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Journal of Drainage and Irrigation Machinery Engin
 
2013 Vol.31 Issue.4
Published 2013-04-25
article
Article
277 Effects of blade geometry parameters on radial force and vibration of inline circulator pump
WU Deng-Hao, YUAN Shou-Qi, REN Yun, ZHANG Jin-Feng
To solve the vibration issue of one inline circulator pump with specific speed of 221, on the premise of having similar energy characteristics, the blade geometry parameters Z，β2，β1 were optimized to lower the vibration amplitude. In order to investigate the effects of blade geometry parameters on pressure pulsation, radial force and vibration of an inline circulator pump, by applying CFX, the full unsteady flow numerical simulations of inline circulator pumps in different flow conditions were executed both on preoptimized impeller A and postoptimized impeller B. The results indicate that the overall pressure pulsation, radial force and radial force fluctuation amplitude of impeller A are higher than those of impeller B; and blade passing frequency and its harmonics are the domain frequencies for pressure pulsation. Meanwhile, to get a deep understanding on the effect of radial force changing on vibration because of changing the blade geometry parameters, the experimental vibration tests were conducted to measure the vibration velocity of inline circulator pumps with impeller A and impeller B. Result is that vibration amplitudes of impeller A are higher than impeller B under different flow conditions, and blade passing frequency and its harmonics are the domain frequencies for pump vibration. In addition, to further study the effect of the changes of pressure pulsation and radial forces caused by changing blade geometry parameters on vibration, vibration velocities of the inline circulator pump with impeller A and impeller B respectively were measured. The vibration results show that, under different working conditions, the vibration amplitude of impeller A is stronger than impeller B. Blade frequency and its harmonics are the main incentives of the vibration of inline circulator pumps. The comparison between computational and experimental results shows that impeller A has higher vibration amplitude because there are higher pressure pulsation, radial forces and radial force fluctuation amplitude it served. The vibration velocity of postoptimized pump is lower than 1.8 mm/s in the flow range from 04Qd to 1.3Qd, and satisfies the ISO 10816 standard.
2013 Vol. 31 (4): 277-283 [Abstract] ( 1850 ) [HTML 1KB] [ PDF 2211KB] ( 2090 )
284 Numerical simulation of unsteady flow in multiphase rotodynamic pumps
YU Zhi-Yi, ZHANG Qin-Zhao, HUANG Ruo, CAO Shu-Liang
To further investigate the mechanism of phase separation and gas accumulation in multiphase rotodynamic pumps, on the assumption of tiny bubbly flow, based on a twofluid model, the gasliquid twophase unsteady flow in a multiphase rotodynamic pump, with an IGVF（inlet gas volume fraction）of 15%, was numerically simulated. In the simulation, the k-ε based SST (Shear Stress Transport) model was used for turbulence; the drag force and the added mass force were taken into consideration in the interfacial momentum transfer terms; the steady solution of single water phase flow was specified as the initial flow field. Under this IGVF, five flow rate conditions were simulated, and taking the most optimal working condition as an example, the twophase flow field and its temporal evolution were analyzed; the evolution characteristic and the calculation method of pump head were explored. The results show that, due to different centrifugal forces on the two phases, the gas is distributed mainly around the hub; affected by the change of the flow passage and the rotation of the impeller, the air mass starts to form at the inlet of the impeller. In addition, the gas volume fraction field and pressure field fluctuate in transportation, which results in severe oscillation of the pump head and instability of the pump system. The comparison of the head characteristics between the simulation and the experiment validates the reliability of the numerical model and method.
