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Journal of Drainage and Irrigation Machinery Engin
 
2016 Vol.34 Issue.11
Published 2016-11-25
921 Influence of re-entrant jet strength on cavitation characteristics of hydrofoil
WANG Wei, XU Ruiduo, YI Qi, WANG Xiaofang
In order to investigate influences of re-entrant jet strength on periodical evolution of cavity attaching to the upper surface of a hydrofoil, several 2D meshes around a hydrofoil at different inflow angles are established. The distributions of pressure, velocity and phase features of cavitating flow field are analyzed by using CFD method. Unsteady cavitating flows over the 2D hydrofoil with different inflow angles are simulated with the RNG k-ε turbulence model and Schnerr-Sauer cavitation model. The re-entrant jet motion features and interaction with cavity are analyzed at 4°, 10° and 12° inflow angles and 0.91 cavitation number. Based on velocity, characteristic length and other parameters, a critical cavitation number is put forward to estimate the strength of re-entrant jet and serves a basis of judgment on change in cavity shape. The results show that the strength of re-entrant jet is an important factor influencing the structure of cavity. It is identified that the magnitude of criterial number can be correlated to different periodical stages and types of cavity.
2016 Vol. 34 (11): 921-926 [Abstract] ( 703 ) [HTML 1KB] [ PDF 3178KB] ( 1032 )
927 Transient numerical simulation and visualization of self-priming process in self-priming centrifugal pump
LU Tianqiao, LI Hong, ZHAN Lianchen
Based on the Euler multiphase model, standard k-ε turbulence model and sliding mesh technique, the self-priming process in a 65ZB-40C self-priming centrifugal pump are simulated. The experimental rotational speed curve of impeller and pressure curve at the pump outlet are taken as the boundary conditions in the simulation. The monitoring planes/surfaces are set in the volute, impeller, air-liquid separation chamber and reflux hole to analyze the changes of air volume fraction, air and liquid velocity and pressure. The numerical results are compared with the observation made by using high-speed camera. The results show that the air-liquid two-phase flow patterns are consistent with the observed pressure, flow rate and rotational speed in experiment. The stable self-priming process occupies the maximum portion of the self-priming time and has the most significant effect on the self-priming performance. In the end of the self-priming process, the flow rate and pressure change abruptly. The water droplets in the air-liquid separation chamber and the bubbles at the outlet of volute nozzle increase and decrease rapidly, showing an apparent transient effect. The gas phase cavity in the center of air-liquid separation chamber is beneficial to the formation of moving bubbles in the volute outlet area and the steady gas discharging from the self-priming pump.
2016 Vol. 34 (11): 927-933 [Abstract] ( 734 ) [HTML 1KB] [ PDF 4158KB] ( 975 )
934 Numerical simulations on clocking effect of impeller-stator in multistage axial-flow pump
FU Heng, LU Jinling, CHEN Nan, FENG Jianjun, CHEN Senlin, LUO Xingqi
In order to study influences of clocking effect of impeller-stator on the performance of multistage axial-flow pump, 3D, unsteady flows in a multistage axial-flow pump are simulated numerically by using CFD method. In the simulations, five positions or clocking positions of a blade leading edge in the second stage impeller relative to the blade leading edge in the first stage impeller are investigated. In the reference case, the angle between two blade leading edges is 0°, and then in the following four cases, this angle is increased by a 9° increment. The pressure fluctuation and pressure loading on blade surfaces are analyzed. It is shown that the maximum variation in the pump head is 4.6% at the clocking position of 36°, but the efficiency is just with a change of 1.2% compared with the reference case. At the first stage impeller outlet, the pressure pulsation amplitude and phase have a small fluctua-tion. The maximum reduction of the pressure pulsation amplitude at the first stage impeller outlet is 16.31%, while the pulsation amplitude, whose average value in time domain and phase at the second stage impeller outlet are affected in a certain degree, causing a 48.27% increasing in the pressure pulsation amplitude and a 1.34% rise in its average value. The pressure loading distribution profiles on the second impeller blade surfaces remain nearly identical at different clocking positions. However, the loading distribution in the case, where the angle between two blade leading edges is 9°, is obviously higher than the other clocking positions.
