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Journal of Drainage and Irrigation Machinery Engin
 
2013 Vol.31 Issue.09
Published 2013-09-25

article
Article
737 Stress characteristics in blades of axial-flow pump based on fluid-structure interaction
Shi Weidong, Wang Guotao, Zhang Desheng, Jiang Xiaoping, Xu Yan
In order to predict the stress and deformation of blades in an axial-flow pump, a coupled solution of flow field in the pump and structural response of the blades was established by using two-way coupling method on Ansys platform-Workbench where CFX was used to compute the flow field, and Ansys dynamic structure code was applied to analyze the stress. The flow field prediction was based on the Reynolds-averaged N-S equations and the RNG two equation k-ε turbulence model; the structure response was handled by the elastic structural dynamic equations. Not only the deformation and stress distribution characteristics caused from fluid-structure interaction were identified, but also the influence of the interaction on the head and efficiency of the pump was analyzed. The results indicated that the maximum displacement occurs on the blade leading edge at impeller tip, but a smaller displacement appears on the blade trailing edge and in the blade root. A significant stress concentration occurs in the inlet side and the contact area of the blade root and the hub. All the stress level and deformation in the blades reduce steadily with increasing flow rate. The head and efficiency predicted by fluid-structure interaction model are lowered compared with those by the rigid structure model.However, this reduction in stress and deformation is very small. 
2013 Vol. 31 (09): 737-740 [Abstract] ( 2433 ) [HTML 1KB] [ PDF 2304KB] ( 1738 )
741 Design optimization of inlet conduit in slanted axial-flow pump installation by orthogonal array experiment
Huang Jianyong, Zhang Feizhen, Zhang Hao, Yang Xiaoxia, Zhang Rui
In order to improve hydraulic performance of a slanted axial-flow pump installation at low flow rate conditions, a simple flow control method J-Groove was utilized to modify inlet conduit structure. J-Groove depth, length, number of grooves and groove stagger angle were selected to be design factors, and each factor has three levels, then nine design cases were determined by using orthogonal array experiment method. The unsteady Reynolds averaged Navier-Stokes equations based on the filter-based turbulence model were solved by using Ansys CFX to obtain the efficiency and head of each pump in those cases at low flow rates.Based on the range analysis method, the computed results were analyzed to get regularities that how the performance of the pump is affected by those factors. It was shown that the pump head is affected by the geometrical factors in the following order: groove depth, length, number of grooves and stagger angle, while the efficiency by the factors in the order: depth, number of grooves, stager angle and groove length. At last, an optimal design was established by using redesign analysis and compared with the original design. The results verified the function of the J-Groove technique in suppressing unsteady flow in the impeller inlet and improving performance of a slanted axial-flow pump installation at low flow rate conditions.
2013 Vol. 31 (09): 741-746 [Abstract] ( 1977 ) [HTML 1KB] [ PDF 1749KB] ( 1265 )
747 Injection molding simulation of plastic impeller and process parameters optimization
Wang Yang, Wang Zhenwei, Wang Weijun, Ye Daoxing
In order to study flow behavior of polymer melt in the process of injection molding. The centrifugal plastic impeller of garden submersible motor-pump(LKS-250P)is chosen as the model. Pro/E and Moldflow software are used to complete the 3D modeling, shape of the plastic part and optimize in injection molding numerical simulation. According to the analysis of gate location and principles of gate design, two different types of gating system of impeller were established. The effect of runner systems on the filling cavity pressure, distribution of welding lines and volumetric shrinkage of the plastic impeller were analyzed by means of moldflow software. Some possible defects in the products were predicted based on the numerical simulation. The optimal runner gate and the injecting process parameters were obtained. The research result shows that the side gate is more suitable than the point gate for impeller injection molding. There are short shot at the outlet of impeller blade and through appropriate increasing the melt temperature and mold temperature which can eliminate defects such as short shot. The application of the CAD/CAE technology is provided a reference for the design and production of plastic centrifugal impeller products as well as the similar products. It has certain engineering value for applications.
