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Research progress in rotating stall in mixed-flow pumps with guide vane |
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LI Wei,*, PING Yuanfeng,, SHI Weidong, JI Leilei,, LI Enda,, MA Lingling,
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Rotating stall is a widespread unstable phenomenon of internal flow in rotodynamic machines, such as mixed-flow pumps and so on, and has a vital influence on performance and even safety of the machines. In this paper, manifestation, inception, formation and propagation mechanisms of the rotating stall are analyzed in terms of performance curve, internal flow structure and pressure fluctuation characteristics in both time and frequency domains in mixed flow pumps with guide vane. A few key factors affecting formation and development of the stall are discussed. Typical manifestations for the rotating stall occurrence in mixed-flow pumps with guide vane include positive slope(saddle shape)in various forms in the head-flow rate curve, and periodically propagating vortex structure in the internal flow field. The unsteady vortex structure can result in a blockage in the flow passages, and subsequently lead to unstable pressure fluctuation. The analysis of leakage vortex morphological structure and motion trajectory provides a new idea for the study on the stall inception in a mixed-flow pump with guide vane. Flow condition is the most direct factor leading to the rotating stall in the pump, especially, the number of stall cells will be impacted significantly with decreasing flow rate. In addition, the number of blades, impeller speed and tip clearance are also the important factors affecting number, propagation speed and development process of stall cells. Based on the research status in rotating stall in recent years in China and abroad, the issue and orientation for further research in the stall in mixed-flow pumps with guide vane in the future are put forward. |
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2019 Vol. 37 (9): 737-745
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746 |
Numerical simulation for suitable working conditions of surface-textured plunger based on CFD |
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HU Song, ZHANG Xinming, ZHENG Long*, REN Luquan
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The flow field between barrel and plunger with textured-surface in a pumpjack was investigated numerically by using CFD method and effects of size of the gap between the barrel and the plun-ger and pressure difference on pumpjack oil leakage flow ratio, load-carrying capacity ratio and friction coefficient ratio were analyzed. Results show that the texture on the plunger surface affects the pressure and velocity fields in the gap. Under the same pressure difference, the oil leakage flow rate and oil mean velocity in the gap increase with increasing gap size. As a result, the influence of the texture on the velocity and pressure fields gets dominated, resulting in a decrease in both leakage flow ratio and friction coefficient ratio, and an increase in load-carrying capacity ratio. For the same gap size, with the increase of pressure difference, the pressure gradient in the gap rises, and the mean velocity becomes fast. Due to the influence of texture on the flow field, the leakage flow rate and friction coefficient ratios decrease but the load-carrying capacity ratio increases. This suggests that surface-textured plungers should be applied in oil fields properly. A bigger gap size and a larger pressure difference will allow the surface texture to demonstrate a resisting effect on the oil fully. In sequence, oil leakage through the gap can be reduced effectively and wear of the plunger can be mitigated to achieve the objectives such as improvement of pump efficiency and prolonging service life-span of the plunger. |
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2019 Vol. 37 (9): 746-751
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752 |
Pressure pulsation characteristics in a series-parallel centrifugal pump with unequal blade pitch |
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CHAI Liping, YU Jiafeng*, LI Yue , YAN Hao, CAO Linsong
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Five kinds of impeller models with unequal blade pitch are established based on automatic balancing theory of rotor-bearing systems to explore the influence of unequal pitch on pressure fluctuation in a series-parallel centrifugal pump. Specially, the performance and pressure fluctuation characteristics of the pumps with these impellers are compared and analyzed to improve the operational stability of the pump. The results show that the head and efficiency of the pump decrease as θmin gets small regardless of running in parallel or in series. When θmin is equal to 56° or 58°, the efficiency is higher than that with equal blade pitch; particularly, the best efficiency appears at θmin=56°. An additional fluctuation energy amplitude peak occurs at 435 Hz, i.e. 1.5 times the blade passing frequency in unequal blade pitch cases, and the amplitude decreases gradually with increasing θmin. As a result, the concentrated distribution of pulsating energy has been mitigated. The distribution of pressure fluctuation amplitude is more uniform and stable but also the energy distribution is more reasonable at θmin=56° in terms of comparison of pressure pulsation characteristics and pulsation energy amplitudes in the dominant frequencies at the monitoring points positioned along the circumference of the volute. |
