Radial Centrifugal Pump Research Articles

Determining the Head Characteristics of Radial Centrifugal Pumps under the Impact of Prewhirl

The flow rate is a significant factor in the operation of centrifugal pumps. The characteristic curve of the pump head is frequently employed in the calculation of the flow rate. Nevertheless, this may be subject to alteration because of prewhirl on the suction side of the pump. Calculating the changes in the head’s characteristic curve reveals a change in hydraulic losses. The impact of prewhirl on hydraulic losses is investigated by experimental and numerical analysis of two radial centrifugal pumps. It is demonstrated that the primary changes occur in the pump impeller losses. Relative velocity is a significant factor in this context. Alterations in the pumps’ configurations result in a range of secondary flows and shock losses at the leading edge of the blades. A physical model, derived on the basis of the relative velocity, is used to predict the characteristic curves of radial centrifugal pumps with prewhirl with a high degree of accuracy. The results demonstrate a notable enhancement in comparison to modelling techniques that do not incorporate the fluctuating hydraulic losses.

Physical Modelling of the Set of Performance Curves for Radial Centrifugal Pumps to Determine the Flow Rate

To depict the pump power characteristics of radial centrifugal pumps, a physical model was developed. The model relies on established empirical equations. To parameterize the model for specific pumps, physically interpretable tuning factors were integrated. The tuning factors are identified by using the Levenberg–Marquardt method, which was applied to the characteristic curve at a constant speed. A cross-validation of the physical model highlighted the advantage of representing the set of performance curves with less deviation compared to approximation functions. Calculating the entire set of performance curves requires only one pump characteristic curve at a constant speed. Therefore, only a single measurement is necessary. Furthermore, the physical model can be used to calculate the changes in the set of performance curves due to prewhirl. This increases the accuracy of flow rate calculations when prewhirl occurs.

State of the Art on Two-Phase Non-Miscible Liquid/Gas Flow Transport Analysis in Radial Centrifugal Pumps Part B: Review of Experimental Investigations

This paper aims to summarize the results of several experimental investigations regarding two-phase liquid–gas flows in radial centrifugal pumps. The main objective is to combine the corresponding experimental results and collect the obtained knowledge to provide a better understanding of this configuration. The simultaneous transport of the two phases, the phase segregation, and the regions of safe or critical pump performance were described for a wide variety of pump configurations. This review covers single- and two-phase pumping conditions, performance degradation, pump breakdown, performance hysteresis, different flow regimes, flow regime maps, flow instabilities, and surging. This manuscript also considers the influence of employing different pump configurations on pump performance and flow regimes. This includes comparisons between closed and semi-open impellers, standard and increased tip clearance gaps, and running the pump with and without an inducer. Many of the results discussed have been published in a series of research papers. They were all collected, summarized, and compared systematically in the present review.

Three-dimensional simulations of liquid/gas flow through radial centrifugal pumps and the effect of bubble coalescence and breakup on the formation of gas accumulations

Three-dimensional liquid/gas flow mixture simulations of a centrifugal pump are performed by a hybrid two-phase solver, which comprises a blending between a Volume-of-Fluid-like interface-sharpening scheme and a classical homogeneous mixture two-fluid model. The hybrid solver is combined with a population balance model and a turbulence-scale adaptive simulation approach. The experimentally measured head drop due to adherent gas pockets at elevated gas loadings is well reproduced. By a thorough validation with optical measurement data, it is shown that the transition from dispersed bubbles to coherent gas accumulations as well as the steady core of gas pockets and their unsteady wake could be captured without any parameter fitting of coalescence and breakup kernels. Regions of high coalescence activity correlate with locations of gas accumulations, stabilizing the gas pockets in the impeller region. Bubble breakup, in contrast, was primarily found in the wake of the accumulation zones where the tip leakage flow of the semi-open impeller re-enters the blade passage. The particular hybrid solver architecture, together with the resolution of turbulence scales and bubble populations, facilitates the reproduction of bubble coalescence and breakup effects on the formation of gas pockets in centrifugal pumps.

