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Journal of Drainage and Irrigation Machinery Engin
 
2017 Vol.35 Issue.1
Published 2017-01-25
article
1 Numeral simulation and experimental study on cavitation behavior of hydraulic retarder model
DONG Liang, XIAO Jiawei, MING Jiayi, LIU Houlin
To study the cavitation behavior of hydraulic retarder, the RNG k-ε turbulence model and Zwart-Gerber-Belamri cavitation model were chosen to simulate the cavitating flow in a single channel of a retarder model when the outer wall of the pump impeller was subject to different pressure levels based on ANSYS CFX. Additionally, a test stand was established to carry out performance tests at reduced pressure levels, and the predicted performance was compared with the measured values to validate the accuracy of numeral simulation. The results show that the error in prediction is 3.24%, indicating the retarder with a better internal cavitation characteristic. With the decrease of pressure on the outer wall of impeller, the vapor first occurs on the blade suction side close to the hub, and then develops toward the middle of blade till covers the most area of the suction side. The vapor is distributed in the radial direction unevenly. The dimensionless cavity area(Sc/S)increases first and then decreases with the increase of radial position(r/R)when the external wall pressure is at 0.25 MPa. The cavitation near the hub position(r/R=0.3-0.5)is more serious. 
2017 Vol. 35 (1): 1-5 [Abstract] ( 1026 ) [HTML 1KB] [ PDF 1665KB] ( 1131 )
6 Pressure pulsation characteristics in pump as hydraulic turbine with guide vanes
SHI Guangtai, LIU Xiaobing, WEI Wenjing, LIU Yang
In order to reduce amplitude of pressure fluctuation in a hydraulic turbine, a single-stage centrifugal pump was used as hydraulic turbine. A set of negative curvature guide vane was added next to the impeller outer diameter, then the performance of the turbine was studied experimentally. The geometric model of the turbine was established using Pro/E software, and the vibrational rule of pressure and pressure fluctuation in various flow passages in the turbines with and without guide vanes was calculated by means of the SST k-ω turbulence model and a CFD software. Additionally, the pressure fluctuation signals in time domain were transformed into frequency domain by making use of fast Fourier transform(FFT), finally, the distribution of pressure fluctuation in both domains were analysed. It is shown that the amplitude of pressure fluctuation in the dominated frequency and the maximum pressure fluctuation are both reduced in the volute with guide vanes, but also the amplitude of pressure fluctuation is decreased in the impeller. Meanwhile, in the draft tube, the fluid flow is stable without vortex, making the amplitude of pressure fluctuation in the dominated frequency decreases greatly. Therefore, the method of adding guide vanes can improve the performance of a pump as hydraulic turbine and reduce the amplitude of pressure fluctuation in its flow passages.
2017 Vol. 35 (1): 6-12 [Abstract] ( 876 ) [HTML 1KB] [ PDF 2499KB] ( 1182 )
13 Effect of wear-ring clearance on performance and flow characteristics of centrifugal pump
GAO Bo, WANG Zhen, YANG Li, DU Wenqiang, LI Changjun
In order to explore the influence of different wear-ring sizes on the performance and flow characteristic in a centrifugal pump, both numerical simulation and performance test are conducted in a centrifugal model pump. Two normal wear-ring clearances(0.25 mm and 0.50 mm)and an abnormal big gap(0.75 mm)are selected. By comparing the pump performance and flow characteristics at every clearance, the influence of wear-ring size on the performance and flow is obtained. It is shown that with increasing clearance both the pump head and the efficiency decrease. The radial thrust on the impeller reaches the largest at 0.50 mm gap, decreases at 0.25 mm, and eventually arrives at the smallest thrust at 0.75 mm. The total pressure is distributed more evenly in the axial cross-section of the wear-ring at a larger clearance. The total pressure near the side chamber decreases, but that near the impeller eye increases. Because of being affected by the centrifugal force on the shroud, the radial velocity magnitude and vorticity of the fluid in the chamber between the shroud and the casing increase gradually with increasing clearance, causing an even more smooth streamline pattern there. 
