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Journal of Drainage and Irrigation Machinery Engin
 
2019 Vol.37 Issue.5
Published 2019-05-25

article
article
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2019 Vol. 37 (5): 1- [Abstract] ( 110 ) [HTML 1KB] [ PDF 2185KB] ( 183 )
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2019 Vol. 37 (5): 2- [Abstract] ( 116 ) [HTML 1KB] [ PDF 370KB] ( 143 )
369 Effects of silt particle on cavitating flow in centrifugal pump
ZHAO Weiguo,HAN Xiangdong,FU Yidong
Based on numerical method, effects of silt particle with certain silt mean diameter and silt concentration on the evolution of cavitation in a centrifugal pump were studied. Silt mean diameter 0.005 mm and silt concentration 1.0% were adopted in numerical simulations. Capitaton flow in a flat-nosed cylinder was simulated to validate the designed algorithm. Cavitaton flows of water and silt-laden water were simulated and compared. The results indicate that the silt particles promote the evolution of cavitation. At the outlet pressure of 6.0?105 Pa, cavitation bubbles do not exist in the water flow, but a few cavitation bubbles appeare in the silt-laden water flow, demonstrating the silt particles induce the formation of cavitation bubbles. At the outlet pressure of 5.29?105 Pa, the vapor volume fraction in the silt-laden water flow is much larger than that in the water flow, indicating that the silt particles enhanc the evolution of cavitation. The properties of silt particle, static pressure, flow field structure, turbulent kinetic energy and density difference have a close relationship with the evolution of cavitation.
2019 Vol. 37 (5): 369-374 [Abstract] ( 153 ) [HTML 1KB] [ PDF 2808KB] ( 189 )
375 High-speed photography experiment on transient air-water flow in self-priming centrifugal pump with separation chamber
LI Hong,LI Shuting,LU Tianqiao
To study the variation of internal flow in self-priming process of the self-priming centrifugal pump, a flow visualizable transparent self-priming centrifugal pump prototype was designed. The pressure, flow rate and rotational speed, etc., were recorded in the self-priming process of the pump with Labview virtual instrument in time domain, and the influence of rotational speed on the outlet pressure and self-priming time of the pump was investigated. Meanwhile, the air-water two-phase flow patterns in the key components of the pump were shot with a high-speed camera at various stages of the self-priming process, and transient variations of the two-phase flow in the pump were analyzed. The results show that the self-priming process of the pump can be divided into three stages in terms of the variations of pressure and flow rate with time, i.e., start-up, stable and sudden change stages. This feature can also be observed in the outlet pressure profiles at different rotating speeds. In the stable self-priming stage, the faster the impeller rotating speed, the larger the fluctuation amplitude in the outlet pressure, the higher the final stable pressure and the shorter the self-priming time. Bubble splitting phenomenon exists in the volute and impeller during the self-priming process. Firstly, a single large bubble is gradually elongated into a bubble in dumbbell shape. Then the connecting channel in the middle of the bubble disappears and the bubble is split into two small ones to promote air separation and complete the self-priming process.
2019 Vol. 37 (5): 375-380 [Abstract] ( 178 ) [HTML 1KB] [ PDF 6664KB] ( 177 )
381 Numerical simulation of flow in coolant pump for special nuclear reactor under positive and negative rotational speeds
YANG Congxin,, ZHANG Yang,*, QIAN Chen,
To identify the characteristics of reactor coolant pump(RCP)under positive and negative constant speeds, numerical simulations of the flow in the model coolant pump scaled down from the real pump with 0.5 scaling factor based on the pump affinity laws were carried out by using the SST k-ω turbulence model and structured-mesh. The flow rate was defined as “+” when the fluid flows into the pump from the inlet, otherwise, it was defined as “-”. The complete characteristic curves were predicted respectively with 16 operating points in the flow range of -0.8Qd - +2.0Qd under positive rotational speed, and 14 operating conditions in the flow range of -1.4Qd - +1.0Qd under negative rotational speed. The results show that at the same flow rate, the head and torque of the RCP under positive rotational speed are always higher than that under negative rotational speed. The impeller head and pump head have different variation trends. The impeller head curve is in upside-down “N” shape as the flow rate in the range of -0.1Qd - +0.4Qd under positive rotational speed, but it is in “V” shape when the flow rate is in the range of -0.4Qd - +0.1Qd under negative rotational speed. The internal flow results show that there is a secondary flow phenomenon in the impeller outlet. This flow pattern is mainly responsible for the drop in the impeller head under low flow rate conditions under positive rotational speed. The large-scale vortices in the impeller and the high-velocity region between the impeller and the radial diffuser are the main reason for the drop in the impeller head curve with negative rotational speed under low flow rate conditions.