2013 Vol. 31 (4): 284-288 [Abstract] ( 1856 ) [HTML 1KB] [ PDF 1946KB] ( 1859 )
289 Casing modification and stress safety of boiler circulation pumps
FAN Yi-Zhang, ZUO Zhi-Gang, LIU Shu-Hong, SHA Yu-Jun, XU Ling-Jun
In order to reduce manufacture cost, it is proposed to modify one boiler circulation pump by using casting method instead of forge method and reducing internal radius of semispherical casing. Based on ASME Code Section Ⅷ Division 2, using Ansys Mechanical software, adopting finite element method (FEM), Miner′s rule and rainflow counting method, static strength usage factors and low cycle fatigue usage factors of four pump casings were calculated. The calculation shows that static strength usage factors and low cycle fatigue usage factors are all smaller than 1; when the internal radius is reduced to 0.875, maximum static strength usage factor is reduced by 7%, maximum low cycle fatigue usage factor by 84%; when wall thickness is increased to 1.375, maximum static strength usage factor is reduced by 19.5%, maximum low cycle fatigue usage factor is increased by 221.4%. The results show that casting material is stress safe; smaller radius can help improve static strength and greatly reduce low cycle fatigue; and larger wall thickness can greatly help improve static strength and significantly reduce low cycle fatigue.
2013 Vol. 31 (4): 289-293 [Abstract] ( 2424 ) [HTML 1KB] [ PDF 1814KB] ( 2235 )
294 Influence of impeller passage structure on performance of doublechannel pumps
ZHAO Bin-Juan, HOU Duo-Hua, CHEN Hui-Long, LIU Zhi-Bin
From the perspective of structural changes of impeller passage, the internal flow field in doublechannel pumps and flow characteristics were studied. Standard k-ε turbulent model and implicit multigrid coupling method were applied to numerically simulate the threedimensional inner turbulent flow of the wholepassage of three types of pumps (scheme a:up circle type, scheme b:straight line type, and scheme c:down circle type). Under  the same flow rate conditions, hydraulic performance were compared and optimal doublechannel impeller passage structure were explored between the three types of pump. It was found that different impeller channel structure presented a certain degree of regularity and diversity of velocity & pressure distribution under the design conditions. Efficient proper volume of impeller channel has been increased both in scheme a and scheme c. In comparison, scheme a has the superior nonblocking performance and the minimum hydraulic efficiency, with a clear pressure drop at the passage inlet; scheme c has the maximum hydraulic efficiency and the lowest head .Comprehensive analysis of the hydraulic performance and nonblocking performance, scheme b with the highest head of 14.46 m and the higher hydraulic efficiency of 78.24%,has superiority,Analysis of steady variable condition properly based on numerical simulation and corresponding test verification,scheme b is the optimum structure of impeller passage in doublechannel pumps.
2013 Vol. 31 (4): 294-299 [Abstract] ( 2155 ) [HTML 1KB] [ PDF 1713KB] ( 2227 )
300 Hydraulic design and performance analysis of low specific speed centrifugal pump
ZHANG Yong-Xue, ZHOU Xin, JI Zhong-Li, CHEN Long, SU Min
By using empirical correlations, basic geometry parameters of impeller were obtained. The impeller profile was adjusted according to given flow cross section area distribution and wrap angles distribution; and the position of the splitter blade was determined according to the relationship between the splitter blade deviation angle and Wiesner slip factor. Based on this method, using the same design parameters (head, capacity, rotation speed, etc) with different factors, four different low specific speed centrifugal pump impellers with different splitter blades (75%, 65%, 55%, 45% long blade length) were designed. By using RANS equations with RNG k-ε turbulence model, three dimensional turbulent flow fields of the designed impeller channels were calculated and analyzed. The effects of four different splitter blades on velocity distribution, pressure distributions along the flow channels and hydraulic performance of centrifugal pump impellers were studied. The results show that the hydraulic head of impeller can be improved by adding splitter blades; long splitter blades will increase hydraulic loss and fraction loss and the increased amount of hydraulic head increases as the splitter blade length decreases. With properlyselected design parameters and properlypositioned splitter blades, the flow in the pump can be improved and its hydraulic performance can be enhanced.
