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Journal of Drainage and Irrigation Machinery Engin
 
2016 Vol.34 Issue.3
Published 2016-03-25

185 Numerical analysis of cavitating flow characteristics in impeller of residual heat removal pump
HONG Feng,, YUAN Jianping, ZHOU Banglun
In order to investigate internal cavitating flow characteristics of the impeller in residual heat removal pumps, the three-dimensional cavitating flow in a residual heat removal model pump is numerically calculated by using the homogeneous mixture cavitation model based on the Rayleigh-Plesset equation and the shear stress transport SST k-ω turbulence model. The hydraulic performance curves, distributions of vapor volume fraction at NPSHA and the blade load profiles at the design flow rate are obtained. The numerical results show that the distribution of vapor volume fraction becomes non-axisymmetric with the decreasing NPSHA, even some blade passages are blocked when NPSHA drops to 2.63 m. Vapor volume fraction distribution varies across blade span; the shorter the distance to the hub is, the higher the vapor fraction on the blade suction side is. Additionally, the cavity in the impeller shows a quasi-steady characteristic before the head starts to be deteriorated rapidly. Due to a sudden change in the primary flow direction near the eye of impeller, the blade load on the blade pressure side shows a sudden increase and drop effect.
2016 Vol. 34 (3): 185-190 [Abstract] ( 921 ) [HTML 1KB] [ PDF 2470KB] ( 737 )
191 Optimization design of multistage centrifugal pump impeller by orthogonal experiment and CFD
WANG Wei, SHI Weidong, JIANG Xiaoping, FENG Qi, LU Weigang, ZHANG Desheng,
In order to improve the hydrodynamic performance of a typical cantilevered multistage centrifugal pump, orthogonal experiment and numerical simulation are carried out when four main impeller geometric parameters including blade outlet width, impeller diameter, number of blades and exit blade angle are changed. A computational fluid dynamics(CFD)code is employed to simulate the three-dimensional steady turbulent flows in the pumps with the designed impellers and the same diffuser. It is shown that the predicted pump performance curves present good agreement with the experimental ones for the original pump model, indicating the numerical prediction of performance is correct and reliable. According to the L9(34)experimental design table., nine impellers are designed and the head and efficiency of the pumps with these impellers are obtained at the duty point. Simultaneously, the effect of geometric parameters on the pump performance is concluded through variance analysis, eventually an optimal set of parameters are resulted. Afterwards, by a comparison of head and efficiency between the optimized and the original models, it is illustrated that there is a significant improvement in performance in the optimized model. It is the absence of swirling and reverse flows and less hydraulic losses as well as the large pressure gradient that are responsible for the performance improvement.
2016 Vol. 34 (3): 191-197 [Abstract] ( 1220 ) [HTML 1KB] [ PDF 2902KB] ( 790 )
198 Measurement of cavitation noise in centrifugal pump
QING Biao,, YU Bo, LAN Wei, HU Jinheng
Cavitation experiments are carried out to tackle cavitation problem a centrifugal pump in the paper by making use of TST6200 dynamic acquisition system, NoiseA2.10 noise test software and a hydrophone with -210 dB sensitivity under three flow conditions(80, 92, 100 m3/h). At the same time, the variation histories of vapour cavity in the stream are recorded by using a camera under these flow conditions. The recorded cavitation noise signals are analysed in frequency domain by adopting power spectrum method. The averaged powers of signal in three frequency bands are determined and the relationships between the signal powers and the net positive suction head available are obtained. It is shown that the characteristics of cavitation signal in the centrifugal pump are mainly involved in the low frequency band, but not obviously demonstrated in the medium and high frequency bands. The results in the frequency domain can reflect the development of cavitation in the pump. The specified powers in the two bands can be used as the thresholds respectively for cavitation inception and critical cavitation. By means of them, the cavitation in a centrifugal pump can be monitored in real time.
