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Journal of Drainage and Irrigation Machinery Engin
 
2016 Vol.34 Issue.5
Published 2016-05-25
369 Unsteady internal flow and thrust analysis of centrifugal pump under gas-liquid two-phase flow conditions
LI Guidong, WANG Yang, Zheng Yi, Ma Xiaohu, Liang Longyi, Hu Rixin
In order to study internal flow patterns and thrust on an impeller under gas-liquid two-phase flow conditions, a centrifugal pump with a specific speed of 129 is selected, and the unsteady three-dimensional flow in th pump is simulated by employing the Eulerian-Eulerian inhomogeneous multiphase flow model based on ANSYS CFX software. The variations of a few fluid flow variables such as pressure loading on blades, gas volume fraction distribution etc are obtained under different gas volume fractions admitted at the pump inlet, the predted head and efficiency are compared with the measured data. The results show that the gas phase is mainly accumlated on the blade suction surface and in the middle part of flow passage at the impeller outlet, further the gas volume fraction on the shroud are higher than on the hub. With increasing gas volume fraction at the pump inlet the flow disortion in the impeller passages becomes severe, henece the flow inhomogeneity between the gas phase and the liquid phase is intensified, and the vortex area is enlarged. From the inlet to the outlet of impeller, the pressure loading on the blade pressure surface reduces faster than on the blade suction surface, but the loading on the suction surface declines quicker near the impeller outle. The imbalance of the radial thurst on the impeller gets worse, and the torque acted on it decreases. 
2016 Vol. 34 (5): 369-374 [Abstract] ( 1343 ) [HTML 1KB] [ PDF 2995KB] ( 1550 )
375 Internal flow characteristics and performance test of two low specific-speed centrifugal pumps
CUI Baoling, FANG Chen, GE Mingya
To investigate into the influence of blade length on internal flow and performance of a low specific speed centrifugal pump, an impeller with 8 full-length blades is designed by updating a refere-nce impeller which has 4 full-length blades plus 4 splitters. The flow field in the pumps is calculated based on the time-averaged Navier-Stokes equation and the Spalart-Allmaras turbulence model, then the internal flow characteristics are obtained. At the same time, the pump performance is tested to validate the performance predicted. It is found that the circumferential velocity is greater than the radial velocity in the volute, and the latter increases slowly with increasing circumferential angle. At the design point, both the head and the efficiency of the impeller with 8 full-length blades are higher than those of the impeller with 4 full-length blades and 4 splitters. The numerical results show that the low pressure area at the inlet of the impeller with 8 full-length blades is larger than that of the impeller with splatters. There exist vortexes in the flow passages of both impellers, and the area covered by the vortexes in the impeller with 8 full-length blades is larger than that in the impeller with splitters. Experimental results have verified the correctness of the numerical computation.
2016 Vol. 34 (5): 375-380 [Abstract] ( 1080 ) [HTML 1KB] [ PDF 2689KB] ( 1084 )
381 Numerical simulation and oil film observation on flow field in impeller of screw centrifugal pump with single-blade
ZHANG Hua, CHEN Bin, SHI Weidong, WANG Bingqi, WANG Zhen
The flow field in a submersible screw centrifugal pump of 240 specific speed with single-blade is studied by using numerical simulation and experimental observation. The pump fluid domains are meshed by using polyhedral cells and the steady turbulent flow in them is calculated by employing the Realizable k-ε turbulence model. The predicted performance curves are compared with measured ones, and the simulated flow field in the impeller is examined against the flow pattern in oil film visua-lization. It is shown that the predicted characteristic curves agree well with the measurements and the calculated streamlines on the impeller flow passage walls are consistent with the oil film observations, suggesting the polyhedral mesh has a better accuracy in flow simulations of the impeller in a screw centrifugal pump. Through an analysis of the internal flow field, a leakage flow around the blade inlet is captured, but it becomes weak gradually with the increase of flow rate. Moreover, under the working conditions of 0.6Qd, 1.0Qd and 1.4Qd, there exists a severe backflow on the hub surface near the blade suction side around the impeller outlet; especially, at 0.6Qd flow rate, the backflow has occupied an area as large as more than 80% the flow channel width. A backflow also exists in the corner between the blade pressure side and the hub; the smaller the flow rate, the more serious the backflow. Under these three working conditions, there exists a larger gradient in the velocity at volute outlet. 
