J Braz. Soc. Mech. Sci. Eng. (2017) 39:2561–2569 DOI 10.1007/s40430-017-0728-6

TECHNICAL PAPER

A mixed‑flow submersible well pump: design features and an investigation of performance Qihua Zhang1 · Yuanhui Xu1 · Li Cao1 · Weidong Shi1 · Weigang Lu1 

Received: 3 July 2015 / Accepted: 31 January 2017 / Published online: 8 February 2017 © The Brazilian Society of Mechanical Sciences and Engineering 2017

Abstract  This work presents a specially designed mixedflow submersible well pump to meet the demand of high handling capacity. To simplify molding process and productivity, an axial-radial guide vane is proposed and its main hydraulic components are made of plastics. To clarify its effect on the performance, a radial guide vane and a space guide vane were developed as well. By comparison of flow fields, the performance of the pump equipped with the axial-radial guide vane is much higher than the radial guide vane and is slightly lower than the space guide vane. However, the molding process for the axial-radial guide vane is simple, and its cost is much lower which meets the growing needs for large specific speed submersible well pumps.

Abbreviations D1 Impeller suction eye diameter, mm Dh Impeller hub diameter, mm g Gravitational acceleration, m s−2 H Pump head, m M Torque of impeller, N m n Impeller rotating speed, r min−1 Ptot Total pressure, Pa Q Pump flow rate, m3 s−1 Usuc Velocity in impeller eye, m s−1 ω Angular velocity of impeller, rad s−1 ρ Fluid density, Kg m−3

1 Introduction Keywords  Mixed-flow · Submersible pump · Hydraulic design · Guide vane · Performance

Technical Editor: Marcio S Carvalho. * Qihua Zhang [email protected] Yuanhui Xu [email protected] Li Cao [email protected] Weidong Shi [email protected] Weigang Lu [email protected] 1



National Research Center of Pumps, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, People’s Republic of China

To keep livestock in regions lacking visible ground water, it is necessary to explore and utilize the underground water resources. For example, in mid-western and northern areas of China, deep wells are widely deployed to keep livestock, and irrigate farms as well. The well is very deep and is commonly exploited using a pump driven by electric power, wind, solar, etc. In addition, in offshore oil exploitation, we foresee an increasing demand for oil submersible well pumps. The increasing market promotes a new wave of research and development on submersible well pumps. Compared to rotating components, i.e., impeller, shaft, bearing, etc., the guide vane is a stationary component, and it is rarely investigated. However, it mainly contributes to the static pressure recovery and affects the stage performance [1]. Even more, guide vane plays an important role in removing pump vibration, hydraulic excitation, and noise for a full range of operation [2–5]. Using LES method, Li et al. [6] investigated the

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instantaneous flow through the guide vane of a mixedflow pump, but no validation was provided by comparison with experiments. By extending the law of Biot– Savart, a two-dimensional vortex method was applied to explore the unsteady vortex between the radial diffuser and impeller for partial flow rate [7]. However, the viscous effect was omitted, which would be dominant in the boundary layer separation flows. Stel et al. [8] numerically investigated the flow pattern within a two-stage diffuser pump for a range of flow rates and rotor speeds, and found that the relevant dimensionless coefficients do not change significantly. However, they only examined the first stage which was not representative for multistage pumps. Gao et al. [9] studied the flow field of a diffuser pump by simulation and experiments, and they preferred to the unsteady method for its better accuracy. Yang et al. [10] presented a detailed flow pattern about the flow path from diffuser to return vane channel by visualization of bubble injection. Si et al. [11] used several experimental techniques to probe blade-to-blade air flow through a diffuser pump. Though many aspects of flow behavior within the diffuser pump have been understood, a large gap still exists between fluid mechanics and the hydraulic design, which is commonly filled by the optimization procedures in conjunction with computational fluid dynamics (CFD) techniques. Through 3D Reynolds averaged Navier–Stokes (RANS) simulations coupled with a radial basis neural network model, Kim et al. [12] achieved an optimal configuration of the vaned diffuser of a mixed-flow pump. Li et al. [13] developed a low-specific mixed-flow pump adopting vaned diffuser with large head. The authors then proceeded to revise the model pump by adjusting blade shapes of impeller and diffuser within the computer aided design (CAD) tool UG NX7.5. Lugovaya et al. [14] presented two types of guide vanes which differ slightly at the transition shape of the intermediate stage cross-section, and they compared the performance of the pump equipped with these guide vanes separately. But they did not come into an exact conclusion that one outperformed another, nor did they describe how to design these guide vanes. Weiten et al. [15] investigated a small stage of radial multistage pump equipped with a single guide vane without radial diffuser, and compared with a common guide vane with radial diffuser. The test showed that the small stage efficiency was relatively lower. However, the small stage head was larger and the axial thrust was relatively smaller. So the small stage can be adapted to the submersible well pumps, removing the restriction of diameter and reducing the axial thrust as well. On this basis, Zhang et al. [16] developed a compact submersible well pump, where a circumferential twisted return guide

