Influence of long and short guide vanes on hydraulic performance of water-jet pump

Different guide vane structures will affect the flow inside the pump,and then affect the transformation of the pressure energy and kinetic energy,and change the velocity distribution of the pump outlet.In order to study the influence of long and short guide vanes on the water-jet pump,on the basis of conventional design,eight schemes of guide vane with different vertical heights were designed in the method of computational fluid dynamics for numerical calculation,the performance curve of water-jet pumps with different long and short guide vanes was obtained,and finally the influence of different guide vanes on hydraulic performance and internal flow was analyzed.The results show that all of schemes reducing the height of blade can improve the head and efficiency.In the schemes reducing the height on the shroud,the guide vanes that the height of the blade is equal to the height difference between hub and shroud in impeller have the highest head and efficiency.In all schemes decreasing the blade height,with the increase of the height difference,the velocity increases gradually and the distribution of turbulence kinetic energy becomes more reasonable in the guide vane outlet.The schemes reducing the height on the hub have more reasonable distribution of velocity and turbulence kinetic energy according to schemes reducing the height on the shroud.The guide vanes of long and short blades can be used to stagger the position of the diffusion flow generated by adjacent blades,which can reduce the effect of the velocity circulation and make the flow of the outlet position more stable.     

Comparative Analysis of Comprehensive Water Quality Identification Index Method Based on Different Weighting Method北大核心CSCD

【Objective】In order to analyze the water quality distribution characteristics of each water quality monitoring section of Qingshui River in Ningxia, provide a basis for water quality assessment, based on three water quality section monitoring data on Qingshui River in Ningxia from 2014 to 2016. 【Method】Using the method of Principal Component Analysis to select the evaluate data and choose representative water quality indicators to issue Comprehensive Water Quality Identification Index evaluation and combined with 3 weighting methods to do further comparative analysis.【Result】The comprehensive water quality identification index show that the Ershilipu section water quality evaluation results for class II water and remained stable. The Sanying section evaluation results meet the class III water in 2014 and 2015 years, the evaluation results meet class IV water in 2016, It shows that the water quality of this section has a trend of decrease. The Quanyanshan section evaluation results for the class II water and reduced year by year, the water quality has become the trend of further good. 【Conclusion】The three section water quality evaluation using different weighting methods reached the water function zoning requirements, there were some defects in the Standard Multiple Method and the Entropy Weight Method, and the Variation Coefficient Method was more suitable than the other two weighting methods. © 2019 Office of Journal of Irrigation and Drainage, Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences. All rights reserved.     

Sap Flow in Tropical Eucalyptus Plantation and Its Response to Environmental Changes北大核心CSCD

【Objective】Transpiration is controlled by many biotic and abiotic factors and in this paper, we studied the sap flow in tropical eucalyptus under different environments. 【Method】The experiment was conducted from January to December in 2016, and the sap flow in the eucalyptus was measured with the thermal dissipation probe under changing environment which was monitored synchronously by a small meteorological station at the Danzhou Forest Farm in Hainan province.【Result】①Temporal change of the sap flow velocity had two peaks in wet season and one peak in dry season. In wet season, the first peak 8.68 mL/(cm2·h) occurred between 11:00 to 11:30 am followed by the second peak 8.68 mL/(cm2·h) occurring between 15:00~15:30. The mean of the peaks in dry season was 7.45 mL/(cm2·h). ②The instantaneous sap flow rate lagged behind the Rh and Ta by 30 min, and the PAR by -30 min, in all seasons. ③The mean daily sap flow velocity was 2.06 mL/(cm2·h), and the maximum sap flow velocity was 4.25 mL/(cm2·h) occurring in 15th July, and the minimum was 0.14 mL/(cm2·h) occurring in 25 th November. The photosynthetically active radiation (PAR), atmospheric temperature (Ta), vapor pressure deficit (VPD) were the main factors affecting sap flow velocity. The diameter of the tree at the breast height was positively related to daily sap flow velocity. ④The monthly average sap flow velocity had a single peak, with its average in wet and dry seasons being 2.53 mL/(cm2·h) and 1.80 mL/(cm2·h) respectively. The maximum monthly average sap flow velocity was 3.42 mL/(cm2·h) occurring in July, and the minimum was 1.80 mL/ (cm2·h) occurring in February, both affected mostly by PAR, Ta and VPD.【Conclusion】The sap flow rate in tropical eucalyptus showed seasonal and diurnal period, and its daily and monthly average was affected mostly by PAR, Ta, and VPD. © 2019 Authors. All rights reserved.     