2013 Vol. 31 (09): 747-751 [Abstract] ( 2426 ) [HTML 1KB] [ PDF 3016KB] ( 1475 )
752 Topological optimization design of Roots pump lobe with ESO method
Chen Xiaoming, Lai Xide, Zhang Xiang, Zhou Xiang
Concerning the safety and stability in operation of Roots pumps which are featured with large flow rate and high speed, the topology of lobe in a two-lobe Roots pump was optimized by means of e-volutionary structural optimization(ESO)method. Since a structural mutation phenomenon occurs du-ring the optimization process, the screening and deletion algorithms are proposed based on the connection traits between singular elements to improve the ESO method, eventually the stability and continuity of the optimization process are ensured. The improved ESO method was realized by using Ansys mechanical parametric design language(APDL). At first, the allowable interval of initial rejection rate was ascertained by using interval approximation and combining with the visual process of program. Then, the topology of lobe in a two-lobe Roots pump was optimized with five kinds of initial rejection rates when it was subject to the 1 500 r/min inertial load. Finally, a reasonably topological structure for the lobe was decided by analyzing maximum stress, strain and displacements in different design cases and sifting among them. Comparing the results of finite element analysis shows that the optimized structure not only experiences more even stress distribution under the inertial load but the material utilization ratio is also improved considerably. The maximum stress, strain and displacement are reduced by 17.7%, 17.5% and 18.7%, respectively, the mass of rotor is decreased by 55%; as a result, the safety and stability can be improved greatly for this Roots pump operating at a high speed and large flow rate.
2013 Vol. 31 (09): 752-757 [Abstract] ( 2091 ) [HTML 1KB] [ PDF 2262KB] ( 1314 )
758 Solid volume concentration distribution of solid-liquid two-phase flow in HD type petrol-chemical process pump
Liu Yi,, Jiang Yue, Han Zhengjie
The steady solid-liquid two-phase flow field in the fist stage of a HD type petrol-chemical process pump is simulated with CFD software by employing the Reynolds Averaged Navier-Stokes equations and the standard k-ε turbulence model as well as SIMPLEC algorithm to explore the distribution pattern of solid particle volume concentration in the double-suction impeller and double-channel volute of the first stage of the pump. The two-phase flow is subject to different solid bulk volume concentrations and particle diameters. The results show that solid volume concentration distribution becomes non-uniform in the double-suction impeller but exhibits a noticed regular pattern with increasing solid particle bulk concentration at constant particle diameter, that is, the concentration is higher near the blade suction side than the pressure side. Besides, solid particles have a tendency to move to the blade suction side. Moreover, the particles move towards the suction side with increasing particle dia-meter at fixed bulk concentration; however, the non-uniformity of solid concentration remains nearly unchanged. In the double-channel volute, solid concentration is distributed unevenly as well; particularly, the local solid particle concentration is increased from section 1 to section 8. Additionally, in the diffuser of volute, the concentration is higher nearly the diffuser side wall with tongue than the opposite side wall of the tongue. The solid particles with large diameter tend to move towards the opposite side wall of the tongue, causing a relatively higher concentration there.
2013 Vol. 31 (09): 758-762 [Abstract] ( 1634 ) [HTML 1KB] [ PDF 3835KB] ( 1040 )
763 3D design of axial-flow pump and numerical prediction of its cavitaion performance
Jin Shuanbao, Wang Yongsheng
The cavitiaton performance of an axial flow pump with suction specific speed of 1 290 was studied by using the 3D inverse design theory and computational fluid dynamics(CFD)technique to improve its cavitation behaviour. A few pump models with different meridional channels and numbers of blades were designed, respectively, at the same condition, i.e. the same flow rate, head, rotational speed; then a suitable meridional channel and a best number of blades were achieved with CFD me-thod. Also, the other pump models with different blade loading profiles were designed by the 3D inverse method, their head, shaft-power and efficiency curves were predicted by CFD me-thod as well, effects of the blade loading on the pump efficiency and cavitation performance were compared and analyzed; eventually, a proper blade loading for an improved suction performance was achieved. A few suggestions were proposed for the pump to have better suction performance. For example, after-loaded blade loading profile, properly increased number of blades and a smooth meridional channel are helpful to improve cavitation perfroamnce of an axial-flow pump.