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J Braz. Soc. Mech. Sci. Eng. (2017) 39:2561–2569

vane was proposed, and its designing process was presented as well. The pump was made of casting steel and is relatively heavy and expensive. Recently, the environment-friendly techniques are increasingly addressed. Wang et al. [17] designed an axial tidal turbine by composites. This technique is free of sea water erosion, promoting a new trend for environment protection. Recently, a series of plastic well pumps have been developed and occupied a major part of market share [18]. However, the demand for mixed-flow pump handling larger flow rate is increasing. In this paper, a mixed-flow pump of moderate to large specific speed was developed. A special radial-axial return guide vane was designed and the plastic molding was used to construct the hydraulic components. Meanwhile, a radial guide vane and a space guide vane were constructed to compare and clarify their effects on pump performance.

2 Problem description In the past decade, composite molding has served as a rapid tool during end-product development of hydraulic components. With many inherent merits like light-weight, lowcost, high-productivity and high-interchangeability of parts, the composite components are increasingly adopted in mass production of submersible pumps, substituting old iron-, or steel-type pumps. On the other hand, the surface roughness of plastic components is much smoother, which also leads to better hydraulic performance. In our previous research, we have successfully developed a series of plastic submersible pumps [18]. In fact, these pumps are usually categorized into the low and medium specific speed pumps. We have engaged in developing the pump for large flow rates for many years. The major difficulty lies in the composite molding process of the hydraulic components of the mixed-flow pump. So we will first analyze the problems involved in the available techniques and proceed to seek a new design strategy for our original purpose. 2.1 Space guide vane Presently, there are two major types of guide vanes for submersible well pumps widely applied in the market. One type is based on the cylindrical shape, the other is based on the space guide vane. The former type is always cylindrical and is mostly constructed by composite molding process, and it is mostly used in low-specific speed circumference. The latter type is always fully twisted and casted by iron or steel, as shown in Fig. 1. The space guide vane is mainly employed in iron and steel made submersible pumps. As we know, the molding techniques for metal casting is rather mature. But for

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continuously twisted surface

3.1 Axial‑radial guide

2 3 4 5

For mixed-flow submersible pumps, the flow path is naturally oriented to the axial and radial direction like the space guide vane. To overcome the molding difficulty, the guide vane should take two segments, i.e., the axial part and the radial part, namely an axial-radial guide vane is proposed and its shape is depicted in Fig. 2. As shown in Fig. 3, it can be clearly seen that the axialradial guide vane is divided by two parts, where a dividing line separates the axial part and the radial part. It is noticed that this dividing line also serves as a molding separation line, from which the axial and radial parts depart and the molding process becomes quite simple.

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Fig. 1  Schematic of a space guide vane

plastic molding process, the molding technique involved becomes rather complex, because the surface of space guide vane is fully twisted, as shown in Fig. 1. With this in mind, an alternative to the space guide vane is put forward hereafter, which would effectively improve the plastic molding as well as its productivity.