Numerical study on two-phase flow in horizontal pipe

Two-phase flow in a horizontal pipe was investigated by using numerical and experimental visualization methods.A horizontal pipe was built for qualitative and quantitative flow visualization.The length of horizontal pipe flow system was 9.5 m and the inner diameter was 51 mm.High-speed video method was used for the qualitative visualization and PIV method was applied for the quantitative visua-lization.The same geometry model was used for the numerical study.Three flow regimes including stratified flow,elongated bubble and slug flow field were generated and visualized by using numerical and experimental methods.The results show that the numerical simulation results are qualitatively si-milar to that of the experimental results.In addition,more quantitative results can be analyzed by numerical method.Development and decay process of slug flow was investigated,showing that the decay of slug heavily depends on the magnitude of nose velocity and its lasting time.It can also be found that the liquid superficial velocity plays a significant role in affecting the slug frequency.When keeping the gas superficial velocity constant,the frequency will increase with the liquid superficial velocity.     

Optimal Design of Vortex Pump Using Approximate Model and the Non-dominated Sorting Genetic Algorithm北大核心CSCD

【Objective】The cavity width L, blade width b2 and the number of blades Z are the most important geometric parameters affecting the performance of vortex pump. This paper aims to present a method to optimize the vortex pump. 【Method】The study was based on approximate model and the non-dominated sorting genetic algorithm II (NSGA-II), in which the pump cavity length, blade width and the number of blades were calculated using the central composite design of DoE (design of experiment). The performance of the designed pump was examined using CFD, and the effect of L, b2 and Z on vortex pump efficiency and shear stress on the blade wall was calculated using the Kriging model. The NSGA-II was used to optimize the geometric parameters.【Result】The optimal parameters calculated from the methods were L=25 mm, Z=8, b2=26.45 mm.【Conclusion】We proved that CFD and NSGA-II can be used in a combination to calculate the optimal parameters of the vortex pump, and they can significantly improve efficiency of the pump and reduce the shear stress on the blade. Our results revealed that the optimization can reduce the width of the non-blade cavity by 16.67%, and increase the number of blades of the impeller and the outlet width of the blade by 1 and 25.95% respectively. At the design flow rate, the optimal design increased pump efficiency by 1.06% and reduced the average shear stress on the blade from 274.37 Pa to 204.57 Pa. The optimal design made the shear stress on the blade more uniform, in addition to reducing the shear stress on the outlet of the blade. © 2019 Authors. All rights reserved.     

Manipulation of vertical fence wake using passive vortex generators

The effect of streamwise vortices generated from passive vortex generators was investigated to manipulate the separation bubble behind the vertical fence. The experiments were carried out in a circulating water channel and the velocity fields were measured using 2D and stereoscopic PIV method.The distance between the vortex generator and fence and the effect of the Reynolds number were investigated. In addition,the effect of boundary layer thickness was also investigated. The averaged recirculation lengths were compared with that of uncontrolled fence flow. The results showed the oscillatory variation of recirculation region appeared under the existence of vortex generators. The reduction of the separation bubble became larger when the fence was submerged in the thick boundary layer with increasing the distance between the generator and fence. When the boundary layer is thin,vortex generator can only suppress the separation bubble under the specific condition.     

