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Journal of Drainage and Irrigation Machinery Engin
 
2015 Vol.33 Issue.3
Published 2015-03-25
article
article
185 Hydraulic performance conversion for low head pumping installation to avoid armful cavitation
Zhou Junliang
In China, the prophase design of a new pumping station project is based on the databases established from existing hydraulic experiments on a series of pump and pumping station models. It is regulated that the geometry of the model of a pump or pumping hydraulic installation must be similar to the geometry of its prototype. However, there is a scale effect, because the ratio of the roughness to the characteristic linear dimension of the model is not exactly equal to that of the prototype, and the volumetric efficiency of the model may not be the same as the prototype. Additionally, the hydraulically smooth regime may exist in parts of the flow passages in a model, suggesting the flow regime differs from that in the prototype. Also, it is allowed that the model pump can be tested at a lower rotational speed than the prototype pump. These two situations result in Reynolds number effect. Because of these two effects, there are signification differences in the prototype performance between the measurement and the estimate by using the affinity laws. Thus various empirical formulas have to be proposed to modify the existing affinity laws. As a result of this, ten or more formulas have been put forward over the world so far. The author proposes an approach to eliminate the scale and Reynolds number effects here. At first, the experimental data from a model are converted into a new set of data for an artificial model whose geometry is similar to the prototype and in which stream velocity and hydraulic efficiency are the same as the prototype by means of an empirical formula with variable overall efficiency. Then the new set of data are converted into the hydraulic performance parameters of the prototype by making use of the affinity laws. This approach can prevent a pump from the harmful cavitation onset on its blades. The approach has been applied to convert the hydraulic performance curve of the prototype pumps in the 1st stage pumping station situated on River Zao from the experimental data of the counterpart model pump. The predicted performance curve agrees well with the recorded one in operation.
2015 Vol. 33 (3): 185-195 [Abstract] ( 1163 ) [HTML 1KB] [ PDF 1575KB] ( 1821 )
196 Numerical analysis of effects of staggered blades on characteristics of double-suction centrifugal pump
Liu Jianrui, Fu Wei, Gao Zhenjun, He Xiaoke, Chen Bin, Tang Fujun
To reduce the pressure fluctuation amplitude in a double-suction centrifugal pump, the blades of both sides of the impeller are separated circumferentially with 0?, 10?, 20?, 30? staggered angles respectively in double-suction pump ES350-585 with a usual double-suction impeller. A structured grid in the flow domains of five pumps with usual and staggered impellers is generated by using Gridpro; subsequently aunsteady, 3D fluid dynamics analysis is launched in ANSYS CFX to obtain pump performance and unsteady static pressure profiles. It is seen that the staggered blades can reduce pressure fluctuation in the pumps effectively. Moreover the pressure fluctuation amplitude decreases with the increasing staggered angle. Importantly, when the staggered is 30?, the pressure fluctuation amplitude in the volute reaches the minimum and the static pressure becomes the most uniform at the entrance to the volute.
2015 Vol. 33 (3): 196-202 [Abstract] ( 1512 ) [HTML 1KB] [ PDF 2924KB] ( 1657 )
203 Performance optimization of low-specific speed centrifugal pump under variable operation conditions
Bu Xuebing, Chen Hui, Li Yongpeng, Wang Wenting
In order to improve the overall efficiency of a low specific speed centrifugal pump at multi-operation point, the hydraulic performance of such a pump is optimized numerically across a flow rate ratio of 8(the maximum flow rate to the minimum one)by making use of a global optimization algorithm based on Latin hypercube sampling and simulated annealing algorithm. Three optimization schemes are exploited, i.e. impeller optimization, volute optimization, and overall(impeller plus volute)optimization. It is shown that the efficiency of the optimized pumps becomes better in all the optimization schemes. The efficiency of the optimized pump in the volute optimization scheme is quit close to that in the overall optimization. However, the improvement of efficiency in the impeller optimization scheme is less than that in the other schemes. Thus, when a centrifugal pump with low specific speed is optimized at variable operation points, the first priority is to conduct a volute optimization. Moreover, in order to improve the overall efficiency of a centrifugal pump at multi-operation point, the design flow rate should be slightly lower than the maximum operation flow rate.
