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Journal of Drainage and Irrigation Machinery Engin
 
2013 Vol.31 Issue.5
Published 2013-05-25
article
Article
369 Effect of oblique angle of blade trailing edge on pressure fluctuation in centrifugal pump
Two impellers, in which the blade trailing edge is with different oblique angles but the blade angle profile remains unchanged, were designed for a centrifugal pump to study the pressure fluctuation features caused from the impellervolute interaction. The unsteady, threedimensional turbulent flow in the pump was simulated by using the SST turbulence model, SIMPLEC algorithm and sliding mesh technique in this paper. Then the performance and pressure fluctuations in centrifugal pumps with those impellers were obtained. It was demonstrated that the pump keeps a relative higher efficiency in an extended flow rate range with decreasing oblique angle; additionally, the pump heads are close to each other for the two impellers at the partloading and design conditions, however, the heads increase at high flow rates. The periodic features in pressure fluctuation are the same for the two impellers, however, the amplitude of the fluctuation and highfrequency components are reduced in the volute and near its tongue. These results can provide a useful reference for the design of centrifugal pump impeller.
2013 Vol. 31 (5): 369-372 [Abstract] ( 2280 ) [HTML 1KB] [ PDF 2063KB] ( 2207 )
373 Test and analysis of abnormal vibration of vertical mixedflow pump
To identify the reasons for the abnormal vibration in a vertical mixedflow pump, the vertical and horizontal vibrations were measured at the low bracket, pump lid and outside column of pump unit by using lowfrequency vibration sensors in startup and normal operation periods, the pump shaft run out were monitored by means of an eddy current sensor as well. The experimental data were processed by the Hilbert-Huang transform (HHT), and the vibration peakpeak displacements were acquired, and the eigenvectors of vibration signals were extracted to diagnose the type of fault; finally, the timefrequency feature in startup period was analyzed in order to search the root reasons for the abnormal vibration. The analyzed results showed that the vibration frequency of the pump unit was close to the unit rotational frequency in the normal operation; additionally, for the shaft orbit is similar to an eccentric ellipse, the type of fault in the unit was unlikely the rotor imbalance. During the starting period, the shaft orbit was chaos and the vibration amplitude was as large as 47.3 times the amplitude in the normal operation, suggesting a violent force might be generated in the starting period and eventually induces the rotor to operate in imbalance. The timefrequency characteristics of vibration signals in a pump can be acquired accurately with the HHT, especially for highly nonlinear signals; meanwhile, this study on vibration generated in a pump during its startup period will provide a new way for pump troubleshooting.
2013 Vol. 31 (5): 373-378 [Abstract] ( 1881 ) [HTML 1KB] [ PDF 2249KB] ( 1932 )
379 Turbulent flows in tubular pump and fluidstructure interaction characteristics of impeller
The RNG k-ε turbulence model and the Ansys Workbench software were used to numerically investigate internal flows in a frontpositioned shaft tubular pump and fluidstructure interaction in its impeller. The simulated performances under different operation conditions are consistent with experimental data.Even though the calculated head is higher and the efficiency is lower than the experimental data, their errors are less than 10%. The velocity and pressure of fluid are uniformly distributed in the whole passage of the pump except in the discharge passage. The spiral streamlines in the front of the discharge passage show that the fluid has a residual velocity circulation after it leaves the vaned diffuser. At the design flow rate, a minimum pressure is seen on the suction surface of blade near the blade leading edge, where cavitation will be apt to occur. In addition, a static structural analysis on the impeller was carried out based on oneway fluidstructure coupling method and the stress and deformation of blades were predicted under different operating conditions. The results show that at the design flow rate, there is a maximal equivalent stress on the pressure surface of blade but at the junction of blade and hub. The total deformation of blade increases with radius, and there is a maximum deformation near the impeller tip. The calculated results will provide a reference for optimization design of tubular pumps.