2016 Vol. 34 (5): 381-385 [Abstract] ( 1120 ) [HTML 1KB] [ PDF 2230KB] ( 1136 )
386 Study on multi-objective genetic optimization of hydrodynamic performance of airfoil 791
WANG Yu, ZHAO Binjuan, CHEN Huilong, QIU Jing, ZHAO Youfei
Firstly, Bezier curve is used to parameterize the suction side of an airfoil to control its thickness profile. Secondly, a surrogate model is established to represent an approximate relationship between the control nodes distributed on the suction side and the performance parameters of airfoil by using uniform experiment design and artificial neural network method. Finally, the optimal thickness profile is obtained based on the multi-objective genetic algorithm(MOGA). Lift-drag ratio F and drag FD of airfoil 791 are served as the optimization objective functions and the control nodes of the Bezier curve are chosen as optimization variables. The result indicates that MOGA is feasible. As a result, the drag is decreased by 4.17%, the lift-drag ratio is increased by 15.33%, and the angle of attack at which a stall appears becomes larger. The optimal location of maximum thickness is more close to the leading edge as near as 0.390 the chord length and the maximum thickness is increased as thick as 0.090 the chord length. When other the objective functions are changed, an optimum airfoil still can be obtained by means of the optimization strategy. Such that the optimization strategy proposed can provide a reference for a study on optimization methods applied in other fluid machines.
2016 Vol. 34 (5): 386-391 [Abstract] ( 1031 ) [HTML 1KB] [ PDF 1535KB] ( 1311 )
392 Matching characteristic between impeller and bowl diffuser in multi-stage centrifugal pump
WANG Kai, WANG Wenbo, LIU Houlin, XIA Chen
The flow field in a three-stage centrifugal pump was simulated by using CFX software based on the standard k-ε turbulence model, the predicted performance curves were compared with the measurements, and good agreement was showed. After a further analysis on the flow details, however, a larger hydraulic loss has occurred in the gap between the impeller and the bowl diffuser as well as in the diffuser itself. In order to reduce the hydraulic loss and improve the matching characteristic of the diffuser to the impeller, four diffusers with different inlet structures are designed. The steady flow in the three-stage pumps with these diffusers is simulated at the design point, and the pump performance, flow pattern and the pressure distribution over the diffuser vane pressure side are analysed. The results show that the diffuser with untwisted inlet and in parallel with the impeller outlet has the best hydraulic performance. The diffuser with twisted inlet results in an increased impeller head, but the hydraulic loss in the gap between the impeller and the diffuser rises, and the pressure at the inlet of diffuser becomes instable. The diffuser with inlet edge in parallel with the impeller outlet can reduce the inside loss to improve the hydraulic performance. Even though the diffuser with inlet edge in parallel with the pump shaft can compromise the interference with the impeller to increase the impeller hydraulic performance, the hydraulic loss in the gap is increased.
2016 Vol. 34 (5): 392-398 [Abstract] ( 1633 ) [HTML 1KB] [ PDF 3186KB] ( 1492 )
399 Pressure fluctuation characteristics of centrifugal pump with low-specific speed at low flow rate
WANG Yefang, YUAN Shouqi, ZHANG Jinfeng, MAO Jieyun, HUANG Xi
In order to investigate into the internal unsteady flow of low specific speed centrifugal pump at various low flow rates, a series of numerical simulations of DES(detached eddy simulation)in an end-suction centrifugal pump of type IS50-32-160 are carried out on the basis of analysis on grid independence. The results show that the tongue has a more important influence on the internal flow in the impeller, causing different size vortices exist in three flow passages near the tongue; the vortices just behind the impeller inlet are close the blade suction side with the same rotation direction as the impeller, but the vortexes near the impeller outlet are in front of the blade pressure side in the reverse direction of the impeller. With declining flow rate the vortexes expand so fast that even block the whole passage, especially in the three passages near the tongue. Meanwhile, a flow separation emerges in the volute nozzle, resulting in a non-uniform outflow. A FFT(fast Fourier transformation)frequency transformation is conducted for the pressure signals picked up at the monitoring points in the impeller and volute, and it is found out that the dominated frequencies in the impeller are the shaft frequency and its integer multiples, and the amplitude of pressure pulsation increases steadily with the radius and from the suction side to the pressure side. In contrast, the dominated frequencies in the volute are the blade frequency and its integer multiples, the more violent the amplitude of pressure pulsation, the smaller the distance to the tongue, eventually, the greatest pulsation occurs on the tongue. The intensity of pressure pulsation at all the monitoring points gets stronger with decreasing flow rate.
