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Journal of Drainage and Irrigation Machinery Engin
 
2014 Vol.32 Issue.3
Published 2014-03-25

article
Article
185 Internal flow characteristics of centrifugal pump at low flow rates
Fu Yanxia,, Yuan Shouqi, Yuan Jianping, Fu Yuedeng, Huang Ping
In order to investigate the performance and internal flow characteristics of centrifugal pump at low flow rates, the type IS160-50-65 end-suction centrifugal pump was selected as computational model. The three-dimensional, steady, turbulent, incompressible fluid flow in the whole pump including a suction pipe, impeller and volute was simulated by means of software Ansys CFX 12.0. Meanwhile the grid independence was checked by employing three sets of mesh to improve the computational accuracy. Finally, both the performance and internal flow characteristics of the pump at low flow rates were analyzed with the mesh just determined. It was shown that the predicted pump head, total efficiency are deviated from the experimental data by 1.47% and 3.61% only under the design condition. As the flow rate is decreased, the predicted head is closer to the tested one to some extent; unfortunately, the estimated efficiency shows increasing disagreement with the experimental value. In addition, the internal flow is quite uniform under the design condition. At low flow rates, however, there is a recirculation in the suction pipe; a reverse flow occurs in the impeller passages as well. The reverse flow is so dominated that it can occupy the entire impeller passages at a certainly low flow rate. At an extreme low flow rate, say 20% design flow rate, the recirculation flow has extended into the whole suction pipe. 
2014 Vol. 32 (3): 185-190 [Abstract] ( 1891 ) [HTML 1KB] [ PDF 2239KB] ( 1620 )
191 Generalized automatic testing and control technology for centrifugal pump
Yang Shuai, Jiang Xinkuo, Wu Dazhuan, Wang Leqin
In order to improve the reliability and applicability of performance testing system for centri-fugal pumps and enhance the automatic degree of testing process at the same time, the structure of a kind of general automatic testing system was constructed in this study. Programmable logic controller(PLC)or data acquisition card was selected as the sensor for signal sampling and the controller for the pumps and valves in the system. Moreover, a touch screen was used as the human-machine interaction. The system software was developed by using configuration software, and other functional modules written with Visual Basic 6.0 to conduct performance curve fitting and generate a test report, etc were embedded. As a result of these, the testing system not only can sample a variety of sensor signals, but also can support various kinds of data acquisition equipments,making the system more flexible and app-licable. In the present work, the composition scheme of the testing system, software programming, curve fitting principle and the realization of test control hardware were described. The obtained results show that the testing system has been greatly improved in degree of automation, communication ability, and performance of human-machine interaction as well as portability because comprehensive application and development of generalized controllers, configuration software and Visual Basic function modules were involved. The proposed system could be promising for testing and maintenance of pump equipment and for design of industrial automated production system.
2014 Vol. 32 (3): 191-195 [Abstract] ( 1476 ) [HTML 1KB] [ PDF 1798KB] ( 1479 )
196 Characteristics of pressure pulsation in multi-stage submersible pump
Shi Weidong, Xu Yan, Zhang Qihua, Wang Guotao, Lu Weigang, Ma Dongqi
In order to investigate the transient operation characteristics of multi-stage submersible pumps, three-dimensional, unsteady numerical simulations were conducted by using the standard k-ε turbulence model, SIMPLEC algorithm based on the sliding mesh technique in Fluent. The perfor-mance of the pump was obtained and compared with the experimental results. Besides, the pressure pulsations at various monitoring points were acquired; subsequently they were analyzed in time and frequency domains, respectively. It was demonstrated that the pressure fluctuation at all the monitoring points changes periodically with time, its number of periods is identical to the number of blades but less affected by the number of guide vane blades, its frequency is close to the blade passing frequency. The frequency of pressure fluctuation within the impeller increases gradually towards the impeller outlet and approaches the maximum value there, while the variation tendency of the frequency is opposite within the guide vane. The mostly dramatic pressure fluctuation occurs at the impeller outlet, the main frequency at various monitoring points is almost equal to the blade passing frequency. The amplitude of pressure pulsation coefficient at the monitoring points in the second stage impeller is higher than the first stage impeller. There still are two peaks in the pressure pulsation profiles in the second stage guide vane, suggesting pressure pulsation is not eliminated completely there. Additionally, the main frequency of pressure pulsation in the first stage guide vane is different from the second stage guide vane.