2016 Vol. 34 (11): 934-940 [Abstract] ( 907 ) [HTML 1KB] [ PDF 2934KB] ( 875 )
941 Numerical calculation of pressure fluctuation in contra-rotating axial flow waterjet pump
WANG Xuebao, PAN Zhongyong, HUANG Dan, ZHANG Xiao, HUANG Zhenjie
The unsteady pressure fluctuations in an optimally designed contra-rotating waterjet axial flow pump are identified by using unsteady numerical simulation under design condition based on CFD method with the SST k-ω turbulence model. A mesh independence analysis shows that the calculated power and head are well consistent with the design data. The monitoring points are mounted at the inlet of front impeller, in the tip region of front and rear impellers, in the axial clearances and at the diffuser inlet. The time domain pressure fluctuation data are recorded at each monitoring point, meanwhile the pressure fluctuation characteristics are analyzed and compared in both time and frequency domains. The simulation results indicate that pressure fluctuation is mainly affected by blade passing frequency, however, the fluctuation in the tip region of the front and rear impellers depend on the number of blades and impellers. Influenced by reverse rotation of the two stage impellers, the pressure fluctuation amplitude in the axial clearance between the front impeller and the rear impeller is the maximum. The pressure fluctuations at the rear impeller outlet and diffuser inlet are mainly influenced by reverse flow from the diffuser.
2016 Vol. 34 (11): 941-946 [Abstract] ( 766 ) [HTML 1KB] [ PDF 2086KB] ( 982 )
947 Research situation and prospect of jet type self-priming centrifugal pump
LI Wei, CHANG Hao, LIU Jianrui, ZHOU Ling, WANG Chuan
Jet type self-priming centrifugal pump is a new structure of the self-priming centrifugal pump, which start before the pump can not be used to achieve the characteristics of rapid self-priming, the new structure of self-priming centrifugal pump has become a hot research topic at home and abroad. The development history of the jet type self-priming centrifugal pump is reviewed; the operating mechanism and structural advantages of the jet type self-priming centrifugal pump are analyzed. On the basis of summarizing the research results, the water pressure from the deflector type asymmetric chamber, bowl valve automatic closing structure, jet nozzle geometry, nozzle contraction angle variables are analyzed in terms of self-priming progress on theory and technology of centrifugal pump, and the future research direction is proposed. In the aspect of hydraulic design, the hydraulic model of different structure is designed, and the influence of various geometric parameters of the impeller on the overall performance of the pump is deeply discussed, the innovative self-priming structure and self-pri-ming mechanism were applied, by using the new principle of self-priming, constantly deepen the impact of structure on performance self-priming, and to determine the method of selecting the optimum geometrical parameters of the various components to improve the performance of jet self-priming centrifugal pump. In the process, breaking the traditional method of manufacturing a casting, the new type of aluminum die casting is applied. For the development of efficient, rapid self-priming, low-power jet self-priming centrifugal pumps provide a realistic basis and theoretical reference.
2016 Vol. 34 (11): 947-952 [Abstract] ( 853 ) [HTML 1KB] [ PDF 1628KB] ( 1242 )
953 Experimental investigation into effects of sump shape on suction vortex
XIAO Ruofu,, LI Ningning,
Serious vortices in pump sumps can lead to cavitation in a pump, subsequently the pump characteristics are affected in operation. In order to improve the flow regime in a sump and prevent vortices from entering into the bell-mouth, a series of high-speed photography and PIV experiments are carried out at different submerged depths and flow rates in an open sump firstly, then, according to visualized flow patterns, two measures, namely a rectangular sump with and without bottom cross, are put forward to improve the flow pattern; finally, their effects on vortex elimination are observed. The results show that the rectangular sump without bottom cross is able to improve the flow regime in the sump and to reduce the minimum submerged depth, the surface spiral vortex intensity can be reduced under the same operating condition. For the rectangular sump with bottom cross, the effect of vortex is suppressed further, and the minimum submerged depth is reduced once more and the surface spiral vortex intensity is dampened. This study makes significant sense in lowering allowable submerged depth and reducing engineering costs of pump sump.
