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
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
We investigates the effect of Taylor-Grtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Grtler vortex is detected by longitudinal average o...We investigates the effect of Taylor-Grtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Grtler vortex is detected by longitudinal average of velocity fluctuation in the channel and defined as TG fluctuation. It has been found that turbulent diffusion is significant in the Reynolds stress transportation at the suction side of rotating turbulent channel in contrast with the turbulent channel flow without rotation and Taylor-Grtler vortex plays an important role in the turbulent diffusion in Reynolds stress transport. The paper focuses on the low and moderate rotation number, but the effect of the rotation number on the Reynolds stress transport is also reported.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supported by the National Natural Science Foundation of China (Grant Nos. 10872109, 10828204 and 10925210)the sponsor from the Sino-French Laboratory LIAMA (97-03)
文摘We investigates the effect of Taylor-Grtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Grtler vortex is detected by longitudinal average of velocity fluctuation in the channel and defined as TG fluctuation. It has been found that turbulent diffusion is significant in the Reynolds stress transportation at the suction side of rotating turbulent channel in contrast with the turbulent channel flow without rotation and Taylor-Grtler vortex plays an important role in the turbulent diffusion in Reynolds stress transport. The paper focuses on the low and moderate rotation number, but the effect of the rotation number on the Reynolds stress transport is also reported.