Manipulation of vertical fence wake using passive vortex generators

he effect of streamwise vortices generated from passive vortex generators was investigated to manipulate the separation bubble behind the vertical fence. The experiments were carried out in a circulating water channel and the velocity fields were measured using 2D and stereoscopic PIV method. The distance between the vortex generator and fence and the effect of the Reynolds number were investigated. In addition, the effect of boundary layer thickness was also investigated. The averaged recirculation lengths were compared with that of uncontrolled fence flow. The results showed the oscillatory variation of recirculation region appeared under the existence of vortex generators. The reduction of the separation bubble became larger when the fence was submerged in the thick boundary layer with increasing the distance between the generator and fence. When the boundary layer is thin, vortex generator can only suppress the separation bubble under the specific condition.     

A wind tunnel experiment of self-starting capability for straight-bladed vertical axis wind turbine

In this study, wind tunnel experiment has carried out to investigate the self staring capability for straight bladed vertical axis wind turbine. The flow visualization has also been performed at the rest of the rotor. The effect of the azimuthal angle of blade position relative to wind direction on the self starting capability was discussed based on the results of flow visualization. The torque and the centripetal force of the rotor when the self starting behavior starts were roughly calculated by using the result of flow visualization of the rotor. It was suggested that there exist the condition of wind speed and configuration of the blade position of the rotor at the rest of rotor to the reach to situational rotation number.     

Orthogonal optimization of flow uniformity at exit section of elbow-inlet passages

Elbow-inlet passage is widely used in large drainage pumping stations.Flow uniformity at the exit section directly determines its hydraulic performance.Flow uniformity must be optimized to improve the operational efficiency of the large axial-flow pumping station.Modeling and numerical simulation methods were used to investigate the elbow-inlet passage,and the accuracy of the calculation results was verified.The key geometric parameters affecting the uniformity of the flow were optimized by the orthogonal experiment design.The optimal schemes were obtained and compared with the original scheme.The results show that flow uniformity V u after optimization is 95.41%,which is increased by 1.04%.The pumping station efficiency is increased by 1.89%,thereby confirming the applicability and accuracy of the proposed scheme,especially for the optimization of flow uniformity of the exit section of the elbow-inlet passage.     

Multi-factor Analysis of the Effective Precipitation for Crops in Semi-arid Region北大核心CSCD

【Objective】The purpose of this paper is to present a method to estimate the effective precipitation for crops in arid region.【Method】The model considered precipitation, soil and crop, and it was based on four modules: canopy interception, soil water tolerance, surface runoff, precipitation and deep percolation. The results calculated by the model were compared to those calculated from water balance using the data measured from the field. We applied the model to calculate spatiotemporal distribution of the effective precipitation for crops in five counties in Hebei plain.【Result】①The coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE) in all results were above 0.85, proving the reliability of the model. ②The effective precipitation for growing season of the wheat-maize in the five counties was 400.03 mm, and the infiltration coefficient of precipitation was 0.84. In wet, normal and dry year, the effective precipitation for crops was 419, 454 and 355 mm respectively, and infiltration coefficient of precipitation was 0.76, 0.86 and 0.83 respectively. The effective precipitation for crops in Luancheng and Yuanshi was higher than that for other counties.【Conclusion】The proposed model was reliable for estimating effective precipitation for crops at large scale in semi-arid region. © 2019 Authors. All rights reserved.     

Numerical study on hydraulic performance of submerged propellers in oxidation ditch

The submerged propeller is an efficient diving mix device,which is applicable for oxidation ditch treatment in industry,city and village wastewater-treatment plant. The impeller structure and reasonable rotating speed are important factors that determine flow field distribution and energy conversion efficiency. So it is necessary to use modern design methods to develop new kinds of high efficiency submerged propellers,and research the flow field characteristics of submerged propellers. On the basis of the existing form drawing,three-dimensional model of submerged propellers and unstructured tetrahedral mesh were generated. Based on Navier- Stokes equations and standard k- ε turbulence model,the flow was simulated by using a simple algorithm. Through changing some design parameters of propellers,the corresponding numerical simulation results reveal that for the same impeller diameter and service area of submerged propellers,the power consumption could be reduced effectively by optimizing blade mounting angle,which can determine the best blade mounting angle and most suitable rotational speed under given conditions. The study can provide theoretical and project guidance for submerged propellers design.     