2013 Vol. 31 (5): 379-383 [Abstract] ( 1970 ) [HTML 1KB] [ PDF 2260KB] ( 1707 )
384 Numerical simulation of unstable characteristics in head curve of mixedflow pump
The threedimensional unsteady flow field in a mixedflow pump was calculated by means of the large eddy simulation (LES), subgrid scale model and sliding mesh technique in order to analyze the instability in head curve and flow characteristics caused from the interaction between impeller and guide vane in the pump under low flow rate conditions. The experimental results showed the headcapacity curve exhibits a positive slope at 60%Qd and 85%Qd operating conditions, and the error between predicted and experimental results is less than 4%, suggesting LES can predict the positive slope characteristic accurately. On this basis, the flow mechanism for the unstable characteristic was analyzed. The simulated results showed that the fluid tangential velocity is distributed nonaxisymmetrically in the impeller inlet evidently. Because of the stall of flow in the impeller and guide vane passages, there is a large scale vortex structure on the blade surface and the hub surface at the leading ledge of guide vane. The scale of the vortices in the guide vane passages is larger than that in the impeller. It is apparent that the pressure fluctuates periodically along the axial direction, allowing the vortex zone extends into the middle of guide vane passage from the suction side of guide vane. The core of large scale vortex is attached to the suction side at the middle span of the guide vane where pressure fluctuation is minimal; moreover, the rotational direction of the core is the same as the impeller.
2013 Vol. 31 (5): 384-389 [Abstract] ( 1921 ) [HTML 1KB] [ PDF 2925KB] ( 1701 )
390 Characteristics of cavitation vibration and noise in centrifugal pumps with different vane wrap angles
In order to identify effects of vane wrap angle on the cavitation induced vibration and noise of centrifugal pumps, a singlestage, endsuction centrifugal pump was chosen as the experimental model, in which the vane wrap angles were 110°, 115°, 120° and 125°, respectively, while the rest geometric parameter of the pump kept unchanged. The cavitation induced vibration and noise signals of the pump with different vane wrap angles were measured under various net positive suction heads available by using a closedloop centrifugal pump test rig, and then the signals were processed and analyzed. The experimental results showed that the vane wrap angle affects the pump cavitation performance without a clear regularity, but there exists an optimal angle indeed. With increasing wrap angle, the vibration intensities picked up at the four monitoring points don′t show a consistent pattern; however, the lowest intensity is founded at the discharge nozzle flange where all the intensity is below 1.0 m/s2. With increasing wrap angle, the peak values of noise signal at shaft rotating frequency decrease, but those at the blade passing frequency change in complicated manner under noncavitating condition. During both cavitation inception and development stage, the peak values of noise signal at the shaft rotating frequency always increase initially and then drop off. Furthermore, the peak values of the energy at 1 750-2 250 Hz also show the same pattern with exacerbation of cavitation.
2013 Vol. 31 (5): 390-393 [Abstract] ( 2563 ) [HTML 1KB] [ PDF 5549KB] ( 2182 )
394 Torsional vibration characteristics of rotor for centrifugal charging pump
The torsional vibration characteristics of the rotor of a centrifugal charging pump for 1 000 MW nuclear power plants were calculated by means of Ansys; and the vibration amplitude under different rotational speeds were obtained. The computational geometry model was built by using Pro/E and its mesh was generated in ICEM. The results showed that the stability of the rotor with three supports is better than the rotor with two supports since all the natural frequencies of the former are significantly higher compared with the latter, suggesting the former will help reduce vibration and noise issued from the pump in operation. When the pump is running at the 4 900 r/min rotational speed, a first order torsional resonance takes place quite clearly because the sixth harmonic frequency of the motor driving torque is around an integer multiple of the first order torsional vibration natural frequency of the rotor. The design operating speed of the charging pump is 4 500 r/min; since it is less than every order critical speed of the rotor, a torsional resonance cannot occur. This indicates that the structure design of the rotor shaft is reasonable.
2013 Vol. 31 (5): 394-400 [Abstract] ( 2044 ) [HTML 1KB] [ PDF 2199KB] ( 2012 )
401 Numerical analysis of flow in pumpturbine operating in Sshape region
In order to study the characteristics of internal flow in a pumpturbine operating in the Sshape region, the flow in the model pumpturbine in a pumped storage power station in China was simulated by using CFD codeCFX. The detached eddy simulation model (DES) that is more precise than the traditional RANS model was applied in the simulation, consequently, the internal flow pattern and performance parameters of the pumpturbine were obtained; and compared with the experimental data and the theoretical analysis results, respectively. It was shown that the results of DES model are quite good, causing the error between the estimated and experimental performance is less than 3%; further, the internal flow in the runner are in good agreement with theoretical analysis as well. As the flow rate decreases, the flow separation phenomenon near the runner inlet was strengthened gradually, and eventually a vortex was developed in the flow passages, causing a blockage to flow. Note that the vortex can induce rotorstator interactions among the runner and double circular cascade, which will results in instability of flow in the whole passage.