2014 Vol. 32 (3): 196-201 [Abstract] ( 2107 ) [HTML 1KB] [ PDF 1588KB] ( 1249 )
202 Path analysis of effects of diffuser geometric parameters on performance of submersible pump
Wei Qingshun,, Sun Xihuan, Liu Zailun
In order to explore effects of diffuser geometric parameters on performance of submersible pump, the diffuser of 250QJ125 submersible pump was redesigned by using an orthogonal experiment design array with various inlet angles, axial lengths and numbers of vanes while the rest geometric parameters of impeller remained unchanged. The flow field of each design was calculated by means of CFD technique and its performance was predicted as well;then the relationships between those parame-ters and the performance were established by employing path analysis. The results show that the vane inlet angle of diffuser affects head and efficiency most significantly, while the number of vanes has a least effect on both performance parameters, the effect of vane axial length is in between. The predicted performance is close to the measurement with a smaller relative error as low as 5.1%. Path analysis not only can identify effects of geometric parameters of diffuser on performance of submersible pump but also can rank the parameters. Nevertheless, this can provide a reference for diffuser hydraulic design to improve performance of a submersible pump.
2014 Vol. 32 (3): 202-207 [Abstract] ( 1659 ) [HTML 1KB] [ PDF 1206KB] ( 1420 )
208 Numerical analysis of flow field and pulsation characteristics in rotary lobe pump
Liu Zhongzu, Wang Qiubo
Pipeline noise increasingly becomes the main obstacle to reduce ship vibration and noise level. Pump equipment are the main source of pipeline noise in various ships, however, there is strictly limitation in lowering flow-induced noise level of a traditional centrifugal pump in which there is a high rotational speed and a strong rotor-stator interaction. Fortunately, the rotary lobe pump has a great advantage in reducing flow-induced noise. 2D and 3D straight and twisted lobes model pumps were built based on the working principle of rotary pump, and the flow field and pressure fluctuation characteristics in those pumps were analyzed by using CFD dynamic mesh method. The results show the flow rate has a linear relation with pump rotational speed but exhibits a periodic property. The pressure is distributed uniformly in the pumps and there is no obvious pressure gradient in the flow field. Howe-ver, there are vortex zones and flow separation phenomenon in the gap between two lobes and in the inlet and outlet of the pumps. The pressure fluctuation can be effectively reduced with increasing number of lobes and by using a spiral wing. Unfortunately, the pressure fluctuation still augments rapidly with increasing rotational speed.
2014 Vol. 32 (3): 208-213 [Abstract] ( 2424 ) [HTML 1KB] [ PDF 2874KB] ( 1257 )
214 Effect of impeller outlet edge inclination on performance of deep well centrifugal pump
Cong Xiaoqing, Yang Ming, Lu Weigang, Chen Guannan
Since a deep well multistage centrifugal pump has to work in a well, its impeller diameter and maximum discharge are restricted by the borehole diameter. In order to improve the pump hydraulic efficiency, its single-stage head must be the highest. In doing so, the sloping angle of the impeller outlet edge of 100QJ10 deep well multistage centrifugal pump was designed to be 10°, 15°, 20°, 25° and 30°, respectively. Then the steady, three-dimensional, incompressible turbulent flows of water in one stage of the pump were simulated based on the RANS equations and standard turbulence model by using a CFD code. The performance, turbulent kinetic energy, velocity and pressure fields were compared among the different impeller structures at the same discharge for an optimal sloping angle to be explored. The results show that the hydraulic efficiency and single stage head are maximum at two di-fferent sloping angles; this means the angle for the highest head is lower than that for the best efficiency. For a compromise, the optimal sloping angle should be 20°. Further, the predicted performance is in good agreement with the tested one. It was confirmed that the best overall efficiency of the pump redesigned with the impeller of 20° outlet edge sloping angle is as high as 58.9%, a 5.9% increment has been achieved compared with the original pumps.
2014 Vol. 32 (3): 214-219 [Abstract] ( 1432 ) [HTML 1KB] [ PDF 1675KB] ( 1272 )
220 Analysis on vibration signal of hydropower unit based on local mean decomposition and Wigner-Ville distribution
Pan Hong,
For a transient signal of a hydropower unit, the existing processing methods for non-stationary signal are unable to get a high time-frequency resolution currently, and the time-frequency characteristics cannot be extracted effectively as well. Therefore, a new method, in which the local mean decomposition(LMD)and Wigner-Ville distribution have been combined together, was proposed to ana-lyze vibration signals of hydropower unit; further it was applied into the analysis on run-out signals in the upper guide bearing of a hydropower unit in its load rejection operation. According to comparison of the time-frequency spectra determined respectively by short-time Fourier transform, wavelet transform and Wigner-Ville distribution, the spectrum given by the present method can capture the instantaneous amplitude and frequency of a transient signal directly. This implies that the proposed method has taken the advantages of both LMD and Wigner-Ville distribution. Meanwhile, the inherent defect, i.e. cross-term interference in Wigner-Ville distribution has been removed. This new method can be used as an effective analysis tool for condition monitoring and fault diagnosis of hydropower units in future.