Fig. 2  Schematic of an axialradial guide vane

3 Guide vane design

3.2 Design features For the axial part, the blade is designed by a series of profiles obtained by the sequential cross sections, i.e., 1–7, as shown in Fig. 3a. Those profiles can be plotted in

front view

back view

axial section cylindrical section

Fig. 3  Design process for the axial-radial guide vane

1 2 3 4 5 6 7

1 2 3 4 dividing line between axial and cylindrical section

(a) blade sections

1 2 3

5

(b) front surface

6 7

4 5

6

7

(c) back surface

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1 2 3 4

4 Numerical investigation of pump performance

5 6

axial section

7

dividing line cylindrical section

Fig. 4  Blade layout of the axial-radial guide vane

two separate drawings, as shown in Fig. 3b, c, which represents the front and back surface of the axial part. Subsequently, the front and back surfaces and the cylindrical parts can be plotted in a single drawing, thus a single blade layout is plotted, as shown in Fig. 4. As the original demand, a pump working at flow rate Q = 20 m3 /h, stage head H = 7.5 m, and rotating speed n = 2850 RPM is developed by plastic molding. And we hereby investigate its performance by comparison with the radial and space guide vane.

Fig. 5  3D models of three type of guide vanes

Fig. 6  Configuration of a twostage calculation model

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4.1 Model configurations Further, a radial guide vane and a space guide vane were developed as shown in Fig. 5. And the main dimensions (hub diameter, shroud diameter, blade number, inlet blade angle, outlet blade angle, etc.) of the radial guide vane and space guide vane are identical to the axial-radial guide vane. The three types of guide vanes are assembled with an identical impeller, respectively. And the configurations are similar, as depicted in Fig. 6. A dual-stage model is set up which includes the suction pipe, the first stage, the second stage, and the discharge pipe. 4.2 Computational grids For the purpose of precision, convergence property, and stability of numerical scheme, the structured grids are set up by ICEMCFD 15.0. The grids for the three types of configuration are depicted in Fig. 7. For better numerical precision, the grids near walls were carefully adjusted to keep yplus value distributed within the

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Fig. 7  Numerical grids of the three configurations

range (30, 200). The MRF (Moving Reference Frame) is applied to the steady-state simulations. The numerical discretization is based on the second order scheme for all variables including turbulent quantities, and the RMS residual tolerance is 10−5. 4.3 CFD setup and boundary conditions The simulations were performed on the platform of ANSYS CFX 15.0. For three types of calculation models, a uniform inlet boundary condition is set considering the average suction velocity, Usuc = 4Q/π(D12 − Dh2 ) , where D1 is impeller suction diameter, and Dh is the impeller hub diameter. The suction and discharge pipe diameter is equal to the impeller suction diameter. And the total length of the calculation model including suction and discharge pipe is same for the three different configurations, as shown in Fig. 7. The flow at the outlet

of the pump is considered fully developed. In this study, a pipeline is fitted onto the pump discharge flange where the pressure at the pump exit is not known in practice, so the fully developed turbulent boundary condition is set on the pump exit. The SST k − ω turbulence model was enabled for all three configurations, while other relevant settings are kept as default recommendations of the CFX package. 4.4 Flow field simulation and analysis Steady-state simulations were performed at a specified flow rate, for three different configurations, respectively. Flow field variables such as velocity, pressure, turbulent kinetic energy, as well as streamlines are analyzed as follows. From Fig. 8, the velocity field is well controlled by the space guide vanes, and is relatively smooth within the axial-radial guide vane. However, the velocity field is

Fig. 8  The velocity vector diagram for the three guide vane geometries at the specified flow rate

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Fig. 9  The streamline distribution within the three guide vane geometries at the specified flow rate

non-uniform along the channel of the radial guide vane. It is observed that the velocity magnitude fluctuates and the direction is not well-guided by the blade. From Fig. 9, the streamline clearly shows that local circulation patterns are observed in each channel of the radial guide vane, and mainly attached to the concave wall of the blade where flow separation is strongly generated. This shows that the radial guide vane is not well suited for handling large flow rate conditions. From Fig. 10, the static pressure distribution is mostly smooth in the space guide vanes, and the contour lines are nearly normal to the channel wall which shows that the static pressure is effectively accumulated, demonstrating good static pressure recovery performance of the guide vane. However, in the radial guide vane, the pressure gradient is not continuously increased through the whole channel, and it is abruptly increased at the outlet region. This may be attributed to the irregular flow field. The pressure gradient distribution within the axial-radial guide vane is relatively moderate among the three types.

