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Journal of Drainage and Irrigation Machinery Engin
 
2018 Vol.36 Issue.2
Published 2018-02-25
article
article
91
2018 Vol. 36 (2): 91- [Abstract] ( 263 ) [HTML 1KB] [ PDF 3289KB] ( 543 )
92
2018 Vol. 36 (2): 92- [Abstract] ( 326 ) [HTML 1KB] [ PDF 1153KB] ( 729 )
93 Numerical analysis of effect of sand volume fractions on erosion characteristics of centrifugal pump
ZHAO Weiguo,, ZHENG Yingjie,, LIU Yi,, HAN Xiangdong,
In order to study the effect of sand volume fractions on erosion characteristics of the centrifugal pump in sandladen water flow, RNG k-ε turbulence model, SIMPLE algorithm, discrete phase model, Finnie ductile material erosion model, and Rosin-Rammler particle size distribution approach were employed. The full threedimensional numerical simulation about solid-liquid twophase flow in the singlestage singlesuction centrifugal pump with a specific speed of 196 was carried out by using Fluent software, and the effect of wall roughness was taken into account. By comparing the test data of the external characteristics of fresh water pump to the numerical simulation result, the reliability of numerical calculation method was verified. The results show that with the increasing of sand volume fractions, the erosion intensity of the centrifugal pump increases gradually, and the key sand erosion position is concentrated on start side of blade, suction side of blade, pressure side of blade close to the blade outlet and the volute near the second section and the fourth section. Additionally, sand tracks tend to be mussy, and head and efficiency of the pump are decreased gradually.
2018 Vol. 36 (2): 93-98 [Abstract] ( 895 ) [HTML 1KB] [ PDF 1796KB] ( 868 )
99 Pressure fluctuation of solid-liquid flow in stator and rotor cascades of pump as turbine
HAN Wei,, LI Xuefeng,*, SU Min, LI Rennian,, CHEN Hao,
In order to study the pressure fluctuation characteristics of solid-liquid flow in stator and rotor cascades of pump as turbine, the centrifugal pump with space diffuser as turbine is chosen, and then the unsteady 3D flow field was simulated based on the large-eddy simulation(LES)and Mixture multiphase flow model with structured hexahedral mesh generated in ICEM. The pressure fluctuations under three different flow in water and solid-liquid two-phase were monitored in the numerical calculation. The results showed that the point P3 between the stator and the rotor and the point P6 in the guide vane are due to the pressure gradient alternating change in the impeller under the water and solid-liquid two-phase, the periodicity of the pressure fluctuations in time domain is obvious, and consis-tent with the blade passing period. The presence of particles reduces the backflow of the draft tube, which makes the pressure fluctuation more stable at the small flow rate, and the existence of particles increases the flow field disturbance at the large flow rate. The results of the pressure fluctuations in frequency domain reveal that the main frequency are of the blade passing frequency(BPF)and the harmonic frequency is a multiple of the blade passing frequency at different conditions, and its amplitude shows exponential decay. The vortex induces second-harmonic in the impeller obviously. The particles enhance the high-frequency pressure fluctuation at the small flow rate while those weaken it at the large flow rate.
2018 Vol. 36 (2): 99-103 [Abstract] ( 649 ) [HTML 1KB] [ PDF 6703KB] ( 841 )
104 Influence of blade shape on performance in inverse umbrella aerator
MING Jiayi*, DONG Liang,, LIU Houlin, ZHAO Yuqi, YAO Han
In order to study the effect of radial straight blade and leaned blade on the performance of inverse umbrella aerator and obtain the flow characteristic of a oxidation ditch driven by two inverse umbrella aerators with different kinds of blade shape, a lab scale oxidation ditch according with geometric similarity, kinematic similarity and dynamic similarity was taken as the research object. The volume of fluid(VOF)model was adopted and the standard k-ε turbulence model was applied to close the governing equations. Through changing the blade shape of inverse umbrella aerator, three-dimensional numerical simulations were conducted. The results show that the power assumption of these two kinds of inverse umbrella aerators is much the same, the blade shape has a significant impact on oxygenation capacity and plug-flow capacity on the inverse umbrella aerator: under the drive of inverse umbrella aerator with radial straight blade, the gas volume fraction of the section crossing the driving shaft in the oxidation ditch is 0.66% higher than that in the oxidation ditch driven by the inverse umbrella aerator with leaned blade; while the inverse umbrella aerator with radial straight blade has a stronger ability to promote the fluid near the surface, the inverse umbrella aerator with leaned blade does better on driving fluid at the bottom of the ditch, with the dead water zone 0.70% less than that in the ditch driven by the inverse umbrella aerator with radial straight blade. The fluid stirred by the inverse umbrella aerator with leaned blade flows to the wall at a higher speed. The flow distribution of the oxidation ditch driven by two inverse umbrella aerators is symmetrical. The downstream inverse umbrella aerator has an ability to lift and accelerate the incoming flow.