Experimental study on inlet vortex in pump sump

In order to study the mechanism of the vortex generation at the bottom of the pump sump below the flare tube, twenty pressure pulsation monitoring points were arranged at the bottom of the pump sump below the flare tube, and the pressure fluctuation experiments were carried out under different flow conditions. The experimental results show that the frequency of pressure fluctuation at the bottom of the pump sump is twice of the rotational frequency of the impeller blade; the vortex below the flare tube is easy to generate under the large flow conditions mainly concentrated at the right front position below the flare tube. The position of the vortex occurring is corresponding to the position of the low-pressure region below flare tube.     

Ammonia Volatilization from Pit Wall under Different N Top-addressing from Water Storage Irrigation Pit in Apple Orchard北大核心CSCD

【Objective】Water storage pit is a common technology to bank precipitation for irrigation in arid region. In this paper, we studied ammonia volatilization from the wall of the pits under different N top-addressing in an apple orchard.【Method】We compared seven nitrogen top-addressing in the experiment: topdressing 600, 300 and 0 kg/hm2 at anthesis stage and fruit enlargement stage respectively. The ammonia volatilization from the wall of the water storage pit was measured using glycerophosphate-ventilation. We analyzed the dependence of ammonia volatilization on soil ammonium, soil nitrate, soil temperature, air temperature and humidity respectively.【Result】Ammonia volatilization increased with the topdressing amount after irrigation and fertilization. Top-addressing after anthesis stage could prolong ammonia volatilization for a significant period with a peak within 52.93 to 576.80 mg/(m2·d) occurring 3~5 days after the top-addressing. Top-addressing during fruit enlargement stage resulted in a short period of ammonia volatilization with a peak within 81.11 to 1 047.79 mg/(m2·d) occurring two days after the top-dressing. The accumulated ammonia volatilization (calculated by N) after one-off topdressing after anthesis stage and fruit expansion stage was 3 332.88~7 052.01 mg and 2 178.14~5 126.97 mg respectively. Compared to one-off topdressing, two top-addressing reduced ammonia volatilization to 2 013.21~ 4 642.11 mg, 34.17%~39.60% lower than that under one-off topdressing after the anthesis stage. Ammonia volatilization from the water storage pit wall accounted for 0.57%~1.40% of nitrogen loss, being the highest under one-off topdressing at anthesis stage followed by one-off topdressing at fruit expansion stage. Ammonia volatilization was positively correlated with soil ammonium and air temperature (P<0.05). Soil temperature and nitrate also played a role in ammonia volatilization. Rise in air humidity and rainfall after fertilization can reduce ammonia volatilization, and the dynamical change in accumulated ammonia volatilization can be well described by the Elovich dynamic equation, in which the rate constant parameter was positively correlated to the amount of top-addressing nitrogen and negatively correlated to soil temperature, both at significant level.【Conclusion】Ammonia volatilization from water storage pit wall can be controlled by managing the amount of fertilizer application and time at which the fertilizer was applied. Our results suggested that reducing the top-addressing amounts and top-addressing twice can effectively reduce nitrogen loss via ammonia volatilization. © 2019 Authors. All rights reserved.     

Numerical simulation on centrifugal pump compressible flow field with different gas volume fractions

In order to study the influence of gas-liquid two phase flow to a centrifugal pump perfor mance and internal flow patterns, the steady three dimensional flow with different gas volume fractions is simulated by applying the Reynolds average N-S equation and mixture gas-liquid two phase flow model, and the compressibility of gas is taken into consideration in the simulation. Then we emphatically analyzed the centrifugal pump characteristic and the gas distribution law in different gas volume fractions. The computational results show that gas volume fraction has a certain influence on the performance of the centrifugal pump, and the efficiency and head of the pump are on the decline with the increase of it. Static pressure in the impeller increases in the radial direction, but the pressure gradient in the flow direction is different under the different gas volume fractions. The gas volume is distributed mainly in the ipsilateral direction of impeller back shroud in the flow channel of the volute. On the suction side of the blade inlet there is an obvious low pressure area, which causes bubbles agglutination and higher gas volume fraction. With the gas entering passage flow, gas volume fraction in the suction decreases and the pressure surface rises gradually. Higher gas volume fraction causes air blocking phenomenon in the flow passage and the discharge capacity reduces. The increase of gas volume makes the turbulent motion within the impeller more and more intense, which leads to more and more energy loss.     

