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Journal of Drainage and Irrigation Machinery Engin
 
2017 Vol.35 Issue.5
Published 2017-05-25

369 Features of internal flow in jet nozzle of self-priming centrifugal pump based on large eddy simulation
LI Guidong, WANG Yang, YANG Xueming, ZHAO Lifeng, WU Wen, HU Rixin
In this paper, large eddy simulation with dynamic sub-grid stress model is adopted to study on fluid dynamics in the jet nozzle of a self-pariming centrifugal pump to examine the effects of transient pressure fluctuation on incipient cavitation characteristics in the pump and the reslts are compared with those obtained by means of the SST k-ω turbulence model. The results show that the time-averaged SST k-ω model cannot adequately simulate the pressure pulsation features at the throat of the nozzle, showing a constant value over time basically. However, the large eddy simulation with dynamic sub-grid stress model is able to get a variable pressure pulsation profil over time, but also the profile agrees well with experimental results, reflecting the actual situation of pressure pulsation. A vrotex ring is formed downstrea the jet in the nozzle, which is generated in the shear layer between the the suctioned fluid with low velocity and the driving fluid of high velocity. The instable vortex induces a voilent pressure fluctuation. A twisted vortex ring propagates downsteam and absorbs the kinetic enegy of the fluid with high velocity. The ring collapses at the thoat to produce the largest prssure pulsation amplide. As a result of this, cavitation is mostly prone to occur there. 
2017 Vol. 35 (5): 369-374 [Abstract] ( 963 ) [HTML 1KB] [ PDF 2328KB] ( 1104 )
375 Experimental study on erosion and suction characteristics of self-excited inspiratory jet
ZHANG Mingxing,, KANG Yong,, ZHOU Yongxiang, LIU Wenchuan,, WANG Aihua,,
A self-excited water-air jet is generated by the sucked air through four holes through the wall of a resonance chamber in front of a jet nozzle. Experiments were performed on this kind of jet to identify effects of inspiratory modes and diameters of suction holes on the self-excited inspiratory jet by examining erosion depth and damaged area in specimens and inspiratory capacity through the holes. The results showed that the erosion depth and damaged area increased with increasing diameter of the suction holes, and the erosion depth increased with the number of holes. Inspiratory modes played an important role in the erosion morphology of specimen and the unique erosion characteristics were observed when air was introduced. Additionally, the damaged area under the asymmetric inlet condition was significantly higher than under the symmetric inlet condition. The inspiratory flow was periodic, and the inspiratory capacity increased with increasing inlet pressure. Not only the inspiratory modes but also the diameter of suction hole affected the inspiratory performance. Particularly, the inspiratory capacity increased with increasing diameter of the suction holes when only one suction hole was in operation, while the best inspiratory performance was achieved at 4 mm diameter when multiple suction holes were open.
2017 Vol. 35 (5): 375-380 [Abstract] ( 763 ) [HTML 1KB] [ PDF 1948KB] ( 861 )
381 Analysis of cavitation characteristics of marine centrifugal pump based on modified Kunz model
WANG Yong, CHEN Jie, LUO Kaikai, LIU Dongxi, LI Yu, YAN Jun
Cavitation erosion may be inevitable when a marine centrifugal pump is in operation. Thus, in order to investigate effects of cavitation on the performance of a marine centrifugal pump, the turbulent pressure fluctuation was involved in the Kunz cavitation model to alter the phase transition critical pressure, i.e. vaporization pressure. A marine centrifugal pump with a specific speed of 132.7 was chosen as a study model and its cavitation performance was predicted numerically and experimentally at different flow rates. It was found that the Kunz model and its updated version both were able to capture the critical cavitation condition, but the head curve due to the updated model was in better agreement with the observed curve. In addition, the vapor volume fraction distribution between two blades and the blade loading distribution based on that improved model were analyzed at the design point.The results showed that bubbles were generated on the pressure suction side near the leading edge at first, then a small amount of bubbles occurred on the blade pressure side with decreasing cavitation number. At last, the impeller passages were fully blocked by bubbles, leading to a declined performance for the centrifugal pump. With the decrease of cavitation number, a low pressure zone occurred near the blade inlet edge firstly, then spread along the blade toward the blade outlet, eventually the low pressure covered the blade pressure and suction sides. The blade loading in the middle streamline of blade 5(the blade near the tongue)was smaller than in blade 2(the blade is axisymmetric with blade 5).With the decrease of cavitation number, the pressure on the blade surfaces was reduced, and there was a zero pressure at the inlet of blade 2, this is mainly caused by cavitation aggravation. 