2018 Vol. 36 (2): 104-110 [Abstract] ( 1685 ) [HTML 1KB] [ PDF 1839KB] ( 858 )
111 Effects of impeller geometry parameters on fracture cavitation performance of centrifugal pump
KANG Junjun*, ZHU Rongsheng, WANG Xiuli, LIU Yong, ZHONG Weiyuan, ZHANG Benying, QI Longxi
To improve the cavitation performance and study the cavitation fracture mechanism of the centrifugal pump, the numerical simulation of cavitation performance in a specific speed 134 centrifugal pump was carried out by changing the impeller inlet diameter, the blade inlet angle and the impeller outlet width. Then the cavitation performance was predicted according to the simulation results, and the bubble distribution in the impeller passage was analyzed under different net positive suction heads. Simulation results showed that with the decreasing of the inlet pressure, the cavitation bubble first occurs at the blade inlet of the suction side, then it diffuses to the impeller outlet with the rotating of the impeller at the same time, and the bubbles flow to the pressure side when the flow area becomes bigger. The main reason why the bubble in the impeller passage is asymmetric is that the pressure on the surface of the impeller is asymmetric because of the static coupling between impeller and volute. Compared to the impeller inlet parameters, the change of the impeller outlet width affects the cavitation performance less. The bending of the blade becomes smaller when the inlet angles become bigger, the flow areas in the blade inlet increase, the cavitation performance is improved and the value of the NPSH decreases under the same inlet pressure. There exists an optimum value for the change of the impeller inlet diameter and the blade inlet angle, which is of importance to the improvement of the centrifugal pump′s efficiency and the cavitation performance.
2018 Vol. 36 (2): 111-117 [Abstract] ( 756 ) [HTML 1KB] [ PDF 2514KB] ( 955 )
118 Test and analysis on pressure pulsation and hydraulic performance of saddle zone in axial flow pump
HE Naichang, TAN Minggao*, LIU Houlin, HUANG Xin, WU Xianfang
In order to analyze the running characteristics of axial flow pump in saddle zone, the pressure pulsation and hydraulic performance of saddle zone in an axial flow pump were tested under diffe-rent conditions. The pressure pulsation and hydraulic performance of saddle zone in the axial flow pump were analyzed. The results show that the H-Q curve of the model pump has an obvious saddle zone under small flow rate conditions in the axial flow pump. Saddle zone is in the flow rate range of 0.50Qd-0.60Qd. There is a minimum head at 0.55Qd which is lower than the head at 0.60Qd by 0.33 m. And the difference is 5.5% of design head. The pressure pulsation at the impeller inlet and pump outlet has an obvious time domain periodicity which reflects the four wave crest and trough behavior in one period. The peak-to-peak value of pressure pulsation at the impeller inlet at 0.55Qd is 2.3 times the value under design condition. The pressure pulsation regularity of guide vane middle and outlet is complex. The main frequency at the impeller inlet is the blade passing frequency. The maximum pressure pulsation amplitude is located at the blade passing frequency of 0.55Qd,which is 27.6% higher than the maximum amplitude of the pressure pulsation at design condition. There appear many low-frequency signals at guide vanes middle and outlet under small flow rate conditions and the pressure pulsation is complicated. The main frequency at the pump outlet shows a blade passing frequency at design condition. The research results can provide a reference for the optimization of unstable running characteristics in the axial flow pump.
