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Journal of Drainage and Irrigation Machinery Engin
 
2014 Vol.32 Issue.8
Published 2014-08-25
article
Article
645 Vortex dynamic analysis of unsteady cavitating flows around a hydrofoil
Zhao Yu, Wang Guoyu, Huang Biao
Vortex dynamics methods were used to analyze the 3-dimensional unsteady cavitating flows around a hydrofoil based on both experimental and numerical results. The experiment was conducted in the cavitation tunnel in Beijing Institute of Technology. High speed video camera technique was used to capture the 3-dimensional cavity evolutions. Filter-based density correction turbulent model and classical interface mass transfer cavitation model were used in the simulations. Comparing with experimental results, the numerical method is able to capture the initiation of the cavity, growth toward the trailing edge, and subsequent shedding. Based on the computations, vorticity transport equations and complex vortex identify methods were conducted to analyze the influence of cavitation on vorticity transport process. Following conclusions can be drawn: re-entrant jet near trailing of attached cavity leads to distinct changes of velocity gradient, which has great influence on production and dissipation of vorticity. Intensive mass transfer between liquid and vapor phase may induce the dilation and baroclinic torque. Two factors mentioned above keep changing and result in unsteady distributions of vorticity. Cavitation may lead to unsteady mass and momentum transfers between liquid and vapor phase, which will change turbulence and vorticity distributions distinctly. With Q and R methods, following conclusions can be drawn: rotation effect is stronger in the area near the leading edge of attached cavity, while rotation and deformation effect work together in area of detached cloud cavity.
2014 Vol. 32 (8): 645-651 [Abstract] ( 1282 ) [HTML 1KB] [ PDF 2027KB] ( 2525 )
652 Numerical calculation of inlet prewhirl flow in low-specific-speed centrifugal pump
Shi Weidong, Li Hui, Wang Chuan, Xu Yuanhui
A single-stage low specific speed centrifugal pump was studied based on the Euler equation and Stodola method on the platform of Fluent considering the inlet prewhirl by using radial inlet guide vanes to study the influence of prewhirl on pump performance. The effect of prewhirl flow on non-overload performance of a centrifugal pump was analyzed through the internal flow field and external chara-cteristic obtained from the numerical simulation of three schemes with different geometric parameters of inlet guide vanes. The results shows: the circumferential velocity at the exit of guide vanes increases with the enhancement of the inlet prewhirl. According to the internal flow field from inside to outside along the radial direction, the circumferential velocity shows the increasing trend and slightly reduces along flow direction without considering the effect of boundary which is different with VuR=constant. Sharp down head curves and flat power curves can be obtained by the enhancement of the inlet prewhirl flow and the efficiency is improved slightly near the region from small flow rate to rated flow. Therefore, it is possible to realize the non-overload performance in the total head range by using prewhirl flow.
2014 Vol. 32 (8): 652-657 [Abstract] ( 2299 ) [HTML 1KB] [ PDF 2279KB] ( 2242 )
658 Hydraulic characteristics and axial force of micro vortex pumps
Zhang Feixi, Wu Peng, Wu Dazhuan, Wang Leqin, Zhang Huiping
Numerical simulation of a new shrouded impeller vortex pump was carried out. The method of solving steady three-dimensional incompressible continuity equation and RANS equations were employed to calculate the hydraulic performance of the vortex pump. The axial bearing mechanism of the oil film toward the impeller was analyzed, and further discussion about the influence of the wedge shaped groove on both sides of the impeller on the bearing capacity of the oil film was made. It was found that the predicted hydraulic property was consistent with test data, which proves the calculating model reliable. In addition, the results show that the axial supporting of floating impeller is rely on the oil film formed on both side of the impeller. The different thickness of oil film results in different radial pressure drops. The thinner one results in the slow pressure drop while the thicker one results in the uniform pressure, which causes an unequal force on impeller and provides the holding power. More-over, the wedge shaped structure enhances the supporting effect. The study is useful for the design and analysis of vortex pumps.
