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Journal of Drainage and Irrigation Machinery Engin
 
2019 Vol.37 Issue.7
Published 2019-07-25
article
article
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2019 Vol. 37 (7): 1- [Abstract] ( 187 ) [HTML 1KB] [ PDF 2764KB] ( 422 )
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2019 Vol. 37 (7): 2- [Abstract] ( 155 ) [HTML 1KB] [ PDF 255KB] ( 389 )
553 Status of research in internal flow in impeller pumps under gas-liquid two-phase conditions
YUAN Jianping, DENG Fanjie, ZHANG Keyu, CUI Qianglei, SI Qiaorui*
2019 Vol. 37 (7): 553-561 [Abstract] ( 257 ) [HTML 1KB] [ PDF 1283KB] ( 494 )
562 Numerical simulation and test of performance of deep-well centrifugal pumps with different stages
SHI Weidong ,*, HOU Yunhe , ZHOU Ling , LI Yuemin , XUE Shaohui
A deep-well centrifugal pump of type 250QJ80 was chosen to be study model and features of the pump performance at different numbers of stages were explored numerically and experimentally, further the root causes for these features were clarified in terms of analysis of internal flow field in the pump. In the paper, software ANSYS-CFX 17.0 was used to carry out numerical predictions on the pump performance based on three pump models with single stage, two stages and three stages, respectively. The computational domain of three models has experienced geometrical modelling and structured-mesh creation, then the water flow field in these models were simulated under a few working conditions based on the standard k-ε turbulence model and standard wall function. The predicted performance of these models was obtained, compared and analyzed against the corresponding experimental data. The results show that the change in pump stages doesn′t affect the performance of the pump with a specific number of stages. However, the head and efficiency of the first stage are higher than those of the se-cond or third stages, while the head and efficiency of the second stage doesn′t differ obviously from the third stage. The main reason for this similarity and difference in the head and efficiency is that the impeller of the first stage is without any pre-swirl, while the impellers of the rest stages are subject to a certain amount of pre-swirl.
2019 Vol. 37 (7): 562-567 [Abstract] ( 255 ) [HTML 1KB] [ PDF 7161KB] ( 462 )
568 Effects of blade leading edge position on hydraulic performances of centrifugal pump
ZHAO Wanyong*,GUO Qiang,
In order to study effects of blade leading edge position on centrifugal pump performance and internal flow field characteristics, five impellers with different blade leading edge positions were designed based on the original impeller of a centrifugal pump, and three-dimensional steady flow fields in the entire flow passage of the pumps with these impellers were carried out based on the SST k-ω and Zwart cavitation models under water single-phase as well as water-sand two-phase flow conditions. The results demonstrate that the suction performance of the centrifugal pump can be improved when the blade leading edge position is moved towards the impeller eye. The reason for this is that for a low specific-speed centrifugal pump its blade leading edge position being moved towards the impeller eye can improve flow conditions, such as flow uniformization, fluid velocity decrease and pressure rise in the impeller inlet. When the edge position is altered in a certain range, the head and efficiency of the pump are affected little. However, if the edge position is extended too much to the impeller eye, the head will be declined considerably because the blades are subject to the impaired capacity of doing work. At the same flow rate, the increase of sand content can degrade the head and efficiency of the pump but also augment the number of cavitation nuclei, thus make the suction performance poor.
2019 Vol. 37 (7): 568-573 [Abstract] ( 214 ) [HTML 1KB] [ PDF 2965KB] ( 454 )
574 Improved centrifugal pump impeller design in terms of blade wrap and exit angles
WANG Yanyan,, ZHAO Weiguo,*, HAN Xiangdong,, ZHENG Yingjie,
Based on computational fluid dynamics(CFD)technology, numerical simulation of flow field in the whole centrifugal pump of KQW250-400 type was performed. At first, the original impeller blade design was altered according to blade design theory, and five impeller models were built by changing the blade wrap angle Φ and the blade exit angle β2. Then, the corresponding hydraulic perfor-mance curves and internal flow fields of the pumps with these different impeller models were obtained numerically. The results indicate that the impeller with blade wrap angle Φ=126° and exit angle β2 = 24° is the optimal and with the best performance, i.e. at the design flow rate Qd=550 m3/h, the calculated head and efficiency are 53.49 m and 87.66%, respectively. Based on the experimental data, the centrifugal pump with the original impeller is subject to a 49.10 m head and a 79.88% efficiency at the flow rate Q=551.381 m3/h in comparison with 51.84 m head and 85.65% efficiency at the flow rate Q=550.823 m3/h for the pump with the optimized impeller. As such the head and efficiency have increased by 2.74 m and 5.77%, respectively, under the design condition; especially, the efficiency curve with the optimized impeller of the centrifugal pump is all above the curve with the original impeller. This suggests that the overall performance of the centrifugal pump has been improved. This outcome is conducive to improving the economic benefits of pump utilization in buildings and subsequently reducing energy consumption.
