A shallowly submerged hydrofoil often induces disturbances on the free water surface by generating numerous vortex structures,leading to phenomena such as wave breaking and droplet splashing.These phenomena involve va...A shallowly submerged hydrofoil often induces disturbances on the free water surface by generating numerous vortex structures,leading to phenomena such as wave breaking and droplet splashing.These phenomena involve various physical mechanisms.In this study,the third-generation vortex identification technique,Liutex,is employed to perform a detailed analysis of the vortex structures generated by the hydrofoil near the free surface.It is observed that these coherent vortex structures strongly entrain surrounding fluid,resulting in air entrainment and bubble sweep-down phenomena.We analyze the bubble dynamics in terms of bubble number density,volume distribution,and number distribution,revealing the dynamic characteristics of bubbles under the influence of vortex structures.Additionally,by tracking the vortex structures,two distinct forms of air entrainment are identified.The analysis of bubble motion using Liutex demonstrates the evolution and distribution patterns of bubble sizes in the turbulent flow field.The results indicate that the third-generation vortex identification technique,Liutex,effectively explains the mechanisms behind free surface breaking induced by the shallowly submerged hydrofoil.展开更多
The northeastern China cold vortex(NCCV)plays an important role in regional rainstorms over East Asia.Using the National Centers for Environmental Prediction Final reanalysis dataset and the Global Precipitation Measu...The northeastern China cold vortex(NCCV)plays an important role in regional rainstorms over East Asia.Using the National Centers for Environmental Prediction Final reanalysis dataset and the Global Precipitation Measurement product,an objective algorithm for identifying heavy-precipitation NCCV(HPCV)events was designed,and the climatological features of 164 HPCV events from 2001 to 2019 were investigated.The number of HPCV events showed an upward linear trend,with the highest frequency of occurrence in summer.The most active region of HPCV samples was the Northeast China Plain between 40°–55°N.Most HPCV events lasted 3–5 days and had radii ranging from 250 to 1000 km.The duration of HPCV events with larger sizes was longer.About half of the HPCV events moved into(moved out of)the definition region(35°–60°N,115°–145°E),and half initiated(dissipated)within the region.The initial position was close to the western boundary of the definition region,and the final position was mainly near the eastern boundary.The locations associated with the precipitation were mostly concentrated within 2000 km southeast of the HPCV systems,and they were farther from the center in the cold season than in the warm season.展开更多
Compressing complex flows into a tangle of vortex filaments is the basic implication of the classical vortex-representation notion.This work focuses on the effectiveness of the local identification criteria in the vor...Compressing complex flows into a tangle of vortex filaments is the basic implication of the classical vortex-representation notion.This work focuses on the effectiveness of the local identification criteria in the vortex representation of wall-bounded turbulence.Basically,five local identification criteria regarding vortex strength and three criteria for vortex axis are considered.Instead of separately evaluating the two classes of criteria,the current work defines vortex vectors by arbitrarily combining the vortex strength and vortex axis expressed by various criteria,and attempts to figure out the most effective one regarding the vortex representation.The effectiveness of these vortex vectors is evaluated based on two aspects:first,the alignment of the vortex axis and vortex iso-surface should be well established,which benefits the simplification of the vortex filaments;second,vortices could be viewed as the"gene code"of turbulent flows,which means reconstructing the velocity fields based on them should be effective.For the first aspect,the differential geometry method is employed to describe the vortex isosurface-axis alignment property quantitatively.For the second aspect,the Biot-Savart law is employed to accomplish the vortex-to-velocity reconstruction.Results of this work provide some reference for the applications of vortex identification criteria in wall-bounded turbulence.展开更多