2015 Vol. 33 (3): 203-208 [Abstract] ( 1107 ) [HTML 1KB] [ PDF 2234KB] ( 1734 )
209 Effects of cross-section and cut-water shapes of volute on flow induced noise in centrifugal pumps
Si Qiaorui, Yuan Jianping, Heng Yaguang, Yuan Shouqi
Volutes have significant impact on the generation and propagation of flow-induced noise in centrifugal pumps. A volute with rectangular cross-section is designed to replace the original one with horseshoe-shaped cross section; subsequently, fluid dynamics simulation and acoustics computation are carried out in a centrifugal pump which is composed of the same impeller and either newly designed or original volute. The generation and propagation of flow-induced noise in the pump is solved by using a hybrid algorithm in which large eddy simulation and acoustic finite element analysis are combined based on the Lighthill acoustic analogy theory. The effects of cut-water of the volute on the pump head, efficiency and acoustic performance are also analyzed by employing two cut-water shapes, namely sharp and round edges. Some simulation results are verified by the existing experimental data. The analysis results show that both kinds of volute produce a similar hydraulic performance and result in a 290 Hz dominating frequency, i.e. blade passing frequency, for the noise. The volute with rectangular cross-section exhibits a better flow pattern than that with horseshoe-shaped cross-section according to the pressure contours, velocity vector distribution and flow direction inside the two pumps. Further the volute with rectangular cross-section lowers the averaged sound pressure level by 5 dB, showing an improved acoustic performance. Compared with the volute with sharp edge cut-water, the volute with round edge cut-water not only demonstrates a better hydraulic performance, but also possesses a more attractive acoustic behavior in account of 4 dB averaged sound pressure level reduction.
2015 Vol. 33 (3): 209-215 [Abstract] ( 1319 ) [HTML 1KB] [ PDF 2864KB] ( 1885 )
216 Flow field simulation and analysis of rotating magnetic photocatalytic wastewater treatment reactor
Wu Chundu, Zheng Kun, Xie Qingjie, Zhu Mingkai, Bai Ge
Environmental equipments should be designed for different wastewater working conditions. However, the internal flow field in a wastewater treatment reactor is extremely complex, thus it is difficult to determine the reactor working conditions and purifying effects based on designer′s experience alone. In order to study the spatial distribution characteristics of flow field in rotating magnetic photocatalytic wastewater treatment reactors, a physical model of such a reactor is built using Gambit, and a series of numerical simulations of 3-D the flow field in it are conducted by means of Fluent, the influences of rotating speed on the liquid flow field characteristics are analyzed at three kinds of speed. The results show that the fluid flow velocity increases with the speed. The fluid flow is weaker at the speed of 0.2 rad/s; even the fluid starts to circulate adequately at the speed of 0.5 rads/s, the flow velocity is still relatively low. At 1.0 rad/s rotating speed, the fluid has a higher turbulent kinetic energy and a uniform flow distribution, but there are vortices in the flow field. An analysis of the flow field characteristics at different rotating speeds cam provide a reference for optimization design of the reactor structure.
2015 Vol. 33 (3): 216-219 [Abstract] ( 1051 ) [HTML 1KB] [ PDF 4686KB] ( 1660 )
220 Effects of blade angle at high pressure end on performance of pump-turbine with high head
Ruan Hui, Liao Weili, Zhao Yaping, Luo Xingqi
Based on a design procedure for low specific speed Francis runners, three kinds of blades with different blade angles at high pressure end are generated while the rest parameter remain unchanged. The steady, three-dimensional turbulent flows in the pump-turbines with those blades are simulated by means of CFD method at five flow rates to identify the effects of the blade angle on the performance in pump and turbine modes and the inflow condition in the turbine mode as well as the rotor-stator interaction in the pump mode. It is proven that the predicted angle of attack is different from the angle prescribed in the design and the runner is subject to a negative angle of attack in the turbine mode, which results in a remarked shock loss and a slight efficiency reduction but the flow in the runner seems little affected. In the pump mode, the larger the blade angle is, the smaller the rotational angle of the guide vanes is. The hydraulic efficiency is the highest in that mode with blade angle 2, which matches the 14? rotational angle of the guide vane and the stay vane. However, the other two kinds of blade angles mismatch the guide vane and the stay vane, causing instable phenomena, such as shock, reverse flow and flow separation and so on, and leading to a serious declination in the hydraulic efficiency.
2015 Vol. 33 (3): 220-225 [Abstract] ( 1590 ) [HTML 1KB] [ PDF 2173KB] ( 1601 )
226 Effects of nozzle inlet conditions on micro-droplet formation
Yang Minguan, Yan Longlong, Wang Yuli, Gong Chen, Lu Jingang
The purpose of this work is to investigate the liquid ejection process of a micro droplet generator by applying a numerical approach. The time evolution of droplet shape characteristics is predicted. The flow behavior in the liquid ejection and droplet formation processes are examined with water as a baseline test fluid in a full ejection cycle. Numerical experiments are conducted to determine droplet ejection characteristics by systematically varying the velocity period, magnitude and amplitude as well as the contact angle at the nozzle inlet. The uniform and steady droplet formation region is exploited at different inertial proportions. The simulations results reveal that the dimensionless number Re,CH, ZF have a significant influence on the behavior of the droplet ejection characteristics, and the uniform and steady droplets can be formed under certain conditions. A lower velocity of the first droplet can be achieved by reducing the three dimensionless numbers. However, the ejection velocity is too low to form the droplet as Re is smaller than 9. The droplet through a hydrophobic surface breaks up later than one through a hydrophilic surface.