2019 Vol. 37 (7): 574-579 [Abstract] ( 265 ) [HTML 1KB] [ PDF 10391KB] ( 508 )
580 Influences of radial clearance between impeller and diffuser on flow field in side chambers of multistage centrifugal pump
PANG Qinglong, JIANG Xiaoping*, ZHU Jiawei, WU Guoqiao, WANG Xinwei, WANG Li
To understand the influence of radial clearance between impeller and diffuser on flow field in two side chambers and optimize hydraulic performance even better, a cantilevered multistage centri-fugal pump was selected as a study model. The flow field in the pump side chambers were analyzed based on combination of computational fluid dynamics(CFD)method and experimental measurement. The numerically predicted performance with the standard k-ε turbulence model showed good agreement with the experimental data, demonstrating CFD method can replace experimental approach in analysis of the flow field in the pump. Three radial clearances designed and the fluid tangential velocity distribution as well as pressure fluctuation in the two side chambers were compared. The results showed that the dimensionless tangential velocity in the front side chamber increases with reducing radius observed, and the fluid rotational angular velocity can exceed the impeller rotational angular speed, but the dimensionless tangential velocity decreases with reducing radius in the rear side chamber essentially. The pressure fluctuations in the radial gap and impeller exit are mainly with a frequency in the range of 0-1 680 Hz, but also the dominant pressure fluctuations occur at diffuser blade passing frequency. The amplitude of pressure fluctuations with the dominant frequency decreases progressively from the first stage to the last stage. The pressure fluctuation in the radial gap is also affected by the number of impeller blades. The secondary dominant pressure fluctuations appear at impeller blade passing frequency, and the pressure fluctuations also exist at the other multiplications of impeller blade passing frequency.
2019 Vol. 37 (7): 580-586 [Abstract] ( 239 ) [HTML 1KB] [ PDF 4920KB] ( 455 )
587 Influence of blade leading edge shape on performance of micro-high-speed centrifugal pump
LI Qiang*, LI Sen, YAN Hao, WANG Daoming, XIA Shengsheng
Three types of blade leading edge shapes, namely basic plan, i.e. the edge is convex towards impeller eye like ordinary centrifugal pump impellers, semi-convex and semi-concave types, were proposed based on the same cross-sectional area at the edge to investigate their influences on performance of a micro-high-speed centrifugal cooling pump. The hydraulic performance and pressure pulsation of the pump were calculated numerically by making use of the SST k-ω turbulence model, and the performance was analyzed comparatively against the corresponding data tested. The results indicated that the simulated hydraulic performance is in good agreement with the tested values and the numerical method and flow model adopted are applicable to the pump. In addition, there are vortices in the impeller passages which are far from the volute diffuser in three plans. Compared with the basic plan, both the head and the efficiency are improved but also the efficiency curve is the most flatty around the best efficiency point in the semi-concave plan. The turbulent kinetic energy distribution near the blade leading and trailing edges is more satisfactory, and the highest circumferential component of absolute velocity at the impeller exit is observed, too. The peak pressure pulsation amplitudes in the volute appear at blade passing frequency and its multipliers, and they decay with increasing distance to the volute tongue in three plans. In the semi-concave plan, however, the peak pulsation amplitudes have reduced even more, exhibiting a favorable condition to stable operations for the pump. These results can provide reference for optimal design of micro-high-speed centrifugal pumps.