2019 Vol. 37 (5): 381-386 [Abstract] ( 191 ) [HTML 1KB] [ PDF 6181KB] ( 182 )
387 Numerical simulation on pressure pulsation in multistage centrifugal pump under several working conditions
HUANG Kaile, YUAN Jianping*, SI Qiaorui, LIN Gang
In order to study the characteristics of pressure pulsation and unsteady flow features in multistage centrifugal pumps, a three-stage centrifugal pump model served as flow simulation object. The DES method was used to simulate the unsteady flow in the pump under four working conditions. The reliability of numerical simulation was demonstrated by comparing the predicted performance with the measured characteristic. Thirty-six monitoring points were set up in the impeller, radial diffuser and return channel in each stage. It is shown that the throat of the radial diffuser is subject to a pressure pulsation in low frequency. At different flow rates, the pressure pulsation presents periodicity and the most pulsation intensity occurs in the radial diffuser, but also the amplitude of pressure pulsation increases when the working point deviating from the design flow condition. At different flow rates, the main frequency of pressure pulsation in the radial diffuser is the blade passing frequency of 327 Hz and the peak amplitude at the blade passing frequency multiplied by an integer is attenuated rapidly. The results provide a theoretical reference to revealing pressure pulsation law in multistage centrifugal pumps.
2019 Vol. 37 (5): 387-392 [Abstract] ( 196 ) [HTML 1KB] [ PDF 3818KB] ( 205 )
393 Three-dimensional multi-parameter design and experiment of axial-flow pump impeller
YU Yunyun,ZHOU Daqing*,DAI Qifan,LIANG Haojie,ZHONG Ziye
To solve the design problem of the axial-flow pump in a pumping station refurbishment projection in the South to North Water Diversion East Route, three-dimensional(3D)multi-parameter design of an axial-flow pump impeller was carried out by using BladeGen software. The whole axial-flow pump geometric model with designed impellers was established, and a structured mesh in the fluid domain was generated. The influences of design parameters of the impeller on the pump external hydraulic performance were analyzed through numerical simulations. Furthermore, the effects of a dominant parameter i.e., blade wrapping angle on pressure and velocity distributions over the blades and cavitation performance were clarified in terms of three wrapping angle profiles. According to the numerical results, design case 6, in which the hub ratio was 0.40, the maximum section thickness in the mid-chord was 10mm, and the blade section was airfoil B, was chosen eventually. In this design case, the pump head was 4.90m, the pump efficiency with suction and discharge pipes was 79.76%, and the impeller efficiency was 92.19% at the design flow rate. These performance parameters has met the design requirements, and were consistent with the corresponding experimental measurements. Therefore, the BladeGen software could produce more accurate 3D multi-parameter designs for an axial-flow pump impeller to reduce both number of design cases and workload in geometry modeling during the optimization process, and result in an improved pump efficiency.