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2019 Vol. 37 (9): 752-757
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758 |
Experimental study on cavitation characteristics of mixed-flow pump during startup |
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CHEN Zonghe, SHI Weidong,*, ZHANG Dengsheng, ZHANG Junjie, ZHANG Zhiwei
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A high-speed photographical experiment was carried out on a mixed-flow pump with 0.25 mm tip clearance during its startup period to study cavitation characteristics of the pump at various flow rates, inlet pressures and startup times. The cavitation phenomena in the pump were observed at 0.80Qd,0.90Qd,1.00Qd and 1.05Qd flow rates and 10 s, 15 s and 20 s startup times. During the initial stage of startup process, since the rotating speed is so low that the pressure in the impeller eye does not reach the saturated vapor pressure of water, no cavitation appears at all. As startup process arrives at its stable stage, cavitating bubbles appear at the impeller tip firstly, then propagate into impeller passages to result in severe cavitation. At the same flow rate, the lower the inlet pressure(cavitation number)is, the more serious cavitation occurs. At the same inlet pressure and flow rate, the degree of ca-vitation in the pump is gradually intensified with startup advancing, and the most serious degree of ca-vitation occurs in the stable stage at different startup times. |
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2019 Vol. 37 (9): 758-762
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763 |
Performance and internal flow characteristics of jet centrifugal pump |
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ZHANG Renhui,*, ZHANG Sidai, TIAN Lei, CHEN Xuebing
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Experiments on suction and hydraulic characteristics were performed at different installation heights in a fluid flow testing system built to investigate self-priming mechanisms in jet centrifugal self-priming pumps in term of the type JET750G1jet centrifugal pump. Also, a series of numerical simulations of cavitating flows in the pump were carried out based on the K-ω turbulence model and Zwart-Gerber-Belamri cavitation model at zero installation height. The experimental results show that the head, shaft-power and efficiency curves drop sharply when the flow rate reaches a certain value; as the installation height increases, however, the flow rate at the point for performance to start to drop steeply gets lowed. The numerical results exhibit that the predicted head, shaft-power and efficiency are basically consistent with experimental values, and the estimated flow rate for performance to start to drop steeply is 0.5 m3/h larger than the experimental value. Because of a smaller area ratio in the jet nozzle, the primed fluid shear layer is rapidly dragged to the wall of the throat, and the lowest pressure appears just after the throat outlet where cavitation inception occurs. As the flow rate increases, the cavities extend rapidly to the eye of impeller. The flow rate at the point for performance to start to drop steeply is exactly the flow rate for cavitation inception in the pump. Thus, the suction performance of a jet centrifugal pump depends on that of the ejector. An ejector can improve the head and self-priming performance of a centrifugal pump, but the high velocity reverse flow and strong shear flow in the ejector will lead to a significant drop in pump efficiency and suction performance. |
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2019 Vol. 37 (9): 763-768
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776 |
Numerical analysis of hydrodynamic characteristics in confluence of mainstream with a tributary in a river-type reservoir |
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LU Jianyu, MAO Jingqiao*, GONG Yiqing,, CAI Haibin, CAO Qing, DAI Huichao, YAN Jie
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Based on the geometry of the confluence of the mainstream with a tributary and their hydrological conditions in a typical river-type reservoir, a three-dimensional hydrodynamic model was developed to investigate the impact of intersectional angle of the tributary with the mainstream on hydrodynamic characteristics in the confluence. Five scenarios were focused in terms of 30? 60? 90? 120? and 150?intersectional angles, respectively. The results illustrate that there is always a high concentration region of turbulent kinetic energy at these intersectional angles, and a positive correlation exist between the turbulent kinetic energy and the angle, that is, both the high turbulent kinetic energy region size and value increase significantly with increasing angle. The maximum bed shear stress always decreases from the confluence to the upstream of the tributary at various intersectional angles. If the angle is less than 90? the coefficient of variation of stream velocity increases first and then decreases from the confluence to the upstream; otherwise the coefficient decreases steadily towards the upstream. Additionally, if the angle is less than 90? both the bed shear stress and the coefficient of variation exhibit a negative correlation with the angle, or a positive correlation exists between them. |
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2019 Vol. 37 (9): 776-781
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782 |
Shafting vibration model with torsion deformation in shaft of hydro-turbine generator units |
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WANG Yongli, ZENG Yun*, XU Liankui, SUN Jiaxiang, ZHAO Meng