2016 Vol. 34 (3): 198-203 [Abstract] ( 1368 ) [HTML 1KB] [ PDF 3126KB] ( 870 )
204 Effect of circumferential setting position of diffuser in concentric volute on impeller radial thrust in centrifugal pump
GUO Bao, LIU Houlin, TAN Minggao, DING Rong, WANG Kai
In order to study effect of circumferential setting position of diffuser in concentric volute on impeller radial thrust, a specific centrifugal pump with diffuser and concentric volute as well as impeller is used as the model, four design cases where the angle α between the trailing edge of the blade pressure side of the diffuser and the volute discharge nozzle wall are considered to be 0°,10°,20°and 30°, respectively. Based on ANSYS CFX, unsteady numerical simulations of the whole flow field in those cases are conducted, the predicted head and efficiency are validated with measurement. Further, the effects of α on performance and impeller radial thrust are clarified. It is identified that the maximal variations in head and efficiency are 1.95% and 1.39%, respectively, and the best pump performance is achived at α=20°. With the increase of α, the amplitude of radial thrust pulsation firstly decreases but increases eventually. At α=20°, the amplitude reaches the minimum value, which is 80% of the largest amplitude. However, the dominant frequencies of radial thrust pulsation initially increase and then decrease with the increasing α. At α=20°, the amplitudes of the first and second dominant frequencies reach the minimum values. The change of α can influence the distribution of radial thrust vector, and the distribution shows an obviously regular pattern at α=0° and 30°. Particularly, the distribution at α=0° may be more suitable. for a long-term operation of this kind of pumps.
2016 Vol. 34 (3): 204-209 [Abstract] ( 1125 ) [HTML 1KB] [ PDF 2985KB] ( 742 )
210 Numerical simulation of cavitation performance of low specific speed centrifugal pump with slotted blades
WANG Yang, XIE Shanfeng, WANG Weijun
In order to improve cavitation performance of a centrifugal pump, a slot is made through each blade near its leading edge in a low specific speed centrifugal pump. Considering three parameters defining a slot, and six hydraulic models are designed. Cavitating flows in these pump models are simulated in CFX by means of steady Reynolds average N-S equations, a cavitation model, which is based on the Rayleigh-Plesset equation, and the RNG k-ε turbulence model. The simulated results show that slots on blade near their leading edge can improve cavitation performance, especially, in the second model the pump cavitation performance is improved more obviously, namely the hydraulic efficiency is increased to 76.46% from 71.56%, and the NPSH is decreased to 3.910 m from 4.447 m, resulting in a 12.1% reduction. At the duty flow rate, the energy inside the flow channels between the two blades is more uniformly distributed, while the head remains changed a little. The simulated results may have some referential value for investigating features of internal flow in a low specific speed centrifugal pump and its performance improvement.
2016 Vol. 34 (3): 210-215 [Abstract] ( 987 ) [HTML 1KB] [ PDF 3292KB] ( 702 )
216 Pump selection of seawater intake pumping station in Saudi Arabia
LIU Chao, XIE Weidong, LI Bin, TANG Hongyan
The design of seawater intake pumping station in a marine infrastructure project in Saudi Arabia and the purchase of the seawater intake pumps for the station should comply with the standard API 610 of centrifugal pumps for petroleum, petrochemical and natural gas Industries. In bid documents of the project owner, the seawater intake pumps are subject to 55 000 m3/h capacity and 16.1 m head at the duty point. However, the transformer capacity is insufficient for the power required by the pumps; meanwhile the quoted price for the pumps is slightly lower, presenting a business risk for potential contractors based on a thorough analysis of the documents. To avoid this risk, the variation of seawater level in the intake is analyzed and the intake is optimized, further the capacity is altered to 50 000 m3/h for pump selection. After the selection is optimized, the selected mixed-flow pumps with diffuser can operate in a range of flow rate of 50 000 to 59 100 m3/h at a higher efficiency of 85% to 87%, showing the transformer capacity is satisfactory. At the same time, the optimized pump should be in integrated structure rather than in pull-out one. 