Considering the differences between the Northeast China Cold Vortex （CV） and the Mid-Summer （MS） rainy period and their corresponding atmospheric circulations are comprehensively analyzed, and the objective identi...Considering the differences between the Northeast China Cold Vortex （CV） and the Mid-Summer （MS） rainy period and their corresponding atmospheric circulations are comprehensively analyzed, and the objective identification methods of defining the annual beginning and ending dates of Northeast China CV and MS rainy periods are developed respectively. The annual beginning date of the CV （MS） rainy period is as follows. In a period from April to August, if daily regional mean precipitation ryi is larger than yearly regional mean precipitation R （or 2R） on a certain day, the station precipitation rs is larger than the station yearly mean precipitation （r/ （or 2（r）） in at least 50% of stations in Northeast China, and this condition is satisfied in the following 2 （7） days, then this date is defined as the beginning date of the CV （MS） rainy period. While the definition of the ending date of the MS rainy period shows the opposite process to its beginning date. With this objective identification method, the multi-year average （1981-2010） beginning date of the CV rainy period is May 3, the beginning date of the MS rainy period is June 27, the ending day of the CV rainy period is defined as the day before the beginning date of the MS rainy period, and the ending date of the MS rainy period is August 29. Meanwhile, corresponding anomaly analysis at a 500-hPa geopotential height, 850-hPa wind, Omega and relative humidity fields all show that the definitions of the average beginning and ending dates of the CV and MS rainy periods have a certain circulation meaning. Furthermore, the daily evolution of the CV index, meridional and zonal wind index, etc. all show that these objectively defined beginning and ending dates of the CV and MS rainy periods have climate significance.展开更多
A novel vortex identification method for the visualization of the flow field is used for the study of the stall process of a transonic compressor.The parameter η4,which is one of the five invariants formed by the sta...A novel vortex identification method for the visualization of the flow field is used for the study of the stall process of a transonic compressor.The parameter η4,which is one of the five invariants formed by the stain rate and vorticity tensors from the theory of modern rational mechanics,is found to have good ability to identify vortex stretching and vortex relaxation/breakdown processes,is introduced here to identify the tip leakage vortices.Compare with former generally used DPH(dynamic pressure head) contour,the new method reveals much more flow details which may advance our understanding of the compressor behaviors.The Vortices details are revealed in both peak efficiency and near stall condition.A possible stall process is also suggested based on the vortices analysis.The tip leakage flow from mid-chord,besides leading edge leakage flow,is also considered to play an important role in the stall process.展开更多
Fishway research is important for mitigating the fragmentation of river habitats caused by hydraulic projects.The vertical slit fishway is a broadly used fishway type because of its high efficiency and adaptability to...Fishway research is important for mitigating the fragmentation of river habitats caused by hydraulic projects.The vertical slit fishway is a broadly used fishway type because of its high efficiency and adaptability to water levels.However,the resulting vortex current disrupts the fish passage hence directly affecting fish migration.This study aims to accurately capture the vortex structure in the fishway and analyze the effect of vortex elements(vortex structure,vortex intensity,etc.)on fish.We conducted an analysis of the 3-D current flow field in the fishway through the utilization of an experimental model and the large eddy simulation(LES)method.Moreover,we captured the vortex information in the fishway at different flow rates using the Liutex vortex identification method and investigated the effect of the vortex on fish migration.The results revealed that the structures inside the fishway pool occupy most of the room,however,the areas with higher vortex strength were primarily located in the vortex near the vertical seam and the mainstream,the vortex strength inside the fishway gradually increases with increasing flow,suppressing fish migration.Fish experienced significantly increased resistance when encountering strong vortices.This suggests that the vortex may act as a physical barrier to fish migration.These findings highlight the potential negative effects of vortex on fish movement and reiterate the importance of understanding vortex dynamics for aquatic environmental management.As an effective tool for identifying vortices in fluid flow,the Liutex method demonstrates features of vortex within the fishway,thereby providing important insights into the interaction between fluid dynamics and aquatic organisms.展开更多
This study investigates turbulent particle-laden channel flows using direct numerical simulations employing the Eulerian-Lagrangian method.A two-way coupling approach is adopted to explore the mutual interaction betwe...This study investigates turbulent particle-laden channel flows using direct numerical simulations employing the Eulerian-Lagrangian method.A two-way coupling approach is adopted to explore the mutual interaction between particles and fluid flow.The considered cases include flow with particle Stokes number varying from St=2 up to St=100 while maintaining a constant Reynolds number of Reτ=180 across all cases.A novel vortex identification method,Liutex(Rortex),is employed to assess its efficacy in capturing near-wall turbulent coherent structures and their interactions with particles.The Liutex method provides valuable information on vortex strength and vectors at each location,enabling a detailed examination of the complex