Since the classical investigation of the Taylor vortex by G. I. Taylor in 1923, many researchers have studied the Taylor vortex as one of the most important vortex types in flow. In this study, the inner cylinder is r...Since the classical investigation of the Taylor vortex by G. I. Taylor in 1923, many researchers have studied the Taylor vortex as one of the most important vortex types in flow. In this study, the inner cylinder is rotating, while the outer cylinder, which is concentric with the inner cylinder, is stationary. In addition, the measurement of the velocity distribution is carried out by the PIV （Particle Image Velocimetry） method. The radius of the inner cylinder is 20 mm, and that of the outer cylinder is 30 mm. In this study, Re = 650-1,200 is assumed. In the upper part of the apparatus, movable ends are fixed to the upper and lower sides of the cylinder to change the aspect ratio. The aspect ratio is defined as the ratio of cylinder height to gap distance. A servo motor to rotate the inner cylinder, a servo-motor control device, a servo amplifier for rotation speed control, and a YAG laser light source are installed in the apparatus. For the visualization of Taylor vortex flow, aluminum powder composed of scale like fine particles is used. As tracer particles used in the PIV method, fluorescent particles with a size of 48 Ixm were used. The governing equations are Navier-Stokes equations with cylindrical coordinates （r, θ, z） and the equations of continuity. Each physical value is nondimensionalized using the angular velocity of the inner cylinder as the representative velocity, and the radius difference between the inner and outer cylinders as the representative length. Discretization of the governing equations is based on the MAC method. The results of EFD and CFD （computational fluid dynamics） are compared. The mode bifurcation is observed, and the flow structure is investigated.展开更多
Taylor vortex flow between two concentric rotating cylinders with finite axial length includes various patterns of laminar and turbulent flows, and its behavior has attracted great interests. When mode bifurcation occ...Taylor vortex flow between two concentric rotating cylinders with finite axial length includes various patterns of laminar and turbulent flows, and its behavior has attracted great interests. When mode bifurcation occurs, quantitative parameters such as the volume-averaged energy change rapidly. It is important to visualize the behaviors of vortices. In this study, a three-dimensional visualization system with respect to time is devised. This system can change the viewpoint of flow visualization, and we can observe the track of a vortex from any point. The volume-averaged energy is projected to the track of the center of a vortex. The proposed system can help to investigate the relationship between the mode bifurcation process and the volume-averaged energy.展开更多
Transition to Taylor vortex flow between two conical cylinders,with the inner one rotating and the outer one stationary,is studied by the numerical method in this article.It is found that the basic flow becomes unstab...Transition to Taylor vortex flow between two conical cylinders,with the inner one rotating and the outer one stationary,is studied by the numerical method in this article.It is found that the basic flow becomes unstable with increasing of Reynolds number（Re ） above a certain critical value Rec =117 and with the further increase of Re to about Re=300,the first stable vortex is formed near the top of the flow system.The annulus is filled with six pairs of vortices at about Re=800.These are confirmed by experimental observations.Moreover,the local extreme values of pressure and velocity are reached at the adjacent lines between neighboring vortices or at the medium lines of large vortices.The local minimum values of velocity and the local maximum values of pressure are reached at the same point,whereas the local maximum values of velocity of the flow are assumed at the point of inflection for pressure.展开更多
Turbulent Taylor vortex flow,which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends,is simulated by applying the devel-opment in Reynolds stress equations mold(RSM)of t...Turbulent Taylor vortex flow,which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends,is simulated by applying the devel-opment in Reynolds stress equations mold(RSM)of the micro-perturbation.This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations.Based on the numerical simulation results of the turbulent Taylor vortex flow,its characteristics such as the fluctuation of the flow field,the precipitous drop of azimuthal velocity,the jet flow of radial velocity,the periodicity of axial velocity,the wave periodicity of pressure distribution,the polarization of shear stress on the walls,and the turbulence intensity in the jet region,are discussed.Com-paring the pilot results measured by previous methods,the relative error of the characteristics predicted by simulation is less than 30%.展开更多
