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Journal of Drainage and Irrigation Machinery Engin
 
2018 Vol.36 Issue.1
Published 2018-01-25
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2018 Vol. 36 (1): 0- [Abstract] ( 497 ) [HTML 1KB] [ PDF 1162KB] ( 1780 )
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2018 Vol. 36 (1): 0- [Abstract] ( 477 ) [HTML 1KB] [ PDF 1792KB] ( 1823 )
1 Progress and prospects of investigation into unsteady cavitating flows
HUANG Biao，WU Qin,，WANG Guoyu
In view of numerically computational models for unsteady cavitating flows, influences of mass transfer model between liquid and vapor phases on cavity development and vortex shedding were summarized. It was identified that cavitation models could produce significant different predictions in different cavity regimes. A density correction-based cavitation model(DCCM)has been proposed in our group, as a result, the unsteady pressure fluctuation characteristics in the wake of a hydrofoil was predicted reasonably well. By considering the multi-scale turbulence structure and local compressibility, a filter-based density correction turbulence model(FDCTM)was put forward and a better prediction was achieved against experimental data. Further, unsteady cavitating flow mechanisms were reviewed and discussed in detail based on existing experimental and simulation efforts on such flows by accounting for cavity shape, flow structure and hydrodynamic force from a cavitating flow characteristic and hydrodynamics point of view. Finally, based on the development tendency of investigation into unsteady cavitating flows and important problems potentially encountered in such a research, specific development directions were debated and prospected.
2018 Vol. 36 (1): 1-14 [Abstract] ( 1119 ) [HTML 1KB] [ PDF 3722KB] ( 2426 )
15 Cavitation characteristics of multiphase pump at low flow rate
LIU Xiaobing,, HU Quanyou, SHI Guangtai,, ZHAO Qin,
The hydraulic performance of multiphase pump is poor at low flow rate. To improve its performance, the cavitating flow field in a multiphase pump was simulated numerically under low flow rate conditions by using the homogenous multiphase flow model, Rayleigh-Plesset equation and standard k-ε two-equation turbulence model. The transport properties of the pump were analyzed under several typical cavitation conditions and the distribution features of cavitation bubbles in the impeller were clarified. The head and efficiency curves of the pump were predicated and compared with the experimental results, validating the reliability of simulation results to some extent. The results showed that the flow around the blade leading edge and the rotor-stator interaction had a great influence on flow separation in the impeller at a low flow rate, and the low pressure zone formed with vortices could aggravate inlet cavitation and reduce the performance of the pump. Cavitation was generated at the blade leading edge near the blade mid-span at first. Then the cavitation got worse on the blade suction side near the leading edge, the closer to the hub, the worse the cavitation. The cavity on the blade suction side could even block the impeller flow passages and intensify the phase separation of flow in the impeller. These results provide a theoretical basis for design optimization, performance improvement and further experimental study on multiphase pumps.
2018 Vol. 36 (1): 15-20 [Abstract] ( 889 ) [HTML 1KB] [ PDF 3155KB] ( 2000 )
21 Numerical simulation of hydraulic turbines with forward-curved blades
LIU Yingying, YANG Sunsheng, KONG Fanyu, WANG Tao, CHEN Kai
The impellers of centrifugal pumps with three different specific speeds were designed with forward-curved blades to study their performance as turbine. Then, the whole internal flow filed in these hydraulic turbines were calculated with structured mesh technique. The performance curves, pressure and velocity fields at different flow rates were analyzed, and the variation of flow field in the impeller and draft tube with flow rate was obtained. The results show that the fluid pressure steadily decreases from the volute inlet to the impeller and draft tube outlet, and the pressure difference between the inlet and the outlet of hydraulic turbine increases gradually with increasing flow rate. A vortex region is found near the blade pressure side, and its position and size vary with flow rate. There is a peripheral velocity component in the cross-section of draft tube, its magnitude varies with flow rate. The hydraulic loss inside a hydraulic turbine with forward-curved blades mainly occurs in the impeller and accounts for more than 60% of the total hydraulic loss for three hydraulic turbines, further the percentage rises with increasing specific speed. Therefore, the optimization design of hydraulic turbine with forward-curved blades should be focused on the impeller.