2016 Vol. 34 (5): 399-405 [Abstract] ( 1234 ) [HTML 1KB] [ PDF 6229KB] ( 1143 )
406 Influence of guide vane opening on performance and flow characteristics of tubular hydro-turbine
KANG Can, LI Liting, LU Guohui
In order to investigate into the effects of guide vane opening on the performance and internal flow characteristics of a tubular hydro-turbine, a series of numerical simulations are performed using ANSYS CFX at three openings such as 1 550, 1 405 and 1 278 mm. Apart from considering the turbine operation head and efficiency, the pressure and velocity distributions in the cross-sections of flow channel, the pressure profiles on the gate vanes and runner blades are analyzed, too. It is found that 1 405 mm is the optimal opening at which the guide vane matches the runner in hydrodynamics exactly. Moreover the cavitating flow in the hydro-turbine is simulated at the best guide vane opening under three operating conditions, namely 0.8Q, 1.0Q and 1.2Q. It is identified that the head and efficiency are reduced significantly due to cavitation. The vapor volume fraction distributions in the runner and draft tube are observed. It is shown that cavitation severity is the least at 1.0Q the design flow rate. At 0.8Q, the cavitation in the runner is the most serious; while at 1.2Q, the cavitation zone extends to the draft tube from the runner.
2016 Vol. 34 (5): 406-413 [Abstract] ( 1372 ) [HTML 1KB] [ PDF 3467KB] ( 1312 )
414 Relative water head of skimming flow over stepped spillways
WEN Mingyi, LIU Hansheng, FAN Lingzhi, LIU Siyuan
In order to study energy dissipation characteristics of stepped spillway, the water head along a stepped spillway is compared with that along a smooth spillway, and a relative hydraulic head concept is introduced in this paper. Three engineered stepped spillway models are measured with slope in range of 1 ∶2.0-1 ∶0.9 and step height ranged in 0.5-2.0 m. The effects of length of flow path, unit discharge, step height and slope on the relative head are studied. The experimental results show that the relative head all along the spillway is less than zero, indicating that the flow energy along a stepped spillway is lower than a smooth spillway. The relative head has a linear relationship with the length of flow path that is subject to a correlation coefficient between 0.998 3 and 0.999 8. The relative head has nothing to with the unit discharge, as a result, the head in the same section is nearly constant at different discharges with an equal or less than 4.5% relative error in comparing with the straight line slope. The step height and slope have a great influence on the relative head, especially, the higher the step height and the steeper the slope, the greater the absolute value of relative head. The experimental data confirm that the relative head of a stepped spillway varies regularly, and it is convenient for practical application and analysis, and also can provide a reference for the design of stepped spillway.. 
2016 Vol. 34 (5): 414-417 [Abstract] ( 790 ) [HTML 1KB] [ PDF 1349KB] ( 1250 )
418
2016 Vol. 34 (5): 418-423 [Abstract] ( 826 ) [HTML 1KB] [ PDF 2456KB] ( 675 )
424 Influence of local blockage on pipe transient frequency response characteristic and its application
LIU Zhiyong, LIU Meiqing, WANG Huachao, WU Yuanwei
Local blockage is a usual fault in pressurized pipe systems. In this study, the influence of a local blockage on the frequency response diagram(FRD)is analyzed and the relationship between the variation pattern of FRD and local blockage parameters, namely the location and resistance coefficient of the blockage is obtained by using transfer matrix method for a pipe system. Then, based on this relationship, a pipe local blockage detection method is proposed and its feasibility is validated through numerical experiments. The results show that the amplitudes of the even harmonics and odd harmonics of a pipe with a local blockage no longer maintain constant compared with a normal pipe, but vary periodically with the harmonic order instead. The main frequency and phase of the odd harmonics reflect the blockage location, and the amplitude of the main frequency is related to the minor resistance coefficient, consequently based on these facts the blockage location and degree can be detected. The numerical experiments confirm that the pipe local blockage detection is feasible based on FRD analysis. 