2019 Vol. 37 (7): 587-592 [Abstract] ( 251 ) [HTML 1KB] [ PDF 3570KB] ( 421 )
593 Modal analysis of super low-specific-speed self-balancing multistage centrifugal pump rotor
YANG Yong-Fei-1, LI Wei-1*, SHI Wei-Dong-2, MA Xin-Hua-1, HE Yong-Guan-1, XU Rong-Jun-3
To grasp vibration characteristics of multi-stage centrifugal pump rotor and avoid occurrence of resonance during pump operation so as to guarantee the stability of operation, modal analysis on the rotor of a super low-specific-speed and self-balancing multistage centrifugal pump was carried out based on the commercial software ANSYS Workbench in this article. Natural frequencies under three conditions namely dry rotor without flow field pre-stress, dry rotor with flow field pre-stress and wet rotor with flow field pre-stress were calculated and compared. Further, the first eight modals of the rotor were extracted and analyzed. It is shown that the natural frequency of reverse precession is lower than that of forward precession for the same order. The natural frequency increases slightly under condition with flow field pre-stress compared with that without pre-stress, indicating that the flow field pre-stress can rigidize the pump rotor in a certain degree. Under wet condition, additional mass, viscous and damping effects of water have intensively decreased influence on the natural frequency, and the mass force of water has a more significant effect on the frequency. By comparing the first four order vibration modes of the pump rotor, it is found that vibration mode and position where the maximum vibration amplitude appears are identical basically under three conditions. The third order vibration is rotational vibration around the pump shaft-axis, while the other three vibrations correspond to bending vibrations with di-fferent directions and shapes.
2019 Vol. 37 (7): 593-599 [Abstract] ( 263 ) [HTML 1KB] [ PDF 6636KB] ( 473 )
600 Strength analysis of remaining bolts as several connection bolts of hydro-turbine head cover in failure
GE Xinfeng*, XU Xu, SHEN Minghui, TAN Linjie, QIAN Julin, ZHANG Changzheng
Aiming at severe accidents such as flooding hydropower plant caused by broken connection bolts of head cover in hydro-generator units, the geometrical and mechanical models of head cover and connection bolts of a hydro-turbine in a hydropower plant were established and analyzed by using finite element method. Based on the finite element method in Ansys, the static element force equilibrium equations were solved numerically, and the stress distribution in the bolts were determined under va-rious working conditions. Firstly, a normal case was established, i.e. the bolt strength was analyzed when all the bolts engaged properly under runaway condition. Then, a few bolt failure cases were taken into consideration to determine the strength of the remaining bolts, namely, the cases where there are 1, 2, 4 and 8 bolts failed which can be distributed 90?symmetrically, side by side and 180?apart. Results show that the maximum stress level in the remaining bolts increases after several bolts are broken due to uneven distribution of the bolts along the circumferential direction. Specially, the more the bolts are broken and the closer the broken bolts are distributed, the less the strength of the remaining bolts is. When the number of failed bolts is 4 and they are distributed side by side, the maximum stress level of the remaining bolts is as high as 744.03 MPa, which is very close to the bolt allowable stress 744 MPa. When the number of failed bolts is 8 and they are positioned side by side, the maximum stress is increased by 19.69% and arrives at 776.21 MPa, which is far beyond the allowable stress, clearly the safe operation of the hydropower plant will be under threat.
2019 Vol. 37 (7): 600-605 [Abstract] ( 334 ) [HTML 1KB] [ PDF 3890KB] ( 431 )
606 Hydrodynamic performance of marine current turbine with diffuser based on overlap grid method
LIU Yao*, LU Rui, CAI Weijun
A numerical simulation method based on overlap grid, i.e. dynamic fluid body interaction(DFBI), was applied to study effects of diffuser on hydrodynamic performance of a marine current turbine in complex current environments in this paper. Since the overlap grid can remove topological constraints between objects and meshes, DFBI can simulate passive motion of a rigid body under action of fluid to realize the simulation of unsteady performance of a passively rotating current turbine. Particularly, the influences of diffuser on the hydrodynamic performance and the surrounding flow field around the turbine were analyzed under different flow conditions comparatively. The result shows that the met-hod used in the paper can accurately monitor the processes such as speed acceleration and rotor adaptive rotation and so on caused from the changes in current flow field around the turbine, and consequently investigating into unsteady performance of the turbine becomes realizable. An installed diffuser can increase the current velocity around the turbine by around 1.2 times, raise the turbine speed by 1.2-fold and improve the turbine power coefficient by about 35%. Under unsteady current flow conditions, the averaged power coefficient is reduced by about 33%. The diffuser can increase the turbine average rotational speed, but also can raise the average power coefficient by approximate 30%.