2018 Vol. 36 (1): 21-27 [Abstract] ( 906 ) [HTML 1KB] [ PDF 2994KB] ( 2026 )
28 Numerical simulation on hemolysis induced by two-stage axial-flow blood pump during pulsating heart failure
ZHOU Bingjing, ZHANG Guijie, JING Teng, WANG Hao, HE Zhaoming,
To understand hemolysis of a blood pump in a pulsatile flow condition, a multi-scale model of the blood pump and cardiovascular circulatory system was built. This multi-scale model consists of a lumped parameter sub-model for the cardiovascular circulation and a three-dimensional distributed parameter sub-model for an axial-flow blood pump. Based on a specific two-stage axial-flow blood pump, the transient outlet pressure and flow rate through the pump were obtained by using the lumped model with Matlab simulation during a cardiac cycle under heart failure conditions. Then, according to the internal hemodynamic characteristics of the blood pump, the transient working condition was divided into a few flow rates, the hemolysis of the pump was predicted based on these flow rates in a quasi-steady manner. Finally, a time-weighted average hemolysis was calculated in one cardiac cycle. The results showed that the pump transient pressure difference-flow rate curve was a closed loop in one cardiac cycle due to the inertia of the blood pump. Besides, the hemolysis and pressure difference exhibited a similar variation trend in one cardiac cycle, the flow rate was in an opposite variation trend. In summary, the study showed that the method of multi-scale model can be used to estimate the hemolysis of a blood pump supporting patient with heart failure.
2018 Vol. 36 (1): 28-34 [Abstract] ( 789 ) [HTML 1KB] [ PDF 1627KB] ( 2185 )
35 Watershed model-based flash flood disaster monitoring and early warning system
JING Shuangyi, WANG Zejun, LI Weiping, XIN Mingliang, REN Bo, HUANG Lizhi
A flash flood disaster monitoring and early warning system was proposed in the paper based on watershed model to improve the accuracy and timeliness of the current system in use so as to minimize residents′ personal injury and private property damage in mountain areas. At first, the system design principle, construction purpose, and basic modelling method were introduced according to the requirements of national water conservancy administration on informatization construction, flash flood disaster prevention and control. Since the rainfall threshold was one key factor in the system, the problems in three existing common methods for determining the threshold, i.e. single station rainfall, regional rainfall, and P-III frequency hydrological curve estimation, were analyzed. Then a watershed rainfall-based method was put forward to decide the rainfall threshold. Finally, a watershed model-based flash flood disaster monitoring and early warning system was developed. The system was used to determine the rainfall thresholds in different periods with different water-holding capacities in some riverside villages in Datong County of Shanxi Province, and estimated thresholds were compared with the measured values. Results indicated that the measured rainfall thresholds were in between the thresholds in high-water-content and low-water-content soils, suggesting the method was feasible. The built watershed-based flash flood disaster monitoring and early warning system for Datong County has promoted mountain flash flood disaster prevention and control work in Datong.
2018 Vol. 36 (1): 35-41 [Abstract] ( 799 ) [HTML 1KB] [ PDF 1307KB] ( 2211 )
42 Influence of tee minor hydraulic loss model on draft tube inlet pressure and upsurge in surge chamber
CHU Shanpeng, ZHANG Jian, YU Xiaodong
Transient hydrodynamic flow in the penstock of a pumped storage power station with surge chamber was simulated numerically in the paper by using method of characteristic and by involving pipe elasticity and water body inertia. In the simulation, the pipe tee was considered as a computational node, the minor hydraulic loss across it was modelled respectively with a constant minor hydraulic loss coefficient, Gardel formula and experimental data. Influences of three models on the pressure at the draft tube inlet and upsurge in the surge chamber were identified. Results showed that the impedance based on the constant minor hydraulic head loss coefficient was the minimum, and the corresponding maximum upsurge and minimum pressure at the draft tube inlet were the highest. The impedance based on the experimental data was the maximum, and the corresponding maximum upsurge and minimum pressure were the lowest. The impedance based on the Gardel formula was in between. The conclusion can provide a reference for estimating maximum upsurge and minimum pressure at draft tube inlet in hydraulic engineering.
2018 Vol. 36 (1): 42-49 [Abstract] ( 934 ) [HTML 1KB] [ PDF 1925KB] ( 2335 )
50 Study of three-dimensional numerical simulation on hydro-brake with baffle
CHENG Wentao,, Wu Yanming,, LI Chao,,, MA Guangfei,, ZHANG Jian
The hydro-brake potentially can be applied to relieve urban waterlogging under a condition without reducing flow-through cross-sectional area. To judge whether it can operate properly in an actual working condition, the performance of a hydro-brake was simulated numerically by using VOF two-phase flow method in CFD. Results show that the experimental curve agrees well with the simulation one, as such the simulation method can reflect the flow characteristics better. The throttling efficiency of hydro-brake is about 18.2% without baffle, but is improved by about 22.7% after a baffle was added. The throttling efficiency of hydro-brake with baffle is generally more than 30.0%, depending on the deflection angle nonlinearly. Specially, if the angle is about 15°, the throttling efficiency can reach as high as 40.9%. 