2013 Vol. 31 (4): 300-304 [Abstract] ( 2198 ) [HTML 1KB] [ PDF 2799KB] ( 1665 )
305 Numerical simulation of freesurface flow in updraftfreeexitflow hydropower turbine
YANG Wei, LIU Zhu-Qing, WU Yu-Lin, GAO De-Yu
To study the turbine′s internal flow more accurately and improve its hydraulic performance, a geometrical model of the whole flow passage, including casing and runner, was established. An unstructured grid was applied to segment the runner, encrypt the grids on the inner surfaces of the runner blades and the casing guide vane. The sizes of grid clusters were made to meet the y+ for turbulence simulation. Based on RNG k-ε turbulence model, the internal flow was simulated. Taking the effect of free surface flow into consideration, by applying volume of fluid method, a simulated internal flow in an updraftfreeexitflow turbine was obtained. On the basis of the computation of simulation results, the internal flow loss was analysed. It was found that the largest loss was between the stay vanes and the runner inlet, which amounted to 73% of the total loss. The flow details show that the step structure of the area was the direct cause of the loss and exacerbated the runner′s inflow condition. Accordingly, where and how to improve the turbine′s energy performance was inferred.
2013 Vol. 31 (4): 305-308 [Abstract] ( 1780 ) [HTML 1KB] [ PDF 1873KB] ( 1654 )
309 Aeration valve improvement of Liziping hydropower plant Francis turbine
ZHOU Tao, ZHANG Hai-Ku, ZHU Xiao-Min, LIU Xiao-Bing, LIU De-Min, DENG Ming-Gui
For Francis turbine, reasonable aeration can weaken vibration and cavitation effectively. The high head turbine of Liziping hydropower plant originally uses holes at turbine bearing flange root to aerate, and which can not have expected function for the whirl area and causes significant vibration. A project of setting cross aeration valve in draft tube is proposed. To prevent the device from falling off and reduce flow resistance and lower whirl whip reaction, the streamline shaped cross aeration was made of highquality stainless steel and had compensating holes placed in the center and back of it. According to the comparison of the vibrations, pressure fluctuations and air admission test before and after the modification, the results show that it can exactly and automatically supply air to the strong vibration region, effectively eliminate pressure fluctuation caused by draft tube whirl whip, the vibration of bearing, brackets and cover are reduced to different degrees respectively, and the draft tube cone swing completely solved. It works well for the stability of hydroelectricity generating units. For other small and mediumsized hydroturbine plants, the aerating device design is referentially valuable.
2013 Vol. 31 (4): 309-312 [Abstract] ( 3921 ) [HTML 1KB] [ PDF 1282KB] ( 2458 )
313 Optimal design for wind and tide with different return periods in Jiangsu seadike projects
YANG Xing, HE Yong, WANG Wei, CHEN Wen-Meng
 In order to obtain the optimal combination of the tide and the wind in seadike design, two different concepts of independent risk and related risk were put forward. Based on these concepts and the theory of probability, a computational model of the two risks was defined and the relationship between the two risks was analyzed. Accordingly, a method for optimizing the two design parameters (tide and wind ) was proposed. By applying the abovementioned optimal design method to some case studies of Lianyungang, Sheyangzha, Tianshenggang in Jiangsu province, it is found that, because of different change tendency between tide and wind, the assumption that tide and wind adopt the same frequency is too conservative for design; the characteristics difference between tide and wind causes regional difference of the best combination of the two parameters; the present Jiangsu seadike design standard of the tide level for "the fiftyyear return period encountering the 10th grade wind", from the perspective of optimal combination, can be further discussed regarding its rationality and safety. To ensure the seadike project′s safety and economy in seadike designing, the coordination between the two types of risks should be taken into consideration. This optimal design method can also be applied in other similar water engineering designs.