State of the Art on Two-Phase Non-Miscible Liquid/Gas Flow Transport Analysis in Radial Centrifugal Pumps Part C: CFD Approaches with Emphasis on Improved Models

Predicting pump performance and ensuring operational reliability under two-phase conditions is a major goal of three-dimensional (3D) computational fluid dynamics (CFD) analysis of liquid/gas radial centrifugal pump flows. Hence, 3D CFD methods are increasingly applied to such flows in academia and industry. The CFD analysis of liquid/gas pump flows demands careful selection of sub-models from several fields in CFD, such as two-phase and turbulence modeling, as well as high-quality meshing of complex geometries. This paper presents an overview of current CFD simulation strategies, and recent progress in two-phase modeling is outlined. Particular focus is given to different approaches for dispersed bubbly flow and coherent gas accumulations. For dispersed bubbly flow regions, Euler–Euler Two-Fluid models are discussed, including population balance and bubble interaction models. For coherent gas pocket flow, essentially interface-capturing Volume-of-Fluid methods are applied. A hybrid model is suggested, i.e., a combination of an Euler–Euler Two-Fluid model with interface-capturing properties, predicting bubbly flow regimes as well as regimes with coherent gas pockets. The importance of considering scale-resolving turbulence models for highly-unsteady two-phase flow regions is emphasized.

Analysis of Fluid Flow in a Radial Centrifugal Pump

The paper presents a validation of the results of a numerical model of radial centrifugal pump flow using a PIV (Particle Image Velocimetry) experimental method. For this purpose, a 3D model of the pump was created in Inventor, which was then used to design a numerical flow model in Ansys in the CFX module. The performance characteristics of the same pump were measured on an experimental test circuit, and vector maps of the flow in the suction pipe were obtained using the PIV method. The results of the experiment—vector fields of fluid velocity distribution in a suction pipe—were then compared with the outputs of the numerical Ansys model, namely the streamlines and pressure distributions. This comparison demonstrated that the numerical model is most consistent with reality if the input variables are the pressure in front of the pump and the mass flow behind the pump. In this case, the model can determine the pressure at the pump inlet with a deviation of 1% to 10% and create streamlines in the suction pipe corresponding to the results of PIV measurements.

INLET RECIRCULATION IN PARTLOAD REGIMES – RADIAL PUMP

Partload regimes of all types of centrifugal pumps are strongly and unfavorably affected by an influence of an inlet recirculation. This negative phenomenon usually occurs at pump suctions, when a circumferential velocity component of the fluid flow (derived from a rotational speed of a rotor) is dominant over an axial velocity component. Such physical effect goes hand in hand with a creation of a pump-head instability, a decrease of an overall efficiency, an excessive noise and pressure pulsations and even a possible cavitation formation. The introduced technical problem was tested/examined for a radial centrifugal pump Ns375 with a volute (spiral casing) and an axial intake domain with two potential countermeasures. Both, a physical experiment and transient numerical simulations were employed and compared on crucial levels.

Two-Phase Flow Simulations of Liquid/Gas Transport in Radial Centrifugal Pumps With Special Emphasis on the Transition From Bubbles to Adherent Gas Accumulations

Abstract In recent optical flow experiments on a transparent volute-type radial centrifugal pump, an accumulation of air bubbles to adherent gas pockets within the impeller blade channels was observed. A transition of unsteady bubbly flow toward an attached gas pocket at the blade suction side was found for increasing air loading of the liquid water phase. This steadily attached pocket shows a distinctive unsteady wake. A reproduction of the transition from bubbly to pocket flow in a three-dimensional (3D) flow simulation demands the treatment of dispersed bubbly flow, on the one hand, and of coherent air regions, on the other hand. Therefore, a hybrid flow solver is adopted based on an Euler–Euler two-fluid (EE2F) method for dispersed flows and features volume-of-fluid (VOF) properties when air accumulations form. A scale-adaptive simulation (SAS) turbulence model is utilized to account for highly unsteady flow regions. For the time being, a monodisperse bubble size distribution is assumed for the dispersed part of the flow. For an operation range close to the design point and rising air loading, the flow transition from bubbly to pocket flow is well captured by the hybrid simulation method. Even an alternating pocket flow in between bubbly and pocket flow regime is predicted. The simulation method is still limited by an appropriate choice of a monodisperse bubble diameter. Therefore, the disperse model part of the hybrid flow solver will be coupled with population balance and bubble interaction models in future studies.