2014 Vol. 32 (3): 220-224 [Abstract] ( 1799 ) [HTML 1KB] [ PDF 1430KB] ( 1062 )
225 Assessment of canal seepage control project in North Plain of Jiangsu and method for selecting optimum scheme
Deng Sheng,, Shao Guangcheng,, Bo Hao, Yu Shuang′en,, Deng Long
An indicator system was established to assess a canal seepage control project based on cost of project, ecological and environmental effect as well as construction technique, thus each seepage control scheme can be evaluated in a scientific manner. As a result, four kinds of canal seepage control schemes in Chuanhang Irrigation District of Suqian in Jiangsu Province were comprehensively eva-luated and the optimum scheme was selected by using a super decision-making software where a multi-attribute decision model, analytic network process and entropy weight fuzzy method were involved. The results showed that the construction technique has the maximum weight, the ecological environment effect has the minimum weight, but the cost of project is in between. The advantages and disadvantages of various seepage control schemes are quite different, namely the relative approximation degree of scheme 1(optimum)is 0.65, then the degree of scheme 4 is 0.37, those of scheme 2 and 3 are in between 0.37 and 0.65. In these assessments the characteristics of canal seepage control in a plain have been presented clearly, and the outcomes are in line with the actual situation of local canals. Obviously, the proposed indicator system can provide a scientific basis for development of canal seepage control project in North Plain of Jiangsu.
2014 Vol. 32 (3): 225-230 [Abstract] ( 1301 ) [HTML 1KB] [ PDF 2102KB] ( 1233 )
231 Pressure characteristics of flow induced by moving cylindrical capsules in hydraulic capsule transportation
Zhang Xuelan, Sun Xihuan, Li Yongye
To explore pressure drop in a hydraulic capsule transportation pipeline and pressure between two moving capsules extensively, the pressure distribution in the annular gap between a capsule and the pipe, the pressure distribution between two capsules as well as the pressure drop across capsules were measured and analyzed by using two capsules(length-100 mm, diameter-60 mm, weight-750 g)in 10 cm apart at 30, 40, 50, 60 and 70 m3/h flow rates. It is shown that the pressure in each test section increases with increasing flow rate. At a certain flow rate, the pressure on the capsule body presents a minimum. The pressure drop across the second capsule is substantially higher than that across the first one. In the annular gap, the pressure is low on the pipe wall and capsule body, but is the highest in the middle of the gap. The pressure shows a decline downstream in the gap of the first capsule, further the pressure gradient in the gap of the second capsule is higher than that in the first one. Under various flow conditions, the pressure distribution between two capsules is uneven in some degree, but the maximum pressure is achieved on the pipe wall and the minimum one is nearly at the pipe centre. The pressure gradient between two capsules increases with flow rate.
2014 Vol. 32 (3): 231-234 [Abstract] ( 1440 ) [HTML 1KB] [ PDF 1405KB] ( 1165 )
235 Pressure distribution in liquid film in water lubricated bearings of high-pressure pump for desalination
Hu Jingning, Xue Yan, Zhang Desheng, Ye Xiaoyan, Gu Rengui, Wang Jing
In order to assess the reliability of liquid film in the water lubricated bearings of a multi-stage high-pressure pump for desalination and to explore the mechanism for bearing a load as well as the factors affecting the mechanism, the pressure distribution in the liquid film was analyzed by solving the two-dimensional steady Reynolds equation with finite difference method and successive over relaxation(SOR)scheme for the discretized linear equations in Matlab. It was shown that the pressure in the liquid film was distributed nonlinearly along the circumferential direction and had a maximum peak at a certain position, but the pressure distribution was parabolic along the axial direction. The pressure profile was affected by length-diameter ratio and eccentricity, particularly, the pressure increased with them. These results are useful for design and selection of the water lubricated bearings of a high-pressure pump for desalination in million-ton processing capacity. It was conformed that the designed bearings have an acceptable reliability and a satisfactory lubrication condition and a sufficient sustainability for loads.