2013 Vol. 31 (09): 763-767 [Abstract] ( 2157 ) [HTML 1KB] [ PDF 12917KB] ( 854 )
768 Effects of guide cone configuration on hydraulic performance of low-head pumping station
Zhou Peijian, Wang Fujun, Zhang Zhimin
In order to investigate effects of guide cone on hydraulic performance of low-head pumping station, five different guide cone configurations, namely straight, hyperbolic, quadratic, arc and elliptical cones are designed for Xinkaihe Pumping Station. The 3D flow field in the flow passages accommodating an axial-flow pump in that station is simulated by employing CFD method. It is turned out that the guide cone has a large effect on flow pattern in the pump sump. All the guide cones can prevent the occurrence of the floor-attached vortices in the pump sump. For the straight, hyperbolic, pa-rabolic and arc cones, one sidewall-attached vortex and two free surface vortices emerge. For elliptical cone, however, only one sidewall-attached vortex and a free surface vortex are identified. Comparing with the case without guide cone, the elliptical cone has reduced the number of vortices. Additionally, guide cones also have a remarked effect on hydraulic loss in the pump sump. The hydraulic loss is the minimum for the sump with elliptical cone, but the loss for the rest cones is larger than the one without guide cone. Comparing the flow at the outlet of sump across the configurations by means of the axial velocity uniformity and velocity-weighted average swirl angle, it was shown the elliptical cone has the best rectification effect on flow. Finally, the hydraulic efficiency was analyzed for the flow passages with various guide cones, and it was demonstrated that the elliptical cone can result in an improved hydraulic efficiency compared with the others.
2013 Vol. 31 (09): 768-773 [Abstract] ( 1828 ) [HTML 1KB] [ PDF 3285KB] ( 1507 )
774 Numerical prediction of critical cavitation number in pump-turbine
Hao Zongrui, Liu Jintao, Wang Leqin
The hydraulic performance and internal flow in a pump-turbine model were analyzed under different cavitation numbers to study effects of the coefficient on unsteady flow in the model by using the SST k-ω turbulence model. The results show that cavitation number can alter the flow pattern in the pump-turbine and the critical cavitation number reflects the energy performance of a pump-turbine. The head of pump-turbine decreases and the efficiency rises at cavitation inception; with development of the cavitation, the head increases considerably, while the efficiency decreases quickly. The cavities are located at the blade suction side near the runner outlet and ring. The change of cavitation number has less effect on the instability of flow in the pump-turbine runner only. If cavitation number is larger, the head of pump-turbine will remain unchanged essentially. Moreover, the head decreases slightly with decreasing cavitation number when cavitation number is in the range of 0.075-0.150. However, the head increases with decreasing cavitation number as the coefficient is less than 0.075.
2013 Vol. 31 (09): 774-777 [Abstract] ( 1953 ) [HTML 1KB] [ PDF 1609KB] ( 1405 )
778 Multi-objective optimization design of horizontal-axis marine current turbine
Guo Pengcheng, Zhu Guojun, Luo Xingqi
Power coefficient and axial thrust coefficient are two important performance parameters of a marine current turbine. Thus a multi-objective optimization design method was proposed to optimize those coefficients for a horizontal-axis marine current turbine. Firstly, the pitch angle distribution curve of the turbine was parameterized by using a Bezier curve; and then the power coefficient and axial thrust coefficient were selected as the objective function, the levels of design factors were decided by the Box-Behnken experimental design method, and a 2nd polynomial relationship between the factors and the objective function was established by making use of response surface technology. At last, the turbine pitch angle curve was optimized by employing NSGA-II algorithm. In the optimization power coefficient and axial thrust coefficient were specified as the objective function, and the determined response surface was used as the individual fitness. It was demonstrated that the thrust coefficient was decreased by 2% and the power coefficient was increased by 0.4% for the optimized turbine. This confirmed the effectiveness of the optimization method proposed here.