2019 Vol. 37 (5): 393-399 [Abstract] ( 208 ) [HTML 1KB] [ PDF 2449KB] ( 181 )
400 Design of sliding bearing wear monitoring sensor in magnetic drive pumps
ZENG Pei*, ZENG Hao, XU Defu, GOU Xiaojun, LI Yongliang, YE Zizao
A novel sensor was designed to realize real-time monitoring of sliding bearing wear in magnetic drive pumps. Based on the structure of magnetic drive pumps, a special sensor structure in which the curved surface measurement was converted into a plane measurement with a detecting wheel was put forward. The detecting wheel made of an anti-corrosion treated magnetic material was fixed on the inner magnetic rotor, and the detecting sensor was installed in the ring-shaped recessed groove in the containment shell. The sensor was a container with a flat detecting plane, which was opposite to the detecting wheel in the axial direction. The sensor was composed of magnet, magnetic flux concentrator and its forehead as well as the Hall IC. The detecting sensor and the detecting wheel form a closed magnetic circuit. Through magnetic circuit analysis, the magnetic circuit was simplified. After the sensor size was decided, all the parameters of the magnetic circuit such as the magnetic permeability of the magnet, the magnetomotive force of the magnet, and the cross-sectional area of the magnetic circuit were constant, thus the output voltage of the Hall IC was related to the change in the area of the magnetic flux concentrator forehead, So, it was associated with radial displacement δ of the detecting wheel. The resolution was 0.122 mm, the linearity was 0.1-2.3, the sensitivity of the sensor was 10mV/mm and the linearity of the displacement characteristic curve of the sensor was improved. The sensor designed in this paper has certain application significance for real-time monitoring of sliding bearing wear in magnetic drive pumps.
2019 Vol. 37 (5): 400-405 [Abstract] ( 196 ) [HTML 1KB] [ PDF 2044KB] ( 148 )
406 Water hammer protection in long-distance water supply project with combined air vessel and surge tanks
WANG Siqi, YU Xiaodong*, NI Weixiang, ZHAGN Jian
Based on the method of characteristics(MOC), the mathematical model of an integrated system including the pump, pipeline, and water hammer protective measures is established in terms of a practical water supply project, and the transient pressure variation process in the system is simulated during a pump sudden stopping period. Based on simulations a low pressure exists at the local high elevation site. To avoid a negative pressure in the pipeline if an orderinary air vessel is involved in the system, then its volumme can be as large as 530.00 m3. To solve this problem, two methods, namlely, air vessel-two-way-surge tank and air vessel-one-way-surge tank, are proposed, their protective effectiveness is analyzed and compared. The results show that the volume of air vessel can be significantly reduced by two protective methods proposed. For the air vessel-two-way-surge tank method, the volume of air vessel has been reduced to 40.27 m3, however, its height reaches as high as 27.00 m, because the tank height is controlled not only by the piezometric head but also by the pump head. For the air vessel-one-way-surge tank method, the tank height is not limited by the piezometric head, and the volume of air vessel is reduced to 43.83 m3. Unforatunantely, more tanks are needed to ensure no negative pressure in the pipeline.
2019 Vol. 37 (5): 406-412 [Abstract] ( 174 ) [HTML 1KB] [ PDF 2244KB] ( 270 )
413 Effect of runner cone length and shaft center hole water feeding on flow characteristics in draft tube
ZHAO Daoli*, GAO Chengfeng, SUN Weipeng, GUO Pengcheng, MA Wei
To investigate the effect of runner cone length and shaft center hole water feeding on flow characteristics of draft tube, the SST turbulence model is used to simulate the three-dimensional unsteady flow in a Francis turbine. Under the rated condition, two cases, i.e. the original runner cone and a longer runner cone are simulated. Under the part-load condition, however, three cases are involved, namely, the original runner cone, the longer runner cone, and the longer cone with shaft center hole water feeding. The streamlines, pressure variations in various cross-sections in the tube, vortex rope and eddy viscosity of flow in these cases are analyzed. The results showed that under the rated working condition the lengthened runner cone can intensify the stability of the flow in the draft tube and improve the turbine efficiency slightly. Under the part-load condition, the lengthened runner cone can reduce the size of vortex rope in the tube but increase the eccentricity of the rope a bit. After a 2% rated flow water feeding is applied to the draft tube, the flow characteristics are improved significantly, the eddy viscosity of the flow in the straight diffusion section is lowered. Both the eccentricity and the rope size are decreased, but also the amplitude of low-frequency pressure pulsation caused by the eccentric vortex rope is reduced considerably.