2013 Vol. 31 (4): 313-317 [Abstract] ( 1968 ) [HTML 1KB] [ PDF 1558KB] ( 1987 )
318 bearing rigidity on characterisitics of natural vibration of shaft system in hydroturbine generating unit
BAI Bing, ZHANG Li-Xiang, ZHAO Lei
To study the characteristics of the lateral natural vibration of the main shaft system in hydroturbine generating unit, with the finite element method the main shaft system was discretized; and with energy method the dynamic equation was obtained. Based on simplified actual parameters, with MATLAB software, fixed frequencies, mode shapes and critical speed of rotation of the shaft system were calculated and influences on critical speed caused by changes in the guide bearing rigidity were analyzed. The results show that when only one guidebearing rigidity is changed, up guidebearing has little influence on critical speed; however, the down bearing and the water guidebearing greatly affect the critical speed. There occurs a “saturated” phenomenon, that is to say, the critical speed remains unchanged when the rigidity reaches or exceeds a certain value. If the rigidity of the three guidebearings is increasing simultaneously, the critical speed can be increased significantly. Change in the up guidebearing has little effect on the modes in the first three orders; Change in the down guidebearing and water guidebearing will result in an opposite mode in a certain mode. It can be concluded that it is necessary to fully consider the effect caused by the guidebearing rigidity in evaluating the critical speed of the shaft system.
2013 Vol. 31 (4): 318-324 [Abstract] ( 2323 ) [HTML 1KB] [ PDF 1495KB] ( 1920 )
325 Numerical simulation of freesurface vortex and theoretical analysis on vortex/sink model
YANG Fan, SHI Xu-Ming, DAI Ren, GUO Xue-Yan, CHEN Tie-Jun, WU Yu-Lin
To study the formulation mechanism of suction vortex and put forward some related theoretical analysis, the phenomenon of freesurface vortex often observed above a drainage intake was simplified into a model of discharging sink water, which was simulated by using VOF (volume of fluid) method and RNG k-ε  turbulent model. The process of suction vortex evolving from freesurface vortex was numerically simulated. By comparing the calculated results with Burgers vortex theory, it is found that the tangential velocity distribution equation in Burgers vortex model agrees with the calculation; and that vortexes gather towards the center is one of the factors that cause the freesurface to depress and eventually become suction vortex. It is also found that the other two velocity distributions in Burgers vortex model, the radial and axial velocity distribution equations, in comparison with the calculation, were theoretically incorrect. To further simplify the model, ruling out tangential velocity, water discharge without vortex was simulated. To clarify the sink effect for surface depression, through theoretical deduction, based on spherical coordinate system, a kind of spherical sink model was proposed, with which a better velocity distribution equation was obtained. “Sink” effect is one of the important factors that lead to suction vortex phenomenon.
2013 Vol. 31 (4): 325-330 [Abstract] ( 1963 ) [HTML 1KB] [ PDF 5215KB] ( 2322 )
331 Simulation of fluid excitation dynamic characteristics of thermowell
CHEN Qing-Guang, XIE Bin, JIA Xiang-Sheng, ZHANG Yong-Chao, FANG Jian-Cheng
In order to reduce the impact of high velocity fluid in high temperature and under high pressure on thermowells, to suppress the fluidexcited vibration, to elaborate the mechanism of the structure vibration resulted from fluidexcited vortex shedding, and to analyze the reasons that caused the fracture of thermowells, a new design scheme, setting up a streamlined block in front of the thermowell to protect the thermowell from fracture, was proposed. Large eddy simulation (LES) technique was utilized to numerically simulate the unsteady flowfields around the specified thermowells with and without the streamlined block respectively. The contours of the total pressures, averaged forces and the pressure fluctuations in time domain and frequency domain on the surface of the thermowell and the streamlined block under the two conditions were obtained. The simulated results show that, the streamlined block can significantly reduce the resultant force acting on the thermowell, suppress the vibration and make the thermowell more reliable. The research provides a new way for optimized structure design of thermowells.