2013 Vol. 31 (5): 401-405 [Abstract] ( 2531 ) [HTML 1KB] [ PDF 12119KB] ( 5935 )
406 Experiment and numerical simulation of hydraulic transients in branched pipe network
The water hammer pressure and fluctuation in a branched pipe network were studied by experiment and the method of characteristics (MOC) when the valve is closed. In experiment a pressure sensor was used to monitor water hammer pressure and fluctuation and the angular displacement sensor was adopted to measure the closing time and opening of the valve. The results showed that the MOC can better predict the maximum water hammer pressure caused by valve closing in the network with a relative error of less than 13%. The pressure wave attenuation in simulation is slower than in experiment because the friction factor of steady flow is used in the simulation. Based on that analysis, the transient flows generated by other five closing schemes of valve have been simulated numerically. It was shown that the maximum water hammer pressure was generated in the network when the two valves at the network end were closed simultaneously; suggesting this case should be avoided in applications. The maximum water hammer pressure was reduced with increasing closing time. For a constant closing time, the maximum water hammer pressure generated by a curved line closing scheme or a twostage straight line closing scheme was lower than that by the one straight line scheme. For the twostage straight line closing scheme, the closing time of the first stage should properly be extended to reduce the maximum water hammer pressure.
2013 Vol. 31 (5): 406-412 [Abstract] ( 2451 ) [HTML 1KB] [ PDF 1690KB] ( 1660 )
413 Effects of surge anticipation valve on water hammer in pumping station
Effects of surge anticipation valve on water hammer process in a pumping station with high head were analyzed by means of the water hammer theory and method of characteristics, the optimized combinations of the related parameters of the valve were explored as well. The transient processes were analyzed under 13 opening and 10 closing modes for the surge anticipation valve. It was found that the surge anticipation valve can effectively suppress the highest pressure in the pumping station system; unfortunately it also can reduce the lowest pressure in the system in some circumstances. The opening time period, fully opening time period and closing time period are the three key parameters that affect the protective effect on water hammer pressure for a surge anticipation valve. There is an optimal combination among them to keep the highest pressure being at the lowest level and with a minimum drop in the lowest pressure. Also, it was found that the valve must be fully opened before the first pressure wave arrives under the accidental pumpstop condition. To avoid further declination in the lowest pressure caused by too much water leakage, it is suggested that the fully opening time period should maintain short. The highest pressure in the system declines with increasing closing time period; so a longer closing time period is more in favor of protective effect on water hammer pressure for an anticipation valve. The results may be useful to water hammer protection with surge anticipation valves in a newly built or existing pumping station with high head.
2013 Vol. 31 (5): 413-417 [Abstract] ( 3077 ) [HTML 1KB] [ PDF 1733KB] ( 2039 )
418 Optimal configuration of pumpedstorage in hybrid power system
Since the capacity of hybrid power system is configured experientially at present causing a high cost and low reliability.  the capacity of wind generator and PV arrays were optimized by using the particle swarm optimization method, while the capacity of pumpedstorage was optimized by means of the global optimization and local optimum methods. Firstly, the capacity of pumpedstorage is configured preliminarily according to the annual load, annual wind and solar energy resources etc; secondly, the capacity configuration is verified and adjusted based on the monthly load, monthly wind and solar energy resources; at last, the configuration is further improved with the typical daily load, daily wind and solar energy resources. For an isolated hybrid Wind-PV-pumped-storage-desalination system, the capacity of pumpedstorage was optimized with the global optimization and local optimum methods. The results showed that the preliminarily configured capacity of pumpedstorage is 120 kW by means of the annual data, but the capacity needs to be updated to 420 kW by considering required monthly loss of power supply probability in the verifying process. Further, because of the volatility of daily load, wind and solar energy resources, an extra loss of power supply probability still exists, thus a certain capacity of storage battery needs to be configured.
