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Journal of Drainage and Irrigation Machinery Engin
 
2013 Vol.31 Issue.7
Published 2013-07-25
article
Article
553 Influence of two types of cut-water shapes on simulated performance of centrifugal pump
Yuan Shouqi, Heng Yaguang, Hong Feng, Yuan Jianping, Si Qiaorui, Hu Bo
A comparative study was conducted between two types of cut-water shapes which significantly affect the performance of a centrifugal pump to improve the accuracy of performance prediction and reduce development costs for the pump. The computational fluid domains include suction pipe, impeller and volute, which were meshed with Ansys ICEM CFD code to generate a structured mesh and the numerical simulation of flow in the pump was accomplished with Ansys CFX. There is the normal velocity boundary condition at the inlet to the suction pipe, and there exists the outlet pressure condition at the discharge of the volute diffuser. The mechanical and volumetric efficiencies were considered to be 89% and 96%, respectively. It was found that the simulated performance for the pump with round cut-water shape is close to the test data at various flow rates. The simulated performance for the pump with rectangular cut-water shape is near the measured result at low flow rates, but shows a relatively noticed difference from the measured one at a high flow rate. According to the pressure contours and streamline plots, the high pressure zone on the round cut-water is relatively stable and the streamlines around it are smooth with increasing flow rate. For the rectangular cut-water shape, however, the high pressure zone is unstable to shed a series of vortices at the design condition and high flow rate. Those vortices alter flow patterns in the volute and eventually result in that the predicted performance differs from the measurement considerably. The reason, why there is a significant difference in the perfor-mance exists between two types of cut-water shapes, has been clarified by analyzing the flow field in the volute. It is confirmed that a round cut-water can make flow pattern in the volute smoother and subsequently improves the pump performance. 
2013 Vol. 31 (7): 553-557 [Abstract] ( 2894 ) [HTML 1KB] [ PDF 3422KB] ( 1846 )
558 Characteristics of cavitating flow of liquid hydrogen in inducer
Wang Xiaobo, Wang Guoyu, Shi Suguo, Wu Qin
A revised Kubota cavitation model to consider the thermal effect and the SST k-ω two-equation turbulence model were applied into the simulation of cavitating flows of liquid hydrogen and water in an inducer to study its cavitation characteristics. Not only the cavitating flows in the inducer under different cavitation conditions with those fluids were numerically predicted, but also the power and cavitation performances were analyzed. It was found that the revised Kubota cavitation model can simulate the liquid hydrogen cavitating flows very well, and a good agreement was achieved between the numerical results and experiment data. Compared with water, the inducer head with liquid hydrogen is higher, and the critical cavitation number and cavity size are smaller. This is due to the diffe-rence in physical properties of two fluids, especially the influence of their thermal effect. Cavitation performance of inducer is obviously improved and its incipient cavitation number is decreased when li-quid hydrogen is used as the working fluid compared with water. 
2013 Vol. 31 (7): 558-564 [Abstract] ( 2134 ) [HTML 1KB] [ PDF 2265KB] ( 1687 )
565 Numerical simulation of transient flow in self-priming centrifugal pump during self-priming period
Li Hong, Xu Dehuai, Li Lei, Tu Qin, Zou Chenhai
The transient air-water two-phase flow field in 65ZB-40 self-priming centrifugal pump du-ring self-priming period was simulated numerically by using the standard k-ε turbulence model, VOF multi-phase model, sliding mesh technique and the velocity profile measured at the inlet of the pump to disclose self-priming mechanism. The transient pressure, velocity and void fraction of the two-phase flow in the pump were acquired at 10 monitoring points in the volute and in 8 zones inside the impeller. The results revealed that the pressure and void fraction experience a rapidly transient process in most area of flow field inside the pump at the early and late stages of self-priming period. At the early stage of self-priming period, the velocity at the impeller entrance, in the cross-sections of volute, reflux hole and inlet to the air separation chamber oscillates, showing a dominated transient effect.