2018 Vol. 36 (2): 118-123 [Abstract] ( 670 ) [HTML 1KB] [ PDF 3544KB] ( 1089 )
124 Effect of rectifier in the draft tube on flow of hydraulic turbine
YANG Lijing*, YAN Chengming, ZHANG Jun, DENG Zhihui
The internal flow of the draft tube is very complicated. There are various problems with the inside of the draft tube and the turbine because of the asymmetrical pressure distribution of its internal cross-section. A rectifying cylinder having openings at both ends of the front and rear ends is arranged in the channel of the draft tube. The CFD technique is used to simulate the typical working conditions, and the influence of the rectifier on the internal flow of the draft tube is discussed. The results show that under normal operating conditions, the pressure distribution of the outlet section of the draft tube is relatively uniform, and when the diameter of the rectifier cylinder is 1.05D1, the increase of the pressure is most obvious. Under different conditions, the hydrostatic distribution of the center of the inlet cross-section of the draft tube and the pressure distribution of the central axis cross-section are calcula-ted, and the pressure fluctuation of the recording point on the wall surface of the inlet pipe at the inlet is monitored. It is concluded that the rectifier has a positive effect on improving the distribution of the pressure field of the draft tube and inhibiting the effect of cavitation when the diameter of the rectifier cylinder is 1.05D1. The pressure gradient of the axial center is reduced in the draft tube with recti-fier. At the inlet cross-section of the draft tube, the vortex is dispersed and the number is reduced, and the pressure difference between the axial center and the wall surface of draft tube is reduced, and the stability of the flow field of the draft pipe increases.
2018 Vol. 36 (2): 124-128 [Abstract] ( 595 ) [HTML 1KB] [ PDF 1836KB] ( 818 )
129 Credit evaluation of water conservancy engineering contracting enterprises based on grey comprehensive evaluation model
FENG Wanru*, LIU Yongqiang
In order to evaluate the credit of water conservancy project contracting enterprises, using grey system theory, the evaluation index system is established from six aspects of comprehensive quality, competitive ability, management level, financial condition, market behavior and enterprise reputation,using the improved grey relation degree method to determine index weight; in addition, the five grade evaluation standard is put forward, and the grey comprehensive evaluation model is constructed.Using the constructed water conservancy project contracting enterprise credit evaluation grey model and taking the new Shuhe River project in Jiangsu Province as an example of a contracting enterprise credit evaluation,it is concluded that the comprehensive credit rating is "general", which is consistent with the conclusion of fuzzy comprehensive evaluation method. Credit details show that the enterprise has better competitive ability, general management level, general financial condition, general reputation, and needs to be improved in the market behavior, in the future, attention should be paid to improving the construction quality, perfecting the rules and regulations and construction records, strictly implementing the acceptance procedures and safety production, and reasonably arranging the construction schedule. Research shows that the grey comprehensive evaluation model for water conservancy project contracting enterprise credit evaluation is feasible and effective, and helps enterprises to improve their own shortcomings, and is of certain reference value to the optimum ranking of water conservancy project contracting enterprises.
2018 Vol. 36 (2): 129-135 [Abstract] ( 531 ) [HTML 1KB] [ PDF 1294KB] ( 850 )
136
2018 Vol. 36 (2): 136-140 [Abstract] ( 487 ) [HTML 1KB] [ PDF 2058KB] ( 673 )
141 Effect of concave-out′s asymmetric airfoil on flow field of H-type vertical axis wind turbine
LI Shoutu,,*, YANG Congxin,,, SHI Guangtai, ZHANG Xuyao,
The H-type vertical axis wind turbine(H-VAWT)is a classic lift-driven vertical axis wind turbine, and it has cluster developing potential and advantages.The research method of numerical simu-lation is adopted and the two-dimensional model is established, flow field structure of H-VAWT of the concave-out′s asymmetric airfoils is analyzed, as well as the flow field distribution is analyzed when the blade numbers of H-VAWT of the concave-out′s asymmetric airfoils change. The results showed that the wake turbulence of H-VAWT of the concaver-out′s asymmetric airfoils is more intense than that of the concaver-in′s asymmetric airfoils, and the recovery capability of wake is weaker, thus influencing the distribution of H-VAWT in the wind field, but regardless of the concave-out and concave-in, the distribution of flow field is basically the same that of out flow field near the turbine; With the increase of blade number, the wake turbulence intensity resulting from H-VAWT of the concave-out′s asymmetric airfoils increases, but regardless of the concave-out and concave-in,the turbulence produced is basically the same when blade number is 3.