2019 Vol. 37 (5): 413-419 [Abstract] ( 214 ) [HTML 1KB] [ PDF 8590KB] ( 179 )
420 Numerical study on coupled condensation of sulfuric acid and steam in heat exchanger for waste heat utilization
JIANG Wei*, JIANG Ting, ZHU Xiangyuan
Low-temperature corrosion characteristics of flue gas heat exchanger surfaces are the key factors affecting the reliability of equipment operation. And an accurate prediction of condensation of sulfuric acid vapor is crucial for investigation into the mechanism of low temperature corrosion characteristics. A coupled numerical model was adopted to predict the condensation of sulfuric acid vapor on the heat exchanger surfaces. By integrating the vapor-liquid equilibrium data of H2SO4-H2O solutions and multi-component diffusion theory, a model for the sulfuric acid pressure on the fin surfaces under the coupled condition is obtained. A rectangular type finned tube heat exchanger was employed to identify the effect of acid vapor content and water vapor content on the sulfuric acid condensation and corrosion by using CFD. The results show that the distribution of acid solution concentration is dependent on the fin temperature. The fin regions with higher temperature also are subject to a higher acid solution concentration. An increase in water vapor concentration can result in a sharp reduction in acid solution concentration and an increase in deposition, indicating a severe risk of low-temperature corrosion. The results can be used as a reference for the safety design of heat exchangers.
2019 Vol. 37 (5): 420-426 [Abstract] ( 405 ) [HTML 1KB] [ PDF 5271KB] ( 167 )
427 Analysis of hydrodynamic characteristics of guide hybrid-bearings for sodium-cooled fast reactor coolant pumps
ZHANG Lingfeng, SUN Jianjun*, MA Chengbo, ZHANG Yuyan
Since the sodium-cooled fast reactor coolant pump is subject to problems associated with journal wear and leakage during its operation, a guide plain bearing with spiral grooves is proposed to improve hydrodynamic characteristics of the gap in the bearing. Based on numerical simulations of CFD, the advantages and disadvantages of the bearings with spiral grooves respectively in the bush and the spindle are compared in terms of their performance. It turns out that the bearing with spiral grooves in the spindle is more effective. Accordingly, the influence of spiral groove structural variables on fluid dynamic characteristics of the bearing gap is explored, and then a preliminary optimized bearing structure is put forward. The results show that the helix angle of spiral groove is a significant factor influencing the support force and deflection angle. Further, with increasing helix angle, the support force rises but the deflection angle decreases. The helix angle and the groove-to-dam width ratio are two factors significantly affecting the leakage. Specially, the leakage increases with increase of the helix angle and the ratio. The number of spiral grooves has no significant effect on the bearing performance. The bearing with 12 spiral grooves, 42? helix angle and 2.0 groove-to-dam width ratio has the best overall performance. These results have certain guiding significance for the hybrid-bearing structure design.
2019 Vol. 37 (5): 427-434 [Abstract] ( 208 ) [HTML 1KB] [ PDF 3121KB] ( 151 )
435 Numerical simulations of crosswind effect on aerodynamic characteristics of propeller
BIAN Ruopeng, ZAN Binghe, ZHU Jianyong*, HE Miao
To study the effect of crosswind on the aerodynamic characteristics of propeller, the aerodynamic characteristics of a propeller were numerically simulated under different crosswind inclinations by solving the N-S equations and S-A turbulence model for unsteady incompressible flows based on sliding mesh technique with CFD software. The numerical results indicate that the instantaneous aerodynamic forces, including thrust, lateral force and torque present a periodic variation in each revolution under crosswind conditions, and this variation becomes more significant with increasing inclination. The time-averaged aerodynamic forces are obtained by averaging these instantaneous aerodynamic forces in each revolution. The time-averaged thrust, lateral force, torque and efficiency increase with enlaring inclination. The efficiency rises to 64.3% at 30? inclination from 53.4% at 0? inclination, because the increase in the thrust is larger than that in the torque. Analysing the pressure distributions on the propeller blade surfaces shows that both the windward and the leeward of the propeller are responsible for the unsteady force. Specially, the higher pressure on the windward and the bigger suction pressure on the leeward lead to the larger force on the propeller. While the smaller pressure on the windward and the smaller suction pressure on the leeward contribute to the smaller force on the propeller.