2013 Vol. 31 (7): 565-569 [Abstract] ( 2040 ) [HTML 1KB] [ PDF 1892KB] ( 1713 )
570 Experimental study on cavitation performance of centrifugal pump with impeller having leading edge slots
Chen Hongxun,, Lin Yuzhan, Zhu Bing
The cavitation performance of a low specific-speed centrifugal pump with impeller having leading edge slots and the conventional one were measured at various flow rates; and the vibration acceleration signals were acquired by the acceleration sensors installed in various locations in the experimental pump casing; eventually the cavitation performance of these two kinds of impellers was compared and the obtained signals indicating the cavitation characteristics were analyzed. The experimental results turn out that a much better cavitation performance has been achieved with the impeller having leading edge slots comparing with the conventional one. After the RMS(root mean square)of the vibration acceleration signals obtained at the Q=26 m3/h condition being analyzed, it was shown that all the normalized energy of the vibration acceleration at three monitoring points increase with decreasing NPSH available; meanwhile, the vibration of the pump with the impeller having leading edge slots is less violent than that with the conventional impeller during the cavitating process. It suggests that the vibration acceleration acquired can monitor the change in the signals effectively before and after cavitation occurs. The signals picked up at the monitoring point near the outlet of the pump is more sensitive to cavitation state, thus this point is more suitable to be used as the cavitation monitoring site compared with the rest monitoring points in this experimental investigation.
2013 Vol. 31 (7): 570-574 [Abstract] ( 1809 ) [HTML 1KB] [ PDF 1534KB] ( 1522 )
575 PIV experimental study on flow field in submersible sewage pump with low specific speed
Chen Bin,, Zhang Hua, Shi Weidong, Ba Yanqing, Dong Mianjie
After the state-of-the-art investigations into low specific speed submersible sewage pumps were reviewed, it was found that the studies mainly focused on numerical calculations, while there is a lack of internal flow field visualization investigations. Therefore, the internal flow field in a submersible sewage pump with specific speed of 60 was measured by means of a 2D-PIV under different operating conditions to reveal the flow structure and development in the impeller from the inlet to the outlet. The pump original structure was modified with a transparent plexiglas to replace the conventional metal material, and the hollow glass spheres were severed as seeding particles for the PIV measurements. The experimental results show that the relative velocity on the blade suction surface near the blade inlet is greater than that on the blade pressure surface while this velocity profile is reverse near the blade outlet due to the Coriolis effect. The velocity gradient at the blade inlet is the largest, and the jet-wake phenomenon at the blade outlet is the most obvious at high flow rates. A flow separation was observed on the blade pressure surface at various flow rates; meanwhile, it moved towards the blade outlet and gradually developed into a vortex rotating in the direction of opposite blade rotation with decreasing flow rate. At 0.2Qd operating point, the vortex is in the center of flow passage at the blade outlet and blocks most of the passage.
2013 Vol. 31 (7): 575-579 [Abstract] ( 1491 ) [HTML 1KB] [ PDF 1823KB] ( 1471 )
580 Evaluating water supply sustainability of Fengjiashan Reservoir
Liu Pingping, Su Xiaoling
The water supply sustainability of Fengjiashan Reservoir was evaluated by means of the sustainable development concept and the theory and method of risk analysis. In the evaluation, five performance parameters such as reliability, resilience, vulnerability, standard deviation and maximum soil water deficit were selected as sustainability index(SI). According to four kinds of water users, namely life, industry, ecological environment and agriculture, proper sustainability indices for these users were established as well. Further a sustainability index was built for the group composed of those four kinds of water users. The results showed that the water supply sustainability by group(SG)is as low as 35% in current situation, especially the SI for agriculture is 29% only. If the agriculture water demand is reduced by 30%, then the reliability and SI for all the users are improved. Under this condition, the SI for agriculture is 40% and the SG for the reservoir is increased to as high as 45%. Therefore, whatever water saving measures should be taken in areas under irrigation to reduce agricultural water demand and enhance the agricultural sustainability and improve reservoir water supply sustai-nability as well as reduce the risk of water deficit, eventually promote the sustainable development of reservoir.