Innovation of Pump as Turbine According to Calculation Model for Francis Turbine Design

The effective utilization of micro hydropower sources is often realized through the use of pumps as turbines (PAT). The efficiency of PAT is about the same as that of the original pump. A further increase in efficiency and power output can be achieved by modifying the parts interacting with the flow, especially the impeller and the adjacent volute casing and draft tube. This paper presents a user-friendly calculation model of Francis turbine design and its application for PAT geometry modification. Two different modifications of a single-stage radial centrifugal pump were designed according to this model. The first modification (Turbine) consisted of a complete revision of the impeller geometry, volute casing and draft tube, which corresponded to a conventional Francis turbine. The second modification (Hybrid) was based on altered calculation model and consisted of a modification of only the impeller, which can be used in the original volute casing. Both modifications were tested on hydraulic test circuit at different heads. A comparison of the results of the Hybrid and the Turbine modification with the unmodified machine (Original) proved an increase in overall efficiency by 10%. Both modifications provided a higher flow rate and torque. This resulted in an overall power output increase—an increase of approximately 25% and 40% due to the Turbine and Hybrid modifications, respectively.

Feasibility study for the application of a neural network for operating condition detection of a centrifugal pump

Artificial intelligence (AI) technology is successfully used in many fields. Originally, AI was developed for image and voice recognition and has been spread out on other fields like detecting deceases, behaviour, traffic movement etc. AI is also applied in fluidmachinery, for example in order to detect defaults in pumps, fans, compressors and turbines.This work verifies the feasibility for the application of a neuronal network (NN) for operation point detection of an impeller pump by vibration signals. Once the NN is trained with the vibration signal, it can recognize the operating point by the vibration signal of the impeller pump.In order to test whether the neural network method is feasible, a pump loop system was built up, which contains a radial centrifugal pump with a replaceable impeller. The vibration signal of the impeller pump is taken for different operating points and used for training a NN. In the first step a simple self-programmed NN in C++ is applied in order to find out a convenient NN-topology for operating point detection. The congruence rate of this simple NN method already reaches about 90%. The research results in this paper show that an operating point can be detected by the application of a simple NN. It is carried out how large the influence of the topology of a NN is in regard to the congruence rate (CR). By further application of AI like convolutional layers, batch normalization etc. a better CR seems to be very likely. From this point of view this contribution reports about a starting point of operating point detection of impeller pumps by the application of a NN.

Numerical Characterization of the Performance Curve of a Regenerative Pump-as-Turbine

Abstract Energy companies in the power generation field are continuously searching for green technologies to reduce pollutant emissions. In that context, small hydropower plants represent an attractive solution for distributed electricity generation. Reverse-running centrifugal pumps (also known as “pump-as-turbines,” PaT) are increasingly selected in that field. Amongst the existing type of pumps, drag-type regenerative pumps (RP) can perform similarly to radial centrifugal pumps in terms of head and efficiency for low specific speed values. For a fixed rotational speed, RPs with linear blades work as pumps or turbines only depending on the flow rate. Such peculiarity makes it particularly intriguing to evaluate RPs working characteristics in the turbine operating mode. In this paper, the performance of three regenerative pump-as-turbines (RPaT) is analyzed using computational fluid dynamics (CFD). The numerical approach is validated using experimental data for both an RP (in the pump working region) and a regenerative turbine (RT) (in the turbine working region). Finally, the numerical simulation of a small-scale RP allows for characterizing both the pump and the turbine regions. Results show that for an RPaT it is possible to find a “switch region” where the machine turns from behaving as a pump to behaving as a turbine, the losses not being overcome by the turbine power output. The analysis of the RPaT also shows the inversion of the flow pattern and the constant positioning of the pivot around which the flow creates the typical helical structure that characterizes RPs.

Design and analysis of a radial centrifugal pump for cryogenic helium based application

A centrifugal pump is a rotordynamic machine that has wide spread application in industry. After analytical design, it is important to check the machine performance by some numerical method to be assured of machine performance before manufacturing. In the present study, a centrifugal pump conforming to a specific process requirement for cryogenic helium fluid has been developed in detail. This involves analytical design derivation of the stator and rotor part, computer aided design (CAD) modelling, meshing and detailed computational dynamic analysis (CFD) analysis. In line with analytical prediction, it is seen from simulation results that the designed machine meets the given requirements with an achieved hydraulic efficiency of 88%.