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The traditional assumption ignoring torsion deformation in the shafting in hydro-turbine generator units(HTGU)may lead to a large deviation from the actual situation in analyses of shafting vibration. Thus, two equations, i.e. shafting vibration equation and rotor motion equation with torsion effect were established based on the Lagrange method. Further, a unified first-order differential equation was configured with them by defining a generalized momentum. Taking the resistance torque on the generator rotor and the driving torque on the turbine runner as the link, a complete HTGU operating simulation system, including the hydraulic system, generator, excitation controller and governor, was established and solved by making use of the second-order Runge-Kutta method. The calculated results show that the considered torsion effect has a little influence on the lateral vibration of the shafting under unit fault disturbance conditions but has a great impact on the torsion deformation in the shaft under stable operating conditions. Under unit fault disturbance conditions, the variation trend of torsional angle between the generator rotor and the turbine runner is basically consistent with that of active power. These simulations show that the torsion vibration model established in this paper can represent essential features of the shafting vibration, and hence it is reasonable. |
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2019 Vol. 37 (9): 782-787
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793 |
Study of liquid properties on electrostatic spray atomizing performance |
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XU Yanming, LIU Jianhe*, LI Xingguang
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Several spraying experiments were carried out by using different liquids under the same charging condition when the liquid flow rate and the charging voltage applied were controlled respectively by using flow valve and ring electrode in high voltage equipment in the paper. The influence of charge voltage and liquid physical properties on droplet size distribution was analyzed by PDA measurement system. Thus, the effect of physical properties on the electrostatic spray atomizing performance was clarified. The results showed that the intensity of the electric field around the nozzle increased with increasing voltage, and the charge on the droplets increased accordingly, eventually the rough droplets were nebulized into fine droplets. The conductivity of the solution is an important factor affecting droplet size. The larger the conductivity, the higher the electric field force around the spraying nozzle, and the smaller the size of the charged droplets. However, if the conductivity of the solution is smaller, the charging voltage will play a dominant role in the droplet size distribution. The viscosity and surface tension of solution have an inhibitory effect on liquid atomization. Under the same charging condition, the droplet size decreases with decreasing surface tension and viscosity. |
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2019 Vol. 37 (9): 793-798
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799 |
MARS-based estimation of reference crop evapotranspiration in Poyang Lake region |
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WU Lifeng,, JU Yan, YANG Xiuxia*, BAI Hua, DAI Panwei
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In order to find the most suiTab. method for calculating reference crop evapotranspiration (ET0), the ET0 estimated by using FAO Penman-Monteith model was used as the standard values, ET0 models of multiple adaptive regression spline (MARS) were established by considering 12 different meteorological factors, and the results were compared with those predicted with generalized regression neural network (GRNN), support vector machine (SVM) and a few empirical correlations proposed by Hargreaves, Irmak-Allen, Makkink, and Pristley-Taylor, respectively. The observed data, including daily maximum and minimum ambient temperatures, solar duration hours, wind speed and relative humidity in 1966—1990 in Nanchang Meteorological Station were used to establish the models and those during 1991—2015 were adapted to validate the models. Results show that the accuracy of three kinds of artificial intelligence algorithms is better than that of the empirical correlations, particularly, MARS has the best accuracy, namely, RMSE, R2 and NRMSE are 0.227 mm/d, 0.982 and 0086, respectively. The accuracy of SVM is ranked in the second place with RMSE, R2, and NRMSE of 0266 mm/d, 0.978 and 0.101. GRNN is in the third place with RMSE, R2 and NRMSE of 0.323 mm/d, 0.962 and 0.123. The MARS method, which is not only with an even better accuracy but also has an explicit mathematical expression, is the optimum method for calculating ET0 in region Poyang Lake. |
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2019 Vol. 37 (9): 799-805
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806 |
Impacts of different aerating methods on dissolved oxygen in brackish water and reclaimed water |
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OUYANG Zan, TIAN Juncang,,*, DENG Huiling, YAN Xinfang,,
