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Journal of Drainage and Irrigation Machinery Engin
 
2014 Vol.32 Issue.10
Published 2014-10-25
article
Article
829 Numerical simulation of vortex breakdown in conical chamber
Dou Huashu, Xiao Meina
Vortex breakdown of swirl flow in an enclosed conical chamber with a rotating bottom wall was studied by numerical simulation, and the influences of Reynolds number and geometric parameters on the development mechanism of vortex breakdown phenomenon were analyzed. The flow was go-verned by the unsteady three-dimensional incompressible Navier-Stokes equations. The finite volume method was used to discretize the governing equations and the Semi-Implicit Method for Pressure Linked Equation(SIMPLE)algorithm was employed to couple the solutions of the system. The unstructured grid is applied to divide the computational domain. The development characteristics of vortex breakdown in the conical chamber derived from the simulation results are as follows: the low pressure region of vortex breakdown with local fluid recirculation would appear near the axis in the conical chamber when the Reynolds number reaches a critical value. As the Reynolds number increases further, the size of the vortex breakdown bubble increases first and then decreases until it disappears and it moves away from the driving surface within the parameter range studied. However, the position where the vortex breakdown first appears and disappears doesn′t change with the variation of the geometry for the conical chamber with the same aspect ratio. From the values of the critical Reynolds number when the vortex breakdown bubble appears, conical chamber suppresses the generation of vortex breakdown compared with cylindrical chambers and the conical chamber(H1/H=0)with the maximum diameter of the top surface has the best suppress effect.
2014 Vol. 32 (10): 829-834 [Abstract] ( 1250 ) [HTML 1KB] [ PDF 3220KB] ( 1462 )
835 Thermodynamics effect on cavitation for high temperature water
Wang Wei, Lin Yin, Wang Xiaofang, Wang Yiming
In order to study the temperature difference in cavitation field for water at room temperature and high temperature and to reveal thermodynamic effect on cavitation, the cavitation field on NACA0066(MOD)airfoil surface was simulated with CFD software based on mass transport equation and full cavitation model. Source term that depicts the thermodynamic effect was added in energy equation by importing UDF code and the saturated vapor pressure was set as a function of temperature. The results show that temperature altered in cavitation field because of absorption of latent heat when cavita-ting, and cavity zone temperature is respectively 0.13, 0.84, 13.00 K lower than that of upper steam, which is respectively at 293, 373, 473 K. In other words, the higher the temperature of the fluid, the greater temperature drop is in cavity zone. Moreover, with decrease of saturated pressure caused by the decrease of local temperature, the length of cavity is shortened.
2014 Vol. 32 (10): 835-839 [Abstract] ( 1303 ) [HTML 1KB] [ PDF 2559KB] ( 1911 )
840 Effects of particle diameter on erosion wear performance of slurry pump
Wang Jiaqiong, Ye Qun, Yan Kewei, Feng Yaoning, Yu Xunan
In order to investigate the influence of particle diameter on erosion wear performance of slurry pump delivering solid-liquid two-phase flow medium, the motion trajectory of particles with diffe-rent particle diameter is calculated based on Lagrange method, k-ε turbulence model, discrete phase zero equation model and Finnie ductile materials erosion model. The impact velocity, impact angle and other parameters between solid particle and machine surface were evaluated by numerical simulation, and the wear rule of solid-liquid two-phase flow in slurry pump are discussed. According to the simulation results,the particles with small diameter distributed relatively uniform in the flow path, had a very small probability of in collision with the hydraulic components, and the erosion wear of the blade was relatively weak. By contrary,the solid particle with large diameter was apt to move toward to the pressure surface and impacted the leading edge of the blade.The impact angle and velocity of the particles with large diameter was greater to the blades and the volute circumferential wall than the small ones, and the erosion wear of the blade was relatively strong. And the large particles might in collision with the hydraulic components many times in the flow channel, causing serious erosion.
2014 Vol. 32 (10): 840-844 [Abstract] ( 1452 ) [HTML 1KB] [ PDF 2134KB] ( 1669 )
845 Rotor dynamic feature of core pulling mixed flow pump during startup process
Liang Xing
Focusing on the abnormal vibration of a core pulling mixed flow pump, the vibration causes were explored by the tested signal analysis, and then the rotodynamic model was established based on the Lagrange equations, which complies with the energy conservation. Comparing the peak-peak va-lue and vibration frequency of tested signals with that of simulated signals, the simulation precision was verified, and the start-up characteristics, such as the shaft orbit and vibration frequency, were simulated to search the vibration mitigation measures. The test signal analysis shows that, the impact force at the start-up process causes the rotor misalignment, and the misalignment will reduce but not disappear when the pump′s rotational speed reaches the design value. The simulation results verify the precision of test analysis, and the internal connection between the accompanied impact force and units vibrations was studied. The powerful impact force is more likely to induce the severe vibration and misalignment. Because the accompanying impact force is induced by motor direct start, to improve unit start-up mode and reduce the impact force can weaken vibration and enhance the operation reliability effectively.