2014 Vol. 32 (3): 235-241 [Abstract] ( 1690 ) [HTML 1KB] [ PDF 4728KB] ( 1602 )
242 Numerical simulation of slit wall effect on Taylor-Couette flow stability
Liu Dong, Zhu Jian, Wang Yingze, Yang Xiaoyong, Wang Chunlin
The Taylor-Couette flows in the gap between two concentric cylinders with smooth and 18-slit walls were studied using CFD method. The CFD method was validated with PIV experiments on the flow between two concentric cylinders with smooth walls and a very good agreement has been achieved. In the simulations, the periodic fluctuation properties in axial and radial velocities were quantized, and their profiles across the radius were discussed too. Importantly, a rule that the Taylor vortex size decreases with increasing Reynolds number was indentified. Interestingly, a Taylor vortex flow was also found in the gap with 18-slit walls at the same Reynolds number as the smooth walls. By comparing velocity and vorticity distributions across in the gap for two different wall profiles, it was found out the slit walls could alter the flow structure and strengthened vorticity significantly, and amplified the Taylor vortex size. As a result, the radial velocity in the mid-gap with slit walls was 20% larger than that with smooth walls. In addition, it was shown that there was an obvious vortex motion in the slit regions based on the predicted flow field in the circumferential plane in those regions. 
2014 Vol. 32 (3): 242-246 [Abstract] ( 1903 ) [HTML 1KB] [ PDF 2043KB] ( 1591 )
247 Method for determining neural network characteristic parameters in fault diagnosis system for wind turbines
Cao Ting, Zheng Yuan
Neural network has increasingly been used in a fault diagnosis system for wind turbines. The choice of input layer characteristic parameters plays an important role in solving the unstable problem in convergence during network training. First of all, the selection of input layer characteristic parameters of neural network was studied in a fault diagnosis system for wind turbines. It was identified that a wind turbine has three typical components, such as gear box, rotor and blade, in which a fault can occur frequently. Then the fault type and its mechanism were analyzed. It was shown that the frequency characteristics of the gear box can be used to characterize its fault types, a fault in the rotor can be related to an axis orbit;however the fault diagnosis of blade needs an acoustic emission system.Based on these ana-lytical results, several kinds of methods for determining the input layer characteristic parameters were proposed at last. For the gear box, the input layer characteristic parameters can be determined by means of time-frequency characteristics of a fault; the parameters for rotor faults can be reflected by its axis orbit, the parameters for the blade faults can be decided by the characteristic data, which are generated on the blade surfaces and can be detected with an acoustic emission system. This approach can provide a reference for neural network establishment of a fault diagnosis system for wind turbine units.
2014 Vol. 32 (3): 247-251 [Abstract] ( 1992 ) [HTML 1KB] [ PDF 1303KB] ( 1388 )
252 Effects of water and fertilizer on soil salinity and yield increase
Shi Haibin, Zhao Qian, Tian Delong,, Yan Jianwen, Miao Qingfeng
In order to achieve an efficient use of fertilizer in saline soil in Inner Mongolia Hetao Irrigation District, several different combinations between type of fertilizer and irrigation quota were made, and then their dynamic impacts on soil salinity and yield increase were studied by using field trials. It was shown that except the urea treatment all the means of soil EC(electrical conductivity)in topsoil and soil profiles under the organic fertilizer, controlled and slow-release fertilizer treatments and usual water-saving irrigation condition are decreased in some degree compared with their initial values after wheat being harvested. The organic fertilizer treatment exhibits an advantage in salt control under the conventional irrigation condition(irrigation quota=1 005 m3/hm2). Both the slow-release and controlled fertilizers have an even better salt control under the water-saving irrigation condition(irrigation quota=750 m3/hm2); as a result, the means of EC in topsoil are decreased by 16.4% and 14.3%, respectively. For the urea treatment, however, the means of EC in topsoil and soil profile are increased respectively by 3.6% and 2.7% under the conventional irrigation condition, and the salinity is slightly higher than that under the water-saving irrigation condition. Although the wheat yield is increased significantly after the four kinds of fertilizer treatments are applied, the slow-release fertilizer can result in a remarked yield increase under the routine and water-saving irrigation conditions. After the water-sa-ving, soil salinity and wheat yield increase are considered comprehensively, the optimized irrigation and fertilization module should be: slow-release fertilizer and diammonium as the basal fertilization, no topdressing during growth period, slow-release fertilizer is 800.4 kg/hm2, diammonium is 350.6 kg/hm2, irrigation amount is 750 m3/hm2. This module leads to a wheat yield as high as 374.5 kg/hm2, which is increased by 2.14% than in the conventional irrigation and fertilizer module. Furthermore, the irrigation water is saved by 25%, and the means of EC in topsoil and soil profiles have been decreased by 18.6% and 16.4%, respectively.