interaction between fluid and particulate phases.As widely acknowledged,the interplay between clockwise and counterclockwise vortices in the near-wall region gives rise to low-speed streaks along the wall.These low-speed streaks serve as preferential zones for particle concentration,depending upon the particle Stokes number.It is shown that the Liutex method can capture these vortices and identify the location of low-speed streaks.Additionally,it is observed that the particle Stokes number(size)significantly affects both the strength of these vortices and the streaky structure exhibited by particles.Furthermore,a quantitative analysis of particle behavior in the near-wall region and the formation of elongated particle lines was carried out.This involved examining the average fluid streamwise velocity fluctuations at particle locations,average particle concentration,and the normal velocity of particles for each set of particle Stokes numbers.The investigation reveals the intricate interplay between particles and near-wall structures and the significant influence of particles Stokes number.This study contributes to a deeper understanding of turbulent particle-laden channel flow dynamics.展开更多
In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within th...In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within the furnace.The melt’s viscosity,which varies across reaction stages,and the operating conditions influence bubble size and dynamics.This study investigates the interplay between melt viscosity and bubble diameter on bubble motion using numerical simulations and experiments.In particular,the volume of fluid(VOF)method andΩ-identification technique were employed to analyze bubble velocity,deformation,trajectories,and wake characteristics.The results showed that bubble ascent velocity increases with bubble size and decreases in viscosity,though viscosity variations minimally affect the maximum velocity.Larger bubbles or those in less viscous melts exhibit greater deformation.Bubbles ascend primarily in straight trajectories with minor lateral oscillations regardless of viscosity.In terms of wake dynamics,vortex sizes grow as viscosity decreases,with bottom-formed vortices expanding significantly with increasing bubble size,while lateral vortices are less influenced.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52131102,52471335)supported by the Research and Application Demonstration Project of Key Technologies for Safeguarding of Container Vessels in Ningbo Zhoushan Port Based on Intelligent Navigation(Grant No.ZJHG-FW-2024-27).
文摘A shallowly submerged hydrofoil often induces disturbances on the free water surface by generating numerous vortex structures,leading to phenomena such as wave breaking and droplet splashing.These phenomena involve various physical mechanisms.In this study,the third-generation vortex identification technique,Liutex,is employed to perform a detailed analysis of the vortex structures generated by the hydrofoil near the free surface.It is observed that these coherent vortex structures strongly entrain surrounding fluid,resulting in air entrainment and bubble sweep-down phenomena.We analyze the bubble dynamics in terms of bubble number density,volume distribution,and number distribution,revealing the dynamic characteristics of bubbles under the influence of vortex structures.Additionally,by tracking the vortex structures,two distinct forms of air entrainment are identified.The analysis of bubble motion using Liutex demonstrates the evolution and distribution patterns of bubble sizes in the turbulent flow field.The results indicate that the third-generation vortex identification technique,Liutex,effectively explains the mechanisms behind free surface breaking induced by the shallowly submerged hydrofoil.
基金supported by the National Key R&D Program of China under Grant No.2018YFC1507302the National Natural Science Foundation of China under Grant No.42175006+1 种基金Jiangsu Youth Talent Promotion Project(2021-084)the Basic Research Fund of CAMS under Grant No.2020R002.
文摘The northeastern China cold vortex(NCCV)plays an important role in regional rainstorms over East Asia.Using the National Centers for Environmental Prediction Final reanalysis dataset and the Global Precipitation Measurement product,an objective algorithm for identifying heavy-precipitation NCCV(HPCV)events was designed,and the climatological features of 164 HPCV events from 2001 to 2019 were investigated.The number of HPCV events showed an upward linear trend,with the highest frequency of occurrence in summer.The most active region of HPCV samples was the Northeast China Plain between 40°–55°N.Most HPCV events lasted 3–5 days and had radii ranging from 250 to 1000 km.The duration of HPCV events with larger sizes was longer.About half of the HPCV events moved into(moved out of)the definition region(35°–60°N,115°–145°E),and half initiated(dissipated)within the region.The initial position was close to the western boundary of the definition region,and the final position was mainly near the eastern boundary.The locations associated with the precipitation were mostly concentrated within 2000 km southeast of the HPCV systems,and they were farther from the center in the cold season than in the warm season.