2013 Vol. 31 (4): 331-334 [Abstract] ( 2028 ) [HTML 1KB] [ PDF 1620KB] ( 2148 )
335 Numerical simulation on dynamic characteristic of closing process of flow swing check valve
LI Shu-Xun, HOU Ying-Zhe, LI Lian-Cui- Zhou-Shi-Hao
Regarding the water hammer phenomenon in closing swing check valve, by applying computational fluid dynamics(CFD) method, a motion equation of valve clack and the 2D geometric model were built; with the control equations composed of continuity equation, Reynolds average N-S equations and the k-ε turbulence model based on the theory of isotropic eddy viscosity, by using Fluentbased calculation methods and physical models, dynamic mesh and UDF in closing two kinds of swing check valve, twodimensional numerical simulation of the internal unsteady flow was performed. From the simulation, the pressure field, velocity vector, pressure curve and velocity curve of the internal unsteady flow were obtained. The results show that, in closing, the original model fluctuated; while the modified model fluctuated slightly, reducing the possibility of sudden changes; the internal flow field became more stable and the flow capacity was improved, the impact of the fluid on valve clack and local energy loss were decreased. The research can be an important reference for swing check valve design and helpful in optimizing valve design.
2013 Vol. 31 (4): 335-339 [Abstract] ( 2646 ) [HTML 1KB] [ PDF 2888KB] ( 2000 )
340 Calculation method of the maximum flow variation and evaluation of factors for microirrigation engineering
ZHU De-Lan, WU Pu-Te, ZHANG Lin
The distribution characteristic of emitters′ flow coefficient is analyzed. When flow coefficient complies with normal distribution, the probability of flow coefficient fluctuating at ±3 times standard deviations is 9973％ (approximating 100％). Thus, the minimum flow coefficient is average flow coefficient minus 3 times standard deviation and the maximum flow coefficient is average flow coefficient plus 3 times standard deviation. Based on the above analysis, a comprehensive flow variation rate calculation formula, taking hydraulic variation, manufacture variation and microterrain variation into consideration, is presented. Then, with emitter manufacturing variation coefficient, flow exponent, pressure difference and average field roughness height as influential factors, flow variation rate and lateral cost sensitivity were analyzed. The results show that emitter manufacturing variation coefficient is the most influential factor, followed by flow exponent and pressure difference. The lateral cost increases dramatically when manufacturing variation coefficient is larger than 004. In designing, emitters with minimal manufacture variation and minimal flow exponent should be elected. For normal drip irrigation systems, when the emitter′s waterdrop is larger than 10m, the effects of local height differences in fields on flow variation can be ignored.
2013 Vol. 31 (4): 340-344 [Abstract] ( 4349 ) [HTML 1KB] [ PDF 1342KB] ( 2643 )
345 Evaluation index system and evaluation models for regional humanwater harmony
KANG Yan, CAI Huan-Jie, SONG Song-Bai
In order to evaluate regional humanwater harmony, the concept of humanwater harmony was introduced and, based on complex system theory and harmony theory, a set of indicators to evaluate regional humanwater harmony was established. With set pair analysis theory and variable fuzzy set theory, set pair analysisvariable fuzzy set model was set up to analyze the development trend of humanwater system. An ideal development state of a system was determined in the spirit of cooperative game theory; a cooperative game distance coordination degree model was established to evaluate coordination degrees of humanwater system. On the bases of development trend and coordination degree, a multiplicative synthesis model is used to evaluate regional humanwater harmony degree. The abovementioned models were applied to assess the humanwater harmony degree of humanwater system from the year 2000 to 2009 in Shaanxi province. The results show that the humanwater harmony degrees were on a slow increasing trend, but still in grade I and II, disharmony and critical harmony. It indicated the level of humanwater harmony in Shaanxi province was still rather low, which is in close accordance with the fact in Shaanxi province. Comparison with fuzzy comprehensive evaluation model showed similar results, which proves the feasibility of the models and reliability of results.