2016 Vol. 34 (11): 953-958 [Abstract] ( 836 ) [HTML 1KB] [ PDF 2219KB] ( 1105 )
959 Material procurement model for channel engineering based on GIS
SHI Xichen, LIU Yongqiang, LI Huimin
In order to optimize the purchasing cost of enterprises and achieve intensive procurement objectives, a material procurement model for channel engineering is developed based on GIS, from the point of view of transportation route planning, by fusing operations research knowledges. At first, the material supply and storage points are decided, then transport routes are chosen by means of a GIS software, finally a route network model for material procurement is built. By applying the Floyd algorithm in graph theory to find the shortest transportation route between the material supply points and the material demand points, then the material transportation costs are figured out, and finally the comprehensive/total unit prices are determined by considering ex-factory prices. On this basis, a linear programming tool is introduced and a linear programming model for purchasing decision is established, in which the purchase quantities between supply and demand points are the variables to be optimized, the total purchase cost serves as objective function, comprehensive unit prices of materials are used as the value coefficient, while the balance of supply and demand are constraint conditions. The mode is solved by using MATLAB and VOGEL approximation method of allocation, respectively, and corresponding results by the two methods are compared. It is shown that the procurement cost can be reduced by RMB￥530 k predicted in MATLAB and RMB￥340 k with the VOGEL method. Obviously, the procurement program determined by the former is more attractive. Note that the purchasing model based on GIS has removed the uncertainty of material transportation route and distance in purchasing and solved the problem of unrealistically high purchasing cost. Naturally, this article provides a supplementary tool for proposing a scientific and reasonable procurement plan.
2016 Vol. 34 (11): 959-966 [Abstract] ( 816 ) [HTML 1KB] [ PDF 1429KB] ( 1119 )
967 Analysis of temperature and thermal deformation of main seal in double mechanical seal in medium with moderate temperature and high viscosity
CHEN Huilong, ZOU Qiang, ZHAO Binjuan, FU Jie, LIU Jinfeng
To grasp characteristics of heat transfer and deformation of the main seal in a double mechanical seal in a medium with moderate temperature and high viscosity, and to understand influences caused by the pressure and temperature of flushing liquid, as well as to provide a reference for the sealing performance improvement and an efficient control on flushing liquid, an AR201 double mechanical seal for emulsion equipment is taken as the study object, then a heat transfer computational model is established, finally, the temperature field is analyzed based on finite element method, and the temperature and deformation of the sealing rings are studied when the pressure and temperature of flushing liquid varing. The results indicate that the highest temperature is near the outside of contact face of two rings, the temperature inside the stationary ring is significantly lower than outside the ring because of the cooling effect of flushing liquid, the temperature in the rotational ring reduces gradually from the contact face along the axial direction. The highest temperature and the maximum thermal deformation rise with increasing pressure and temperature. The maximum deformation and its magnitude caused from the change in flushing liquid operating parameters are closely related to the material of the rings. Properly choosing operating pressure and temperature for a flushing liquid can be a measure to effectively improve the sealing performance. As AR201 mechanical seals, the flushing liquid with a pressure in 0.8-0.85 MPa and a lower temperature can help reduce wear on the two end faces more favourably.