2017 Vol. 35 (5): 381-386 [Abstract] ( 978 ) [HTML 1KB] [ PDF 1912KB] ( 786 )
387 Development of a series of high efficiency seawater desalination high pressure pump
WANG Jiabin, YE Xiaoyan, LI Xiupeng, HU Jingning, LI Caihong, ZHENG Jianbo
The seawater desalination high pressure pump is one key equipment in seawater desalination systems. In order to develop a series of products of high efficiency reverse osmosis seawater desalination high pressure pump and realize its industrialization, a large number of work, such as design of both overall structure and axial thrust balance device, selection of both bearing lubrication and wear-resistant materials and so on, was done in the pump development, trial production and testing based on latest techniques developed in national scientific and technological support projects by combining the new development trend of manufacturing technology in desalination high-pressure pumps in the world and by considering actual requirements of pump end-users on the pump performance. As a result, three series of products of high pressure pumps are developed for seawater desalination systems with 5 000, 10 000 and 15 000 tonnes daily output, respectively.The problems in existing products of the high pressure pump and the situation of a less varied variety in the products are turned over. Based on production, experiment and user application, it is shown that the performance of these series of products has reached the same level of the similar products in the world.
2017 Vol. 35 (5): 387-392 [Abstract] ( 1235 ) [HTML 1KB] [ PDF 3037KB] ( 822 )
393 Hydrodynamic and structural characteristics of horizontal axis current turbine under different pitch angles
LIU Heng, WANG Wenquan, YAN Yan
Based on the results of a two-dimensional hydrofoil obtained by computational fluid dynamics(CFD), the best angle of attack for the hydrofoil determined firstly by means of the lift to drag ratio chart at various angles of attack. The three-dimensional blades of a horizontal axis current turbine with 20 kW rated power were designed by using the Wilson method in Matlab. The hydrodynamic characteristics of the current turbine, such as the power, moment and axial thrust coefficients were predicted using CFD under different pitch angles and tip speed ratios. The static structural characteristics were also calculated using finite element method under various hydro-loads, the stress and strain in the blades were analyzed. The results showed that increasing pitch angle in the range of 1°-5° could be helpful to reduce the starting moment at a low tip speed ratio, moreover, increasing pitch angle can reduce the axial load, deformation and stress when the axial flow velocity is too high. The power coefficient of the turbine can reach to 0.301 and its structure can meet the requirements of material strength under the optimal operating condition. These achievements can be favourable to the design and optimization of marine current turbines.
2017 Vol. 35 (5): 393-397 [Abstract] ( 938 ) [HTML 1KB] [ PDF 1753KB] ( 716 )
398 Dynamic response of hydro-turbine set shaft system under stochastic hydraulic excitation
BAI Bing, ZHANG Lixiang
The forces acting on a hydro-turbine generator set shaft system were analyzed, including the nonlinear oil film force in the guide bearings, mechanical unbalanced forces on the rotor and runner, the unbalanced magnetic force on the rotor, and the hydraulic imbalance force on the runner. Then a nonlinear dynamic model for the shaft system was established, and the stochastic hydraulic excitation in the model was simulated with a zero mean, identically independent distributed(i.i.d.)signal, and its magnitude was changed by adjusting the random variance. The responses of the key parts(rotor, runner and guide bearings)to the changes in rotational speed, eccentric mass and exciting current, namely amplitude-time history curves, trajectory, amplitude spectra and Poincare diagram and bifurcation patterns, were obtained by solving the dynamic model equations. Results showed that the rotational speed and eccentric mass have a considerable influence on the vibration response of main parts in the shaft system. And the lateral throws at the turbine guide bearing and runner become obviously bifurcated as the stochastic hydraulic excitation increases. The excitation has strong influence on the vibration mode and stability of the shaft system.