2016 Vol. 34 (5): 424-429 [Abstract] ( 1055 ) [HTML 1KB] [ PDF 1478KB] ( 1042 )
430 Accuracy assessment of rainfall forecast and analysis on water-saving irrigation strategies during rice growing seasons in South China
LUO Yufeng,, MA Zhen, LYU Xinwei, GUO Longzhu, CUI Yuanlai, XIANG Zhao
Increasing effective rainfall is one of strategies for saving irrigation water, unfortunately there is an uncertainty in future rainfall, thus accuracy assessment of rainfall forecast is necessary for effective rainfall use. Taking the Guanfu Plain Irrigation District as an example, we collected 7-day lead time rainfall forecast data in three seasons of early and late rice(2012—2015)from the National Meteorological Centre of China, and the observed rainfall data, then analyzed the forecast accuracy by using correct forecast rate, threat score(TS), false alarm rate(FAR), missing alarm rate(MAR)and receiver operating characteristic(ROC)curve. Furthermore, strategies for increasing effective rainfall are proposed based on the accuracy assessment. The results show that the correct forecast percentage of rain/no rain during the rice growing seasons has reached 76.3%, the MAR is lower but the FAR is higher in the early rice season than in the late rice season. The difference in TS for light rain during the early and late rice seasons is not significant; for middle and above rainfalls, however, the TS in the late season is lower than in the early season. The areas under the ROC are greater than 0.5 for all 1-7 days lead time, implying that the correct forecast percentage is higher than the FAR and all the forecasts are positive, thus the correct forecast percentage can be used in irrigation management. The correct forecast percentage is ranged from 80.1% to 88.6% in the re-greening, milk-maturing and yellow-maturing stages of early rice. Thus if a light rain or above is forecasted, then there should be no or less irrigation. The correct forecast percentage is slightly lower and ranged from 64.9% to 77.2% in the early tillering, late tillering, jointing/booting, and heading/flowering stages. Therefore, if a continuous clear day or slight rain is forecasted, then irrigation should be applied according to the crop requirement. However, if a medium or above rainfall in 2-3 days is forecasted, then irrigation amount should be reduced. Although the accuracy in the early rice season is lower than in the late rice season, the forecasted and actual rainfall events are even more in the early rice season, so that the irrigation amount can be decreased if a medium or above rainfall is forecasted. After a decision on irrigation amount is made by taking an account of rain forecast accuracy, not only natural rainfall will be utilized sufficiently but also water wasting can be avoided to achieve the water saving goal.
2016 Vol. 34 (5): 430-435 [Abstract] ( 841 ) [HTML 1KB] [ PDF 1674KB] ( 1115 )
436 Effect of preanthesis drought on fruit yield and quality of postanthesis waterlogged tomato
YUAN Min,, SHAO Guangcheng,, CUI Jintao,, GUO Yuxiang, ZHU Meiru
In order to extend the waterlogging resistance of crops themselves and seek the approaches for supporting tomato production under waterlogging condition in South China, the effects of preanthesis drought on morphological characteristics, quality and yield of post-anthesis waterlogged tomatoes are investigated under rain-shelter cultivation condition. The results show that the post-anthesis waterlogging stress can significantly restrain the crop growth and decrease the yield as well as deteriorate the quality of tomato with normal water supply at seedling stage. Compared with the normal treatment without drought stress, the pre-anthesis drought hardening can improve the growth and development of the root systems and enrich the contents of soluble sugar, soluble solids, organic acid and vitamin C. Among the three preanthesis drought hardening cases, the highest yield is achieved in T4 treatment. Further, the root mass, root-shoot ratio, fruit density and the content of soluble sugar, soluble solid, organic acid and vitamin C in tomatoes are increased, but the above ground and total dry matter mass and single fruit mass are decreased with reducing irrigation at the seeding stage. Through a principal component analysis, it is found that treatment T5 is with the best comprehensive evaluation score on the quality.