2019 Vol. 37 (7): 606-611 [Abstract] ( 210 ) [HTML 1KB] [ PDF 3088KB] ( 410 )
612 Interaction effects of spray parameters on pesticide spray droplet drift
ZHOU Ruiqiong,*，ZHANG Huichun，ZHOU Hongping，ZHENG Jiaqiang，HU Hanchun
A wind tunnel was built with an air speed in the range 0-6 m/s. The droplets containing fluorescein sodium were collected by carbon fiber rods in the vertical and horizontal directions. The content of fluorescein sodium was measured by using fluoremeter. The SPSS software was used to analyze influences of spray parameters and their interactions on spray drift. The results showed that nozzle type, pressure, spray medium and wind speed had a significant impact on droplet drift deposition. The influence of four experimental factors on the drift deposition from the most important to the least important is as follows: wind speed> nozzle type > spray medium >pressure. There are interactions between spray parameters, especially, spray medium and nozzle type, wind speed and nozzle type, wind speed and spray medium, spray medium and nozzle type and wind speed exhibit a substantial interaction, the interactions in the rest spray parameters are insignificant. At all sample positions, deposits on the collectors are reduced at lower wind speeds. However, the droplet drift is intensified as both pressure and wind speed increase. To reduce the drift, we should pay attention to the choice of wind speed in actual field pesticide spray operation. The drift retardant Greenwet 720 can control the drift effectively but the surfactant Greenwet X-100 increases the drift. Investigations into the mechanism of interaction effects of spray parameters on spray droplet drift are of great theoretical and practical significance to decrease of droplet drift, improvement of spraying operational efficiency, enhancement of pest control and reduction of environmental pollution.
2019 Vol. 37 (7): 612-617 [Abstract] ( 234 ) [HTML 1KB] [ PDF 4445KB] ( 458 )
618 Analysis on influences of feeding flow rate on flow characteristics in deep-sea ore hydraulic transport equipment
XU Hailiang,*, ZHOU Yongxing, YANG Fangqiong,, WU Bo,
A three-dimensional fluid domain model of deep-sea ore transport equipment, which consists of a storage tank, a bell valve and a separator, was established, then the solid-liquid two-phase flow field in the equipment was simulated based on the computational fluid dynamics software-Fluent to study effects of feeding flow rate on solid-liquid flow pattern and operational performance of the equipment. Specially, influences of feeding flow rate on ore particle concentration, velocity and pressure distribution in the equipment were compared, and then ore particle velocity and slurry separation efficiency were analyzed. The results show that the average concentration of ore particles in different sections of the storage tank keeps being around 8 kg/m3, but the maximum concentration increases obviously when the feeding flow rate varies in the range of 200-320 m3/h. With increasing feeding flow rate, the fluid motion is more complicated, and the flow becomes even more chaotic, and the local reverse flow is more significant. The slurry pressure in the storage tank increases gradually, and the static pressure gradient is similar to each other in different sections, but the maximum dynamic pressure varies considerably. with the increase of feeding flow rate, the efficiency of ore slurry separation decreases, i.e. less ore particles flow into the storage tank and more particles deposit on bottom of the separator. In consequence, the feeding flow rate should be controlled at less than 280 m3/h under actual operational conditions of the equipment.