2018 Vol. 36 (2): 141-145 [Abstract] ( 705 ) [HTML 1KB] [ PDF 1749KB] ( 878 )
146 Enhancement approaches of aerodynamic performance of lift-type vertical axis wind turbine considering small angle of attack
ZHAO Zhenzhou*, QIAN Siyue, ZHENG Yuan, WANG Ruixin, ZENG Guanyu
The azimuth angles of 0° and 180° are zero and the torques of both azimuth angles of vertical wind turbine are negative during the blade rotating in a circle with angle of attack in the conversion of positive and negative as well, thus reducing the average torque of the blade and the overall perfor-mance of the lift-type vertical axis wind turbine. This paper summarized the research status of performance improvement of the lift-type vertical axis wind turbine nowadays, pointed out that the current research was mainly aimed at improving the high-performance area of the big angle of attack in the impeller overall body, blade structure and flow field situation instead of reducing the impact of small angle of attack area. In order to solve this problem, two methods of improving the aerodynamic performance of vertical axis wind turbine considering the effect of small angle of attack are proposed: the interference airflow method and the new variable-pitch strategy. The former mainly eliminates the 0 ° and 180 ° azimuth angles of the zero angle and the negative moment, the latter reduces the influence of the special azimuth angle by changing the range of the high performance area and produces a new performance point. Double disk multi-flow tube model is established based on the blade momentum theory. It is applied to the NACA0012 airfoil, the two-blade Φ type and the H-type vertical wind turbine with the rotation radius of 2 m, and the corresponding programming is calculated by Matlab programming language section. The results show that these two methods greatly reduce the negative torque range and the overall effect is improved significantly, and the up disk is better than the down disk.
2018 Vol. 36 (2): 146-153 [Abstract] ( 780 ) [HTML 1KB] [ PDF 1707KB] ( 1412 )
154 Drag-lift conversion characteristics of vertical axis wind turbine with adapting wind speed
QU Jianjun, WANG Jingyuan*, XU Mingwei, LI Yan
In order to study change rules of VAWT-SWS operating mode, a vertical blade wind turbine with movable and fixed blades was designed and fabricated. At the same time, a straight blade vertical axis wind turbine with the same shape as the movable-fixed blade was produced. Under the condition of fixed wind speed and wind turbine height, influences of the number of blades and diameter of wind turbine on the drag-lift operation mode of self-adaptive wind speed vertical wind turbine were studied by increasing the number and length of the support arm. By means of wind tunnel experiment, the variation of torque of wind turbine with speed ratio is obtained, and compared with the vertical wind turbine with the same parameters, the working mode of the adaptive wind speed vertical axis wind turbine was determined by the proximity of the torque as the criterion. The results show that under certain conditions, the adaptive wind speed vertical axis wind turbine can automatically convert the wor-king mode, which can reduce the required speed ratio for wind turbine resistance conversion by increasing the number of blades, and increases the required speed ratio by increasing the diameter of the wind turbine. The results can provide theoretical guidance for the design of adaptive wind speed vertical axis wind turbine.
2018 Vol. 36 (2): 154-158 [Abstract] ( 650 ) [HTML 1KB] [ PDF 1567KB] ( 766 )
159 PIV visualization experiment on static flow field of Savonius wind turbine
LI Yan,, ZHAO Shouyang, QU Chunming, FENG Fang,, LI Qizhi
In recent years, the vertical axis wind turbines (VAWT) which take Savonius wind turbine as a typical representative have rapidly developed. In order to verify the influence of Savonius wind turbine parameters on static starting performance, the overlap ratio was taken as a study object, and three kinds of Savonius wind turbine models with different overlap ratios, namely 0, 02, 05 were selected, using PIV test system to analyze flow field around blades under the conditions of the same Reynolds number and different azimuth angles. At the same time, the numerical simulations were carried out for the corresponding models, and the torque characteristics and surrounding flow field were analyzed. The distribution of vortex and energy utilization of Savonius wind turbine with different overlap ratios were revealed by comparing the experimental with the calculated result. The results show that the rotor with a certain degree of overlap ratio can eliminate vortex flow near the blade attachment surface, which can make the flow more stable, enhance the torque coefficient and improve the static starting performance; however, too large overlap ratio will weaken the direction of the airflow in the clearance, and it is easy to cause new vortex which reduces its static starting torque, so only the appropriate overlap ratio can improve the static starting performance of Savonius wind turbine.