2014 Vol. 32 (8): 658-662 [Abstract] ( 2373 ) [HTML 1KB] [ PDF 1667KB] ( 4549 )
663 Hydraulic optimization of radial guide vanes in two-stage centrifugal pump
Cao Weidong, Liu Guanghui, Liu Bing
In order to improve the hydraulic performance of radial guide vanes in two-stage centrifugal pumps, four factors of guide vane including the area of throat, diffuser angle, back vanes numbers and height of back vanes were selected to meet the L9(34)orthogonal experiment requirements, so nine different guide vanes were designed. Based on ANSYS CFX, the whole flow field of two-stage pump was simulated by using the standard k-ε turbulence model and the fully implicit coupled algorithm. The heads and efficiencies of nine design schemes were obtained. The head and efficiency was selected as the criterion of the test, the effects of geometrical parameters on heads and efficiencies were studied by using orthogonal test method, and the primary and secondary factors of the design parameters were all analyzed by ways of variance analysis. The area of guide vanes throat has great effect on two-stage pump performance. According to the test results, an optimum scheme was put forward. The simulation results of the optimum scheme show that the head of the pump at rated flow point is of 211.70 m and the efficiency is of 47.63%. Compared to the original radial guide vane, the head and efficiency are significantly improved by 1.24 m and 4.00% respectively. 
2014 Vol. 32 (8): 663-668 [Abstract] ( 2335 ) [HTML 1KB] [ PDF 1345KB] ( 1944 )
669 Numerical investigation of viscosity impact on rotary lobe pump performance
Li Yi, Jiang Xiaojun, Qian Haohai
In order to study the effect of the transmission medium viscosity on lobe pump efficiency, the 3D modeling software was used to build parametric models of the lobe pump. The size function was applied to mesh the lobe pump model and the grid near the rotors was refined. On the computational fluid dynamics software platform, the numerical simulation of lobe pump was performed with RNG k-ε turbulence mode and dynamic mesh technique. By comparing the lobe pump efficiencies with diffe-rent transmission media, the impact of medium viscosity on the lobe pump efficiency was revealed. The results show that when the pressure differential is increased from 0.1 MPa to 0.6 MPa, the volumetric efficiency corresponding to each viscosity of the medium is decreased, but the medium with larger viscosity(>250 cP)is less sensitive to pressure differential. When pressure differential is constant and rotation speed is increased from 200 r/min to 600 r/min, volumetric efficiency of low-viscosity fluid medium(<100 cP)has been significantly improved, and the high-viscosity fluid medium changes only slightly. Along with the increase of medium viscosity, the rotation speed for the maximum efficiency of lobe pump decreases. This paper has reference value for a reasonable selection of lobe pump in different operational conditions and improvement of lobe pump efficiency.
2014 Vol. 32 (8): 669-673 [Abstract] ( 1848 ) [HTML 1KB] [ PDF 1566KB] ( 1718 )
674 PIV measurements of inner flow field in an inward radial diffuser under multi-conditions
Huang Ping, Zhang Li, Zhou Ling, Fu Yanxia, Lu Weigang
In order to understand the flow pattern of the diffuser internal flow field and improve the diffuser hydraulic design method, a special test rig was designed and installed to investigate the flow fields in an inward radial diffuser by using the particle image velocimetry(PIV)technique. The test model is one stage of a deep-well multistage centrifugal pump, two water lubricated plain bearings were used to support the pump shaft, and a mirror placed in 45° was used to reflect the flow field of diffu-ser. The velocity flow fields under a variety of operational points were obtained by using the phase averaged method. The results show that the flow in the diffuser is uniform and stable at the design flow rate. At the larger flow rates, the flow is blocked by the finite throat area and a considerable shock loss is generated at the diffuser inlet. At the lower flow rates, flow separation and vortices appear, and the vortex intensity is strengthened with reducing flow rate. Meanwhile, the position of vortex core is mo-ving from the location nearby diffuser suction side to the middle of diffuser. Large hydraulic losses produce at the diffuser inlet, and the diffuser inlet setting angle have a significant effect on the pump performance. The flow area in the middle of diffuser passage needs to be further adjusted to improve the flow pattern under lower flow conditions.