2013 Vol. 31 (09): 778-782 [Abstract] ( 1789 ) [HTML 1KB] [ PDF 2204KB] ( 1323 )
783 Analysis on improvement of model draft tube by vortex-generators
Tian Xiaoqing, Zheng Yuan, Pan Huachen, Sun Bin
In order to develop a new type of draft tube with vortex-generators, the working mechanism of vortex-generators was analyzed in some extent, then a series of experimental model draft tubes with vortex-generators were designed by combination with the theory of draft tube; finally, verifying simulations and experiments were conducted on those models. In accordance with geometrical characteristics of the model draft tube, a structured mesh was generated by considering the near-wall function. The share stress transport(SST)model was used in the turbulent flow simulation. The blades of vortex-generator were installed between two sections in the tube, one is the section where a vortex starts to be generated and the other is the section where the vortex begins to be developed, then 55 different wor-king conditions were simulated. Finally, energy recovery coefficients were calculated, and the optimum blade installation was identified. It was shown that two pairs of counter rotating vortex-generators should be installed in the section where a vortex starts is generated and the angle between the generator and the draft tube center line should keep being 15°. A conforming experiment was conducted under this installation scheme, and 3.2% improvement in energy recovery coefficient have been observed. This suggests that the position where vertex-generators are installed is the section where a vortex starts to occur. This proposal can be useful to hydropower stations being constructed and those being refurbished.
2013 Vol. 31 (09): 783-787 [Abstract] ( 1956 ) [HTML 1KB] [ PDF 2281KB] ( 1258 )
788 Approximately analytical solutions of thermal-mechanical coupling flow field in spiral-grooved dry gas seals
Ding Xuexing, Su Hong,, Zhang Haizhou, Zhao Fang, Zhang Weizheng
To study flow characteristics in the gap of a spiral-grooved dry gas seal that is subject to irregular deformation caused from external forces under high speed and pressure operating conditions, a set of analytical solutions for deformation of sealing ring and gas film thickness are obtained when the ring is underwent either a mechanical force or a thermal load. Then an approximately analytical solution for the gas film thickness is got when the seal is in the thermal-mechanical coupling state by placing the deformation due to the mechanical force upon that because of the thermal load. Based on that solution, a theoretical leakage flow rate through the gap is derived. At last, the theoretical leakage flow rates are compared with their experimental values in four cases, that is without any deformation, with thermal deformation, with mechanical deformation and with thermal-mechanical coupling deformation. The results show that the leakage flow rate increases with increasing pressure. In the case with the mechanical deformation, the predicted leakage flow rate is larger than the experimental value. The lea-kage is not only less than the experimental value but also shows a larger error against the experiment in the case with the thermal deformation. Comparing with the other cases, the error of leakage flow rate between prediction and measurement is the smallest in the case with the thermal-mechanical coupling deformation. For the application in engineering, the proposed method that considers the thermal-mechanical coupling deformation can provide a theoretical basis for spiral groove structure optimization, and then the objective that controls the leakage flow rate can be achievable.
2013 Vol. 31 (09): 788-793 [Abstract] ( 1651 ) [HTML 1KB] [ PDF 1459KB] ( 1024 )
794 Effects of nozzle parameters on rotating conical abrasive jet and experiments
Li Guangrong, Ge Yingfei, Zheng Yong, Xue Xiaoqiang
To investigate the characteristics of abrasive jet from a conical nozzle, which is composed of a casing and a core with spiral-grooved cylinder, a series of jet impingement experiments were conducted. The parameters that can affect characteristics of jet include number of grooves, diameter of central hole in cone, working pressure, distance between nozzle outlet and target. The effects of every parameter on jet cross-section shape were investigated by single factor experiment method, a few regression equations were fitted based on the experimental data, and the reasons why those effects were shown are analyzed theoretically. The results showed that the jet cross-section shape is a solid circle or a ring. The ring ou-ter diameter becomes larger with increasing working pressure, while the inner diameter of the ring is almost the same. The impinging load of jet with single groove on the target is lower than that with two or three grooves. With increasing diameter of central hole the outer diameter of jet cross-section is decreased gradually. The cone angle of jet is almost unaffected. There is an optimum range of target distance; the outer diameter of jet cross-section gets large nearly linearly with increasing target distance; meanwhile the inner diameter is expanded as well. These experimental results can provide the basis for nozzle and spiral grooves geometrical parameters optimization and working pressure determination, and establish a theoretical and experimental basis for further improvement in jet performance.