2017 Vol. 35 (5): 398-403 [Abstract] ( 874 ) [HTML 1KB] [ PDF 1635KB] ( 677 )
404 DEM-based numerical simulation of unsteady gas-solid two phase flow in a fluidized bed and experimental validation
SHI Weidong, ZHANG Lingjie, ZHOU Ling, LU Weigang
In this study, the Euler-Lagrange method based DEM(discrete element method)is used to simulate the unsteady gas-solid two phase flow in the initial stage of three-dimensional bubbling fluidized bed to break the bottle-neck in the Euler-Euler model in which the force of particle collisions is not taken into account. Based on experimental observations made by high speed photographic technique in the initial stage of flow in the fluidized bed, a comparison is conducted between experiment and simulation in terms of changes in bed height, bubble size and particle phase motion characteristics. In the initial stage, the predicted results are in good agreement with the experimental data, particularly, the predicted height of bed and the shape of bubbles are basically the same as the measurements. Unfortunately, at a time moment near the bubble breakup, the predicted bubble diameter and height of bed are smaller than the experimental measurements. However, from the point of view of both fluid flow pattern and particle motion trajectory, DEM can solve the dense two-phase flow accurately, but also can describe the dynamic characteristics of a gas solid fluidized bed. The results presented in this study have important significance in guiding engineering practice. 
2017 Vol. 35 (5): 404-409 [Abstract] ( 890 ) [HTML 1KB] [ PDF 1668KB] ( 1166 )
410 Experiment on drag reduction in axial flow check valve based on separated transition model
YU Jianping, LUO Xiao, FU Jia, ZHANG Xiheng, ZHENG Rongbu, CHEN Zongjie
Axial flow check valves have been widely used in oil and gas long distance pipelines, compressors in large ethylene equipment and large pumps. The flow resistance reduction in a check valve can play an important role in saving energy in production systems. Traditionally, check valves are designed by using inviscid potential flow theory and optimized by means of the standard turbulence model. In the paper, the RNG k-ε model, transition SST model and transition K-Kl-ω model were adopted to calculate the separation of boundary layer over a blunt axisymmetric body and the skin friction drag. The calculated results were compared with experimental data and it was shown that three models were able to simulate the condition of separation of a boundary layer correctly. The vortex shape predicted by the transition K-Kl-ω model is more close to the experimental result. The traditional RNG k-ε model cannot reflect the transitional process and the change in skin friction drag before and after transition. But the transition SST, K-Kl-ω models, which are based on empirical theory of turbulent intensity both can predict the change in resistance caused from the transition, accordingly the calculated results of them are consistent with the experimental observations. The flow resistance coefficient calculated by the transition K-Kl-ω model is close to the experimental data with a 7% error, suggesting the model is more accurate than the traditional RNG k-ε model. Finally, the transition K-Kl-ω model was used to optimize the structure of an axial flow check valve. The optimized result showed that a smoothly divergent channel can lead to the best effect on drag reduction.
2017 Vol. 35 (5): 410-416 [Abstract] ( 971 ) [HTML 1KB] [ PDF 7889KB] ( 522 )
417 Photovoltaic optimization of solar-powered linear move sprinkler irrigation system
CAI Shibiao, ZHU Delan,, GE Maosheng, LIU Kenan, LI Dan
Photovoltaic(PV)systems have been widely used in agricultural production sector such as water pumps and tractors. Additionally, a solar-powered linear move sprinkler irrigator has been developed for precision agriculture and low energy consumption purpose, but its PV configuration strategy needs to be optimized. A PV system configuration method was put forward in this study according to the seasonal power requirement of sprinkler. Two indexes, namely the loss of power supply probability(LPSP)and the energy excess percentage(EXC)were selected as the constraints, and the minimum cost of life cycle cost(LCC)was specified as the objective function. By means of the meteorological data in Yangling, the PV system configurations of driving and pumping units were optimized. The optimal tilt angle of the PV panel is around 15°in Yangling and 12 PV modules and 3 battery groups can meet the power requirement of a 4-day irrigation cycle. This method can be used in PV system design and optimization of linear move sprinkler irrigation, and it provides a reference to the application of solar energy in agricultural machinery. 