2017 Vol. 35 (1): 13-17 [Abstract] ( 1368 ) [HTML 1KB] [ PDF 4846KB] ( 1748 )
18 Effects of wear-ring clearance on performance of high-speed centrifugal pump
YANG Congxin, QIANG Pan, AN Sha, XU Nan, LIU Junnian
In order to clarify effects of wear-ring clearance on the performance of high-speed centrifugal pump, a centrifugal pump with speed of 38 500 r/min is studied. Firstly, 16 cases are generated by combining the clearances of the front and rear wear-rings with 0.01 mm increment, then the performance of the pumps with these wear-ring clearances is predicted by means of numerical simulation. The results show that when the rear wear-ring clearance is smaller, the efficiency and shaft power are more sensitive to the change in the front wear-ring clearance. Likewise, when the front wear-ring clearance is kept smaller, the efficiency and shaft power are sensitive to the change in the rear wear-ring clearance too. The head of pump decreases with increasing rear wear-ring clearance at a constant front wear-ring clearance. However, the head rises slightly with increasing front wear-ring clearance at a constant rear wear-ring clearance. Even though the leakage through the front and rear wear-ring gaps decreases with increasing flow rate whatever both the clearances are, the efficiency and head are lower, and the head varies more significantly against flow rate with two increasing clearances. The hydraulic resistance in a wear-ring gap is mainly to generate a liquid static pressure drop because the velocity of liquid does not change obviously at the wear-ring outlet. With the increase of wear-ring clearance, the static pressure drop and dynamic pressure at an axial position rise in the wear-ring clearance. 
2017 Vol. 35 (1): 18-24 [Abstract] ( 1100 ) [HTML 1KB] [ PDF 1988KB] ( 1356 )
25 Effects of spiral volute type on performance of high specific speed centrifugal pump
ZHANG Xia, YUAN Shouqi, ZHANG Jinfeng, HUANG Xi
In order to study the internal flow field in two high specific speed centrifugal pumps with different volutes, a pump with logarithmic spiral splitter is designed based on a pump with single logarithmic spiral volute. The cross-sectional area and the main parameters of two pumps are identical. A series of numerical simulations are conducted by making use of the SST k-ω turbulence model and ANSYS 14.5 software to obtain the unsteady, three-dimensional and turbulent flows in the centrifugal pumps with single and double volutes under different operational conditions. The performance of the pump with single volute are tested to validate the accuracy of simulations. It is found that the pump with double volute is subject to a better hydraulic efficiency and higher head at high flow rates. However, the effect of the splitter on the performance is minor under design and part-load conditions. In addition, the pressure fluctuations in the double volute pump are less than those in the single volute pump, especially at the outlet, suggesting the splitter can damp pressure fluctuations effectively. It can be seen that the flow in the double volute is smoother than that in the single volute based on the streamline patterns in the diffuser. Compared with the single volute pump, the double volute centrifugal pump can undergo a reduced radial thrust, especially at high flow rates. The results are valuable for the hydraulic design of high specific speed centrifugal pumps in some degree.
2017 Vol. 35 (1): 25-31 [Abstract] ( 1014 ) [HTML 1KB] [ PDF 3245KB] ( 1182 )
32 Performance analysis of bulb tubular pumps in first phase of South-to-North Water Diversion Eastern Route Project in China
ZHANG Rentian,, ZHU Honggeng, BU Ge, SHAN Haichun, ZHOU Wei, YAO Linbi
Bulb tubular pumps have been installed in six pumping stations in the first phase of the South-to-North Water Diversion Eastern Route Project in China. For the difference in their structure, there exist differences in their performances. In this paper, experimental results of the model pumping systems are analyzed firstly, the methodologies and measures for optimal hydraulic design are introduced. According to the results in acceptance model tests conducted, the pump performances are superior to the guaranteed ones in the contracts. By using dimensionless head, flow rate coefficients and suction specific speed, a comparison of hydraulic performance among six pumping systems in the same pump model is carried out. The results show that the dimensionless head-flow rate curves are basically identical for six pumps, and their best efficiency is all as high as above 80%, demonstrating an excellent performance even these bulb tubular pumps are subject to different structures. In the light of the measured performance data on site, it is confirmed further that these bulb tubular pumps do have excellent performance and better operational stability, and the performance data are better than the predictions by making use of model test. The bulb tubular pump is suitable for low head pumping stations in the South-to-North Water Diversion Project in China.
2017 Vol. 35 (1): 32-41 [Abstract] ( 877 ) [HTML 1KB] [ PDF 3408KB] ( 1314 )
42 Design and fish survival rate prediction of fish-friendly axial-flow pump for pumping stations
PAN Qiang, SHI Weidong, ZHANG Desheng, ZHAO Ruijie
A large number of fish suffer from injury and mortality when passing through a traditionally designed pumping station. In order to improve the survival rate when fish passing through the flow channels in a pumping station, fish mortality rates are predicted under various operational conditions in a conventional axial-flow pump by using a blade strike model which is with a better accuracy against experimental data. It is shown that the fish mortality rate at the design point is up to 68% theoretically in that pump. Based on this model, a fish-friendly hydraulic design approach is proposed for an axial-flow pump to have better fish survival rate, and effects of a few design parameters on the rate are analyzed. It is turned out that number of blades and rotational speed are two major factors influencing blade strike probability. Because the pump head is almost twice sensitive to the rotational speed than to the number of blades, the impeller is kept having two blades to reduce the blade strike probability for fish. The chord length of blade is increased to cope with the head drop caused by reduced number of blades. To limit the axial length of pump, the increased proportion of chord length is a little bit small. The forward swept and extended leading edge can reduce strike velocity, i.e. the velocity component perpendicular to the leading edge, significantly, thus the leading edge is the primary factor affecting strike mortality rate, while the thickened leading edge is the secondary factor for the rate. However, these two factors can induce a stronger radial velocity component, causing a low hydraulic efficiency and poor cavitation performance. The fish mortality rate is all below 30% at any operating points, and the rate has been declined to 13% from initially 68% at the design point as fish passing through the fish-friendly pump, thus fish survival is remarkable. This study can provide a reference for development of fish-friendly axial-flow pump and its application in pumping stations.