Visualization of two-phase gas-liquid flow in a radial centrifugal pump with a vaned diffuser

The operation of centrifugal pumps with gas-liquid mixtures is a common problem in the oil and gas industry. The main problem is related to the accumulation of gas inside the Electric Submersible Pump (ESP) impellers, which causes degradation of the pump pressure-rise. Literature about global performance parameters of centrifugal pumps operating with gas-liquid flows is limited, and studies focused on understanding the complex flow patterns occurring inside impellers are even scarcer. In this scenario, this work presents an experimental work developed to carry out, simultaneously, head evaluation and high-speed flow visualization in a two-stage centrifugal pump with radial-type impellers and a vaned diffuser. The pump casing and the first stage impeller were replaced by equivalent pieces reproduced with great fidelity using a transparent material in order to allow flow visualization while minimizing the effect of non-original pump parts on performance. Results show flow pattern transitions in the impeller channels when the rotating speed, the inlet gas flow rate and the liquid flow rate are changed, whereas only a single flow pattern was observed in the diffuser for the whole range of tested operating conditions. In addition, increasing the rotating speed causes, in general, a decrease of the bubble diameters inside the impeller, improving the pump's ability to handle higher gas flow rates and ultimately extending the operational window of the pump. This analysis can provide a source of data that can be useful to support theoretical models or to validate numerical simulations.

Vibration and acoustic emission monitoring of a centrifugal pump under cavitating operating conditions

Centrifugal pumps are widely used in industry and cover a significant percentage of the total energy consumption of a power plant. This fact makes the application of efficient maintenance tools to be of crucial importance and obliges researchers and engineers to develop reliable detection methods for special types of malfunction, such as cavitation. Cavitation is a hydrodynamic mechanism that affects the steady and dynamic operation of a pump and is usually responsible for its head and efficiency reduction, as also for premature wear and destruction of the impeller. The stochastic nature of the phenomenon and the complex flow characteristics, as well as the noise from the mechanical components of the pump complicates the detection of cavitation. For this reason the use of several sensors in combination with advanced signal processing techniques is often proposed for the successful identification of two phase flow in the signal obtained. In this study, a radial centrifugal pump is tested under various flowrates in order to derive its cavitation characteristic curves. At the same time, the signal obtained from various vibration and acoustic emission sensors is recorded. The sensors are located at the rolling bearings that support the overhung impeller, and close to the suction of the pump, where the static pressure takes its minimum value. Subsequently, by processing the digitized signals of all noise and vibration measurements both in time and frequency domains, it is possible to identify the appearance of cavitation. Finally, the results show that the position of the sensor and the acquisition characteristics undoubtedly affect the detection of cavitation.

Development of a One-Dimensional Model for the Prediction of Leakage Flows in Rotating Cavities Under Non-Uniform Tangential Pressure Distribution

Regenerative pumps are characterized by a low specific speed that place them between rotary positive displacement pumps and purely radial centrifugal pumps. They are interesting for many industrial applications since, for a given flow rate and a specified head, they allow for a reduced size and can operate at a lower rotational speed with respect to purely radial pumps. The complexity of the flow within regenerative machines makes the theoretical performance estimation a challenging task. The prediction of the leakage flow rate between the rotating and the static disks has the greatest impact on the prediction of global performance. All the classical approaches to the disk clearance problem assume that there is no relevant circumferential pressure gradient. In the present case, the flow develops along the tangential direction and the pressure gradient is intrinsically non-zero. The aim of the present work is to develop a reliable approach for the prediction of leakage flows in regenerative pumps. A preliminary numerical simulation on a virtual model of a regenerative pump where the disk clearance is part of the control volume has been performed for three different clearance aspect ratios. The outcome of that campaign allowed the authors to determine the behavior of the flow in the cavity and choose correctly the baseline hypotheses for a mathematical-physical method for the prediction of leakage flows. The method assumes that the flow inside of the disk clearance is two-dimensional and can be decomposed into several stream-tubes. Energy balance is performed for each tube, thus generating a system that can be solved numerically. The new methodology was tuned using data obtained from the numerical simulation. After that, the methodology was integrated into an existing one-dimensional code called DART (developed at the University of Florence in cooperation with Pierburg Pump Technology Italy S.p.A.) and the new algorithm was verified using available numerical and experimental data. It is here demonstrated that an appropriate calibration of the leakage flow model allows for an improved reliability of the one-dimensional code.

Electrodiffusional flow diagnostics in a centrifugal pump

This paper presents electrodiffusional measurements of the wall shear rate at the impeller surface of a radial centrifugal pump. Twelve probes of different radii and at different positions along one blade were used in a pump with an open six bladed impeller. By means of throttling and speed control the operating point of the pump was adjusted and the influence on the wall shear rate was studied. The measurements were related to the analytical solution for a free rotating disc and the shear gradients were in the same order of magnitude.