Pump Stage Research Articles

Numerical simulation of unsteady flow in a multistage centrifugal pump using sliding mesh technique

In this work, three-dimensional, unsteady Reynolds-Averaged Navier?Stokes (RANS) equations with standard k-e turbulence models are solved by employing sliding mesh technique within an entire stage of a multistage diffuser pump to investigate transient flow field and pressure fluctuations due to the interaction between impeller and diffuser vanes. Sliding mesh calculation is carried out as the impeller zones slide (i.e., rotate) relative to diffuser zone along the grid interface in discrete time steps. The complicated time-periodic and spatial-periodic characteristics as well as rotor?stator interaction phenomena inside the pump stage are simulated and analysed to understand dynamic variation of the interior flow field and interference and finally to aim at optimal design.

Special features of a digital speckle interferometer for determining vibration characteristics of heavy-loaded elements of an aircraft fuel pump

The results of vibration tests for heavy-loaded elements in the auger-centrifugal stage of an aircraft fuel pump performed with the use of an interference-free digital speckle-interferometer created at the Samara State Aerospace University are presented. The speckle-interferograms of an auger and a centrifugal wheel of the auger-centrifugal pump stage in different conditions of attachment and dynamic loading are given. The data obtained may be of sufficient importance in the development of aircraft fuel pumps for a specified service life.

An Engineering Model of a Disc Pump Stage for Heavy Oil

AbstractAn engineering model of a laminar flow in a disc pump stage of simple design is developed and an approximate analytical solution for a flow in the disc rotor obtained. A rough analytical model for the vaneless diffuser is also found. The performance of a disc stage as it depends on the fluid viscosity, the flow rate, and a channel number is analyzed.

A charge pump for driving CMOS active pixel reset

To overcome the limitation of low image signal swing range and long reset time in four transistor CMOS active pixel image sensor, a charge pump circuit is presented to improve the pixel reset performance. The charge pump circuit consists of two stage switch capacitor serial voltage doubler. Cross-coupled MOSFET switch structure with well close and open performance is used in the second stage of the charge pump. The pixel reset transistor with gate voltage driven by output of the pump works in linear region, which can accelerate reset process and complete reset is achieved. The simulation results show that output of the charge pump is enhanced from 1.2 to 4.2 V with voltage ripple lower than 6 mV. The pixel reset time is reduced to 1.14 ns in dark. Image smear due to non-completely reset is eliminated and the image signal swing range is enlarged. The charge pump is successfully embedded in a CMOS image sensor chip with 0.3 × 106 pixels.

A new approach to procedure for calculating head characteristics of worms and axial-vortex pump stage

Liquid flow in a worm, known as axial-vortex stage (AVS), is regarded, when the worm is fitted in a smooth bushing and in a vane cascade (vane lattice), like in a positive displacement pump operating with a leak, as a reverse flow. In such a case, the worm and AVS head equals the hydraulic loss in the reverse flow, and the calculation procedure in this case is much simpler. It is shown that calculation using geometric parameters of the worm and AVS yields values that agree well with experimental values.

HYDRAULIC BEHAVIOUR OF UNCONVENTIONAL RADIAL PUMP STAGES

This paper investigates the hydraulic behaviour of unconventional radial pump stages observed utilizing the CFD analyses. The main emphasis was put on the influence of radial pump stage (RPS) geometry on the basic flow direction in the pump regime. In order to preclude defining the flow direction as a boundary condition, a closed hydraulic system was modelled to investigate the hydraulic behaviour of the RPS and its energy characteristics. It was confirmed that centripetal flow through the RPS is possible in the pump regime, but not without the installation of an appropriate stator on the inner rotor radius. The influence of the inner rotor radius stator geometry on the basic flow direction in the pump regime is discussed. The manner of the operation type switching between centripetal and centrifugal pumping achieved with the variation of the hydraulic losses within the closed hydraulic system is explained. In addition to the closed hydraulic system calculations used for investigation of the RPS operation in the pump regime, the open hydraulic system was modelled to determine the energy characteristics of the analysed radial pump stages in other operating regimes. All operating regimes of the important RPS cases are presented by means of four-quadrant charts.

Improving the hydrodynamic performance of diffuser vanes via shape optimization

The performance of a diffuser in a pump stage depends on its configuration and placement within the stage. The influence of vane shape on the hydrodynamic performance of a diffuser has been studied. The goal of this effort has been to improve the performance of a pump stage by optimizing the shape of the diffuser vanes. The shape of the vanes was defined using Bezier curves and circular arcs. Surrogate model based tools were used to identify regions of the vane that have a strong influence on its performance. Optimization of the vane shape, in the absence of manufacturing and stress constraints, led to a nearly 8% reduction in the total pressure losses compared to the baseline design by reducing the base separation.