2017 Vol. 35 (1): 42-49 [Abstract] ( 874 ) [HTML 1KB] [ PDF 1505KB] ( 1691 )
50 Numerical simulation of corrosion inhibitor behavior
GAO Xueqi, ZHANG Xiaoxiao, WANG Jianjun
In order to realize an effective repair and a supply of inhibitor in a follow-up normal injection process for an inhibitor to exhibit corrosion protection effect, the distribution of corrosion inhibitor in a gas pipeline needs to be studied in detail. Software Fluent was used to simulate the gas and liquid turbulent flow and inhibitor distribution in a pipeline based on the Euler-Euler model, RNG k-ε turbulence model and VOF method. The distribution of inhibitor liquid film along the inner wall of the gas pipeline is obtained, and the influences of surface tension of the corrosion inhibitor on the liquid film distribution under scouring and gravity are clarified. The results show that the inhibitor settles toward pipe bottom due to the gravity, which accounts for 1/3 of the cross-section of the pipe. The secondary flow in the elbow can destroy the initial distribution of corrosion inhibitor, and drive the inhibitor along the secondary flow path to damp it on the bottom of the elbow. Therefore, the pipe and elbow top should be monitored carefully in engineering practice. The higher surface tension the inhibitor possesses, the more adhesion work the pipe wall has, in consequence the more uniform distribution of corrosion inhibitor and the higher inhibitor volume fraction adhered to the wall. As a result, the highest corrosion inhibitor volume fraction can be as large as 100%. It suggests that an inhibitor with stronger adhesiveness and higher surface tension should be chosen in pre-filming process.
2017 Vol. 35 (1): 50-55 [Abstract] ( 876 ) [HTML 1KB] [ PDF 2695KB] ( 1098 )
56 Analysis on dynamic characteristics of aerostatic dry gas seals with three degrees of freedom perturbation
XU Hengjie, SONG Pengyun
Currently, studies on aerostatic dry gas seals are mostly limited to their steady characteristics, while little attention has been paid on their unsteady characteristics, which are very important to allow the seals to have excellent operating performance so far. Hence the aerostatic dry gas film pressure governing equations and unsteady Reynolds equations are solved by using small perturbation and finite difference methods under the condition of three degrees of freedom perturbation. The influences of squeeze number, frequency number and supplying gas pressure on the unsteady characteristics are investigated. The results show that the axial direct dynamic gas film stiffness increases with increasing squeeze number, frequency number and supplying gas pressure, but the direct dynamic gas film stiffness in two angular directions is little influenced by the squeeze number. The axial direct damping coefficient and direct damping coefficients in two angular directions decrease with increasing squeeze number and supplying gas pressure. The axial direct damping coefficient decreases fast when the squeeze number is less than 20. The cross coupled dynamic stiffness and damping coefficients of two angular directions have an axisymmetric feature. The coupled dynamic stiffness and damping coefficients have a little relation with squeeze number when the number is in the range of 1-40, but increase with the increasing number if the number is larger than 40.
2017 Vol. 35 (1): 56-64 [Abstract] ( 913 ) [HTML 1KB] [ PDF 1644KB] ( 1000 )
article
65 Modeling and testing of tea tree water stress
SUN Daozong,, WANG Weixing,, TANG Jinchi, JIANG Sheng
The canopy temperature, air temperature and humidity, soil heat flux, soil moisture, net solar radiation, wind speed and other factors are observed when tea trees are growing in a greenhouse under different irrigation conditions in winter and spring, then a lower limit equation of canopy temperature difference is determined by using the Idso empirical model. Finally, the curves for representing tea tree moisture content status are obtained by observing the diurnal and seasonal variation curves of tea crop water stress index(CWSI)under different moisture contents. Additionally, the difference in CWSI between Jackson theoretical model and Idso empirical model is analyzed. Since drought often happens in spring and winter in South China, the field data are collected manually in September-December and January-March next year. The various parameters related to CWSI are extracted, and the water stress index models for winter and spring are developed, respectively. The results reveal that there is no significant difference in tea tree water stress index models between winter and spring. In winter, the coefficients A and B in the model are 1.265 and -0.220, while they are 1.230 and -0.214 in spring. It may be because the tea tree is perennial crop and the leaf area index is similar in spring and winter.