2016 Vol. 34 (11): 967-973 [Abstract] ( 719 ) [HTML 1KB] [ PDF 1976KB] ( 965 )
974 Analysis on characteristics of flow in regulating valve and pipe system of water storage tank for boiler in ultra-supercritical power plants
HE Qingzhong, GUO Bin, DONG Xuelian, ZHANG Cheng, LIU Jia, CHEN Xuefeng
In view of faced problems in flow structure design in the research and development of regulating valve of water storage tank for boiler in ultra-supercritical power plants in China, combining the cavitation erosion of valve plate in the previously designed regulating valve in a specific plant, a series of numerical simulations of two-phase cavitating flow field in a regulating valve and pipe system are carried out by using CFD code in Fluent. In the simulations, the RNG k-ε. turbulence model and full cavitation model are used to validate fluid flow structure and to optimize the valve structure, especially, a cone valve and its pipe system are paid attention. The results show that cavitation occurs seriously in the throat of the original cone valve under design condition due to the very narrow opening. Particularly, the vapour volume fraction is above 90% and the flow velocity is as high as 143 m/s, leading to damage to the valve plate by cavitation eventually. To eliminate the cavitation, a new type of valve structure is put forward. The results show that the vapour volume fraction is reduced by 21.6% and the fluid velocity is decreased by 80% near the throat, suggesting the cavitation phenomenon has been suppressed to some extend and the pipe system is capable of safe operation. The simulated results exhibit the flow field distribution in the valve and pipe system more clearly, and provide theoretical references for the design and optimization of regulating valves, as well as promote the nationalization of this kind of valve.
2016 Vol. 34 (11): 974-978 [Abstract] ( 801 ) [HTML 1KB] [ PDF 1951KB] ( 920 )
979 Spatial distribution, contamination and potential ecological risk evaluationof heavy metals in farmlands around Maoping leadzinc mining area
WANG Weihua, LEI Longhai,
Soil samples in the farmlands around Maoping leadzinc mining area are collected to determine the concentrations of Cr, As, Ni, Pb, Zn, Cu and Co. It is found that the concentrations of Zn, Co and As are as high as 1.92, 1.47 and 1.12 times the initial values, respectively. The substrate effect is ranked in the order of NiCo>As>Ni>Cu>Cr>Pb. The potential ecological risk index of seven metals are in the order of Co>As>Ni>Cu>Pb>Cr>Zn, and at the moderate risk level as well. The ecological risk index (RI) distribution diagram illustrates that the severely polluted zone is located in the south of the southeast region in the studied mining area, and the pollution diffuses outwards, fortunately, the entire studied area are at the moderate risk level.
2016 Vol. 34 (11): 979-989 [Abstract] ( 873 ) [HTML 1KB] [ PDF 2358KB] ( 952 )
990 Changing law of nitrogen concentration in paddy water under alternating drought and flooding stress
GUO Rong,, ZHOU Wei, GAO Shikai,, WANG Mei,, CAO Ruizhe,, YU Shuang′en,
NH+4-N and NO-3-N concentrations in paddy water under alternating drought and floo-ding stress are studied with lysimeter experiment during jointing-booting and panicle initiation stages by using water level as a regulation index. The experimental results show that NH+4-N is the major form of nitrogen in paddy surface and ground water. Alternating drought and flooding stress has significant influence on the change of NH+4-N and NO-3-N concentrations in paddy water. Compared with FFTD(first flooding and then drought), the mean NH+4-N and NO-3-N concentrations are significantly greater in FDTF(first drought and then flooding)water. The NH+4-N and NO-3-N concentrations are decreased in FFTD and FDTF surface water. Moreover, the mean NH+4-N and NO-3-N concentrations are significantly higher in paddy water under the flooding stress than under drought stress. In addition, NH+4-N and NO-3-N concentrations can be sharply increased in paddy water when a drought stress is followed by a flooding stress. Therefore, drainage should be avoided when the re-flooding occurs after drought.
2016 Vol. 34 (11): 990-994 [Abstract] ( 779 ) [HTML 1KB] [ PDF 1425KB] ( 880 )
995 Effect of regulated deficit irrigation and nitrogen nutrition on growth and water use efficiency of Jatropha curcas L.
