Influence of Cross-Sectional Flow Area of Annular Volute Casing on Transient Characteristics of Ceramic Centrifugal Pump
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The annular volute is typically used in a slurry pump to reduce the collisions between solid particles and the volute tongue and to achieve a better resistance to blocking. However, only limited studies regarding annular volutes are available, and there is no systematic design method for annular volutes. In this study, the influence of volute casing cross-sectional flow area on the hydraulic loss, pressure pulsations, and radial force under varying working conditions in a centrifugal ceramic pump are discussed in detail. Experimental tests were conducted to validate the numerical results. The results indicated that, when the volute casing flow area increases, the hydraulic performance decreases marginally under the rated working conditions, but increases at the off-design points, specifically under large flow condition. However, the volute casing with a larger flow area has a wider high-efficiency region. In addition, the increase in the volute casing flow area will decrease the pressure pulsations in the volute, regardless of the working condition, and decrease the radial force on the shaft, therefore, providing an improved pump operational stability. It is anticipated that this study will be of benefit during the design of annular volutes.
KeywordsAnnular volute Centrifugal pump Cross section Transient characteristics Pressure pulsation Radial force
As far as the authors are aware, only limited studies have been reported in open literature considering centrifugal pumps with annular volutes, although numerous studies have reported the transient characteristics of conventional spiral volute casings. In this study, the influence of the cross-sectional area of the annular volute of a ceramic centrifugal pump on the transient characteristics and the pump hydraulic performance are investigated. Two volute casings were custom-built to experimentally validate the numerical results. It is anticipated that this study will be of benefit in the design of ceramic slurry pumps.
2 Pump Geometry
Primary geometric dimensions
Suction branch diameter Ds (m)
Discharge branch diameter Dd (m)
Impeller eye diameter D1 (m)
Impeller exit diameter D2 (m)
Leading edge width b1 (m)
Trailing edge width b2 (m)
Leading edge blade angle β1 (°)
Trailing edge blade angle β2 (°)
Blade wrap angle φ (°)
Back blade width bb (m)
Volute chamber width b3 (m)
Diameter to volute tongue D3
3 Numerical Method
3.1 Calculation Domain and Grid Generation
Grid independence analysis
Head H (m)
Efficiency η (%)
The transient flow through the modeled pump was simulated using the commercial software ANSYS CFX 14.5, which utilized the finite volume method to solve the unsteady three-dimensional Navier–Stokes equations. Because of the fast convergence and the accurate hydraulic performance achieved compared to other turbulence models, the standard k-ε model was selected to complete the turbulence equation, with the standard wall function for the treatment of the flow in the boundary layer based on the refined grids . All the solid walls in the computational domain were set as no-slip walls with a roughness of 0.2 mm. The surfaces of the impeller and back blades were set in a rotating reference frame with a rotational speed identical to the nominal operating speed of the pump [28, 29]. All the other surfaces were set in a stationary frame. The transient rotor–stator model was attached to the interfaces between the rotating and stationary regions. An axial velocity, based on the variation of the flow rate, was provided at the inlet boundary located at the suction branch. In addition, the outlet boundary was set as an opening with a specified static pressure in the case of the upstream influence of backflow on the primary flow domain. A high-resolution technique was used for the discretization of the advection scheme and turbulence terms. The second-order backward Euler method was applied for the transient scheme. The convergence criterion was set as 1 × 10−5 for the scaled residuals, with at least 20 iterations per time step. The time step was set as 0.000172414 s, as this provided a blade rotation of 3° between iterations, which means an impeller rotational period covers 120 time steps. Ten impeller revolutions were required when the flow reached a clear periodic regime. The data of one additional impeller revolution was then extracted to analyze the transient flow characteristics for each case. The data include the maximum, minimum, time-average, and standard deviation of the selected flow variables, including static pressure, total pressure, relative velocity, and absolute velocity.
4 Validation of CFD Results
5 Results and Discussion
5.1 Hydraulic Loss in Volute Casing
5.2 Analysis of Flow Rate Distribution at Cross-Sections
5.3 Pressure and Velocity Distribution in Volute Casing
5.4 Pressure Pulsations in Annular Volute
5.5 Radial Force
When the volute casing flow area increased, the hydraulic performance decreased marginally at the rated working condition but increased at off-design points, specifically under the large flow condition. However, the volute casing with a larger flow area had a wider high-efficiency region.
The nonuniform circumferential static pressure distribution at the volute casing inlet and the vortex structure at the cross-sections were the primary reasons for the hydraulic loss in the volute under the rated and small flow conditions. However, for the large flow condition, the backflow at cross section I and the large velocity gradient from cross section VIII to the throat cross section were the primary reasons.
The greatest pressure pulsation occurred approximately 30° backward of the volute tongue. An increase in the volute flow area decreased the pressure pulsations in the volute regardless of the working condition, and decreased the radial force on the shaft, which resulted in an improved operational stability of pump.
It is anticipated that this study would be of benefit during the design of annular volutes. The annular volute cross-sectional area should be appropriately greater than cross section VIII of the spiral volute casing to achieve an improved hydraulic performance under large flow condition and an improved pump operational stability. However, it should be noted that a greater annular volute cross-sectional area will require a larger pump, which will increase material costs and make transportation more logistically difficult. Therefore, the cross-sectional area of the annular volute should be comprehensively considered during the design.
YT was in charge of the whole trial; YT wrote the manuscript; SY, JL, and FZ assisted with sampling and laboratory analyses. All authors read and approved the final manuscript.
Yi Tao, born in 1988, is currently a lecturer at Wuxi Vocational Institute of Arts and Technology, China. He received his PhD degree from National Research Center of Pumps and System Engineering and Technology, Jiangsu University, China. His research interests include solid–liquid two-phase flow and design of slurry pumps.
Shouqi Yuan, born in 1963, is currently a professor and a PhD candidate supervisor at National Research Center of Pumps and System Engineering and Technology, Jiangsu University, China. He has received 16 prizes for science and technology advancement at province or ministry level. He has published 3 books and more than 240 papers. His research interests include the theory, design and CFD of pumps and fluid machinery.
Jianrui Liu, born in 1952, is currently a professor and a PhD candidate supervisor at National Research Center of Pumps and System Engineering and Technology, Jiangsu University, China. His research interests include fluid machinery engineering
Fan Zhang, born in 1987, is currently a PhD at National Research Center of Pumps and System Engineering and Technology, Jiangsu University, China. His research interests include flow characteristics in fluid machinery.
The authors declare no competing financial interests.
Supported by National Natural Science Foundation of China (Grant No. 51779107), Jiangsu Provincial Natural Science Foundation of China (Grant No. BK20170548), Postdoctoral Science Foundation of China (Grant No. 2017M611724), and Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).
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