficiency in the initial values.

Centrifugal pump performance enhancement: Effect of splitter blade and optimization

The shape of impeller blades of a centrifugal pump affects the best efficiency point (BEP), and splitter blades improve the pump performance at BEP. In this work, multiple parameters such as number of blades, length of splitter blade, splitter blade angle at hub, and wrap angle were modified to maximize head and minimize input power. The problem was solved by a numerical and experimental approach. Initially, an impeller was designed and tested in a laboratory setup. The same impeller was simulated in a computational fluid dynamics (CFD) solver, checked the accuracy of the CFD results, optimized by an in-house surrogate-based optimization code and finally the optimal designed manufactured and tested again. The mix and match of the splitter blade with the other parameters improved the pump performance i.e. head by 8.2% and overall efficiency by 3%. The improvement was due to the reduction in pressure fluctuations and uniform blade loading throughout the impeller blade span.

An in-depth numerical analysis of transient flow field in a Francis turbine during shutdown

Power production from intermittent renewable energy resources, such as solar and wind, has increased in the past few decades, leading researchers and engineers to establish techniques to preserve a stable electrical grid. Consequently, hydraulic turbines are being used more frequently in transient operating modes to regulate the grid. The present work provides a comprehensive numerical study on the transient flow field of a high-head Francis turbine model throughout the shutdown sequence. The computations were performed using OpenFOAM, utilizing the SST-SAS turbulence model. A Laplacian smoothing scheme is employed to conduct the mesh deformation of the guide vane domain. The time-averaged draft tube velocity field at the steady Best Efficiency Point (BEP) is validated against experimental data. Then different aspects of the transient flow field in the shutdown sequence are carefully assessed and explained for the first time. Short-Time Fourier Transform (STFT) analysis is carried out on the fluctuating part of the static pressure and force signals. High-amplitude low-frequency oscillations, due to the formation of a Rotating Vortex Rope (RVR) were observed during a specific period of the shutdown sequence. Thereafter, at deep part load conditions, the RVR vanishes and, a wide range of stochastic frequencies are identified at minimum load. A signal coherence analysis was accomplished to distinguish the deterministic and stochastic frequencies. The variation of the velocity field in the draft tube is described in detail with the help of velocity triangles. An in-depth explanation of the formation and variation of vortical structures during the whole sequence is presented. The physical mechanism of formation and destruction of the RVR is thoroughly explained.