2014 Vol. 32 (8): 674-678 [Abstract] ( 1481 ) [HTML 1KB] [ PDF 1932KB] ( 1453 )
679 Calculation and analysis of leakage of Francis pump-turbine
Min Zheng, Liang Changping, Dong Zhiqiang, Liu Dianxing, Qin Daqing, Wei Xianzhu
In order to determine the leakage of Francis pump-turbine, the theoretical formula method was employed based on empirical parameters, and the CFD numerical simulation method using Navier-Stokes equations, RNG k-ε turbulence model and structured grid technology was used to calculate the leakage of a large reversible unit with the guide vane opening at 60%, 70%, 80% and 90%, and then a comparative analysis of the results of this two methods was done. The results show that the theoretical formula method involves the selection of empirical parameters, which leads a larger degree of dependence on computing experience, and has certain blindness and inaccuracy. When calculating the leakage under the turbine condition, the head of the points are equal, thus leading to that the leakage curve is a parallel straight line. It cannot reflect the real law between the leakage and the working conditions. By comparing the performance curves calculated by the CFD numerical simulation with the testing performance curves, the agreement of the results are better, verifying the accuracy of CFD numerical simulation and the feasibility of the clearance leakage calculation. It can describe the clearance flow more accurately and overcome the drawbacks of the theoretical method in calculation. 
2014 Vol. 32 (8): 679-684 [Abstract] ( 1851 ) [HTML 1KB] [ PDF 2866KB] ( 1608 )
685 Siltation features and into canal characteristics at water intake of lateral for Yellow River irrigation area
Zhao Linlin ,, Ma Tailing, Yu Jian, Li Chao, Hu Sheng, Li Quan
Inner Mongolia Dengkou pumping irrigation area was considered as the research object, of which channel water from Yellow River. The thickness of silting in front of the intake pumping station before opening and after stopping pump in four irrigation period was measured, and water draw rate and sediment concentration into the canal was tested during the pump working. The siltation features and into canal characteristics at water inlet were studied. Results show that the velocity ratio and diversion width of the Yellow River upstream of the intake are the main factors of influence on sediment into the canal, when the flow velocity is reducing, and diversion width is increasing, the influence of cross current is more intense when more bed sediment is brought into water intake. For the lateral intake, the water mainstream area is moving to the downstream. Under both effects of flat backflow and cross current, the bed sediment distribution thickness in front of water intake appears greater at intake upstream than downstream. The block sand bar in front of intake can effectively prevent the bed load into the canal, the results indicate that the top of the block sand bar is below the free surface within 1.6 m, not only the sediment into the canal can be greatly reduced, and the better flow regime can be obtained to prevent pump cavitation.
2014 Vol. 32 (8): 685-690 [Abstract] ( 1345 ) [HTML 1KB] [ PDF 1537KB] ( 1604 )
691 Differential algebra model simulation for hydro turbine with elastic water column
Zeng Yun, Zhang Lixiang, Qian Jing, Xu Tianmao, Guo Yakun
The simulation method was used to verify the differential algebra model of hydro turbine with elastic water column. Firstly, the derivation procedure of hydraulic dynamic differential equation with elastic water column was given, and the Simulink simulation module of the nonlinear hydro turbine was established. Comparing the differential equation model of hydraulic system with other traditional me-thods, such as the transfer function, higher order transfer function, different form transfer function and characteristic line, the changes of hydro turbine power and head in transient were analyzed, the precision and applicability of the differential equation model in hydro turbine transient procedure were stu-died. Results show that head and power values of the nonlinear differential algebra model of hydro turbine in transient are consistent with that of other traditional methods, and proposed model can meet the requirement of researching the transient characteristics of hydro turbine.