2018 Vol. 36 (2): 159-165 [Abstract] ( 662 ) [HTML 1KB] [ PDF 4319KB] ( 1170 )
166 Analysis of vertical axis wind turbine power changing with rotating speed from vertical and horizontal flow fields
JI Wenju,, WANG Jianwen,, XUE Shuo*, XIAO Chang, GAO Zhiying,
To further clarify the effect of the rotor′s rotating speed on the vertical axis wind turbine′s power output, taking a small vertical shaft wind turbine as the study object, based on the Fluent calculation software, using the SST k-ω turbulence model combining with sliding grid technology, and using the SIMPLE algorithm iteration and the second-order windward format, we calculated the vertical axis wind turbine in the unsteady state and obtained the wind turbine′s power output at different rotating speeds. Comparing the calculated with the experimental result, we confirmed the law of wind turbine′s power changing with a rotating speed. Wind turbine′s velocity field study gives the wake velocity contours of the longitudinal profile at different locations, and the low-speed section in the wake longitudinal profile velocity contours presents a vertical symmetry and horizontal asymmetry phenomenon. At the same time, by comparing the wind turbine′s wake flow field longitudinal profile velocity contours and the horizontal vorticity field contours at different rotating speeds, it is found that wind turbine has the maximum absorption wind energy and the minimum vorticity loss at a rated speed. And the cause of this phenomenon is analyzed. From the longitudinal flow field and the transverse flow field, we analyze the reason for wind turbine′s biggest power output at the rated speed,more clearly revealing the mecha-nism of wind turbine′s output power changing with the rotating speed. Research, from a dual angle of the longitudinal cross-section and the horizontal cross-section, shows the change of wind turbine′s flow field, which can provide the reference for the design of the vertical axis wind turbines and the aerodynamic performance improvement.
2018 Vol. 36 (2): 166-171 [Abstract] ( 569 ) [HTML 1KB] [ PDF 1666KB] ( 919 )
172 Characteristic analysis of dry-wet condition and temperature trend in Yuanmou dry-hot valley(DHV)in resent 60 years
LIU Yanwei, WANG Shuying*, TU Xinglei, YANG Qiliang
In order to study the characteristics of the dry-hot conditions in recent 60 years in Yuanmou dry-hot valleys(DHV)area, this paper selects the micro-meteorological data collected from the Yuanmou Meteorological Station to calculate the reference crop evapotranspiration and relative moisture index. Trend and mutation were calculated and analyzed by linear propensity estimation me-thod, Mann-Kendall method and sliding t-test method. The results showed that the average humidity was increasing in the annual and seasonal scale, seasonal average humidity size is summer> autumn> winter> spring. Climate tendency rate size is winter(1.99%/10 a)>spring(1.43%/10 a)>autumn(1.21%/10 a)> summer(0.93%/10 a). The seasonal average temperature and the minimum temperature showed a trend of decline, summer> spring> autumn> winter. Climatic tendency rate in the following order: spring> winter.>summer> autumn. The maximum temperature in summer was the highest and the trend was decreasing. On the annual and other seasonal scales showed a trend of decline. The biggest temperature increased in spring. Yuanmou dry-hot valleys(DHV)area towards the direction of the development of wet and cooling, the drought situation has eased. The drought situation is still grim, spring and summer is the key stage of drought resistance.
2018 Vol. 36 (2): 172-178 [Abstract] ( 729 ) [HTML 1KB] [ PDF 1642KB] ( 889 )
179 Experiment study of effects of strength and stress-strain curve characteristics of Ordos Pisha-sandstone remolded soil
LI Mingyu, LI Xiaoli*, CHEN Suhang, ZHANG Qiang, CHANG Ping, WU Shangyun
The research area of this research project is Zhungeer Banner in the southern part of Erdos, Inner Mongolia, with the local reddish purple sandstone remolded soil as the research object. This test is conducted under different numbers of freeze-thaw cycle and different confining pressure by using TSZ-6A full automatic static triaxial apparatus. The results show that: in each of the freeze-thaw cycles under different confining pressure, Pisha-sandstone remolded soil stress-strain curve presents the characteristics of the strain hardening; stress-strain curve roughly experiences three stages with the increase of axial strain: Nearly completer elastic range and Strain hardening stage and Yielding stage. In order to quantitatively analyze the strength parameters of Pisha-sandstone under different freeze-thaw cycles, the strength parameter degradation coefficients KC and KΦ were introduced, and the degradation trend function of strength parameters was obtained by fitting the degradation coefficient curve.Then analyze the hardening properties and softening properties of stress-strain curve of Pisha-sandstone remolded soil after comparing the relationship between Pisha-sandstone peak strength and residual strength under different numbers of freeze-thaw cycle. Utilize Kq to analyze the deformation of Pisha-sandstone directly.
2018 Vol. 36 (2): 179-184 [Abstract] ( 552 ) [HTML 1KB] [ PDF 1518KB] ( 870 )
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