2018 Vol. 36 (1): 50-54 [Abstract] ( 765 ) [HTML 1KB] [ PDF 1514KB] ( 2098 )
55 Analysis on performance of dry gas seal in centrifugal compressor for transporting natural gas
SUN Xuejian, SONG Pengyun
Centrifugal compressors for transporting nature gas are usually with dry gas seals and applied in high pressure condition, thus generally the natural gas has to be used as lubricant of the seals. Under a high pressure condition, as a mixed real gas, the behavior of natural gas is quite different from that of ideal one. In this paper, the Redlich-Kwong equation was used to express the behavior of a mixed real gas, and the gas film pressure governing equations proposed by Muijderman for narrow grooves were modified and solved. Finally, based on various models for natural gas, influences of mixed real gas on the gas film pressure, leakage rate, film stiffness and opening force in a spiral groove dry gas seal was studied. Moreover, a comparison was made in sealing performance among the real natural gas, ideal natural gas case and methane(real gas and ideal gas). Results showed that the susceptibly compressed mixed real gas(Z<1)increased the leakage rate, pressure at the groove root, opening force and film stiffness, especially for the leakage rate. Although most component of the natural gas was methane, the sealing performance of natural gas was significantly different from that of methane gas. It was improper that the performance of dry gas seals in a centrifugal compressor for transporting natural gas was analysed by using methane gas only.
2018 Vol. 36 (1): 55-62 [Abstract] ( 733 ) [HTML 1KB] [ PDF 1954KB] ( 2178 )
63 Effects of post-irrigation aeration on pakchoi water use efficiency and nutrient uptake characteristics in three kinds of soil
LEI Hongjun,, LI Ke,, FENG Kai,, PAN Hongwei,, YANG Hongguang,
Post-irrigation aeration can improve anoxic environment of crop root rhizosphere and increase crop yield. Hence investigating into effects of post-irrigation aeration on crop growth and nutrient absorption characteristics can provide a scientific guidance for application of aerobic irrigation technique. Three typical soils(clay soil in Zhengzhou, silty loam soil in Luoyang and sandy loam soil in Zhumadian)in Henan Province were collected and pakchoi was selected as experimental crop. Two groups, namely post-irrigation aeration(MV)and control(CK), were established in pot experiments under subsurface trickle irrigation conditions in a greenhouse, and then the crop water use efficiency and nutrient absorption characteristics were studied. Results showed that the crop root activity, root dry weight and net photosynthetic rate in MV group were significantly improved compared with those in CK group. The transpiration rate in MV group was increased by 20.61%, 15.98% and 33.33% in the clay, silty loam and sandy loam soils, respectively. The yield and water use efficiency were increased by 38.08% and 52.70%, and the absorption efficiency of nitrogen, phosphorus and potassium were increased by 61.65%, 66.54%, and 104.83% in the clay soil. In the sandy loam soil, the absorption efficiency of phosphorus and potassium were increased by 50.60% and 73.65% and the absorption efficiency of phosphorus and potassium were increased by 40.84% and 26.19%. These differences in the parameters between MV and CK groups are all of statistical significance(P<0.05). As such post-irrigation aeration can improve both water and nutrient use efficiencies and yield of pakchoi in the clay soil significantly. 
2018 Vol. 36 (1): 63-68 [Abstract] ( 843 ) [HTML 1KB] [ PDF 1365KB] ( 2295 )
69 Effect of nutrient solution irrigation volume and frequency on winter and spring pepper under soilless cultivating conditions
WANG Shenglin, FAN Zhenling, GAO Yanming, LI Jianshe
To understand effects of nutrient solution irrigation volume and frequency on pepper growth, fruit quality and water use efficiency, a few experiments were performed by using a commercial nutrient solution named Yangdashuai based on soilless cultivation method. In the experiments, three nutrient solution irrigation volumes were provided, namely, in seedling stage, the nutrient irrigation volumes were W1(300 mL), W2(400 mL), and W3(500 mL)per plant in every day, in blossoming period, the volumes were doubled, in fruiting stage, the volumes were tripled. Further, three solution irrigation frequencies, such as T1(2 times per day), T2(3 times per day)and T3(4 times per day), were specified, and each frequency remained through the entire pepper growth period. The results show that when the nutrient solution irrigation volume was W2, the correlation between above ground part and underground part was the best for the pepper. The water use efficiency of W1T2 treatment was the highest, 18.13 kg/m3, unfortunately the pepper yield was the lowest. The total root surface area in W3T1 treatment was the largest, 754.54 cm3. In W3T2 treatment, the pepper was subject to the best growth, namely, the tallest plant and the biggest stem diameter, excellent fruit quality and better water use efficiency. Therefore, W3T2 treatment has provided the optimal nutrient solution irrigation volume and frequency.