2013 Vol. 31 (5): 418-421 [Abstract] ( 1781 ) [HTML 1KB] [ PDF 1456KB] ( 1847 )
422 Determining installation position and number of submerged propellers in oxidation ditch by CFD
The problems, such as too high energy consumption for oxidation ditch operation and how to decide submerged propellers installation position, exist in sewage treatment plants currently, thus the flow in an oxidation ditch was simulated based on the Navier-Stokes equations, standardturbulence model and SIMPLE algorithm. The threedimensional submerged propeller model was built by the existing blade pattern drawing, and the fluid domains were meshed with unstructured tetrahedral cells. The shaft power of submerged propeller and the velocity distribution in various crosssections of the oxidation ditch were estimated under different working conditions; meanwhile, the flow field driven by the propeller was investigated as well. The results indicate that on the premise of the submerged propeller installation parameters unchanged, altering the installation position of submerged propeller can avoid the back mixing phenomenon caused from a too strong driving force. Besides, the sludge deposition problem, which is caused from too low flow velocity resulted by too much attenuation of the driving power in the bends, also can be solved. By properly adjusting the number of submerged propellers, a minimum power density can be determined to meet the driving force needed for mixing. Thus not only the velocity in the oxidation ditch has met the requirement, but also the minimum energy consumption has been achieved. The study can provide a theoretical guidance for determining the installation position and number of submerged propellers.
2013 Vol. 31 (5): 422-427 [Abstract] ( 2288 ) [HTML 1KB] [ PDF 4848KB] ( 1902 )
428 Estimate of minor pressure drop in flow channel of high pressure multiway valve
To solve the problems, such as large pressure drop and high energyconsuming in the flow channels in the multiway valve which centralizes control on multiactuator, and the motor for right travel is not sensitive enough etc, the hydraulic oil flow in the channel of the valve was analyzed and the effect of the channel structure on the minor pressure drop was clarified. In doing so, the geometry model of the right travel link of the multiway valve in an excavator was built by using Pro/E and the turbulent flow in the model was simulated by means of CFD SIMPLEC techniques. The results showed that in addition to the pressure drop in both the main valve port and the conduit between the inlet and the check valve, there is a significant pressure drop in the passage between the check valve port and the outlet. The pressure drop is proportional to the axial length of the passage; however, it is less affected by the angle of the passage. The drop is inversely proportional to the eddy scale and the number of vortex cores. The pressure drop in the multiway valve is measured as well, and the predicted drop is consistent with the experimental observations, suggesting the findings based on the analyzed results are reliable.
2013 Vol. 31 (5): 428-433 [Abstract] ( 2334 ) [HTML 1KB] [ PDF 7564KB] ( 1295 )
434 Analysis of principal components of wastewater affecting soil water repellency
In order to identify the effect of irrigation wastewater quality on soil water repellency, the repellency of five oils samples, which belong to three types of waterrepellent soils collected in Israel, was measured for the domestic sewage with 12 different degrees of water pollution. The measured water drop penetration time (WDPT) on the heterogeneity soils was normalized, and the principal components analysis (PCA) was conducted for the nine individual water quality indices in those sewages. Subsequently, the aggregative index (F) of sewage quality was calculated, and the relationship of WDPT to F and individual water quality indices was analyzed. The results showed that there was a positive correlation between WDPT and F for clay and loamy soils, i.e. WDPT rises with increasing F; for sandy soils, however, there was no significant correlation, i.e. WDPT is not affected by degree of water pollution. The results of multiple linear regression showed that there was a significant positive correlation between WDPT and two principal components for clay and loamy soils. Furthermore, the influence of the first principal component was more dominated than the second one.