LI Jie, YANG Qiliang, XU Man, JIA Weibing, LEI Longhai, XU Tianyu, WU Jinbo, LIU Xiaogang
To explore effects of regulated deficit irrigation and nitrogen nutrition on growth and water use efficiency of Jatropha curcas L., a set of pot experiments are conducted at four water levels(WLWH, WHWL, WLWL, WHWH)and three nitrogen levels(NZ: 0, NL: 0.2 g/kg, NH: 0.4 g/kg). It is shown that the growth and irrigation water use efficiency at WLWH levels are significantly higher than WHWL. With increasing nitrogen level, the irrigation water use efficiency shows a maximum value at NL level. Compared with NHWHWH, the height, total dry matter and irrigation water use efficiency are decreased by 31%, 35% and 13%, irrigation water is saved by 27%, and nitrogen fertilizer dosage is reduced by 50%, respectively, at NLWLWH levels, but the plant stem diameter, root-shoot ratio are increased by 13% and 20%. In the first stage of growth(40-90 d), less water is demanded, moderate deficit irrigation can improve the irrigation water use efficiency. In the second stage of growth(90-140 d), more water is on demand for vigorously growing, increasing irrigation water can promote plant growth and dry matter accumulation greatly. Even though a deficit irrigation in the whole growth period can improve the ability to adapt to the environment, the plant production decreases. After a comprehensive analysis, NLWLWH is the best irrigation and nitrogen fertilization scheme under arid area conditions for Jatropha curcas L. 
2016 Vol. 34 (11): 995-1002 [Abstract] ( 844 ) [HTML 1KB] [ PDF 1638KB] ( 863 )
1003 Variable frequency and adjustable constant pressure automatic control irrigation system and its application
HE Wuquan,, ZHANG Hua, HE Xinye, ZHANG Yufeng
In a sprinkler irrigation system with long pipe, there is a constant frequency(50 Hz)motor to derive the pump for delivering water. If the irrigating area or elevation change greatly in an irrigation field, the sprinkler irrigation uniformity will become unsatisfactory. In order to solve this problem, a variable frequency and adjustable constant pressure automatic control irrigation system is proposed. In the system, frequency conversion and automation technique are combined, and it is a kind of mechatronic-intelligent device with variable frequency motor and closed-loop fully automatic control function, and it can control for one or more AC 380 V, 50 Hz pump motors automatically at the same time. An electrical circuit is designed for setting different constant pressure levels. As a result, the system can vary the pressure in a pipe network automatically according to the pressure levels prescribed, by opening and closing the electromagnetic valves installed in the network; eventually, an automatically adjustable constant pressure water supply irrigation process is realized. Through the analysis of an engineering project, it is shown that the maximum difference in sprinkler system head is 12.89 m while the pump operating at 50 Hz, by using variable frequency adjustable constant pressure control system, however, the maximum difference in the sprinkler head is 3.38 m, which has met the requirement on pressure variation. Also, this system has a few advantages, such as water saving, energy saving, high degree of automation, convenient operation and management, guaranteed safe operation of pipe network and pump. It allows a pump to supply water to the sprinkler under a prescribed pressure level according to an irrigation field partition, thus the irrigation uniformity of sprinkler is favourable and satisfactory.
2016 Vol. 34 (11): 1003-1007 [Abstract] ( 828 ) [HTML 1KB] [ PDF 1374KB] ( 923 )
1008 Energy consumption analysis of hydraulic turbine of JP75 hose reel irrigator
CHENG Jun, TANG Yue, TANG Lingdi
For study on energy consumption of various hydraulic components of the hydraulic turbine of JP75 hose reel irrigator, the external characteristic of the turbine is tested and the flow field is numerically simulated based on a commercial software STAR-CCM+. According to an analysis of pressure and velocity distributions in the turbine, the energy consumption in the connection between the impeller and the inlet pipe is 44.80%, while the whole consumption of the connection is 52.18%. It is also shown that a serious energy consumption are associated with a high pressure gradient and appearance of vortex. Based on this, the original hydraulic turbine design is optimized. As a result, the turbine total efficiency is significantly improved, the total head is reduced obviously and the nominal output power is guaranteed, eventually the goal of optimization has been achieved.
2016 Vol. 34 (11): 1008-1012 [Abstract] ( 859 ) [HTML 1KB] [ PDF 2480KB] ( 874 )
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