2014 Vol. 32 (10): 845-851 [Abstract] ( 1382 ) [HTML 1KB] [ PDF 2359KB] ( 1427 )
852 Effect of filing blade outlet on centrifugal pump flow field and impeller strength
Bai Yu, Liu Houlin, Dong Liang, Liu Yongfu, Wang Baoqin, Tang Xiaochen
The performance of centrifugal pumps can be improved through filing blade outlet when the head is slightly lower than the actual demand.After filing the impeller of a single-stage single-suction centrifugal pump, the head and efficiency rise by 9.8% and 6.7% respectively. The unsteady nume-rical simulation of whole flow field of the pump was executed at design condition with CFX software, and the change of the flow field was analyzed. Based on ANSYS Workbench, the one-way fluid-structure interaction of impeller was calculated and the effect of filing blade outlet on impeller strength was analyzed. Results show that, the increase of absolute velocity and the decrease of relative velocity can make the head increased after filing. The adverse pressure gradient on blade outlet edge with filed blades decreases obviously, preventing the separation of boundary layer. The losses of friction and se-paration are decreased, so the efficiency is improved. Impeller maximum equivalent stress changes with the phase after filing blade outlet. But the impeller maximum total deformation is greater than original impeller at every phase.The research provides a reliable method for improving flow field of centrifugal pump.
2014 Vol. 32 (10): 852-857 [Abstract] ( 1344 ) [HTML 1KB] [ PDF 2838KB] ( 1584 )
858 Vibration characteristics study of centrifugal pumps
Ma Huifang, Zhang Zhinan, Chu Hao
Effects of the flow rates on the vibration characteristics of a centrifugal pump were investigated using experimental methods and the flow rate three-dimensional spectrum graph methods. The test data at 5 test points under 7 flow rates, including small flow rates, high flow rates and the designed flow rate, were collected and analyzed. Results show that the relationship(V-Q)between vibration intensity(V)and flow rate(Q)is more complicated than that(η-Q)between efficiency(η)and flow rate(Q). Peaks of V-Q curves are related to fluid-induced vibration during the changing process of flow rate. There have significant difference between V-Q curve of axial vibration test and that of radial vibration test, while the latter basically have the same trend. Flow rate three-dimensional spectrum graph is able to reflect the changing process during the flow rate change. In addition, the spectrum characteristics of the fluid-induced vibration and the relationship between the best efficiency point(BEP)and vibration intensity were discussed.
2014 Vol. 32 (10): 858-863 [Abstract] ( 1348 ) [HTML 1KB] [ PDF 3205KB] ( 1659 )
864 ANN based modeling and transient process optimization of pumped storage power station
Zeng Hongtao, Wang Zhixin, Tian Wengang, Lin Linlin
Modeling and parameters optimization in transient processes of governing system of large a pumped storage power station with long pipeline were studied. According to the actual parameters of a certain pumped storage power station, Matlab/Simulink toolbox was utilized for modeling and simulation of these subsystems. More specifically, friction resistance coefficient and water elasticity were taken into consideration in modeling of pressure diversion system with long water pipeline to accurately simulate hydraulic vibration characters in the pipeline. BP neural network and RBF neural network were adopted and compared in modeling of pump turbine to avoid the errors caused by dealing complex "S" characteristic curve of pump turbine. Based on the established pumped storage governing system simulation model, improved orthogonal experiment method was applied in parameter optimization and simulation of no-load frequency disturbance transient, load disturbance transition and load shedding transient of pumped storage governing system. According to the results, the established model can reflect the actual characteristics of pumped storage units to some extent, and improved orthogonal experiment method is efficient and effective in figuring out the best parameter group within the given scope. The results can provide guidance for modeling of governing system of large pumped storage units, and can set references and theoretical basis for actual optimal control of transient processes in pumped sto-rage units.
2014 Vol. 32 (10): 864-870 [Abstract] ( 1706 ) [HTML 1KB] [ PDF 1600KB] ( 1539 )
871 Effects of closing characteristics of surge anticipation valve on water hammer for a pumping station
Wang Ling, Wang Fujun, Li Xuenan, Zou Zhichao
In order to get the hydraulic performance of surge anticipation valve on water hammer protection, the mathematical models of pump and surge anticipation valve were established. Effects of 5 closing characteristics of surge anticipation valve on water hammer process in a pumping station at Ningxia Guyuan area were analyzed by means of method of characteristic. The results show that the water leakage reaches maximum when the surge anticipation valve with needle valve type is in fully open. The flow decreasing rate through the valve is approximately equal to the valve′s opened area decreasing rate in the closing process of the valve. The pressure surge at the outlet of pumping station tends to reach a new steady state rapidly if the surge anticipation valve with butterfly valve type is adopted. It also turns out that when the closing characteristics of surge anticipation valve is from increasing dece-leration to decreasing deceleration, the highest pressure values tend to decline and the lowest pressure values tend to increase for the entire system. Therefore, better water hammer protection effect is obtained with the closing characteristic as decreasing deceleration.