2015 Vol. 33 (3): 226-232 [Abstract] ( 1130 ) [HTML 1KB] [ PDF 2063KB] ( 1863 )
233 Comparative analysis of three types of straightener in long range firefighting water cannon
Xiang Qingjiang, Shi Zhefu, Li Hong, Chen Chao
Three types of straightener are designed which have approximately the same cross section area. In the two cases where the straighteners take up the same volume and surface area as the flow passage, the numerical simulations of flow in the water cannon are studied at 1 500 m3/h design flow rate. The results show that the flow pattern is improved evidently when the straighteners are installed, and the axial velocity near the outlet increases more greatly than the case without straightener. The total hydraulic loss is ranged from 0.10 to 0.13 MPa, and its 55% occurs across the straightener. Although the bullet-shaped straightener(shape Ⅲ)has the smallest total hydraulic loss, the rectifying effect is poorer than the double-circle section straightener(shape Ⅰ)and the multi-rectangular section straightener(shape Ⅱ). Moreover, the bullet-shaped straightener has a streamlined inlet structure, causing a less dynamic pressure loss. The surface area of straightener exhibits a more significant rectifying effect than the volume does. The maximum average turbulent kinetic energy is found at the outlet of water cannon without straightener. The energy declines once a straightener is installed. However, there is a suitable length for a straightener, once this length is selected, the position of straightener in cannon tube has little influence on the rectifying effect.
2015 Vol. 33 (3): 233-238 [Abstract] ( 2131 ) [HTML 1KB] [ PDF 1540KB] ( 1900 )
239 Assessment of suitability of farmland drainage water reuse based on fuzzy pattern recognition
Wang Shaoli,, Liu Dagang, Xu Di,, Chen Haorui,
An index system is put forward to evaluate the reuse suitability of farmland drainage water in arid and semi-arid regions threatened by salinization based on fuzzy pattern recognition model. For each index, the range of standard value for every classification is specified by analyzing the relevant literature and existing technical standards comprehensively. The weight of each index is determined by making use of the analytic hierarchy process(AHP). The index system is applied to assess the reuse suitability of drainage water in five typical farmlands in Yinbei Irrigation District, Ningxia. It is shown that except Qianjin farmland the water reuse suitability in the rest farmland is all at the second grade. Particularly, the index values in the middle and late periods of irrigation are less than those in the early period of irrigation, suggesting the water reuse suitability is better than in the middle and late periods. In the middle and late periods, crops need more irrigation but fresh water is in shortage; further the crops are not sensitive to salt. Thus it is feasible to reuse a certain amount of drainage water for irrigation in those periods.
2015 Vol. 33 (3): 239-245 [Abstract] ( 1240 ) [HTML 1KB] [ PDF 1434KB] ( 1516 )
246 Comparison of methods for computing soil hydraulic conductivity measured by disc infiltrometer
Gao Xuemei,, She Dongli,, Fang Kai
Soil hydraulic conductivity is one of the most important soil hydraulic parameters. Precisely measuring and computing the conductivity not only can promote the theoretical study on water flow process in an unsaturated soil but also can provide a scientific basis for reasonable determination of technical parameters in irrigation and drainage of farmland. To check the applicability of various methods for computing hydraulic conductivity, a series of infiltration experiments are conducted on the soils collected from vegetable and tea gardens by using a disc infiltrometer with 10 cm and 20 cm discs under four different negative pressure heads, namely -9, -6, -3, and 0 cm. Then the conductivities are figured out by means of different computing methods. The results show that the hydraulic conductivity is less affected by the disc diameter, the conductivities given by various methods are nearly the same, and a smaller disc is therefore recommended for the field test. It is suggested that the choice of computing method for the conductivity depends on type of soil, for example, the conductivity of the soil from cultivated land such as a vegetable garden should be estimated by making use of a steady flow model, while for the soil in a tea garden, the transient flow model should be adopted. At the same pressure head, the hydraulic conductivity is obviously dependent on type of soil. The variations of hydraulic conductivity calculated by using different methods are almost the same under four pressure heads for two kinds of soil.