2017 Vol. 35 (5): 417-423 [Abstract] ( 1024 ) [HTML 1KB] [ PDF 1603KB] ( 707 )
424 Spatial variability and scale effect of soil bulk density of farm land in South China
XU Cuilan, HOU Shunan, YAO Zidong, ZHANG Fei, SHE Dongli
Taking a typical farm land in South China as the test field, the spatial variability and scale effect of bulk density of soils harvested at different soil depths(0-10, 10-20 cm)in the selected field were analysed by using classical statistical and geostatistical methods, and the spatial interpolation of soil bulk density in the field was estimated. The results indicated that the coefficient of variation(CV)of bulk density was small and the variation was weak. A semi-variogram analysis showed that the C0/(C0+C)values of the measured soil bulk density were lower than 10%, indicating the spatial heterogeneity resulted from the spatial variability of soil bulk density was significant. For the scale effect, the CV decreased firstly and then increased with increasing sampling interval. By adjusting the location of sampling points("re-sampling"), it was found that the CV of soil bulk density was small(6.32%-7.92%)and the correlation distance decreased when the sampling interval increased. It was suggested that the sampling interval affected CV a little after the interval was decreased to a certain value. The spatial distribution pattern of soil bulk density in two layers also showed a spatial correlation based on the density spatial interpolation and contours, i.e. a significant positive correlation with a correlation coefficient of 0.76. Furthermore, the spatial variability of soil bulk density was affected by human activities largely.
2017 Vol. 35 (5): 424-429 [Abstract] ( 857 ) [HTML 1KB] [ PDF 1478KB] ( 843 )
430 Drought evolution characteristics and trend prediction in Inner Mongolia based on standardized precipitation index
HAN Zhihui, LIU Xiaogang, HAO Kun, YU Ning, LIU Yanwei, YANG Qiliang
To explore the evolution characteristics and trends of drought over the years in Inner Mongolia, standardized precipitation index(SPI)in the recent 51 years(1960-2010)was calculated with the daily precipitation data from 43 weather stations in Inner Mongolia, the annual and seasonal drought frequency, its station frequency ratio and drought intensity were analysed, and the trend of drought was predicted by using the Hurst index. The results showed that the annual drought frequency was in the range of 10.46%-33.66%, the highest frequency(33.66%)occurred in Hulun Buir, and the lowest one(10.46%)was in Ejina of Alxa League, additionally, the monthly and seasonal drought frequencies were consistent with the yearly drought frequency. The highest station frequency ratio was 45.74%, and the lowest one was 15.50%, particularly, the regional, partly regional and local droughts occurred in 11, 26 and 14 years, respectively. The drought intensity was mainly mild and moderate, and the maximum intensity was 1.14 in 15 years. Drought frequency was relatively high in spring, summer and autumn with a mean of about 30%, while in winter the frequency was 25.41%, moreover the drought frequency was distributed unevenly between the weather stations, for example, the drought frequency was 0 at 4 stations including Ejina. Station frequency ratio increased at the rates of 0.177/10a and 0.006/10a in summer and autumn, decreased at the rates of 0.033/10a and 0.156/10a in spring and winter, respectively. The variation trend of drought intensity was basically the same as the station frequency ratio in seasonal scale. The SPI sequence exhibited a remarked Hurst phenomenon in Inner Mongolia, and the index(0.5687)was more than 0.5, indicating that the drought degree could sustain for some time, while the frequency of the occurrence of moderate drought and above showed a decreasing trend. 