Calculating the characteristics of immersed centrifugal pumps

A simple graphical calculation method is proposed for determining the characteristics of pump stages at the design stage for the rotors and the directing gear in multistage centrifugal immersed pumps.

Operating regimes of an unconventional radial pump stage

This paper presents some phenomena concerning the stability problem of the basic flow direction observed within the CFD analyses of an unconventional radial pump stage (RPS). In order to preclude defining the flow direction as a boundary condition, a closed hydraulic system was modelled to investigate the operating behaviour of the RPS and its energy characteristics. It was shown that the basic flow direction through the RPS is determined by the level of hydraulic losses within the closed hydraulic system. Combining the closed and open hydraulic system calculations, all possible operating regimes of the analysed RPS are presented by means of 4-quadrant chart.

A database of PIV measurements within a turbomachinery stage and sample comparisons with unsteady RANS

This paper describes an experimental database obtained using two-dimensional Particle Image Velocimetry (PIV) measurements within an axial turbomachinery stage, and presents sample unsteady Reynolds Averaged Navier–Stokes (RANS) simulations to illustrate its applicability for turbomachinery model validation. The experiments are performed in a refractive-index-matched facility that provides unobstructed view, and cover the entire second stage of a two-stage axial pump. The data were obtained at ten different rotor phases covering one rotor blade-passing period, and at mid-span. Several features of the data at selected phases have already been presented and discussed in prior publications. Here we present the complete database together with sample CFD results. Two-dimensional unsteady RANS simulations are performed using the commercial flow solver FLUENT™, with two standard turbulence models, i.e. Renormalization Group (RNG) k-ϵ and Reynolds Stress Transport Model (RSM). The spatially non-uniform inlet velocity and turbulence boundary conditions are provided from the experimental data. Detailed side-by-side comparisons of measured and computed velocity as well as turbulence fields within the entire stage are presented using line distributions within the rotor–stator gap and the stator wake regions, as well as whole-field animations. The results show that, although there is reasonable agreement, in general, between the experimental results and the computational simulations, some critical flow features are not correctly predicted. The turbulent kinetic energy levels are generally too high in the simulations, with substantial amount of unphysical turbulence generation near the blade leading edges, especially in the case of RNG k-ϵ model. Also, wake diffusion is underestimated. The results highlight the usefulness of comparisons that cover the entire unsteady flow in a passage, as afforded by the present database and side-by-side animations.

High efficiency MOS charge pumps based on exponential-gain structure with pumping gain increase circuits

Novel MOS charge pumps utilizing an exponential-gain structure and pumping gain increase (PGI) circuits with high voltage transfer efficiency to generate boosted output voltages are described. By using the PGI circuits, the threshold voltage problem of the MOSFET used as a switch is solved, and the limitation of the diode-configured output stage is removed. Thus, the boosted output voltage increases linearly as compared to the pumping stage number. An exponential-gain structure is also presented as a further application of the PGI circuit. By using this structure, fewer voltage pump stages are needed to obtain the required output voltage. For 1.5-V supply voltage operation, a four-time series (1.5 V-to-6 V) is demonstrated using the new techniques. Simulation and experimental results have shown that this design has good efficiency with a low-input supply voltage such as a one battery cell.

터보펌프 축추력 조절용 캐비티 베인에 대한 수치해석적 연구

The magnitude of the axial force acting on turbopump bearings has a great influence on the operational reliability and service life of a turbopump. In the turbopump under current investigation the cavity vanes are introduced to the pump shroud casing to control the axial thrust of the turbopump. To investigate the effect of the cavity vanes, 3D computational flow analyses for a propellant pump stage including an inducer, impeller, volute and secondary flow passages are performed with and without the vanes. The results show that the cavity vanes are very effective in reducing the magnitude of axial thrust without notable changes on the overall performance of the turbopump.

High-efficiency regulator for on-chip charge pump voltage elevators

Proposed is a linear regulator topology for on-chip charge pump voltage elevators. As opposed to the case of conventional schemes, the pass transistor of the regulator feeds the last stage of the charge pump rather than the output load. Key advantages of the proposed solution are reduced silicon area and improved power efficiency.

Correlation Between Specific Speed and Cavitation Characteristics of Vane Pumps

An axial vortex pump stage has been developed. Its application has remarkably improved cavitation characteristics of condensate pumps and helped raise the cavitation factor to as high as 4500–5000. This has also helped increase the rotation speed of the pump shaft and reduce the mass and dimension characteristics of the stage.