基金the National Natural Science Foundation of China(Grant Nos.11902371 and 91852204)China Postdoctoral Science Foundation(Grant No.2019M653172).
文摘Compressing complex flows into a tangle of vortex filaments is the basic implication of the classical vortex-representation notion.This work focuses on the effectiveness of the local identification criteria in the vortex representation of wall-bounded turbulence.Basically,five local identification criteria regarding vortex strength and three criteria for vortex axis are considered.Instead of separately evaluating the two classes of criteria,the current work defines vortex vectors by arbitrarily combining the vortex strength and vortex axis expressed by various criteria,and attempts to figure out the most effective one regarding the vortex representation.The effectiveness of these vortex vectors is evaluated based on two aspects:first,the alignment of the vortex axis and vortex iso-surface should be well established,which benefits the simplification of the vortex filaments;second,vortices could be viewed as the"gene code"of turbulent flows,which means reconstructing the velocity fields based on them should be effective.For the first aspect,the differential geometry method is employed to describe the vortex isosurface-axis alignment property quantitatively.For the second aspect,the Biot-Savart law is employed to accomplish the vortex-to-velocity reconstruction.Results of this work provide some reference for the applications of vortex identification criteria in wall-bounded turbulence.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.41205040 and 41375078)the State Key Development Program for Basic Research,China(Grant No.2012CB955203)the Special Scientific Research Project for Public Interest(Grant No.GYHY201306021)
文摘Considering the differences between the Northeast China Cold Vortex （CV） and the Mid-Summer （MS） rainy period and their corresponding atmospheric circulations are comprehensively analyzed, and the objective identification methods of defining the annual beginning and ending dates of Northeast China CV and MS rainy periods are developed respectively. The annual beginning date of the CV （MS） rainy period is as follows. In a period from April to August, if daily regional mean precipitation ryi is larger than yearly regional mean precipitation R （or 2R） on a certain day, the station precipitation rs is larger than the station yearly mean precipitation （r/ （or 2（r）） in at least 50% of stations in Northeast China, and this condition is satisfied in the following 2 （7） days, then this date is defined as the beginning date of the CV （MS） rainy period. While the definition of the ending date of the MS rainy period shows the opposite process to its beginning date. With this objective identification method, the multi-year average （1981-2010） beginning date of the CV rainy period is May 3, the beginning date of the MS rainy period is June 27, the ending day of the CV rainy period is defined as the day before the beginning date of the MS rainy period, and the ending date of the MS rainy period is August 29. Meanwhile, corresponding anomaly analysis at a 500-hPa geopotential height, 850-hPa wind, Omega and relative humidity fields all show that the definitions of the average beginning and ending dates of the CV and MS rainy periods have a certain circulation meaning. Furthermore, the daily evolution of the CV index, meridional and zonal wind index, etc. all show that these objectively defined beginning and ending dates of the CV and MS rainy periods have climate significance.
基金This research work is supported by the GEAE USA ProgrammeNational Science Foundation of China(NSFC)project No.10477012.
文摘A novel vortex identification method for the visualization of the flow field is used for the study of the stall process of a transonic compressor.The parameter η4,which is one of the five invariants formed by the stain rate and vorticity tensors from the theory of modern rational mechanics,is found to have good ability to identify vortex stretching and vortex relaxation/breakdown processes,is introduced here to identify the tip leakage vortices.Compare with former generally used DPH(dynamic pressure head) contour,the new method reveals much more flow details which may advance our understanding of the compressor behaviors.The Vortices details are revealed in both peak efficiency and near stall condition.A possible stall process is also suggested based on the vortices analysis.The tip leakage flow from mid-chord,besides leading edge leakage flow,is also considered to play an important role in the stall process.