2013 Vol. 31 (5): 434-439 [Abstract] ( 1851 ) [HTML 1KB] [ PDF 1588KB] ( 1560 )
440 Experiment on water and nitrogen distribution in soils under ridgefurrow irrigation with ammonium nitrate solution
 In order to provide guidance to reasonable design of irrigation technique and system in ridgefurrow intercropping fields, the infiltration characteristics and soil water and nitrogen distributions in four soil textures under ridgefurrow irrigation with ammonium nitrate solution were investigated in laboratory experimentally by using rectangular soil chambers to simulate the twodimensional infiltration in the irrigation. The distributions of water, nitrate, and ammonium in the soils were clarified. The soil wetting front was also recorded against infiltration time. The results showed that the cumulative infiltration of fertilizer solution and its infiltration rate tend to decrease with increase in clay content of soil texture because of greater soil specific surface area. Note that the increasing slope of the cumulative infiltration curve is significantly dependent of soil texture. The Horton infiltration model with three underdetermined parameters is fairy precise in estimating infiltration of fertilizer solution, in which the steadystate infiltration rate has very practical and is one important reference quantity for determining the flow rate in ridgefurrow irrigation. The wetted front migrates far away in the lateral and vertical directions in coarser soils at the same infiltration condition, the vertically wetted distance is longer than the laterally wetted one, and the wetted front is like an ellipsoid with a long axis in the vertical direction. The relation of laterally wetted distance to infiltration time can be described by an exponential function, while the vertically wetted distance has a linear relation to the square root of infiltration time. It was illustrated that the nitrate accumulates on the boundary of wetted front, but the highest ammonium concentration appears near furrows. The ridgefurrow fertigation technique should be implemented in finer soils to reduce deep percolation of water and nutrients below the root zone and improve water and fertilizer use efficiency in ridgefurrow intercropping fields.
2013 Vol. 31 (5): 440-448 [Abstract] ( 1687 ) [HTML 1KB] [ PDF 2328KB] ( 1780 )
449 Effect of tooth angle and pitch of labyrinth channel on performance of emitter
An emitter with labyrinth channel was used as the study model, the channels were designed by using a full factorial experiment for two factors with four levels, the liquidsolid twophase flows in them were simulated numerically by means of Fluent 6.3. Influences of tooth angle and pitch on the hydraulic and anticlog performances of emitter were explored. The results showed that discharge coefficient can be correlated to tooth angle and pith with a positive relationship; moreover, the discharge coefficient increases with increasing tooth angle and pitch. The influences of tooth angle are more complicated; when the tooth angle is more than 120°, the flow regime index decreases initially then increases with increasing tooth pitch; when the tooth angle is less than 120°, however, the index decreases firstly, then increases with increasing tooth pitch. It was proposed that the anticlog performance can be analyzed by certain range of suspended sand particle concentration. The level of the maximum particle concentration in the channel is not completely proportional to the size of the area of high concentration, but the higher the maximum concentration, the greater chance the suspended particles to gather together and the greater the probability that a local sediment happens; at last the size of the area of high concentration gets larger and the emitter becomes clogged more easily.
2013 Vol. 31 (5): 449-455 [Abstract] ( 1668 ) [HTML 1KB] [ PDF 2810KB] ( 1689 )
456 GPSbased land slope leveling technique and its implementation
In order to improve the land slope leveling accuracy and achieve high quality irrigation, a GPSBased land slope leveling system was developed. The system consists of GPS receiver, vehiclemounted IPC, controlconversion module, hydraulic system and earthmoving equipment. And the software of the system is programmed in Visual C++ 6.0. The system can measure farmland topography instantaneously, and perform land slope leveling. First of all, the GPS receiver is installed in the earthmoving equipment to measure farmland topography in a serpentine path; the topography data are corrected with a correction algorithm to reduce the error. Then, a threedimensional topography is visualized and a farmland slope model is established by using the corrected data to obtain the expected slope reference elevation. Finally, the realtime elevation is compared with the slope reference elevation, the comparison result is input to the controlconversion module, and its output signals are used to drive the hydraulic system for leveling the land. The land slope leveling implementation was carried out in a land with 180 m longitudinal size and 1/1 000 longitudinal slope. The results showed that the standard deviation is about 5 cm, the mean elevations at top and bottom of the slope is about 40.62 m and 40.78 m, respectively, causing a 16 cm difference in elevation compared with 18 cm theoretical differences. Thus, the preliminary goal has been achieved.
2013 Vol. 31 (5): 456-460 [Abstract] ( 1592 ) [HTML 1KB] [ PDF 1753KB] ( 1691 )
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