2014 Vol. 32 (10): 871-876 [Abstract] ( 1174 ) [HTML 1KB] [ PDF 1532KB] ( 1630 )
877 An approximately analytical method of characteristics of spiral groove dry gas seals under slip flow conditions
Song Pengyun, Zhang Shuai
The film of dry gas seal is very thin at low speed, and the micro-scale effect slip flow has great influences on dry gas seals. In order to calculate the performances of dry gas seals at low speed, the spiral groove dry seals were taken as an example, and the effective viscosity coefficients equation was used to modify the pressure controlled equation from Muijderman′s spiral narrow groove theory. The modified equation was solved in order to find the influence law of different slip flow models to dry gas seals′ opening force, leakage rate and film stiffness. The result from above equation is compared with the result from the finite element method under different shaft speeds and film thicknesses. The comparison indicates that the results of opening force, leakage rate and film stiffness based on the approximately analytical method quite close to the results from the references. When the gas film thickness is 0.6-1.2 μm at the same shaft speed, the opening force and film stiffness decrease while increasing the film thickness. The opening force, leakage rate and film stiffness increase with the increasing shaft speed. The result of different slip flow models are basically in coincidence.
2014 Vol. 32 (10): 877-882 [Abstract] ( 1103 ) [HTML 1KB] [ PDF 1623KB] ( 1483 )
883 Mesoscopic seepage field of saturated soil with lattice Boltzmann method
Shen Linfang, Wang Zhiliang, Li Shaojun
According to the porosity of soil, the two dimensional porous structure of soil is established by using random allocation method. Based on Lattice Boltzmann method, the two dimensional model for simulating saturated soil seepage is constructed by setting the non-equilibrium extrapolation scheme at the inlet and outlet boundary, and the bounce-back scheme at the soil particles boundary as well as left and right boundary. The corresponding matlab program is programmed to simulate the velocity distribution of seepage field with constant soil porosity and inlet velocity. The results show that the velocity in the whole seepage area is relatively uniform in the process of seepage. The velocity is higher in the region of good connectivity and large porosity.The greater of the soil porosity, the higher of seepage velocity, and the majority of seepage velocity is lower than the inlet velocity. When soil porosity is constant, the higher of the inlet velocity, the wider of the distribution of seepage velocity. Therefore, lattice Boltzmann method could effectively simulate the seepage condition of soil and provide a new research approach for further study of seepage mechanism.
2014 Vol. 32 (10): 883-887 [Abstract] ( 1090 ) [HTML 1KB] [ PDF 1925KB] ( 1750 )
888 Aerodynamic performance of H type vertical axis wind turbine under condition of low wind speed
Yang Congxin, Li Shoutu, Wang Xiuyong
Based on independently developed airfoil of H type vertical axis wind turbines(H-VAWT)as the research object, the aerodynamic performance and three-dimensional effect of H-VAWT at the low wind speed condition are analyzed using the numerical simulation methods.The results showed that at the low wind speed condition, the change of the wind speed or rotating speed have a significant influence on the performance of the H-VAWT while keeping the tip speed ratio constant. The tip speed ratio is more sensitive than rotational speed considering the effect of wind speed. For the low wind speed case, H-VAWT works in the low tip speed ratio area,even if the rotational speed is high. Setting reasonable wind speed and rotational speed is necessary in the numerical simulation. Without considering the wind shear, three-dimensional effect is influenced by the tip vortex. The tip vortex mainly located in 0° azimuth angle play an important role. The three-dimensional effect is also influenced by the flow field inside, and the effect increases while the rotational speed increases. Further research on H-VAWT can use these results as references. 
2014 Vol. 32 (10): 888-893 [Abstract] ( 1416 ) [HTML 1KB] [ PDF 2972KB] ( 1308 )
894 Accurate models of interpreting soil electrical conductivity based on EM38-MK2
Lü Zhenzhen, Yang Jingsong, Liu Guangming
Takes the modern Yellow River Delta as the object of study, soil electrical conductivity(1∶5)was measured in laboratory by collecting soil samples stratified and apparent soil electrical conductivity in horizontal and vertical mode measured at the sampling points by EM38-MK2. In order to investigate models to interpret soil conductivity based on electromagnetic induction meter(EM38-MK2), the relationship between soil electrical conductivity at different depths and soil apparent electrical conductivity under different modes respectively was studied using regression and multiple stepwise regressions to assess soil salinity distribution pattern rapidly at different depth in regional scale. The results show that soil apparent electrical conductivity of each mode has a significant correlation with soil electrical conductivity at different soil layers. Interpretation accuracy of soil electrical conductivity is higher in combined soil electrical apparent conductivity of each mode than that single-mode; prediction accuracy of electrical conductivity for subsurface soil and deep soil are increased by combining soil apparent electrical conductivity with surface soil electrical conductivity. The results may provide ideas for rapid measurement and evaluation of soil salinization and saline soil improvement and utilization to save costs and improve efficiency.