2016 Vol. 34 (3): 216-219 [Abstract] ( 1375 ) [HTML 1KB] [ PDF 1465KB] ( 1006 )
220 Numerical simulation and experiment on flow fields in underwater self-excited pulse jet device
GAO Chuanchang, XIE Keyu, LIU Xinyang, HU Yazhou, MA Wenliang
A series of experiments on underwater self-excited pulse jet are made by using a self-developed test platform and the axial and radial distributions of pressure around an underwater self-excited pulse jet are obtained. Then, the flow fields inside and outside the jet are simulated, the corresponding velocity and pressure distributions are acquired and compared with the experimental data. The results show that obvious low frequency pulses can occur for the self-excited pulse jet under non-submerged condition. Under submerged condition, however, because part of the jet energy is consumed in the submerged water body so much that it is hard for cavitation to form in the chamber and to generate obvious pulse, further the stagnation pressure is reduced significantly. The radial pressure distribution is basically the same in different depths of the water, approximately yields the Gaussian distribution. The axial stagnation pressure is decreased with the increasing distance to the target, and its attenuation characteristic is similar to that for continuous jet and under non-submerged condition, just the decay rate is even faster. A low pressure zone in the jet core, two symmetrical negative pressure zones and a high pressure impinging zone exist in the flow field in the chamber of the underwater self-excited pulse jet device. Vortexes are generated near the bottom casing, and the flow field is similar to the jet flow in the chamber, but without a core.
2016 Vol. 34 (3): 220-226 [Abstract] ( 919 ) [HTML 1KB] [ PDF 2150KB] ( 703 )
227 Effects of propeller layout position on flow characteristics in oxidation ditch
CHEN Bin, WANG Bingqi, ZHANG Hua, WANG Qiang, WANG Zhen
To avoid sludge deposition in a running track type oxidation ditch, the layout position of four propellers is altered when the pool structure remains unchanged. The steady fluid flow field in the whole ditch is simulated by means of STARCCM+ software plus the standard k-ε turbulence model when these propellers are in operation. The velocity distribution in each section in the ditch and the velocity distribution in the whole flow field as well as the dead water zone are analysed to specify the optimal propeller layout position for the pool. Results show that the propellers′ position has a great influence on velocity distribution, and a too large or too small distance between a propeller and the middle baffle wall can lead to an uneven velocity distribution and an enlarged dead water zone. Especially, when the distance is about 0.85 times the sum of the circular baffle wall radius and the distance of the circular baffle wall centre to the middle baffle wall, the average fluid velocity is as high as 0.35 m/s in the major sections observed with the smallest dead water zone. Flow separation zones are inevitable at the back of the circular baffle wall and the two ends of middle baffle wall, but they can be diminished by changing propellers′ position. In addition, there is an obvious vortex phenomenon in the corners of the ditch by virtue of the interaction between the propellers and the pitch walls.
2016 Vol. 34 (3): 227-231 [Abstract] ( 1107 ) [HTML 1KB] [ PDF 2613KB] ( 717 )
232 Study on optimization of upstream pumping mechanical seal based on response surface method
CHEN Huilong, LIU Jinfeng, REN Kunteng, LI Tong, FU Jie, ZOU Qiang, YIN Yunxiao
To achieve a more effective optimization method for upstream pumping mechanical seals, based on cavitation model, the spiral groove geometrical parameters, such as groove depth h, spiral angle α, groove diameter ratio β and groove width ratio γ are considered as the design variables and the leakage through the seal is used as the objective function. Then, 50 mechanical seals are designed by means of uniform experimental design method, and the values of objective function are calculated by CFD to establish regression models of the objective function with respect to these variables. The response surface method is used to analyze the interaction of between the design variables and their effects on the leakage by making use of the leakage contours generated in MATLAB. Consequently, the optimal ranges of the design variables are determined. The fluid dynamics in three seals with design variables in the optimal ranges is simulated to decide the optimal combination of the design variables. It is confirmed that it is feasible to use the response surface method in upstream pumping mechanical seal optimization. When the groove depth h, spiral angle α, groove diameter ratio β and groove width ratio γ are in range of 6-12 μm, 16°-20°, 0.35-0.55 and 0.45-0.6, respectively, the mechanical seal performance is even better.