2013 Vol. 31 (7): 580-585 [Abstract] ( 1626 ) [HTML 1KB] [ PDF 1453KB] ( 1456 )
586 Check dam system planning optimization based on mutation model
Zhang Xianqi, Peng Xiaofei, Fan Ruiqi
The check dam system planning is a typical multi-criteria decision problem of complex system since the factors such as water and sediment control capacity, intercepting sediment capacity, silting land capacity and investment return and so on should be taken into account. The multi-criteria decision making of complex system usually has fuzziness and uncertainty. By making use of the advantage of catastrophe theory in dealing with the fuzzy and gray problems, an indicator system for evaluating check dam system planning was put forward, and a mathematical model was established to optimize the planning based on the mutation classification evaluation method, and then a detailed procedure was described to apply the model. The method has been applied to optimize the planning of check dam system in Liujian River, basin of Yanshi City. Firstly, all the indexes of bottom level were made dimensionless and normalized, and then the importance of each indicator was quantified by aggregation mechanism of the normalized formula; Finally, the optimum planning could be obtained by comparing total value of mutation subjection function of each planning. The total values of mutation subjection function of planning I, II and III are 0.959 2, 0.918 1 and 0.948 4 respectively, thus planning I is optimal. This result is consistent with that derived from the traditional method, suggesting the mutation model is reasonable and feasible for check dam system planning optimization.
2013 Vol. 31 (7): 586-591 [Abstract] ( 1858 ) [HTML 1KB] [ PDF 1418KB] ( 1485 )
592 Working mechanism and exhausting characteristics of mini-exhaust valve
Wu Dazhuan,, Liu Qiaoling,, Lai Zhounian,, Wang Leqin,
To study the working mechanism and exhaust characteristics and establish a theoretical base for performance prediction and design optimization of a mini-exhaust valve, CFD simulations were carried out to obtain the exhaust characteristics and internal flow field, and then they were verified with experiment. The model of whole flow passage was established and 3D flow field in it was calculated, the flow field structures, closing pressure, pressure and velocity distributions in the valve were presented when the valve discharges air and oil, respectively. The influences of valve position on ball lift and passage size on closing pressure were analyzed. A comparison of CFD simulation results and those gi-ven by general analytical formula was made. A test device was established to measure the closing pressure in oil and air exhausting conditions. The results showed that the CFD predicted closing pressure is consistent with experimental observation. The pressure estimated by the analytical formula is different from the CFD prediction under oil exhausting condition. However, agreement in the closing pressure between CFD and analytical formula is good in air exhausting condition. The closing pressure in an enlarged model of the valve passage remains the same as the original valve. The CFD simulation method and its results can be applicable in design and optimization of min-exhaust valve.
2013 Vol. 31 (7): 592-597 [Abstract] ( 1670 ) [HTML 1KB] [ PDF 1743KB] ( 2245 )
598 Abrasive flow uniform surface polishing method and experiment for cycloidal pump inner rotor
Ding Jinfu, Zhang Kehua, Xu Yongchao, Yuan Liangliang, Cheng Guangming
In order to reduce the surface roughness of the inner rotor of cycloidal pump, a polishing method was proposed to realize a uniform surface polishing by using abrasive flow machining(AFM)on the surface of inner rotor. A mold core was made and installed outside the inner rotor in such a way that the gap between the core and the rotor keeps being constant to establish a uniform flow field around the rotor and allow the rotor surface experiences nearly the same wall shear stress. A power law model was established to represent the rheological property of the abrasive and water mixture and used to analyze the distribution of shear rate and shear stress in AFM process; further the distributions of velocity, shear rate and shear stress of the abrasive media over the processed surface were simulated by means of COMSOL Multiphysics CFD module. The results showed that if there was no mold core installed the non-uniform shear stress leaded to uneven roughness over the processed rotor surface; however, after the mold core was available, the rotor surface experienced uniform shear stress. In this case, the maximum difference in surface roughness Ra was reduced to 0.277 μm from 0.847 μm after 20 processing cycles. The processing efficiency and surface finish quality have been improved substantially.