The study investigated Taylor vortex flow between rotating double cylinders using a convolutional neural network (CNN). By combining numerical results of vortex flow for specific periods after vortex onset, the resear...The study investigated Taylor vortex flow between rotating double cylinders using a convolutional neural network (CNN). By combining numerical results of vortex flow for specific periods after vortex onset, the researchers aimed to determine if mode discrimination was possible in the combined images. They used images taken at various intervals: 20 images at 1 second, 30 images at 1.5 seconds, 40 images at 2 seconds, 50 images at 2.5 seconds, 60 images at 3 seconds, and 67 images at 3.35 seconds after vortex onset. The goal was to compare the accuracy rates in predicting the mode development process of the vortex. The study concluded that the mode development process of the Taylor vortex can be discriminated by combining images taken at specific time intervals after the vortex occurs and training the CNN with these images as teacher data. The results showed that the most efficient prediction of the mode development process was achieved when 50 images taken at 2.5 seconds were used for learning. This highlights the potential of using CNNs in fluid dynamics research, specifically in analyzing and predicting the behavior of vortex flows.展开更多
More and more researchers have paid attention to Taylor-Couette flow whose axial dimension is much larger than other dimensions.However,featured by the limited axial length of the bearing,its flow field and convective...More and more researchers have paid attention to Taylor-Couette flow whose axial dimension is much larger than other dimensions.However,featured by the limited axial length of the bearing,its flow field and convective heat transfer between the rotator and the stator are highly conglutinated with the leakage at the end of the clearance.An investigation was conducted on the flow field and convective heat transfer of small-scale Taylor-Couette flow induced by end leakage through means of numerical simulation and experimental measurement.The static pressure and temperature of the stator were captured by a micromanometer and a time-resolved infrared camera,respectively.Large Eddy Simulation(LES)was performed to reveal the instantaneous and mean flow field of the shearing flow.Results show that the flow field and convective heat transfer are tightly associated with the presence of end leakage.As approaching the end of the clearance,the flow is dominated by the axial flow induced by the end leakage,and then a series of Taylor vortices gradually distorts and tilts as moving downstream.Along the angular direction,the maximum and minimum static pressures take place near minimum clearance height,respectively.The static pressure along the angular direction and the axial velocity near the minimum clearance height as well as the Nusselt number increase with increases of the rotational Reynolds number and the eccentricity ratio while decreasing with an increase of the dimensionless clearance height.Both natural convection by buoyancy and forced convection by the shearing flow play a significant role in convective heat transfer.Compared with classic Taylor-Couette flow,the occurrence of leakage decreases the maximum static pressure while increasing the minimum static pressure.The formation and evolution of the Taylor vortex are dominated by the axial flow.展开更多
文摘Since the classical investigation of the Taylor vortex by G. I. Taylor in 1923, many researchers have studied the Taylor vortex as one of the most important vortex types in flow. In this study, the inner cylinder is rotating, while the outer cylinder, which is concentric with the inner cylinder, is stationary. In addition, the measurement of the velocity distribution is carried out by the PIV （Particle Image Velocimetry） method. The radius of the inner cylinder is 20 mm, and that of the outer cylinder is 30 mm. In this study, Re = 650-1,200 is assumed. In the upper part of the apparatus, movable ends are fixed to the upper and lower sides of the cylinder to change the aspect ratio. The aspect ratio is defined as the ratio of cylinder height to gap distance. A servo motor to rotate the inner cylinder, a servo-motor control device, a servo amplifier for rotation speed control, and a YAG laser light source are installed in the apparatus. For the visualization of Taylor vortex flow, aluminum powder composed of scale like fine particles is used. As tracer particles used in the PIV method, fluorescent particles with a size of 48 Ixm were used. The governing equations are Navier-Stokes equations with cylindrical coordinates （r, θ, z） and the equations of continuity. Each physical value is nondimensionalized using the angular velocity of the inner cylinder as the representative velocity, and the radius difference between the inner and outer cylinders as the representative length. Discretization of the governing equations is based on the MAC method. The results of EFD and CFD （computational fluid dynamics） are compared. The mode bifurcation is observed, and the flow structure is investigated.
文摘Taylor vortex flow between two concentric rotating cylinders with finite axial length includes various patterns of laminar and turbulent flows, and its behavior has attracted great interests. When mode bifurcation occurs, quantitative parameters such as the volume-averaged energy change rapidly. It is important to visualize the behaviors of vortices. In this study, a three-dimensional visualization system with respect to time is devised. This system can change the viewpoint of flow visualization, and we can observe the track of a vortex from any point. The volume-averaged energy is projected to the track of the center of a vortex. The proposed system can help to investigate the relationship between the mode bifurcation process and the volume-averaged energy.
