An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry (PIV) was used to measure the free surface vortex flow field at different developm...An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry (PIV) was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.展开更多
Based on the Navier-Stokes equations with considering the effect of the Coriolis force, the finite volume method was employed to discretize the governing equations, the SIMPLE method was adopted to solve the discretiz...Based on the Navier-Stokes equations with considering the effect of the Coriolis force, the finite volume method was employed to discretize the governing equations, the SIMPLE method was adopted to solve the discretized equations, and the flow field in a barrel with an outlet at the center of the bottom was simulated. The numerical results agree well with the experimental data. From the Lagrangian, the relations among the acceleration, the Coriolis force and the viscosity force were analyzed. The results show that the Coriolis force is the major factor that causes the formation of the vortex. The flow fields in the flume under different incoming flow conditions were numerically simulated using the software Fluent. The numerical simulations show good agreement with the experiments for the shape and position of the vortex.展开更多
The surface vortex in a spillway tunnel intake was investigated in a physical model of the Xiluodu hydropower station.The velocity fields were measured using the particle tracking velocimetry technique.The tangential ...The surface vortex in a spillway tunnel intake was investigated in a physical model of the Xiluodu hydropower station.The velocity fields were measured using the particle tracking velocimetry technique.The tangential velocity formula of the surface flow field was derived based on the Navier-Stokes equations,and this formula greatly improved the consistency between the numerical and experimental data.Also,the formula has the advantage of describing the tangential velocity more accurately than previous formulas.The current research is based on established engineering practices,and the results provide a valuable reference for actual projects designed to prevent and eliminate surface vortexes.展开更多
The effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks were investigated.Particle distribution and power consumption were analyzed by experiments and numerical simulations ...The effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks were investigated.Particle distribution and power consumption were analyzed by experiments and numerical simulations in both baffled and unbaffled tanks agitated by a Rushton impeller.In unbaffled tanks,a non-aggregation rule was applied and the average dispersion index was found to serve as a reasonable prediction of the full drawdown of floating particles.The critical impeller speeds in an unbaffled tank were higher than those in a tank with vertical baffles.At each immersion depth in a baffled tank,particles distributed more uniformly and more power was consumed.Comparison of snapshots of the baffled and unbaffled tanks shows that the surface vortex increases the drawdown speed while it decreases the particle distribution uniformity and power consumption.Therefore,the use of baffles to suppress the surface vortex provides for a more uniform particle distribution in stirred tanks.展开更多
The stratospheric influences on the non-uniform variation in early spring(March–April,MA)surface temperature over Eurasia is investigated based on the ERA-Interim,NCEP-1,and NCEP-2 reanalysis data for the period198...The stratospheric influences on the non-uniform variation in early spring(March–April,MA)surface temperature over Eurasia is investigated based on the ERA-Interim,NCEP-1,and NCEP-2 reanalysis data for the period1980–2016.A lead–lag correlation is found between preceding winter(December–February,DJF)stratospheric polar vortex displacements(SPVD)and the MA west–east seesaw pattern in surface temperature over Eurasia.Further analysis reveals that the East Asian jet stream may act as a bridge linking DJF SPVD and MA surface temperature over Eurasia.A positive change in SPVD is associated with a decelerated polar jet stream and an accelerated East Asian jet stream in the troposphere in DJF.The East Asian jet stream signal can persist into MA.As a result,anomalous southerly/northerly winds prevail over western/eastern Eurasia,accounting for the west–east surface temperature seesaw over Eurasia.展开更多
基金the National Natural Science Foundation of China (Grant No. 10772108)the ShanghaiLeading Academic Discipline Project (Grant No. Y0103)
文摘An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry (PIV) was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.
基金Project supported by the National Natural Science Foundation of China(Grant No.10772108).
文摘Based on the Navier-Stokes equations with considering the effect of the Coriolis force, the finite volume method was employed to discretize the governing equations, the SIMPLE method was adopted to solve the discretized equations, and the flow field in a barrel with an outlet at the center of the bottom was simulated. The numerical results agree well with the experimental data. From the Lagrangian, the relations among the acceleration, the Coriolis force and the viscosity force were analyzed. The results show that the Coriolis force is the major factor that causes the formation of the vortex. The flow fields in the flume under different incoming flow conditions were numerically simulated using the software Fluent. The numerical simulations show good agreement with the experiments for the shape and position of the vortex.
基金Supported by Tsinghua University Initiative Scientific ResearchProgram (No 2009THZ07060)the State Key Laboratory ofHydroscience and Engineering of Tsinghua University (Nos2008-ZY-5 and 2009-TC-2)
文摘The surface vortex in a spillway tunnel intake was investigated in a physical model of the Xiluodu hydropower station.The velocity fields were measured using the particle tracking velocimetry technique.The tangential velocity formula of the surface flow field was derived based on the Navier-Stokes equations,and this formula greatly improved the consistency between the numerical and experimental data.Also,the formula has the advantage of describing the tangential velocity more accurately than previous formulas.The current research is based on established engineering practices,and the results provide a valuable reference for actual projects designed to prevent and eliminate surface vortexes.
基金This work was supported by the National Natural Science Foun-dation of China under Project Nos.51474109,51609090,and 51679097.
文摘The effects of surface vortex on the drawdown and dispersion of floating particles in stirred tanks were investigated.Particle distribution and power consumption were analyzed by experiments and numerical simulations in both baffled and unbaffled tanks agitated by a Rushton impeller.In unbaffled tanks,a non-aggregation rule was applied and the average dispersion index was found to serve as a reasonable prediction of the full drawdown of floating particles.The critical impeller speeds in an unbaffled tank were higher than those in a tank with vertical baffles.At each immersion depth in a baffled tank,particles distributed more uniformly and more power was consumed.Comparison of snapshots of the baffled and unbaffled tanks shows that the surface vortex increases the drawdown speed while it decreases the particle distribution uniformity and power consumption.Therefore,the use of baffles to suppress the surface vortex provides for a more uniform particle distribution in stirred tanks.
基金Supported by the National Natural Science Foundation of China(41210007 and 41375083)
文摘The stratospheric influences on the non-uniform variation in early spring(March–April,MA)surface temperature over Eurasia is investigated based on the ERA-Interim,NCEP-1,and NCEP-2 reanalysis data for the period1980–2016.A lead–lag correlation is found between preceding winter(December–February,DJF)stratospheric polar vortex displacements(SPVD)and the MA west–east seesaw pattern in surface temperature over Eurasia.Further analysis reveals that the East Asian jet stream may act as a bridge linking DJF SPVD and MA surface temperature over Eurasia.A positive change in SPVD is associated with a decelerated polar jet stream and an accelerated East Asian jet stream in the troposphere in DJF.The East Asian jet stream signal can persist into MA.As a result,anomalous southerly/northerly winds prevail over western/eastern Eurasia,accounting for the west–east surface temperature seesaw over Eurasia.