Influence of liquid water content on wind turbine blade icing by numerical simulation

In order to research the influence of liquid water content(LWC) on blade icing of wind turbine,a numerical simulation method for blade icing was established.The numerical simulation was based on low speed viscous N-S equation.The trajectory equation of water droplets was established by Lagrangian method.The mass and energy conservation equations of the water droplets impacting on the surface of the blade were solved based on control body theory.Three sections along blade span wise of a1.5 MW wind turbine were decided to simulate icing.Five kinds of LWC were selected for simulation including 0.2,0.4,0.6,0.8 and 1.0 g/m3 under two ambient temperatures of-10 ℃ and-20 ℃.The medium volume droplet diameter(MVD) was 30 "m.The simulations included icing shape on blade surface,dimensionless icing area and dimensionless maximum stagnation thickness.Furthermore,the flow fields around both the iced blade airfoil and the original one were simulated and analyzed.According to the results,the typical icing characteristics of icing shape,icing area and thickness were greatly affected by the difference of LWCs.This study can provide theoretical reference for the research on antiicing and deicing of wind turbine blade.     

Effects of Biochar for Abating Salt Stress and Promoting Seeding Growth of Winter Wheat in a Saline Soil北大核心CSCD

The surface soil of the Yellow River Delta is rich in salt, which makes the soil salinized, compact and barren. The salinization hazard with NaCl as the main component directly affects the quality of coastal soil. Adding biochar to saline-alkali farmland can improve soil properties and promote crop growth.【Objective】The purpose of this paper is to clarify the changes of soil salt ions and winter wheat seedling growth after adding biochar to saline soil.【Method】A field experiment was conducted to investigate the effects of low dose (0~4 g/kg) of Reed carbon on soil salt ions, potassium-sodium ratio in wheat seedlings, potassium utilization efficiency and seedling biomass.【Result】The application of biochar could reduce the salt ions in soil solution, increased the potassium-sodium ratio in the winter wheat seedlings and the potassium use efficiency of the wheat seedlings, and increased the seedling biomass of winter wheat; The salt reduction and the incremental effect under the addition of 4 g/kg biochar use was the most obvious. Compared with CK, the Na+ in soil solution decreased by 9.43%, the K/Na and potassium use efficiency of seedlings increased by 56.80% and 25.48%, respectively, and the biomass of wheat seedling increased by 15.72%.【Conclusion】Biochar application can promote the increase of biomass by holding Na+ in soil solution and increasing K/Na and potassium utilization of winter wheat seedlings. The research can provide a theoretical basis for the process mechanism of biochar for salt reduction and fertilization, increase efficiency and increase yield, and provide preliminary guidance for the feasibility of biochar for salinized soil improvement. © 2019 Office of Journal of Irrigation and Drainage, Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences. All rights reserved.     

Quantitative visualization of Taylor-Couette flow with helical protrusion using optical and ultrasound imaging method

The simplified flow of drilling process in the soil hardening or oil rig site was experimentally investigated. Two flow models were used in this study. One is the concentric cylinders with helical protrusion at the inner cylinder. The other is the concentric plain wall cylinders with axial flow. The ra dius ratio and aspect ratio of both models are the same with 065 and 48, respectively. The mud is the typical fluid seen in the soil hardening processes. We used not only the water and but also the mud for the working fluid in this study. We used the optical PIV for the water flow measurement and echo PIV for the mud flow. In case of the water study, the dominant vortical structures appeared in both the protrusion and plain model with axial flow. In case of mud flow, the vortices shown in the water model disappeared and the push and pull up motion by the protrusion is dominant. We believe this information can be useful to understand the flow physics of drilling process in the complex fluid flow.     