2016 Vol. 34 (3): 232-237 [Abstract] ( 965 ) [HTML 1KB] [ PDF 2181KB] ( 755 )
238 Factor analysis and application of drainage modulus of local depression in polders along Yangtze River
DUAN Shengpo, WU Yubai,, JIN Qiu, SHAO Xiaohou
Serious waterlogging disasters occur frequently in local depressions of polders along Yangtze River, so that it should be managed at first of the moment. Focused on the local depressions of polders in Jiangdu District, the relationships between drainage modulus, drainage acreage, water surface ratio, depth of river and recurrence period are established based on hydrology analysis and calculation. The reasons of waterlogs occur in a typical local depression are inferred, which were followed by the effective preventive measures. The results indicate that the partial correlation coefficient between drainage modulus and drainage area is -0.905, which has the strongest correlation. Furthermore, flooding peak runoff and waterlogging drainage modulus are larger because of the fast floodwater conflux speed in local depressions. The main reasons for the occurrence of waterlogging disaster in local depressions include a lack of river network, large interval between rivers and small drainage modulus as well as unreasonable layout of drainage system. Based on this analysis, a series of measures are put forward to prevent from waterlogs, namely shrinking the interval between rivers, increasing water surface ratio, fully using regulation and storage capacity of waterway. Finally, a drainage pipe network and a layout of waterways, which are suitable to the hydrologic characteristics of local depressions, are proposed.
2016 Vol. 34 (3): 238-243 [Abstract] ( 868 ) [HTML 1KB] [ PDF 1546KB] ( 795 )
244 Effects of drought-waterlogging stress and environmental factor on sap flow of tomato under rain shelter
DENG Sheng, YU Lei, SHAO Guangcheng, KONG Qiongju, LU Jianghai
Based on pot cultivation experimental data of tomato under rain shelter, the diurnal variation of sap flow velocity is analyzed at different irrigation amounts and under various weather conditions. The environmental factor, i.e. independent variable, includes solar radiation, ambient temperature, air relative humidity and soil moisture. The sap flow velocity is correlated to these factors by using path analysis and grey relational analysis, the correlation coefficient, coefficient of determination and grey relational degree have been determined. The results indicate that the diurnal variation of sap flow changes significantly under different weather conditions. Particularly, it presents a single-peak curve on sunny day, but bimodal peak one at 10:00 and 14:00 on cloudy day. The sap flow is small and shows a little fluctuation in the rain. A diurnal variation curve of sap flow of at different irrigation amounts can reflect the status of drought hardening and waterlogging, and a slight deficit can resist waterlogging to improve sap flow. Unfortunately, once the deficit is beyond a certain limit, it can reduce the flow significantly. Solar radiation is the most sensitive factor affecting the sap flow because its coefficient of determination is as high as 0.91. Both methods have achieved consistent results. 
2016 Vol. 34 (3): 244-250 [Abstract] ( 1265 ) [HTML 1KB] [ PDF 1586KB] ( 746 )
251 Progress in research on soil water redistribution
JIN Shijie, FEI Liangjun, FU Yuliang
Soil water redistribution has significant effects on local ecosystem and agriculture in arid and semi-arid farmlands in the Loess Plateau. In a redistribution proess, soil water moves in unsaturated soil under the potential gradient. This article reviews and summarizes theories and models in soil water redistribution achived in China and abroad from point of view of both physics and biology. It is found out that the progress is mainly affected by cultivation measures, rainfall intensity, initial moisture content and irrigation method from point of view of physics. The developed mathematical models based on soil water characteristic curve and its hysteresis, soil water flux method, and soil water motion equations etc are clarified. It is also identified that the soil water redistribution can effectively regulate soil moisture condition in root layer and enrich community structure and improve soil nutrient; but the process can be influenced by soil moisture, species and soil properties.