文摘Transition to Taylor vortex flow between two conical cylinders,with the inner one rotating and the outer one stationary,is studied by the numerical method in this article.It is found that the basic flow becomes unstable with increasing of Reynolds number（Re ） above a certain critical value Rec =117 and with the further increase of Re to about Re=300,the first stable vortex is formed near the top of the flow system.The annulus is filled with six pairs of vortices at about Re=800.These are confirmed by experimental observations.Moreover,the local extreme values of pressure and velocity are reached at the adjacent lines between neighboring vortices or at the medium lines of large vortices.The local minimum values of velocity and the local maximum values of pressure are reached at the same point,whereas the local maximum values of velocity of the flow are assumed at the point of inflection for pressure.
文摘Turbulent Taylor vortex flow,which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends,is simulated by applying the devel-opment in Reynolds stress equations mold(RSM)of the micro-perturbation.This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations.Based on the numerical simulation results of the turbulent Taylor vortex flow,its characteristics such as the fluctuation of the flow field,the precipitous drop of azimuthal velocity,the jet flow of radial velocity,the periodicity of axial velocity,the wave periodicity of pressure distribution,the polarization of shear stress on the walls,and the turbulence intensity in the jet region,are discussed.Com-paring the pilot results measured by previous methods,the relative error of the characteristics predicted by simulation is less than 30%.
文摘The study investigated Taylor vortex flow between rotating double cylinders using a convolutional neural network (CNN). By combining numerical results of vortex flow for specific periods after vortex onset, the researchers aimed to determine if mode discrimination was possible in the combined images. They used images taken at various intervals: 20 images at 1 second, 30 images at 1.5 seconds, 40 images at 2 seconds, 50 images at 2.5 seconds, 60 images at 3 seconds, and 67 images at 3.35 seconds after vortex onset. The goal was to compare the accuracy rates in predicting the mode development process of the vortex. The study concluded that the mode development process of the Taylor vortex can be discriminated by combining images taken at specific time intervals after the vortex occurs and training the CNN with these images as teacher data. The results showed that the most efficient prediction of the mode development process was achieved when 50 images taken at 2.5 seconds were used for learning. This highlights the potential of using CNNs in fluid dynamics research, specifically in analyzing and predicting the behavior of vortex flows.
基金The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China(Nos.51776097 and 52206091)the Aeronautical Science Foundation of China(No.201928052008)+1 种基金the Natural Science Foundation of Jiangsu Province,China(No.BK20210303)the Advanced Jet Propulsion Innovation,China(No.HKCX2022-01-001).
文摘More and more researchers have paid attention to Taylor-Couette flow whose axial dimension is much larger than other dimensions.However,featured by the limited axial length of the bearing,its flow field and convective heat transfer between the rotator and the stator are highly conglutinated with the leakage at the end of the clearance.An investigation was conducted on the flow field and convective heat transfer of small-scale Taylor-Couette flow induced by end leakage through means of numerical simulation and experimental measurement.The static pressure and temperature of the stator were captured by a micromanometer and a time-resolved infrared camera,respectively.Large Eddy Simulation(LES)was performed to reveal the instantaneous and mean flow field of the shearing flow.Results show that the flow field and convective heat transfer are tightly associated with the presence of end leakage.As approaching the end of the clearance,the flow is dominated by the axial flow induced by the end leakage,and then a series of Taylor vortices gradually distorts and tilts as moving downstream.Along the angular direction,the maximum and minimum static pressures take place near minimum clearance height,respectively.The static pressure along the angular direction and the axial velocity near the minimum clearance height as well as the Nusselt number increase with increases of the rotational Reynolds number and the eccentricity ratio while decreasing with an increase of the dimensionless clearance height.Both natural convection by buoyancy and forced convection by the shearing flow play a significant role in convective heat transfer.Compared with classic Taylor-Couette flow,the occurrence of leakage decreases the maximum static pressure while increasing the minimum static pressure.The formation and evolution of the Taylor vortex are dominated by the axial flow.