2017 Vol. 35 (5): 430-439 [Abstract] ( 671 ) [HTML 1KB] [ PDF 5260KB] ( 867 )
440 Effects of water and nitrogen coupling on nitrogen absorption and yield of winter wheat
QIN Shanshan, HOU Zongjian, WU Zhongdong, MA Donghao, ZHANG Jiabao, HUANG Ping
Improving water and fertilizer use efficiencies is one of the fundamental ways to solve resources and environmental problems in the North China Plain. A series of long-term experiments were made in a typical specified field in the North China Plain, Fengqiu, Henan Province to clarify the influence of water and nitrogen fertilizer coupling on nitrogen absorption and utilization as well as grain yield of winter wheat. In the experiments, five nitrogen levels were used, at each level, there are there irrigation wet layers. The results indicated that the best nitrogen fertilizer amount was 235-250 kg/hm, and the irrigation wet layer was 37-40 cm thick in Fengqiu, the yield and nitrogen utilization rate of winter wheat could be affected if a nitrogen fertilizer amount was more or less than this best one. The impacts of irrigation on the total nitrogen content in plant, nitrogen utilization rate and yield of winter wheat are closely related to characteristics of rainfall. The lack of rainfall in critical growth periods such as stem elongation and ear emergence stages can lead to a significant decrease in yield of winter wheat. An appropriate irrigation can improve the yield, but too much irrigation cannot help to increase it further. Irrigation shows a little influence on plant nitrogen content in the case of sufficient precipitation. If rainfall is insufficient, increasing irrigation can hamper the nitrogen transfer from straw to grain. 
2017 Vol. 35 (5): 440-447 [Abstract] ( 858 ) [HTML 1KB] [ PDF 1444KB] ( 1445 )
448 Study on water distribution uniformity of non-circular nozzles at low pressure
ZHOU Xiaoyin, LI Hong, JIANG Yue
According to the principle of equal nozzle cross-section area, a few nozzles with different shapes were designed to study their effect on the distribution of sprinkler irrigation at low pressure. The nozzle hydraulic performances were measured, the spraying uniformity of different nozzles were analyzed by using Matlab software. Additionally, the spatial flow pattern with different nozzles were observed with high speed photographical technique. The results show that the flow rate decreases gradually with increasing nozzle cone angle at the same pressure, the flow rate through the squared cross-section nozzle is the largest, that through the triangular cross-section nozzle is the smallest. The nozzle wetted radius firstly increases then decreases with increasing cone angle, and the circular and triangular cross-section nozzles are subject to the longest and shortest wetted radius, respectively. Based on high-speed photographical images, it can be seen that the jet breaking length issued from the triangular cross-section nozzle is the shortest, while the breaking length from the circular cross-section nozzle is the longest. With increasing nozzle cone angle, three nozzle jet breaking lengths show a decreasing trend. Composting the nozzle wetted radius and the atomization effect, it can be known that the circular cross-section nozzle with 45 degrees cone angle is the best. Moreover, it is found that the combined water distribution uniformity coefficient of the non-circular cross-section nozzles is evidently better than the circular nozzle based on measurements.
2017 Vol. 35 (5): 448-453 [Abstract] ( 809 ) [HTML 1KB] [ PDF 1705KB] ( 782 )
454 Design and optimization of worm drive based transmission system for hose reel sprinkler
LI Ke, TANG Yue, ZHAO Jin
In order to expand the range of speed ratio of hose reel sprinkler and increase its transmission ratio as well as improve its efficiency, the DC motor driven transmission system of JP75 hose real sprinkler is redesigned and optimized by involving a worm drive. In the new transmission system, there are two transmission ratios, depending on the speed of spraying vehicle, and the number of stages of the transmission is reduced since a partial spur gear transmission has been replaced with the worm drive. The key parameters of the system, such as number of gear teeth and face width coefficient and so on in various stages of the spur gear transmission and worm drive are optimized by using Matlab genetic algorithm toolbox according to their design parameters preliminarily decided. In the optimization, transmission efficiency and gearbox volume are used as the objective functions with continuous and discrete variables. The optimized and experimental results show that the transmission efficiency is improved by 13.77% and 13.11% at two transmission ratios, respectively, and the gear box volume is decreased by 10.30% compared to the initial design values. The newly designed transmission scheme can be a useful reference for transmission system update of a hose reel sprinkler. 
2017 Vol. 35 (5): 454-460 [Abstract] ( 960 ) [HTML 1KB] [ PDF 4015KB] ( 692 )
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