2013 Vol. 31 (4): 345-351 [Abstract] ( 1771 ) [HTML 1KB] [ PDF 1345KB] ( 1522 )
352 Characteristics of annulus moving boundary flow in straight pipe segments of different widths
ZHANG Xue-Lan, Sun-Xi-Huan, Li-Yong-Ye
To further explore the influence of different factors on the hydraulic characteristics of the moving boundary annulus flow, through tests and theoretical analyses, annuluses with widths of 25,20,15,10 mm respectively were studied. The test was carried out in the straight pipe segment of the pipeline system, whose control volume is 60 m3/h, using barreled feed pipe carriage weighted 750 g. The research shows that the moving boundary annulus flow in straight pipe segment is turbulent morphology. Pressure values of measurement points in the annulus cross section tend to cluster as the width of the annulus increases. In the same section, pressure around the moving boundary of carriage is lower and pressure around the fixed pipe wall is higher. With the same width, the axial velocity sectional distribution is more uniform in the middle section than in the back or front. And the distribution is a layered one around the carriage body of which higher around the dynamic boundary and lower around the fixed border. When the width is 20mm, the axial distribution uniformity is best. Circumferential velocity shows uneven distribution in sections along the carriage under various conditions of different annulus widths.
2013 Vol. 31 (4): 352-357 [Abstract] ( 1747 ) [HTML 1KB] [ PDF 2452KB] ( 1483 )
358 Ventilation control model for temperature and humidity environment in greenhouse based on ANFIS
GE Jian-Kun, WANG Shun-Sheng, LUO Jin-Yao
To regulate the temperature and humidity environment in greenhouse by controlling vent opening intellectively, on the principle of thermal balance and water vapor quality balance, two nonlinear differential models for air temperature and humidity inside greenhouse respectively were constructed. Based on ANFIS, with trapezoid and Gaussian membership functions respectively, two fuzzy controllers for greenhouse ventilation control were set up, including choosing variables, quantifying the domain, defining fuzzy sets, choosing membership functions and controller training. By combining the controllers and the controlled object, with ventilation as input and greenhouse temperature as output, using Matlab, Simulink simulations were established. By applying observed data of two kinds of typical weather, the performance of two control systems was simulated and tested．The results show that, compared with the Gaussian controller, the greenhouse fuzzy controller with a trapezoid membership function is more sensitive, and has a better control effect on the indoor environment, which effectively reduces the fluctuation extent of temperature and humidity in greenhouse and optimizes control function. The research has certain reference value for the development in intelligent control of the greenhouse microclimate.
2013 Vol. 31 (4): 358-363 [Abstract] ( 2138 ) [HTML 1KB] [ PDF 1834KB] ( 2072 )
364 Effect of freezing and thawing process on FDR′s measuring volumetric water content of soil
ZHANG Ai-Li, GAO Lei
In order to study the effect of freezing and thawing process on FDR(frequency domain reflectometry)′s measuring volumetric water content of soil, the TDR-3 soil moisture sensor, based on FDR, was used to measure volumetric water content of soil at different temperatures ranged between -20-20 ℃, controlled by the temperature box in laboratory. The results show that, before freezing process above 0℃, during thawing process, the volumetric water content of soil measured by FDR increases or decreases as the temperature increases or decreases; the volumetric water content of soil, measured by FDR, decreases as temperature decreases during freezing process; and increases as temperature increases during thawing process. At the same temperature, the volumetric water content of soil measured during freezing process is higher than that measured during thawing process; at 0 ℃, the difference between them is maximal, which is significantly affected by the initial volumetric water content of soil and temperature. The results are valuable for improving the reliability of measuring the volumetric water content of soil by applying FDR in freezing and thawing process.
2013 Vol. 31 (4): 364-368 [Abstract] ( 2929 ) [HTML 1KB] [ PDF 1572KB] ( 2064 )
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