2013 Vol. 31 (09): 794-799 [Abstract] ( 1336 ) [HTML 1KB] [ PDF 1443KB] ( 1190 )
800 Method for predicting nitrogen concentration in water on lower Mississippi River in USA
Yan Baowen, Mark D. Tomer, Wen Deping
In order to investigate pollution and eutrophication caused from agricultural nonpoint source pollution in river water, it is essential to predict the relation between the concentration of nitrate nitrogen in a river and the runoff for such an ion-dominated pollutant. Hence, the lower Mississippi river with intensive farming land in USA was chosen as a model and the nitrate nitrogen concentration, runoff water quality data collected from Vicksburg Hydrological Station on the river were analyzed. Then the whole runoff data set was separated into daily and monthly individual data sets by using Baseflow program, furthermore, the individual runoff data sets were extended and complemented by using Loadrunner Program of Yale University to form a continuously daily nitrate nitrogen concentration series; eventually, the monthly concentration sequences were established. The monthly nitrate nitrogen concentration in the water body was predicted by means of neural network method, as a result, the corresponding procedure and predication formulas were proposed. The results showed that the average error between predicted and observed concentrations is 7.5%, implying the procedure and formulas proposed are accurate and feasible. It suggests that this method can be applied to predict monthly nitrate nitrogen concentration in a real river.
2013 Vol. 31 (09): 800-804 [Abstract] ( 1519 ) [HTML 1KB] [ PDF 1495KB] ( 1220 )
805 Effect of sleeve length on characteristics of wetted front during bubble-root irrigation
Chen Junying,, Wu Pute,, Zhu Delan, Zhang Zhitao,, Fan Xiaokang
In order to study the effect of sleeve length on the characteristics of wetted front in bubble-root irrigation, a series of experiments were done to measure the wetted front of a clay loam soil formed during bubble-root irrigation in which five sleeve lengths(10, 15, 20, 25 and 30 cm)and two kind of sleeve materials, namely PVC and Polypropylene(PP)were used, respectively. The result showed that there is a linear relationship between the radius of wetted front on soil surface and logarithm of time for the two kinds of sleeves. The time when soil surface starts to be wetted is unrelated to the sleeve length. The radius and depth of wetted front in soils are increased with increasing sleeve length for both kinds of sleeves and a power function with time is exhibited. For the radius and depth of wetted front, their power indexes are 0.38 and 0.17 in the case of PVC sleeves. For PP sleeves, the power index of wetted front radius is 0.40, the index of wetted front depth, however, is decreased with increasing depth and a linear relationship remains between the index and sleeve length. Further, prediction mo-dels were built for determining the maximum radius of wetted front on soil surface and the deepest depth of wetted front in soil from a known radius of wetted front on soil surface at a time instance. It was confirmed the accuracy of the models is satisfactory. The results can be useful for designing sleeves and determining space and width of ridge in a farm field.