2014 Vol. 32 (8): 691-697 [Abstract] ( 2032 ) [HTML 1KB] [ PDF 1421KB] ( 1659 )
698 Thermal-structural coupled analysis of gap between rotary valve′s body and rotor
Gong Enxiang, Xia Tian, Yang Yan, Cai Wanfeng, Hu Haipeng
The gap between body and rotor plays an important role in the safe operating of rotary valve. Based on the finite element method, thermodynamic and pseudo-fluid method, a thermal analysis about the body and rotor of rotary valve was carried out, and the temperature distribution was obtained. Based on the thermal-structure coupling strain analysis, thermal distortion was obtained, and through the deformation the requirement of the gap values between rotary valve body and rotor was found. Body temperature decreases gradually from inside to outside, the temperature of the rotor blades distributes evenly, and the temperature values on both ends of the rotor is lower. As the temperature of the material increases, the gap between the valve body and the rotor gradually increases. Material impact on the value of the gap between the rotor forces can be neglected. With the pressure on valve body increa-sing, the valve body clearance value between the rotor increases. For supporting greater force, other structural such as reinforcement can be added to the body to increase the structural strength.
2014 Vol. 32 (8): 698-702 [Abstract] ( 1148 ) [HTML 1KB] [ PDF 1466KB] ( 1565 )
703 Dynamic and static performance of flow stability valve
Li Sihai,Huang Liuyi,Wei Wei.
2014 Vol. 32 (8): 703-710 [Abstract] ( 1307 ) [HTML 1KB] [ PDF 1696KB] ( 1420 )
711 Effect of drip irrigation pattern and irrigation lower limit on yield and quality of cotton
Shen Xiaojun, Zhang Jiyang, Sun Jingsheng, Li Mingsi, Wang Jinglei, Liu Hao
To explore the high-quality irrigation index of cotton under drip irrigation, a field experiment was conducted to investigate the effects of different irrigation lower limits on seed cotton yield, fiber quality and water use efficiency of cotton under subsurface drip irrigation with film mulching(SSDI)and surface drip irrigation with film mulching(SDI)in Shihezi, Xinjiang Autonomous Region. The results show that water consumption during squaring stage increases with irrigation lower limit rising, and the water consumption of water deficit treatments during blooming-boll forming stage are lower than control experiment. It is beneficial to improve seed cotton yield under moderate water stress(60% FC)during squaring stage and no water stress(75% FC)during blooming and boll forming stage(SDI-7 and SSDI-7), and comparing to the control treatment, seed cotton yield is improved by 14.48%(SDI-7)and 11.60%(SSDI-7). Water treatments has no obvious influence on lint percentage and uniformity of cotton fiber, and the effect of water stress on length of cotton fiber during squaring stage and blooming-boll forming stage increases with irrigation lower limits decreasing. Mode-rate water stress at squaring stage can increase the breaking tenacity of cotton fiber. Compared with surface drip irrigation under film mulching, subsurface drip irrigation can improve seed cotton yield and irrigation water use efficiency of cotton at the same water treatment. This research suggests that the irrigation model with 30 mm of irrigation water quota and irrigating at lower limits of 60% FC and 75% FC during the squaring stage and flowering-boll forming stage, respectively, can be taken as suitable irrigation index of drip irrigation cotton to save irrigation water, to increase seed cotton yield and to improve cotton fiber quality in Reclamation Area of Shihezi, Xinjiang Autonomous Region.