基金supported by the National Natural Science Foundation of China(Grant Nos.52069009,51369013).
文摘Fishway research is important for mitigating the fragmentation of river habitats caused by hydraulic projects.The vertical slit fishway is a broadly used fishway type because of its high efficiency and adaptability to water levels.However,the resulting vortex current disrupts the fish passage hence directly affecting fish migration.This study aims to accurately capture the vortex structure in the fishway and analyze the effect of vortex elements(vortex structure,vortex intensity,etc.)on fish.We conducted an analysis of the 3-D current flow field in the fishway through the utilization of an experimental model and the large eddy simulation(LES)method.Moreover,we captured the vortex information in the fishway at different flow rates using the Liutex vortex identification method and investigated the effect of the vortex on fish migration.The results revealed that the structures inside the fishway pool occupy most of the room,however,the areas with higher vortex strength were primarily located in the vortex near the vertical seam and the mainstream,the vortex strength inside the fishway gradually increases with increasing flow,suppressing fish migration.Fish experienced significantly increased resistance when encountering strong vortices.This suggests that the vortex may act as a physical barrier to fish migration.These findings highlight the potential negative effects of vortex on fish movement and reiterate the importance of understanding vortex dynamics for aquatic environmental management.As an effective tool for identifying vortices in fluid flow,the Liutex method demonstrates features of vortex within the fishway,thereby providing important insights into the interaction between fluid dynamics and aquatic organisms.
文摘This study investigates turbulent particle-laden channel flows using direct numerical simulations employing the Eulerian-Lagrangian method.A two-way coupling approach is adopted to explore the mutual interaction between particles and fluid flow.The considered cases include flow with particle Stokes number varying from St=2 up to St=100 while maintaining a constant Reynolds number of Reτ=180 across all cases.A novel vortex identification method,Liutex(Rortex),is employed to assess its efficacy in capturing near-wall turbulent coherent structures and their interactions with particles.The Liutex method provides valuable information on vortex strength and vectors at each location,enabling a detailed examination of the complex interaction between fluid and particulate phases.As widely acknowledged,the interplay between clockwise and counterclockwise vortices in the near-wall region gives rise to low-speed streaks along the wall.These low-speed streaks serve as preferential zones for particle concentration,depending upon the particle Stokes number.It is shown that the Liutex method can capture these vortices and identify the location of low-speed streaks.Additionally,it is observed that the particle Stokes number(size)significantly affects both the strength of these vortices and the streaky structure exhibited by particles.Furthermore,a quantitative analysis of particle behavior in the near-wall region and the formation of elongated particle lines was carried out.This involved examining the average fluid streamwise velocity fluctuations at particle locations,average particle concentration,and the normal velocity of particles for each set of particle Stokes numbers.The investigation reveals the intricate interplay between particles and near-wall structures and the significant influence of particles Stokes number.This study contributes to a deeper understanding of turbulent particle-laden channel flow dynamics.
基金Supported by Yunnan Fundamental Research Projects(Nos.202301AT070469,202301AT070275)supported by Yunnan Major Scientific and Technological Projects(No.202202AG050002).
文摘In bottom-blown copper smelting processes,oxygen-enriched air is typically injected into the melt through a lance,generating bubbles that ascend and agitate the melt,enhancing mass,momentum,and heat transfer within the furnace.The melt’s viscosity,which varies across reaction stages,and the operating conditions influence bubble size and dynamics.This study investigates the interplay between melt viscosity and bubble diameter on bubble motion using numerical simulations and experiments.In particular,the volume of fluid(VOF)method andΩ-identification technique were employed to analyze bubble velocity,deformation,trajectories,and wake characteristics.The results showed that bubble ascent velocity increases with bubble size and decreases in viscosity,though viscosity variations minimally affect the maximum velocity.Larger bubbles or those in less viscous melts exhibit greater deformation.Bubbles ascend primarily in straight trajectories with minor lateral oscillations regardless of viscosity.In terms of wake dynamics,vortex sizes grow as viscosity decreases,with bottom-formed vortices expanding significantly with increasing bubble size,while lateral vortices are less influenced.