2016 Vol. 34 (5): 436-442 [Abstract] ( 938 ) [HTML 1KB] [ PDF 1337KB] ( 1091 )
443 Comprehensive evaluation of effectiveness of coastal land remediation projects in coastal areas of Jiangsu Province
LIU Bin, ZOU Yutian, YU Kuanwei, XU Cuilan, SUI Xueyan, DING Jihui, SHE Dongli
In order to carry out a large scale land remediation in coastal areas in Jiangsu Province, a method is needed for evaluating the remediation effectiveness quantitatively. Based on four coastal land remediation projects completed in the coastal areas of Jiangsu Province, 27 evaluating indices are chosen to cover four aspects such as capital investment, process management, project implementation and comprehensive benefits. Then a comprehensive evaluation model is established by using statistical methods and expert consultation. Finally, project comprehensive benefits are evaluated and the follow-up suggestions and measures are put forward to provide a scientific basis for benefit evaluation of land remediation in the coastal areas. The results show that the overall benefit of the 4 land remediation projects is significant, and most of the indices have met the requirements by the program, showing remarked economic, social and ecological benefits. Since there is a larger gap in value between the individual indices in each project, the comprehensive evaluation of effectiveness of coastal land remediation projects needs to be improved more substantially. These evaluation outcomes have provided a basis and reference for specific improvements in practice of coastal land remediation.
2016 Vol. 34 (5): 443-448 [Abstract] ( 1606 ) [HTML 1KB] [ PDF 1262KB] ( 1181 )
449 Optimization design of nozzle and numerical simulation of internal flow field in low-pressure sprinkler
ZHANG Qian, YUAN Shouqi, LIU Junping, BAO Ya
In view of poor spray uniformity and short range in low-pressure sprinklers, various special-shaped nozzles are designed based on a principle of identical cross-sectional area. Then ANASY CFX is applied to simulate three-dimensional internal flow field in these sprinklers. The numerical simulation results are validated by using the measured performance parameters of low-pressure sprinklers, including range, water distribution and raindrop diameter. The simulated results show that the region occupied by high velocity at the outlet of inverted U shaped nozzle is the largest and the velocity profile keeps consistent with increasing working pressure, showing a very good advantage in extending the range and improving the spray uniformity. The experimental results show that the range of inverted U shaped nozzle is about 1.110 times that of the circular nozzle, which is basically around 2% lower than the prediction. At a 300 kPa working pressure, the drop diameter generated by the inverted U shaped nozzle is 4.21 mm as the minimum, showing the best atomization performance. The water distribution in that nozzle is approximately triangular, all the uniformity coefficients are more than 82%. With increasing distance, the water through the circular and rounded rectangular nozzles rises first, and then decreases, and all their uniformity coefficients are lower than the inverted U shaped nozzle. In conclusion, the hydraulic performance of the inverted U shaped nozzle is better in comparison with the others, particularly, the range is increased on the basis of uniformity improved.
2016 Vol. 34 (5): 449-454 [Abstract] ( 1204 ) [HTML 1KB] [ PDF 1703KB] ( 1127 )
455 An investigation into fault diagnosis of hydro-turbine unit based on EMD multifractal spectrum
XUE Yan′gang
To diagnose faults in of a hydro-turbine unit accurately and precisely, a fault diagnosis model for vibration signal of hydropower units is built based on the EMD, multi-fractal spectrum and improved BP neural network in this paper. A series of vibration signals under various conditions, such as normal rotor system, oil film whirl in bearings, rotor imbalance, and rotor misalignment etc. are acquired from a hydro-turbine unit. At first, the EMD components of these vibration signals are obtained through empirical mode decomposition. Then the waveform samples are extracted by using EMD coefficients according to the signal waveform tendency curves. Thirdly, the eigenvalues alpha(q)and f(q), are extracted from the waveform samples by means of multifractal spectrum algorithm. Finally, the eigenvectors are input into a BP network for classification and recognition. The trained neural network is applied to all the samples and the test accuracy is 100%. The results show that the multi-fractal spectrum not only is feasible for fault diagnosis of hydropower unit but also can improve the precision of diagnosis and enhance human-computer interaction.
2016 Vol. 34 (5): 455-460 [Abstract] ( 971 ) [HTML 1KB] [ PDF 1879KB] ( 1251 )
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