2015 Vol. 33 (3): 246-252 [Abstract] ( 1363 ) [HTML 1KB] [ PDF 1480KB] ( 1677 )
253 Growth and quality of greenhouse tomato under cycle aerated subsurface drip irrigation
Lei Hongjun,, Zang Ming,, Zhang Zhenhua, Liu Xin,, Xu Jianxin,,Pan Hongwei,
Aerated subsurface drip irrigation refers to a kind of crop irrigation method in which aerated water is ejected into the root zone of a plant by using subsurface drip irrigation(SDI)system. It can enrich air content in the water significantly and eases temporal hypoxia in the root zone of plants in clayey soil under SDI system, subsequently increases crop productivity. The effects of aerated subsurface drip irrigation on growth, yield, and quality of greenhouse tomato are investigated by using yellow clayey soil in Zhongmou County, Henan Province. Compared with the control treatment, the crop water use efficiency(WUE)in the aerated treatment is increased by 20.72%, the fruit yield is improved by 29.15% at the first five harvests, and the harvest date is moved up under the same irrigation quota. Also, the stomatal conductance of tomato is raised by 30.51% and the plant vigour is enhanced. The viteamin V content, soluble solid and sugar-to-acid ratio are increased by 13.25%, 8.62% and 22.05%, but the total acid content and fruit rigidity are decreased by 15.50% and 11.19%, respectively, suggesting the quality of tomato has been improved greatly. Furthermore, the longest root length is increased by 16.75% and the root-to-canopy dry weight ratio rises by 25.81%. The results suggest the aerated subsurface drip irrigation can promote tomato plants to grow in the yellow clayey soil in green houses, to speed the mature process of fruit, to increase the yield of crop and to improve the quality of tomato.
2015 Vol. 33 (3): 253-259 [Abstract] ( 2386 ) [HTML 1KB] [ PDF 1496KB] ( 2022 )
260 Reasonable canal-to-well irrigation water quantity ratio in irrigation district based on groundwater balance
Li Jiancheng, Wei Xiaomei, Deng Kangjie
Based on a groundwater balance model, the groundwater balance in different frequency typical years is analyzed in Jinghui Canal Irrigation District in Shaanxi Province. The results show that the precipitation recharge, canal seepage and the field irrigation infiltration and well irrigation regression recharge are the major recharge sources of groundwater in the irrigation district, accounting for 85.99%-82.89% of the total recharge. However, the artificial exploitation is the main discharge way of groundwater, and the exploitation quantity of water accounts for 69.7%-72.86% of the total exploitation for the use of agricultural irrigation, human and animals and the industrial water supply. Regarding 2010 as the reference year and 2020 as the planning year, four different development scenarios are established by considering the irrigation district development plan, then the groundwater depths in those scenarios are calculated by using the groundwater balance model, which is ranged from 0 to 0.07 m. By minimizing the change in groundwater level, the reasonable canal-to-well irrigation water quantity ratio is determined to be in a range of 1.49-1.53 in different frequency typical years acquired. This study provides a basis for groundwater to be utilized in a more sustainable and efficient manner in the irrigation district.
2015 Vol. 33 (3): 260-266 [Abstract] ( 1105 ) [HTML 1KB] [ PDF 1475KB] ( 1649 )
267 Fluid-structure interaction analysis of deflector in vertical sprinkler
Tang Pan, Li Hong, Chen Chao, Liu Zhenchao, Zou Chenhai
Taking the deflector of a vertical sprinkler as a study model, the driving force applied on the deflector by the water jet is analyzed and measured. Based on the fluid-structure interaction principle, a numerical model for describing the driving force is built initially and validated by the experimental results. The fluid pressure profile obtained from a flow field simulation is imposed onto the deflector, then solid mechanics and free vibration analyses are carried out on it. The results show that the maximum error in the horizontal and vertical components of the driving force between simulation and experiment is 15.98%, which reduces with the increasing pressure. The maximum deformation is mainly distributed in the much curved part of the deflector. Eventually, the 1st through 6th order natural frequencies and corresponding vibration modes are obtained. When the deflector works under the frequency of less than 122.6 Hz, its vibration mode is usually in the first order. In order to improve the stability and reliability of the deflector in operation, its local configuration may need to be redesigned or a material with even stronger strength is adopted.
2015 Vol. 33 (3): 267-272 [Abstract] ( 1276 ) [HTML 1KB] [ PDF 3126KB] ( 1618 )
273 Cutting thickness model comparison considering cutting tool deflection in micro milling
Liao Dong
To use a more accurate method to simulate the trajectory of the tip of micro milling process,and decrease the micro cutter tip movement errors. This paper describes the use of trochoidal tip trajectory, and considering the impact on the tool deflection process. Besides, an improved theoretical model was established for the instantaneous chip thickness, the course focused on the tool rotation, the tool deflection and the impact on the amount of feed per tooth momentary cutting thickness, meanwhile, a variety of different cutting thickness models were compared. The simulation results show that the thickness from the model of the instantaneous cutting thickness considering cutting tool deflection was very close to the real trajectory, which verified the accuracy of the improved model. In addition, the thickness of the instantaneous cutting increases with the increases of cutting tool deflection, the greater the feed amount, the more significant the impact.
2015 Vol. 33 (3): 273-276 [Abstract] ( 1105 ) [HTML 1KB] [ PDF 1409KB] ( 1823 )
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