Efficiency Criterion of Immersion Oil Pump Stage

A relationship is proposed for determination of efficiency of pump stage with due regard for the effect of several factors: mainly head and efficiency plus, for instance, effect of flatness of the slope of the efficiency-flow rate curve.

Navier–Stokes modeling of a Gaede pump stage in the viscous and transitional flow regimes using slip-flow boundary conditions

A three-dimensional model for a Gaede pump, based on the Navier–Stokes equations with no-slip boundary conditions, was introduced by the authors in a previous work. A commercial computational fluid dynamics code was used to obtain the solution in an outlet pressure range corresponding to the viscous laminar regime and incipient transition to molecular flow and the validation against the experimental data showed a good level of accuracy in terms of compression ratio. However, the mechanical power dissipation predicted by the no-slip model shows a trend diverging from the measured data for decreasing pressure, in the transitional flow regime. As most of the mechanical power is dissipated into heat by viscosity, slip-flow boundary conditions are introduced here in order to model the transitional effects on the wall shear stress and improve the accuracy of the Navier–Stokes description at low pressure. The calculation is carried out up to Knudsen numbers Kn≈1, showing a very good agreement of the Navier–Stokes model, even close to molecular flow conditions, and leaving a residual error acceptable for design purposes. The model is used to analyze the flow fields in the Gaede pump and explain its behavior. The slip model needs just one adjusting parameter, i.e., the momentum accommodation coefficient, but exhibits a small sensitivity to its variations. Hence it can predict the compression ratio and power dissipation of Gaede pumps of any size in their whole operating pressure range, from the laminar viscous regime down to the transition to the molecular flow regime.

Multidimensional flow modeling of the compression test of a Gaede pump stage in the viscous regime

Two-dimensional and three-dimensional models for a Gaede pump, based on the Navier–Stokes equations, are developed and a commercial Computational Fluid Dynamics code is used to solve them. We simulate a compression test in an outlet pressure range (30–2500 Pa) corresponding to the viscous laminar regime for an experimental pump. Experimental data are collected in order to validate the developed model. The pump tested is the high pressure stage of a commercial hybrid turbomolecular vacuum pump and can work in both transition and viscous regime, according to the operating pressure. The data show that the standard Couette–Poiseuille one-dimensional analytic model, developed by Helmer and Levi to describe the Gaede pump behavior and operating principle, has a limited accuracy when it is used as a design tool and not just as a physical model. The two-dimensional and the three-dimensional model results are compared with the experimental data showing an increasing level of agreement, with only a 10% maximum difference for the three-dimensional model in terms of compression ratio. The different flow structures shown by the models are critically analyzed to explain the different level of agreement.

Choice of design operating conditions for a submersible pump stage

Choice of design operating conditions for a submersible pump stage

An Overset Finite-Element Large-Eddy Simulation Method With Applications to Turbomachinery and Aeroacoustics

A numerical method for the prediction of an unsteady fluid flow in a complex geometry that involves moving boundary interfaces is presented in this paper. The method is also applicable to the prediction of the far-field sound that results from an unsteady fluid flow. The flow field is computed by large-eddy simulation (LES), while surface-pressure fluctuations obtained by the LES are used to predict the far-field sound. To deal with a moving boundary interface in the flow field, a form of the finite element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain-decomposition programming model. The validity of the proposed method is shown through two numerical examples: prediction of the internal flows of a hydraulic pump stage and prediction of the far-field sound that results from unsteady flow around an insulator mounted on a high-speed train.

Hydrodynamic Design of Pump Diffuser Using Inverse Design Method and CFD

A new approach to optimizing a pump diffuser is presented, based on a three-dimensional inverse design method and a Computational Fluid Dynamics (CFD) technique. The blade shape of the diffuser was designed for a specified distribution of circulation and a given meridional geometry at a low specific speed of 0.109 (non-dimensional) or 280 (m3/min, m, rpm). To optimize the three-dimensional pressure fields and the secondary flow behavior inside the flow passage, the diffuser blade was more fore-loaded at the hub side as compared with the casing side. Numerical calculations, using a stage version of Dawes three-dimensional Navier-Stokes code, showed that such a loading distribution can suppress flow separation at the corner region between the hub and the blade suction surface, which was commonly observed with conventional designs having a compact bowl size (small outer diameter). The improvements in stage efficiency were confirmed experimentally over the corresponding conventional pump stage. The application of multi-color oil-film flow visualization confirmed that the large area of the corner separation was completely eliminated in the inverse design diffuser.