2014 Vol. 32 (3): 252-257 [Abstract] ( 1493 ) [HTML 1KB] [ PDF 1244KB] ( 1118 )
258 Effects of gravel coverage on CFD-based near-surface wind field
Zhao Wenju, Song Jianshu, Ma Xiaoyi, Zhao Tinghong
Wind erosion is one of the main reasons for land desertification in Northwest China. To su-ppress the desertification progress and promote both agricultural and livestock production, many protective measures, such as gravel and vegetation coverage, crop stubble and so on, have been applied in barren lands in Northwest China. In consequence, the near-surface wind field was improved significantly and the wind erosion has been reduced effectively, and the soil moisture has been maintained, eventually the land degradation has been slowed down. In the paper, the three-dimensional, steady near-surface wind fields around a series of gravel coverage were simulated by CFD method for 2.0 mm-12.0 mm gravel size at 5 m/s and 13 m/s wind speeds, respectively; meanwhile, field observations were conducted. The results show that at the same height above the ground the degree of reduction of near-surface wind velocity rises with increasing gravel size until the size reaches 10.0 mm; once the size is beyond that value, the degree doesn't change with gravel size basically. The increment in degree of reduction of wind velocity increases with gravel size; moreover, at the same gravel size, the degree of reduction decreases with height apart from the ground. It was found out that the degree of reduction of wind velocity is insensitive to change in wind velocity by comparing the results at 5 m/s and 13 m/s wind speeds. The predicted degree of reduction of wind speed matches the field observation as good as more than 89%. This study can provide a theoretical basis for development of ecological agriculture in an arid area.
2014 Vol. 32 (3): 258-262 [Abstract] ( 1399 ) [HTML 1KB] [ PDF 1436KB] ( 1207 )
263 Modeling effects of different irrigation managements on root-zone soil salinity
Chen Yanmei,, Wang Shaoli,, Gao Zhanyi,, Guan Xiaoyan,, Hu Yaqiong,
Taking Shahao canal irrigation region in Hetao irrigation district as an example, effects of different irrigation management on root-zone soil salinity were explored based on the SaltMod model in the paper. The model was calibrated and validated by using the data in 2008—2010, then the root-zone soil salinity in that region was simulated and predicted. The results showed that under the present irrigation and drainage conditions, the soil salinity not only stayed in a stable level, but has exhibited a slightly desalinated tendency, it was predicted that the root-zone salinity would be reduced by 3% after 10 years. During crop growth stage, the exchange between water and salt is remarked in the vertical direction; to control the soil salinity, irrigation water amount should be kept as small as possible. In winter, the root-zone soil salinity was decreased with increasing irrigation quota, but the slope of increase in the salinity was gradually decreased. According to the crop planting structure in a local irrigation district and comprehensively considering water saving irrigation, crop production, water and salt concentrations in the soil of root-zone, it is suggested that optimal irrigation net quota should be 2 700-3 500 m3/hm2 in crop growth stage, the quota in winter should be about 2 700 m3/hm2.
2014 Vol. 32 (3): 263-270 [Abstract] ( 1483 ) [HTML 1KB] [ PDF 1730KB] ( 1473 )
271 Experiments on chromium migration from soil to surface runoff water
Tong Juxiu,, Liu Yang,, Sun Huaiwei
To explore the surface runoff water pollution caused from heavy metals in agricultural soil, the Cr(VI)migration features from soil to surface runoff water were investigated by using indoor simulated rainfalls and the soils with adsorptive Cr(VI)solute. It was identified that the dissolvable Cr(VI)mass concentration in surface runoff water decreased with time in a power function according to the observed dissolvable Cr(VI)mass concentrations in the surface runoff water and the mass rate of dissolvable Cr(VI)melted into the surface runoff and subsurface drainage water under different conditions. Also, the poorer the subsurface drainage, the larger the initial soil volumetric water content, and the more shallow the maximum depth of collected water on the soil surface, the greater the Cr(VI)mass concentration and mass rate of dissolvable Cr(VI)melted into the surface runoff water from the soil. When the surface runoff and subsurface drainage water co-existed, the mass rate of dissolvable Cr(VI)melted into the subsurface drainage water was much higher than into the runoff water. This su-ggested that the most dissolvable Cr(VI)has gone into the subsurface drainage water.
2014 Vol. 32 (3): 271-276 [Abstract] ( 1938 ) [HTML 1KB] [ PDF 1568KB] ( 1234 )
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