2014 Vol. 32 (10): 894-900 [Abstract] ( 1165 ) [HTML 1KB] [ PDF 2303KB] ( 1371 )
901 High-speed photography analysis on cavitation of Venturi injector
Yan Haijun, Wang Zijun, Chen Yan
During the operation of Venturi injector, when the negative pressure in throat portion gets lower, the suction flow rate will increase. But a lower negative pressure will cause cavitation easily, which may damage the surface of internal structures and finally affect the suction flow rate and the fertigation uniformity of micro-irrigation system. The internal flow of a Venturi injector with 1.5 inch dia-meter for both inlet and outlet was observed using high-speed photography technique. The relations between the cavitation characteristics, the inlet pressure, and pressure differences between inlet and outlet were analyzed. The impact of cavitation on the injection performance was also investigated. The results indicate that the cavitation occurred firstly in the junction of constriction and throat portions. With the increase of the pressure difference, cavitation gradually aggravated and the bubbles extended from the throat to the diffusion portion, meanwhile the growth rate of the suction flow rate decreased gradually. When the pressure difference increased to a certain value, the critical cavitation occurred, while the suction flow increased no longer. The increase of suction flow rate would impact on the working fluid, causing the bubbles to move toward the upper side of the diffusion portion and distributed unevenly. The reflux phenomenon occurred obviously in the rear of the diffusion portion leading the bubbles shed periodically.
2014 Vol. 32 (10): 901-905 [Abstract] ( 1401 ) [HTML 1KB] [ PDF 1648KB] ( 1536 )
906 Influence of dripper discharge on cotton root distribution and water consumption under pot cultivation
Sun Hao,, Li Mingsi, Li Jinshan,, Han Qibiao,, Feng Junjie,, Jia Yanhui,
Taking cotton as subject, cotton root distribution and water consumption were measured at each growth stage under five different dripper discharge(0.5,1.0,1.5,2.0,2.5 L/h). The results show that in the soil depth direction, cotton root length didnot concentrate in the surface layer, but 10-30 cm under soil surface, and with dripper discharge increasing, the mostly concentrated place of root length transferred to shallow soil layer. The vertical distribution of cotton root weight could be described as the negative exponential function of soil depth, the largest root weight was observed in soil surface layer, and the ratio of deep root weight declined with the dripper discharge increasing. On the horizontal direction, the cotton root length and root weight all reduced gradually from the cotton stem to both sides of it, and with dripper discharge increasing, the ratio of root length(or root weight density)below the cotton stem decreased, but the ratio of root length(or root weight density)in both sides increased, cotton root changed from compact structure to extended structure. The field water consumption of cotton in the whole growth period showed as bimodal type curve, but with dripper discharge increasing, water consumption intensity at seedling stage increased, the moment of water consumption depth moving down delayed, and the highest water consumption period postponed. 
2014 Vol. 32 (10): 906-913 [Abstract] ( 1205 ) [HTML 1KB] [ PDF 2015KB] ( 1487 )
914 Structural and fractal characteristics of biofilm attached on surfaces of sediments in Yellow River for drip irrigation
Wang Weinan, Xu Feipeng, Zhou Bo, Feng Ji, Li Yunkai
Drip irrigation with Yellow River water has become an important way to solve water shor-tage. However, emitter clogging is a major problem for extending drip irrigation. The scanning electron microscope(SEM)technology and fractal theory were used to analyse the surface topography characteristics of sediment particles in the Yellow River. The results showed that there was a complex biofilm on the surface of sediment particles, which consisted of solid suspended particles, microorganism and extracellular polymers(EPS). The surface topography of sediment particles expressed the fractal and multifractal characteristics, while the multifractal singularity spectrum was more suitable to characterize the complex surface topography of sediment particles.With its huge surface area, a large amount of microorganism could be adsorbed on the sediment surface in the Yellow River, and the extracellular polymers secreted by microorganism was up to 276.08-360.68 mg/L. Innovative or novel control strategies need to be established for emitter clogging of drip irrigation with Yellow River water. The sediment particles and the interaction between sediment particles and microorganism should both be considered to seek more effective methods to control emitter clogging. 
2014 Vol. 32 (10): 914-920 [Abstract] ( 1119 ) [HTML 1KB] [ PDF 11500KB] ( 918 )
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