2019 Vol. 37 (5): 435-440 [Abstract] ( 201 ) [HTML 1KB] [ PDF 3918KB] ( 144 )
441 Analysis of diffluence ratio and internal flow characteristics of three-way control valve
SUN Caizhen, LI Hong*, TANG Pan
To investigate the diffluence ratio and internal flow characteristics of a three-way control valve, the SIMPLE algorithm was used to simulate the internal flow field by using the standard k-ε turbulence model. By changing the inlet flow rate and the rotational angle of valve core, the internal flow characteristics and the diffluence ratio variation laws were studied. The simulated and experimental results are in good agreement each other. The results show that the valve can shunt effectively when the rotational angle varies from 15° to 75°. With increasing angle, the horizontal diffluence ratio increases at first to 0.55 at 35°, then decreases to 0.40 at 55°, finally keeps increasing to 1.00. This variation tendency agrees with the change in the ratio of the horizontal outflow area to the total outflow area. With increasing angle, the inlet pressure increases firstly and then decreases but reaches the peak at about 45°, the pressure curves are generally symmetrical about 45° line. This change tendency is consistent with the entrance flow area of the regulating part. The flow area contracts in the connection part between the inlet and the core, and the throttling leads to the highest flow velocity there and the highest pressure at the entrance.
2019 Vol. 37 (5): 441-446 [Abstract] ( 189 ) [HTML 1KB] [ PDF 3133KB] ( 178 )
447 Research progress in irrigation mode selection of high-efficiency water-saving agriculture
ZHANG Liang, ZHOU Wei,, LI Daoxi*
With development of water-saving agriculture, high-efficiency water-saving irrigation has become a key way to solve the shortage of agricultural water resources. It is quite important that a high-efficiency water-saving irrigation mode is selected based on the need of regional sustainable development and local conditions. However, there is still a series of problems unsolved in selection of agricultural high-efficiency water-saving irrigation mode now. Based on the above background, the relevant study results were reviewed in terms of influencing factors analysis, comprehensive performance evaluation and risk analysis of mode selection of agricultural high-efficiency water-saving irrigation. It turned out that the influencing factors were selected more randomly with a strong bias and lack of a set of standardized and scientific index and selection criteria currently. Comprehensive performance evaluation was subject to numerous levels, dynamic variables and uncertain factors with considerable fluctuation. Especially, the social performance and ecology environmental performance were difficult to quantify. As a result, a unified and recognized performance evaluation index system and its corresponding practical evaluation model were in shortage. The selection of high-efficiency water-saving irrigation mode was limited by multi-risk factors. Additionally, classification and identification of these risk factors were relatively complicated, and the quantitative relationships between the factor selecting risk and irrigation performance were difficult to determine. Furthermore, the development trend in investigation of high-efficiency water-saving irrigation modes was prospected.
2019 Vol. 37 (5): 447-453 [Abstract] ( 205 ) [HTML 1KB] [ PDF 1681KB] ( 211 )
454 Effects of film-uncovering time on soil enzyme activity and maize nitrogen uptake under drip irrigation
ZHANG Shoudu, LI Yanfeng*, LI Jiusheng
Effects of film-uncovering time and fertilization on soil urease activity, asparaginase activity and maize nitrogen uptake were studied under drip fertigation conditions to provide theoretical basis and reference for the optimal film-uncovering time of maize with mulched drip irrigation in Northeast China. Three film-uncovering treatments and a bare soil treatment were set in experiment. In each treatment, fertilization and no fertilization were included, thus there were 8 treatments totally. The results show that the soil urease activity decreases significantly with increasing soil NH+4-N and moisture in uncovering film treatments in seedling stage, uncovering in heading stage and filming in the whole growth period of maize, but the difference between film uncovering treatments is not significantly statistical. The asparaginase activity in soil does not change significantly with covering duration. The maize nitrogen uptake can increase significantly in three film uncovering treatments, but the nitrogen uptake declines in filming treatments in the whole growth period of maize under fertilizing condition. The correlations of soil urease activity with soil water, soil temperature and soil inorganic nitrogen content are significantly statistical, but the urease activity reduces because of the increase of both soil water and NH+4-N. The soil asparaginase activity does not have a relationship with soil water, soil temperature and soil inorganic nitrogen content. Therefore, the uncovering film treatments in seedling stage and uncovering treatments in heading stage can allow the soil enzyme activity to maintain a suitable. activity level and provide a more favorable soil environment for the growth of maize.
2019 Vol. 37 (5): 454-460 [Abstract] ( 157 ) [HTML 1KB] [ PDF 2314KB] ( 169 )
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