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The relationships of dissolved oxygen in brackish water and reclaimed water with time and temperature were clarifed experimentally to find out the best aerating method. In experiment design, eight treatments were assigned, namely micro-nano bubble generating device(F1), 12 gas stone fired oxygen pump(F2), 28 gas stone fired oxygen pump(F3), Venturi(F4), Venturi+12 gas stone fired oxygen pump(F5), Venturi+28 gas stone fired oxygen pump(F6), micro-nano bubble generating device+12 gas stone fired oxygen pump(F7), micro-nano bubble generating device+28 gas stone fired oxygen pump(F8)at 20 ℃ water temperature, and seven temperatures(F9)such as 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃ and 45 ℃ as well as brackish water(W1)and reclaimed water(W2)were applied in oxygen dissolving. The results show that the dissolved oxygen increases by 59.65%, 53.10%, 44.43% and 39.47% in treatments F3W1, F1W1, F2W1 and F4W1, respectively compared with CKW1. Compared with CKW2, fortunately, the dissolved oxygen rises by 80.17%, 78.04%, 60.13% and 55.22% in F3W2, F1W2, F2W2 and F4W2, respectively. Based on CKW1, the dissolved oxygen increases by 73.98% and 67.79% in F8W1 and F7W1, respectively; Interestingly, in terms of CKW2, the dissolved oxygen is ascended by 100.21% and 94.67% in F8W2 and F7W2, respectively. Unfortunately, compared with CKW1, the dissolved oxygen is increased by 63.84% and 57.44% in F6W1 and F5W1, respectively. Simiarly, compared with CKW2, the oxygen is increased by 0, 79.45% and 73.79% in F6W2 and F5W2, respectively. Finally, compared with CKW1, when the water temperature rises from 15 ℃ to 45 ℃ the dissolved oxygen in F9W1 is decreased by 0, 9.82%, 12.86%, 14.86%, 26.56%, 29.43% and 34.24%, respectively. In parallel, compared with CKW2, temperature rise in F9W2 leads to an increase in the dissolved oxygen by 0, 15.32%, 15.69%, 19.24%, 23.65%, 25.59% and 32.55%, respectively. In terms of the maximum dissolved oxygen, the best aerating method is the case: micro-nano bubble generating device+28 gas stone fired oxygen pump(F8W1 9.83 mg/L, F8W2 9.39 mg/L). |
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2019 Vol. 37 (9): 806-814
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Application of entropy weight based fuzzy analytic hierarchy process in water and fertilizer coupling effect evaluation of winter strawberry under trace quantity irrigation |
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XING Liwen ,, CUI Ningbo *, DONG Juan , ZHAO Lu, LIU Shuangmei
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A regression model of comprehensive indices evaluating yield, quality and water and fertilizer utilization efficiency of winter strawberry under trace quantity irrigation condition was established in terms of water and fertilizer doses by using fuzzy analytic hierarchy process(FAHP)based on entropy weight method. The water and fertilizer coupling effect on the yield, quality and water and fertilizer utilization efficiency was evaluated, and the optimal doses of water and fertilizer were determined. The results showed that the maximum comprehensive evaluating index was achieved with the following fertilizer doses: 721.96 kg/hm2(N), 360.98 kg/hm2(P2O5)and 721.96 kg/hm2(K2O)with 60.41% lower and 90% upper irrigation water limits. The corresponding yield, utilization efficiency of irrigation water and fertilizer utilization efficiency were 27 008.69 kg/hm2, 84.48 kg/m3 and 15.60 kg/kg, respectively. Compared with conventional drip irrigation mode, the optimized trace water and fertilizer amounts irrigation water and fertilizer management mode can increase the yield by 27.26%, the irrigation water utilization efficiency by 22.27% and the fertilizer utilization efficiency by 26.35%. The prediction model produced in this paper has a high reliability, and the optimized water and fertilizer doses predicted by the model can provide guidance on greenhouse strawberry production in a certain degree. |
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2019 Vol. 37 (9): 815-821
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Status and prospect of research in preprocessing methods for measured signals in mechanical systems |
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TANG Shengnan, ZHU Yong*, LI Wei, CAI Jiaxi
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In condition monitoring and fault diagnosis of mechanical systems, the preprocessing of measured signal is a necessary link and a basis ensuring subsequent feature extraction and reliability of health assessment. In the article, the results achieved by existing preprocessing methods for measured signals are reviewed. The status of signal conversion methods is described, and the outcomes of signal component extraction methods are introduced. Moreover, the development trend of measured signal preprocessing in mechanical systems is analyzed and prospected. Much work in update of existing traditional time-domain and frequency-domain integration methods and their performance improvement still needs to be exploited in-depth. Intelligent processing methods can obtain complete data source, which reflects the state characteristics of equipment, and are still worthy being investigated further. As the mechanical equipment gradually tends to be intelligent, multi-functional, the efficient and green the preprocessing technology for measured signals in mechanical systems will face new challenges. Advanced signal preprocessing methods should be explored to carry out precise intelligent fault diagnosis and prediction based on information of equipment operating state. Such methods can find extensive applications in scientific research and engineering practice in the future. |
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2019 Vol. 37 (9): 822-828
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