2019 Vol. 37 (7): 618-624 [Abstract] ( 256 ) [HTML 1KB] [ PDF 2998KB] ( 383 )
625 Improvement of soil point source infiltration gauge in hillside forest land application
LIANG Yushi,XIA Weisheng*,DING Haodong,WANG Xiaofang,YANG Yunfan
To solve the problem that data in soil point source infiltration experiment is difficult to read, and the error value is relatively large in data of automatic measurement in hillside forest environment, an artificial recognition function is added to improve the experimental precision. The improved soil infiltration measurement instrument was used to measure infiltration rate of the hillside forest land in Mountain Heng, and the results were summarized through an analysis of infiltration rate influencing factors and their curve fitting. Results show that the measured infiltration rates and their fitted curves are consistent with the characteristics of infiltration rate of common soil. This verifies that the point source infiltration experiment is feasible in the infiltration measurement of hillside forest land and the application scape of point source infiltration experimental method has been expanded. The updated soil source infiltration apparatus using the artificial identification reduces the experimental error to 0.3%-31% and the accuracy in infiltration rate measurement of hillside forest land has been improved greatly.
2019 Vol. 37 (7): 625-631 [Abstract] ( 237 ) [HTML 1KB] [ PDF 4993KB] ( 383 )
632 Experiment on one-dimensional infiltration characteristics of clay loam soil with different water repellency
CHAI Hongyang,, CHEN Junying,*, ZHANG Lin, WANG Jiarui,, LIU Chang,
To explore the effect of water repellency on the infiltration characteristics of clay loam, indoor water infiltration experiment was conducted in this paper. There were five kinds of clay loam with different water repellency degrees. The investigated soil water infiltration characteristics include wetting front, infiltration rate, cumulative infiltration, soil moisture and water redistribution. The applicability of three soil infiltration empirical models under different water repellency conditions was analyzed. The results showed that the soil infiltration rate was reduced, and the time required for wetting front migration was increased significantly with increasing water repellency. The time for the wetting front to travel the same distance was increased significantly, especially the time for 40 cm travelling distance in soil with strong repellency was 63% longer than that in hydrophilic soil. With increasing water repellency, the cumulative infiltration was reduced and the cumulative infiltration of S4 was decreased by 27% compared with S0 at the end of infiltration. The infiltration rate was also decreased with the increase of water repellency, and the saturated infiltration rate was 37% of that in hydrophilic soil. Both the moisture of soil profile and the change in moisture of redistributed soil profile in the same time were decreased with increasing water repellency. The power function model can simulate the migration process of wet front and the variation of cumulative infiltration with time. For the soil with slight repellence, the Philip model and the Kostiakov model were subject to a better accuracy in fitting the relationship between infiltration rate and time, while the Kostiakov model was even more suitable for the soil with strong repellency. The study can provide a basis for the infiltration theory of repellent soil.
2019 Vol. 37 (7): 632-638 [Abstract] ( 242 ) [HTML 1KB] [ PDF 1802KB] ( 436 )
639 Influence of drought and flood alternation stress in different growth stages on rice yield and components
CAO Ruizhe*, GAO Shikai
Using water level in rice fields as a regulation index of drought and flood alternation stress, the changes of rice growth, yield and components in different growth stages under drought and flood stress were studied experimentally in the paper. Field experiments were conducted by employing evapotranspiration absorption(ETA)bed in tillering, jointing and booting, heading and flowering as well as milky stages. The drought and flood alternation stresses occurred in four major growth periods could affect rice yield, especially the stress in jointing and booting stages, which could reduce the yield by 14.67% and 20.16% in maximum, respectively. The stresses in tillering stage could decrease number of rice panicles by 5.76% to 8.94%. The stresses in jointing and booting stages as well as heading and flowering stages could decrease number of grains per panicle by 6.07% to 9.57%. The stresses in hea-ding and flowering stages as well as milky stages could decline seed setting rate, especially, that in heading and flowering stages, which resulted in reductions of seed setting rate by 5.89% and 7.24% in maximum. The stress in milky stage could lower thousand grain weight by 3.81% and 5.70%. The successive drought and flood alternation stresses in multiple growth stages can produce a superposition effect and affect rice yield severely. This situation should be avoided as much as possible in ordinary rice planting.
2019 Vol. 37 (7): 639-644 [Abstract] ( 239 ) [HTML 1KB] [ PDF 1940KB] ( 486 )
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