2017 Vol. 35 (1): 65-70 [Abstract] ( 834 ) [HTML 1KB] [ PDF 1421KB] ( 1065 )
71 Effects of soil texture and water pressure on moistube infiltration in vertical inserting mode
YU Xiaodi, LIU Xiaogang, ZHU Yifei, QI Yuntao, YANG Qiliang, TANG Jiankai
Vertically inserted moistube is one of new water-saving irrigation technology and suitable for fruit and economic trees planted in equal row space. In order to investigate the interactive effect of soil type and water head on the infiltration characteristics of vertically inserted moistube, three soil textures(sand, sandy loam and red loam)and three water heads(1.0, 1.5 and 2.0 m)were used, and infiltration rate, cumulative infiltration, wetted soil volume and the characteristics of soil water content distribution were measured. It is shown that the infiltration rate at different times is accorded with the modified Horton model. The cumulative infiltration volume is as a parabolic function of irrigation time. The wetted soil volume expands with increasing water head, and is small on top but big on bottom, approximately pear-shaped. The growth rate of wetted soil body is relatively slow when the water head is low, the growth rate reaches the maximum in the first 4-6 hours after infiltration, and the growth process yields logarithmic normal distribution. The soil type has a significant influence on the soil water content, but the effect of water head is weak. The soil water distribution uniformity of red loam and sandy loam(>80%)is higher than that of sand(<70%). The results can provide a theoretical basis and practical reference for rational applications of moistube irrigation.
2017 Vol. 35 (1): 71-79 [Abstract] ( 1057 ) [HTML 1KB] [ PDF 1628KB] ( 1044 )
80 Experimental study on free infiltration characteristics of muddy water film hole irrigation
HU Jianqiao,, WANG Jinghui, ZHANG Jiangxiang, CHENG Ziyong
The influences of sand content on free infiltration characteristics of muddy water film hole irrigation and water content distribution in wetted soil are studied experimentally. Through indoor free infiltration of clean water film hole irrigation experiments with four different sand contents in muddy water, the relationships between free infiltrations of muddy water film hole infiltration parameters, wetting front transport parameters and wetted soil water content distribution parameters after the irrigation and the different sand contents are established. A cumulative infiltration model per unit film area, wetting front transport model, wetted soil water content distribution model and film infiltration declining feature due to the increasing sand content are put forward. It is demonstrated that with increasing muddy water sand content, the cumulative infiltration decreases and less than that of clean water under the same condition. The infiltration coefficient K decreases with increasing sand content, but the infiltration index α increases with the increasing content. In the same infiltration time, with increasing sand content, the vertical and horizontal wetting front transport distances are gradually reduced. With increasing distance from the center of film hole, the water mass content in wetted soil reduces gradually in the vertical and horizontal directions. The sand contents in muddy water can reduce film hole irrigation infiltration in comparison with clean water, particularly, the higher the sand content, the smaller the infiltration rate.
2017 Vol. 35 (1): 80-86 [Abstract] ( 898 ) [HTML 1KB] [ PDF 1468KB] ( 1051 )
87 Analysis and test on influence of caudal-fin on performance of valve-less piezoelectric pump
GE Zhentao, JI Jing, LAN Yubin, HU Xiaoqi, QIN Tingting, HU Caiqi
In order to study the performance of a valve-less piezoelectric pump with caudal fin and identify the influence of piezoelectric vibrator-caudal fin on the pumping flow, a modal analysis on wetted piezoelectric vibrator-caudal fin was conducted in ANSYS. The first three working frequencies and corresponding vibration modes were obtained. Then the flow and performance of the piezoelectric pumps with and without caudal fin were simulated by making use of Fluent, and compared with the experimental results. In simulations, when the excitation peak voltage is 100 V and the frequency is 800 Hz, the pumping flow in the piezoelectric pump with caudal fin is 65.34 mL/min, while it is 5.32 mL /min in the pump without the fin. In experiments, when the excitation peak voltage is 100 V and the frequency is 800 and 760 Hz, the pumping flow in the piezoelectric pump with caudal fin is 60.25 and 75.65 mL/min, but it is 4.1 and 4.6 mL/min in the pump without the fin, respectively. This is proved that the extra flow rate in the valve-less piezoelectric pump with caudal fin is mainly caused from the caudal fin driving effect. Based on the comparison of tested and experimental pumping flow rate, the correctness of simulation analysis has been confirmed.
2017 Vol. 35 (1): 87-92 [Abstract] ( 857 ) [HTML 1KB] [ PDF 1614KB] ( 1160 )
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