From Fig. 11, it shows that the turbulent kinetic energy level is lowest within the space guide vanes, and is highest in the radial guide vane. Furthermore, high levels of turbulent kinetic energy are generated near the inlet region. From the flow field analysis, we can further state that the radial guide vane is not a suitable design strategy for the large flow rate situation. To tackle this problem, a twisted inlet feature such as the axial-radial guide vane design strategy is necessary. However, the performance of the axial-radial guide vane is still worse than the space guide vane, and its improvement remains to be further performed. 4.5 Performance simulation and analysis A series of simulations were conducted. Based on the numerical simulations, the stage head is calculated as follows:

H=

(Ptotdis − Ptotsuc ) , ρg

Fig. 10  The static pressure distribution for the three guide vane geometries at the specified flow rate

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(1)

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Fig. 11  The turbulent kinetic energy distributions for the three guide vane geometries at the specified flow rate

Fig. 12  Pump performance curves

where Ptotdis is the stage total pressure at pump discharge, and Ptotsuc is the stage total pressure at pump suction. Then, the stage efficiency is calculated as follows:

Eff =

ρgQH , Mω

(2)

where M is the stage torque of the pump impeller, and ω is the rotating angular velocity of the impeller. From Fig. 12, it is clear that the performance of the pump equipped with the axial-radial guide vane is better than the radial guide vane and is worse than the space guide vane. Especially, at large flow rate, the pump performance of the axial-radial guide vane roughly equals to the space guide vane, and greatly exceeds that of the radial guide vane.

5 Prototype pump testing To verify the conceptual design, a ten-stage pump is designed and tested. The main hydraulic components, i.e.,

Fig. 13  Hydraulic component samples

the plastic sample of the impeller and the axial-radial guide vane are shown in Fig. 13. The testing is performed at the laboratory of the National Research Center of Pumps, as shown in Fig. 14a. The prototype pump is mounted on the pipeline as shown

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Fig. 14  Prototype pump test pipeline

Fig. 15  Prototype pump performance curves

in Fig. 14b. The pump is then put underwater and the testing is performed automatically. The test result is shown in Fig. 15. The peak efficiency approaches 50% at the flow rate of 24 m3/h. For a 4-in. pump, this flow rate exceeds most of the products in the market. And the most important point is that the cost of this type of pump is much lower, as well as its weight and mobility.

6 Conclusion To exploit underground water resources, the submersible well pumps are widely applied in farms, mountain and desert areas, etc. Furthermore, oil field exploration takes on a growing tendency in recent years. To meet this demand, especially for the moderate to high specific speed range, a mixed-flow submersible well pump is developed in this study. The main components of the

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pump were constructed by composite molding process. Under a relatively low rotating speed, the composite components can usually maintain the strength level up to 5 in. diameter. To facilitate molding process and improve productivity, an axial-radial guide vane was proposed and tested. To explore its hydraulic performance, a space guide vane and a radial guide vane were developed in the meantime for comparison. The numerical simulations were conducted to verify the validity of the hydraulic design. The flow field analysis shows that the pressure loss and turbulent kinetic energy of the space guide vane is lowest, and the difference between the space guide vane and the axialradial guide vane is relatively small, but the gap between the space guide vane and the radial guide vane is largest. Although the space guide vane in fact represents the most efficient type of structure, its blade surface is twisted and the structure is rather complex and difficult for plastic molding.

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In general, the design strategy of the mixed-flow submersible well pump is economically viable. Especially, with the axial-radial guide vane, the plastic molding process is greatly improved. Meanwhile, this technique is anti-erosive and environment-friendly. To conclude, the mass production of this pump is promising. Nevertheless, a deliberate revision of the inlet blade shape of the axialradial guide vane is necessary. Acknowledgements  The authors are grateful for the support by the National Natural Science Foundation of China (No. 51309118), the Natural Science Foundation of Jiangsu Province (No. BK20130527) and the Six Talent Peaks Project of Jiangsu Province (No. ZBZZ-016).

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