2016 Vol. 34 (3): 251-259 [Abstract] ( 2588 ) [HTML 1KB] [ PDF 1330KB] ( 1032 )
260 Experimental study on dynamic tri-axial test of saturated gravel soil of Toutun river basin in Xinjiang
ZHANG Lingkai
The dynamic deformation properties of saturated gravel soil are studied under a dynamic loading by using tri-axial test in laboratory. The effort is mainly focused on the influence of vibration frequency, consolidation pressure and consolidation stress ratio on the dynamic constitutive relation and dynamic modulus of elasticity. It is indicated that the dynamic stress-strain curve is of hyperbolic type, and approaches gradually towards the stress axis direction with the increase of consolidation pressure and consolidation stress ratio, but the vibration frequency has a less effect on the stress-strain curve of the gravel soil. The dynamic elastic modulus decreases with the increase of dynamic strain, but remains nearly unchanged at last. The vibration frequency affects the curves less because the experimental data are generally in the same zone; the consolidation pressure and consolidation stress ratio, however, demonstrate a great influence on the curves. The Ed/Ed max-εd curves under different vibration frequencies and consolidation pressures have a relatively good normalization property, while those under various consolidation stress ratios do not.
2016 Vol. 34 (3): 260-264 [Abstract] ( 942 ) [HTML 1KB] [ PDF 1526KB] ( 622 )
265 A fully automatic control photovoltaic pumping system based on AVR microcontroller
SHI Aiping, XU Guanjie, SHI Jian
In this paper, a control structure based on AVR microcontroller is proposed to explore a novel adaptive maximum power point tracking(MPPT)algorithm for photovoltaic(PV)pumping systems. DC-AC converter duty cycle is derived according to the principle of genetic algorithm and by combining the genetic algorithm and perturbation and the observation(P & O)method for duty cycle to search the maximum power point of the photovoltaic pumping system quickly and overcome interference on the controller caused by the dramatic changes in the external environment. The adaptability and stability of the MPPT method based on the genetic algorithm are validated in Simulink environment. Water pumping experiment is made on a test rig built for the designed photovoltaic pumping system to realize MPPT. It is shown that the system can respond the continuous change in climate exactly, causing a stable overall efficiency as good as 60%. There is a 10% improvement in comparison with the 50% efficiency of ordinary PV systems. Therefore, the developed system can provide a reliable control on the load of PV pump, but also its operation is sable with a higher overall efficiency. The work can provide a reference for optimal control of photovoltaic pumping systems. 
2016 Vol. 34 (3): 265-269 [Abstract] ( 948 ) [HTML 1KB] [ PDF 2229KB] ( 765 )
270 Analysis of working mechanism and hydraulic performance of two-way flow channel stabilizer in bubbler irrigation emitter
GUO Lin, BAI Dan, WANG Xinduan, HE Jing
In order to study on the hydraulic performance of the structure of two-way flow channel stabilizer in bubbler irrigation emitter, the inner structure of the stabilizer is modelled with three geometrical parameters, namely the angle α between the two splayed baffles, the angle β of V-shaped baffle, and the throat width d of the two splayed baffles. The experimental models have been designed by changing those parameters. The experimental models are manufactured by laser engraving technology, and the flow rates are measured under nine pressures ranged in 0.05-0.21 MPa. The experimental results are fitted by multivariable regression method, showing the models are subject to an excellent hydraulic performance with a flow regime index in 0.476 to 0.501. Meanwhile, the minor hydraulic loss coefficients across the models are calculated. The coefficients are between 18.3 to 19.8, nearly 4-10 times the minor loss coefficients across a traditional flow channel when the operating head is ranged in 5 to 15m, suggesting the designed stabilizers show an excellent energy dissipation behavior. Mathematical relationships between flow regime index and geometrical parameters are developed by using multivariable regression method with Gauss-Newton algorithm based on Minitab software in which the number of iterations is set to be 200. The results show that the regression is significant in statistics in both Significance test and correlation coefficient test. The relationships provide a theoretical basis for parameterized design, structure optimization, development and application in agricultural engineering.
2016 Vol. 34 (3): 270-276 [Abstract] ( 1088 ) [HTML 1KB] [ PDF 1430KB] ( 775 )
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