2013 Vol. 31 (09): 805-810 [Abstract] ( 1254 ) [HTML 1KB] [ PDF 1193KB] ( 1147 )
811 Variation characteristics of salinity in water of drainage ditches in saline lands
Pan Yanxin, Luo Wan, Jia Zhonghua, Li Jin, Chen Yuan
The drainage ditches in the saline lands around Lupuotan Lake,Shaanxi Province are periodically full of water due to the blockage of drainage outlet and received huge amount of irrigation water returned from two upstream irrigation districts, causing a change in salinity concentration in the water body of the drainage ditches. To reveal the actual variation characteristics of salinity, the salinity in the water of three drainage ditches was monitored over two years. The results showed that the increase in salinity was apparent in the drainage ditches during the dry season from upstream to downstream in the studied lands, and the electrical conductivity of water in the upstream ditches was varied between 2 and 14 ms/cm, but it was as high as 25.2 ms/cm in the downstream ditches. The fresh water from two upstream irrigation districts was recharged into the drainage ditches regularly, and the salt accumulation was destroyed. As a result, the salinity was diluted by more than 10 times and the electrical conductivity of that water was lowered down to 1.9 ms/cm. Such periodic dilutions allow a relatively low salinity level to be kept and a salt balance to be maintained in the water body of the drainage ditches studied.
2013 Vol. 31 (09): 811-815 [Abstract] ( 1691 ) [HTML 1KB] [ PDF 1216KB] ( 1320 )
816 Effects of pretreated straws on soil evaporation and straw decomposition rate
Wang Zengli,, Wang Zhen, Feng Hao,
Effects of the pulverized and ammoniated straw on soil evaporation and decomposition rate of straw were investigated comparatively through indoor soil column experiments. The results showed that after straws was applied in soil, its cumulative evaporation was raised in great deal, but the powdered and ammoniated straws could decrease the evaporation considerably. Additionally, if they were mixed with other inorganic soil amendments and applied in soil, an even significant reduction in the evaporation could be achieved and soil drought tolerance was improved. When the long or powdered straws were applied in soil alone, the percentage of water loss(pwl)by evaporation was increased substantially. The pulverized and ammoniated straws could reduce pwl. Interestingly, once they were blended with inorganic soil conditioner and fertilized, the time period without soil evaporation was extended. The decomposition climax of straw mainly occurred in 30 days. In short term the length of straws had a little effect on decomposition rate; the pulverized and ammoniated straws increased the rate remarkably. There are significantly correlations between the evaporation indices, such as cumulative evaporation, rate of evaporation, pwl, so that they can better characterize soil evaporation feature.
2013 Vol. 31 (09): 816-821 [Abstract] ( 1263 ) [HTML 1KB] [ PDF 1108KB] ( 1238 )
822 Evolutionary tendency of agriculture water requirement and its driving force under changing environment
Li Ping, Wei Xiaomei
According to the meteorological data of over 30 years at 11 weather stations and cultivated area information of 20 years in Baojixia Irrigation District, the variation characteristics of climate and crop planting structure were analyzed, the crop and agriculture water requirements were calculated; then the evolutionary tendency of agriculture water requirement was investigated and the driving factors that affect the agriculture water requirement were disclosed by using principal component regression method. The results showed that temperature in the irrigation district rises significantly, but relative humidity and wind speed reduce obviously, evaporation and sunshine hour increase somewhat, but precipitation decreases to some extent. Agricultural planting structure of the irrigation district changes greatly, the ratio of food crop planting area over economic crop planting areas decreases markedly, for instance, it is diminished to 1.83 in 2010 from 4.08 in 1991. The ratio of food crop planting area over total crop planting area decrease too, for example, it is reduced to 0.40 in 2010 from 0.46 in 1991. The water requirement of four kinds of crops, namely wheat, corn, canola and cotton shows an increa-sing tendency, especially the water requirement of canola exhibits the highest increasing rate, about 3.558 mm/a; however, the agricultural water requirement has an decreasing tendency and its decline rate is 3.35×107 m3/a. The major driving factors that affect the agricultural water requirement are planting area, precipitation and evaporation. Declining precipitation and increasing evaporation result in a markedly increased water requirement, however, the decreasing crop planting area causes a signi-ficantly reduced agricultural water requirement.
2013 Vol. 31 (09): 822-828 [Abstract] ( 1799 ) [HTML 1KB] [ PDF 1244KB] ( 1254 )
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