2018 Vol. 36 (1): 69-76 [Abstract] ( 828 ) [HTML 1KB] [ PDF 1530KB] ( 2055 )
77 Rice tillering and plant height dynamic responses to drought and flood alternating stress
ZHANG Yidi, YU Shuang′en, GAO Shikai, WANG Mei,WANG Jiao, LI Si
In practice of rice production, rice plants are often in drought and flood alternating stress. In order to understand rice tillering and plant growing dynamics under drought and flood alternating stress, the influence of drought and flood alternating stress on number of tillering and plant height was studied by using pit test. Then, a dynamic model for number of tillering was used to fit the change of tiller, and a Logistic growth model was applied to fit the dynamic change of plant height. Results showed that the drought and flood alternating stress could inhibit rice tillering in different degrees in tillering, jointing booting, and flowering stages. Specially, flood could promote, but drought could suppress rice plant height to grow in tillering, jointing booting, and flowering stages. The dynamic model could fit the number of tillers well and had practical significance. The Logistic model could fit the dynamic height better and was feasible. The results in the paper can provide an effective and scientific basis for proposing rational irrigation schemes and improving rice yield. 
2018 Vol. 36 (1): 77-81 [Abstract] ( 801 ) [HTML 1KB] [ PDF 1365KB] ( 2027 )
82 Experiments on air and water suction capability of 30PY impact sprinkler
XIANG Qingjiang, XU Zhengdian, CHEN Chao
To allow an impact sprinkler to work in a low working pressure, an air admission structure can be installed coaxially in the water tube of sprinkler to form a water-air two-phase jet. The admitted air can make an impact sprinkler have a more uniform water distribution of irrigation. Further, the air admission pipe can convey liquid fertilizer or pesticide during irrigation, making the impact sprinkler multifunctional. In this paper, a series of experiments were carried out to investigate the capacity of an air admission structure for sucking both air and water into an impact sprinkler. The suction capacity is measured by water mass flow rate and vacuum degree. The structural parameters include inner diameter d, suction pipe engaging length L and nozzle convergent angle θ. All experimental work was conducted by employing 30PY impact sprinkler. When the nozzle convergent angle θ is increased from 30° to 65° under the same working pressure, the water flow rate reduced, and affected the two fluid mixing ratio in the sprinkler. The reference engaging length is zero, where the air admission pipe outlet jut meets the sprinkler nozzle outlet. When the suction pipe engaging length was varied in the range of -4 to 6 mm, the suction capability increased to the maximum from zero gradually and L=2 mm is recommend because the suction capability was close to the maximum at this length. The sucked water flow rate increased with increasing sprinkler working pressure and inner diameter. Results of this study have formed a base for air admission impact sprinkler application in engineering.
2018 Vol. 36 (1): 82-87 [Abstract] ( 1001 ) [HTML 1KB] [ PDF 1555KB] ( 1877 )
88 Numerical simulation of cavitation characteristics of Venturi injector
CHENG Qian, HUANG Xiuqiao, LI Hao, HAN Qibiao
The cavitation characteristics of one post-optimized Venturi injector were investigated by numerical simulation, in order to explore declination in the injection performance caused by cavitation and to reveal the mechanism of energy loss in the flow field of Venturi injector. Results show that when the pressure difference across the Venturi increases, the suction pressure decreases continuously and the suction flow rate rises. Once the suction pressure decreases to the minimum, the suction pressure will keep constant, so does the suction flow rate. Then if the pressure difference is increased further, cavitation will occur in the junction between the throat and the diffuser firstly, and then and expand downstream gradually along the diffuser wall. By contrasting the total hydraulic heads at various cross-sections along the Venturi injector axis at different pressure conditions, the energy loss at the throat increases with increasing pressure difference, but it is about half the total energy. Once the cavitation occurs, the energy loss at the throat will keep constant, while the energy loss across the diffuser will be enlarged. This is because cavitation development can deteriorate the flow condition in the diffuser and produce large-scale vortices around the cavities, which consume even more energy. The increased energy consumption results in a sudden and rapid decrease in the injection efficiency.
2018 Vol. 36 (1): 88-92 [Abstract] ( 1028 ) [HTML 1KB] [ PDF 1988KB] ( 2089 )
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