2013 Vol. 31 (7): 598-604 [Abstract] ( 1791 ) [HTML 1KB] [ PDF 10301KB] ( 1152 )
605 Approximately estimating pressure distribution in gas lubricated spiral grooved face seal under non-isothermal conditions
Chen Kan, Huang Zepei, Yao Jin, Zhang Zhi
The analytical methods for estimating pressure distribution on the end face of a dry gas seal(DGS)were reviewed, and then a novel algorithm for non-isothermal conditions was proposed in this paper based on the Whipple infinite narrow-groove theory. The Tripp function was used to get a temperature profile along the radius on the end face. The heat conductivity angle of gas was selected to be 3 times the conductivity angle of liquid based on experience. To solve the adjusted Gabriel differential functions more conveniently, a curve fitting method was applied to obtain an approximate analytical function of temperature profile T(r). The differential equations were solved by using 4th-order Rung-Kutta method. Compared with the results in literature, the pressures at groove bottom pg obtained by the present method are increased by 6.8%, 5.0%, 2.7% when the film thicknesses are 5.08, 3.05, 2.03 μm, respectively. And this result is consistent with the existing pressure distribution characteristic on a DGS end face. Compared with FEA(finite element analysis), the present novel method can easily be applied in engineering.
2013 Vol. 31 (7): 605-610 [Abstract] ( 1716 ) [HTML 1KB] [ PDF 3122KB] ( 1373 )
611 Migration and transformation of Cd and Cr in paddy soil-plant system under controlled irrigation
Peng Shizhang, Qiao Zhenfang,, Xu Junzeng, Zhang Jiangang, Jin Xiaoping
The aim of this study is to determine the effects of irrigation pattern on leaching, migration, and transformation of Cd and Cr in a paddy soil-plant system. The concentrations of Cd and Cr in rice plant and paddy soil were measured in field plot experiments. The results showed that the leaching contents of Cd and Cr were reduced by 53.3% and 19.3% under controlled irrigation compared with flooding irrigation, thus the contents of Cd and Cr in paddy soil were decreased under the controlled irrigation; but there is no significant difference in Cd and Cr contents between controlled and flooding irrigation for the paddy soil after fertilization. The contents of Cd and Cr in 0-20 cm depth paddy soil were decreased by 1.2% and 0.6% in controlled irrigation compared with flooding one, suggesting irrigation pattern leads to different binding forms of Cd and Cr in the paddy soil. In most of time, the accumulated contents of Cd and Cr in the plant bodies above and under soil were higher in controlled irrigation than in flooding irrigation, implying the controlled irrigation can enhance Cd and Cr concentrations in plants. The Cd content in rice seeds was near the tolerance(0.2 mg/kg)in food products re-commended by National Food Safety Standard, China, but the Cr content was higher than the corresponding tolerance(1.0 mg/kg)in food products in controlled and flooding irrigation, thus there is a potential risk in Cr content over the tolerance. Clearly, these two kinds of irrigation are unhelpful in prevention from heavy metal pollution, and the rice seeds produced in those irrigation patterns can affect human health. 
2013 Vol. 31 (7): 611-616 [Abstract] ( 1421 ) [HTML 1KB] [ PDF 1457KB] ( 1757 )
617 Approximate analytical model for high-order power function of solute transport in soil
Wei Feng,, Wang Quanjiu, Zhou Beibei
To simulate the soil solute transport and estimate the transport parameters with a simple analytical model, an approximate six-power function model for describing the distribution of solute concentration was developed based on six-power function concentration profile assumed and the extended boundary layer theory describing the soil solute transport. The solute concentration profiles predicted by using the model proposed with different power indexes were compared and analyzed at two time instances(t=360, 720 min)and a long distance(120-450 cm). The simulated results showed that the solution of six-power function method is more close to the exact solution compared with other power models when the pore water velocity is 0.01 cm/min at a short time experienced(t=360 min)in a long traveling distance(x>50 cm). More computations indicated that the small pore water velocity(v≤0.01 cm/min)has little effect on the boundary layer distance. In that case, a series of error analysis on the transport parameters estimated with different boundary layer distance formulas were also carried out. The results indicated that the transport parameters such as diffusion coefficient and delay factor in the solute convection-dispersion equation can be decided precisely by using the boundary layer distance predicted with six-power function model based on measured results by means of instrument with higher sensitivity.