2014 Vol. 32 (8): 711-718 [Abstract] ( 1442 ) [HTML 1KB] [ PDF 1343KB] ( 1458 )
719 Water footprint of grain production based on crop water consumption
Liu Di,, Cao Xinchun,, Wang Yubao,
According to the water footprint and crop water consumption theory, the production water footprint of crop calculation model based on the actual crop water consumption was presented. Taking on the winter wheat and summer maize in the Guanzhong Region of Shaanxi Province as the objective of the study, the production water footprint of the grains in 1998, 2005 and 2010 were calculated and analyzed. The results show that: the water consumption of a certain crop(winter wheat or summer maize)in the same year is varied form district to district. Compared with the crop water requirement, average water consumptions of wheat and maize in three years are 16.2% and 12.4% lower respectively. Variable trends of the virtual water content of winter wheat and summer maize have reduced year by year, and average virtual water content are 0.96 and 0.77 m3/kg respectively. The proportion of blue water in virtual water of wheat is 10%-40%, and the change range of maize is 20%-50%,meanwhile, the proportion of blue water between regions has not a significant change trend. The production water footprint of grain were 7.01, 5.98 and 6.07 billion m3 in the three representative years, and all of them are larger than the local water resources when the proportion of blue water footprint is 29.1%; The calculation of water footprint based on the actual consumption of crops has great significance on the scientific research and policy based on water footprint and virtual water trade. 
2014 Vol. 32 (8): 719-724 [Abstract] ( 1616 ) [HTML 1KB] [ PDF 1086KB] ( 1910 )
725 Soil-bin test device of vertical spiral opener
Zhang Quanquan, Li Pingping,, Zhu Changshun, Wang Jizhang, Liu Jizhan, Xu Yunfeng
In order to study the power consumption under different combinations of forward speed, rotational speed, opening furrow angle and depth of furrow, a kind of soil-bin test device of vertical spiral opener was introduced for the soil-bin experimental test. With computer and acquisition cards as control center, a measurement and control software were programmed based on LabVIEW to collect, display and analyze the data of motional parameters such as rotational speed, torque and power consumption, et al. The device were tested in the soil-bin under the experimental conditions considering 250 r/min as rotational speed, 0° as the opening furrow angle, 250 mm as the depth of furrow, and 3 m/min, 4 m/min, 5 m/min as the forward speed respectively. The cutting power consumption obtained by theoretical model can be used to validate the experimental results. The test results show that the device can simulate the whole process of the vertical spiral opener cutting the soil, and the maximum error between calculated and experimental values is 11.05%.
2014 Vol. 32 (8): 725-729 [Abstract] ( 1892 ) [HTML 1KB] [ PDF 3309KB] ( 1630 )
730 Spatial variation of soil physical characteristics and calibration factor of Philip infiltration formula
Wu Shiliang, Nie Weibo, Ma Xiaoyi
With a soil field infiltration test in the Yangling area as the basis, Philip′s infiltration equation was calibrated by using the calibration theory. The calibration coefficient and the spatial variability of soil physical properties were analyzed using the multifractal method, and based on the joint multifractal theory, a pedo-transfer function of calibration factors was constructed. The research has shown that the calibration results of arithmetic calibration factors are the most optimum. Calibration factors and soil physical properties within the research area possess multifractal characteristics, and on single and multiple scales, the spatial variability of calibration factors, sand content and organic matter content are relatively strong. The spatial variability of calibration factors and sand content is composed of high values in different scale intervals, and the spatial variability of coarse dust content is composed of low values in different scale intervals. On a single scale, there is relatively significant correlation between calibration factors and the content of organic matter as well as clay particles, and on a multiple scale, there is a significant correlation between calibration factors and soil bulk density, clay particle content and organic matter content. The soil transformation function of calibration factors from joint multifractal theory has relatively small calculation errors, and the pedo-transfer function from joint multifractal analysis can possesses a strong theoretical basis and value.
2014 Vol. 32 (8): 730-736 [Abstract] ( 1522 ) [HTML 1KB] [ PDF 1266KB] ( 1651 )
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