Spatiotemporal Changes in Hydro-chemistry of Groundwater in Irrigation District within the Kaidu River Basin北大核心CSCD

【Objective】This paper studied the spatiotemporal changes in hydro-chemical properties of groundwater in irrigation districts within the Kaidu River basin, as well as the factors that affect these changes.【Method】Groundwater samples were taken in January, March, July and September in 2017 from the irrigation area in the Kaidu river basin. Spatiotemporal change in hydro-chemical properties of the groundwater and its impacting factors were analyzed using statistics, spatial interpolation, and Piper and Gibbs diagram.【Result】①The groundwater quality was generally good, with low TDS and being dominated by HCO-3, Na+, Ca2+ and SO2-4. The mean TDS was high in winter and low in summer, and it was related to the depth of groundwater table. ② Na+, Ca2+ and SO2-4 varied erratically both in time and space. ③The hydro-chemical type of the groundwater in the studied area was HCO-3-SO2-4-Na+-Ca2+, and remained almost unchanged in the four seasons. ④The rock weathering appears to affect the hydro- chemical propertied of the groundwater most. The impact of human activities was mainly in spring, summer and autumn in the oasis and lakeside region, and it was stronger in irrigation season than in non-irrigation season.【Conclusion】Our results suggest that pumping groundwater for irrigation should be rationally managed and the associated change in chemical properties of the groundwater should be monitored; this applies not only to the studied sites but also to regions on the southern slope of the Tianshan Mountain. © 2019 Authors. All rights reserved.     

Numerical study of hydrofoil surface j etflow on cavitation suppression

Cavitation caused vibration and noise of hydraulic machinery. To some extent,cavitation made fatigue damage in advance. Many scholars found that the re-entrant jets were the reasons of the shedding of cavities. To suppress cavitation,based on the idea of blocking the re-entrant jets,a special surface flow structure of 2D hydrofoil was proposed. The through-hole was made in the proper position of the hydrofoil. The incoming flow can outflow from this jet-hole automatically depending on the pressure difference between pressure side and suction side. Re-entrant jet growth can be weakened by optimizing the jet-hole geometry. Based on the standard k-ε turbulence model and Schnerr Sauer cavitation model,under different cavitation numbers( σ) and jet-angles( β) for NACA0066( 2D) hydrofoil with 8° angles of attack,cavitation field numerical analysis was carried out. The results show that 2D hydrofoil cavitation flow had a strong unsteadiness. Making a jet-hole at the junction between the re-entrant jet and cavity can effectively minimize cloud cavitation. For a certain cavitation condition,optimal jet-angles( β) can be obtained to control cavitation growth. For the same β,the effects of cavitation suppression were changed with different cavitation numbers( σ). Consequently,suitable jet-angle and jet-position could extend the stable operating range of the hydrofoil.     

Responsive Change in Groundwater Table in Karst to Precipitation and Yellow River in Pingyin County北大核心CSCD

【Objective】This paper aims to unravel the relationship between groundwater table fluctuation in karst and the precipitation and water level of the Yellow River at Pingyin in Shandong province.【Method】The analysis was based on data measured from groundwater in two karsts in the proximity of the Yellow River, precipitation and change in water level in the river from 2007 to 2018. The response of groundwater table fluctuation to precipitation and water level in the Yellow River was calculated using cross- correlation analysis, continuous wavelet transform and cross- wavelet transform.【Result】Both precipitation and groundwater table fluctuation had a 12- month period. The responsive change in groundwater table lagged behind the precipitation by 1~8 months, and the water level in the Yellow River by 0~10 months. The precipitation and groundwater table oscillated with a period of 0.86~1.20 a and 0.86~1.36 a respectively, while the oscillation period of the Yellow River water was 1 a and 3 a. The average velocity at which water flowed from the Yellow River to the karst was 21.62~ 25.53 m/d.【Conclusion】The responsive change in groundwater table in the karst in Pingyin to water level in the Yellow River was slightly slower than to precipitation. © 2019 Authors. All rights reserved.