2013 Vol. 31 (7): 617-622 [Abstract] ( 1783 ) [HTML 1KB] [ PDF 1917KB] ( 1616 )
623 Variation trends and influencing factors of shallow soil salinity in arid area of Xinjiang
Wang Shaoli,, Jiao Pingjin,, Xu Di,, Qu Xingye,
Annual variations of shallow soil salinity and its influencing factors were evaluated by using statistical and other correlation analysis methods in the irrigation district of 125 group of seventh division commander in Xinjiang based on the salinity collected in 0-30 cm soil layer at 169 points during 2002—2008. The results showed that the average soil salinity has been a decreasing trend since 2002, and the desalinization ratio of soil has decreased to 18%. The soil salinity is mainly affected by rainfall, followed by soil texture, service life of drip irrigation installation, soil background salinity and groundwater depth, but all those are not significant compared with rainfall. A wider variation range of shallow soil salinity is observed in light soil than in heavy soil, and the light soil is prone to salt accumulation and desalinization. There is no obvious difference in shallow soil salinity between various service lives of drip irrigation installation. The relationship between shallow soil salinity and annual rainfall is established based on the difference between an annual rainfall and the averaged rainfall over recent years as well as the difference in shallow soil salinity between the next year and this year. With the relationship, 192 mm balance rainfall is proposed to keep shallow soil salinity in stable; further, the soil salinity and water control measurers in the next year can be predicted according to the diffe-rence between the rainfall in the current year and the balance rainfall.
2013 Vol. 31 (7): 623-628 [Abstract] ( 2067 ) [HTML 1KB] [ PDF 1486KB] ( 1720 )
629 Infiltration models for different textures of water-repellent soils
Song Hongyang, Li Yi,, He Chansheng
In order to study the infiltration characteristics and mechanism in water-repellent soils deeply, one-dimension vertical infiltration experiments were conducted on water repellent soils with four different textures. The accumulation infiltration, infiltration rate and wetting front length were analyzed by using diagram when the infiltration was in progress, the soil moisture profiles were examined as well. The correlation between infiltration rate and time was predicted by means of four different models and compared with the measurements. The relationship between accumulation infiltration and wetting front length was described by a linear function. The results showed that for those hydrophobic soils there is a time instance at which the infiltration characteristic is changed. Thus the infiltration process can be divided into two stages: fore-stage and post-stage. The Kostiakov equation can describe the i-t relationship of hydrophilic soils and that at the fore-stage of hydrophobic soils very well, compared with the other models. Different hydrophobic soils show relatively large difference in infiltration rate during the post-stage of infiltration. The correlation between wetting front depth and accumulation infiltration can be described by a linear model in each of the two stages for hydrophobic soils, respectively. An effect, which the soil moisture in the upper-layer of hydrophobic soil is higher than hydrophilic soil,was observed.
2013 Vol. 31 (7): 629-635 [Abstract] ( 1537 ) [HTML 1KB] [ PDF 1648KB] ( 1767 )
636 Rainwater harvesting potential and its spatial-temporal variation in Loess Plateau of China
Zhang Baoqing,,, Wu Pute,,, Zhao Xining,,, Wang Yubao,,
In order to alleviate the co-existing situation of severe water shortage and soil erosion, the rainwater harvesting potential(RWHP)during 1971—2010 in the entire Loess Plateau of China was estimated by using the variable infiltration capacity(VIC)model, the total harvesting potential, individual potential and their spatial-temporal variation characteristics were compared among various river basins in the plateau. The results showed that the total RWHP was relatively considerable high in the Loess Plateau and the soil moisture available was one major component of the RWHP. Particularly, there was an even higher total RWHP in Hekouzhen-Longmen, Jing-Luo-Wei, Fen-Yi-Luo-Qin River Basins. Because the RWHP of surface runoff has a higher percentage in the total RWHP and most of sediments in the Yellow River originate from those basins, the development and application of techniques such as rainfall runoff gathering, storage and supplementary irrigation with rainwater should be paid more attention in those basins for surface runoff water to be regulated and utilized reasonably and eventually to relieve soil erosion and hazard of water shortage. Although the annually averaged RWHP in the entire Plateau exhibited slightly decreasing trends during the past four decades, the trends were not significant at the 95% confidence level(Mann-Kendall test). The annual RWHP was decreased from the southeast to northwest in the Plateau, the regions with high RWHP mainly concentrated in the middle reaches of the Yellow River.
2013 Vol. 31 (7): 636-644 [Abstract] ( 1575 ) [HTML 1KB] [ PDF 2418KB] ( 1840 )
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