针对工程中关心的振荡圆柱绕流问题,采用同位网格系统中的 SIMPLE算法求解 N S方程,以及动网格技术模拟圆柱的运动边界,对均匀来流中的横向振荡圆柱绕流场进行数值模拟,计算了振荡圆柱升力系数、阻力系数随时间的变化曲线,以及不同相位...针对工程中关心的振荡圆柱绕流问题,采用同位网格系统中的 SIMPLE算法求解 N S方程,以及动网格技术模拟圆柱的运动边界,对均匀来流中的横向振荡圆柱绕流场进行数值模拟,计算了振荡圆柱升力系数、阻力系数随时间的变化曲线,以及不同相位时的流线矢量图和涡量等值线分布图。为验证模型的可靠性,对静水中的振荡圆柱流场进行模拟,与实验及数值计算结果吻合较好。展开更多
Numerical simulations of a low-mass-damping circular cylinder which can oscillate freely at transverse and streamwise directions are presented in this work.The Navier-Stokes equations are solved with finite volume met...Numerical simulations of a low-mass-damping circular cylinder which can oscillate freely at transverse and streamwise directions are presented in this work.The Navier-Stokes equations are solved with finite volume method,and large eddy simulation of vortex is also performed in the calculation.In order to implement dynamic mesh,overlapping grids are generated to lessen the computation for mesh field itself.Self-excited vibrations are firstly calculated to obtain the average amplitudes and frequencies of the target circular cylinder in the current flow situation,and then forced oscillations are implemented with parameters obtained in vortex-induced vibrations previously.With slight amplitude modulation,time series of displacements in vortex-induced vibrations are essentially harmonic.Regarding the fluid force,which are larger in forced oscillations than those in corresponding self-excited cases because the fluid subtracts energy from the forced cylinders.The phase angles between forces and displacements are 0° and 180° for self-excited case and forced case respectively.In vortex-induced vibrations,the interactions between fluid and structure produce some weakly energetic vortices which induce the modulations of amplitude and frequency.展开更多
Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d/D_c and thickness ratio t_d/D_c is studied by a 3D(three-dimensional) numerical model d...Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d/D_c and thickness ratio t_d/D_c is studied by a 3D(three-dimensional) numerical model developed in this paper, and compared with the results obtained through 2D(two-dimensional) numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method.Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns: ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio D_d/D_c and thickness ratio t_d/D_c are discussed in detail.展开更多
A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number(Re=300) placed in a recirculation water channel. A stepper motor was used to rota...A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number(Re=300) placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise-and-counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry(PIV) technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and timeaveraged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed.The effects of four rotation angle and frequency ratios F r(F r=f n/f v, the ratio of the forcing frequency f n to the natural vortex shedding frequency f v) on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤F r≤1.0.展开更多
Particle Imaging Velocimetry(PIV) is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail.At the same oscillation frequency and amplitude,the mean streamwise velocity alon...Particle Imaging Velocimetry(PIV) is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail.At the same oscillation frequency and amplitude,the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length.Meanwhile,the longer the flexible tail is,the larger its deformation is.In order to study the influence of flexible tail length on the wake pattern of the experimental model,the relationships between the swirling strength Λ ci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed.Moreover,the convection tracks and the Λci of vortex cores for different flexible tails are discussed.展开更多
文摘针对工程中关心的振荡圆柱绕流问题,采用同位网格系统中的 SIMPLE算法求解 N S方程,以及动网格技术模拟圆柱的运动边界,对均匀来流中的横向振荡圆柱绕流场进行数值模拟,计算了振荡圆柱升力系数、阻力系数随时间的变化曲线,以及不同相位时的流线矢量图和涡量等值线分布图。为验证模型的可靠性,对静水中的振荡圆柱流场进行模拟,与实验及数值计算结果吻合较好。
基金supported by the National Natural Science Foundation of China(Grant No.50538050)
文摘Numerical simulations of a low-mass-damping circular cylinder which can oscillate freely at transverse and streamwise directions are presented in this work.The Navier-Stokes equations are solved with finite volume method,and large eddy simulation of vortex is also performed in the calculation.In order to implement dynamic mesh,overlapping grids are generated to lessen the computation for mesh field itself.Self-excited vibrations are firstly calculated to obtain the average amplitudes and frequencies of the target circular cylinder in the current flow situation,and then forced oscillations are implemented with parameters obtained in vortex-induced vibrations previously.With slight amplitude modulation,time series of displacements in vortex-induced vibrations are essentially harmonic.Regarding the fluid force,which are larger in forced oscillations than those in corresponding self-excited cases because the fluid subtracts energy from the forced cylinders.The phase angles between forces and displacements are 0° and 180° for self-excited case and forced case respectively.In vortex-induced vibrations,the interactions between fluid and structure produce some weakly energetic vortices which induce the modulations of amplitude and frequency.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51239007 and 51179077)the Sino-UK Higher Education Research Partnership for Ph.D.Studies
文摘Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d/D_c and thickness ratio t_d/D_c is studied by a 3D(three-dimensional) numerical model developed in this paper, and compared with the results obtained through 2D(two-dimensional) numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method.Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns: ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio D_d/D_c and thickness ratio t_d/D_c are discussed in detail.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51409231,51479175,and51679212)Zhejiang Provincial Natural Science Foundation of China(Grant Nos.LY14E090009 and LR16E090002)+2 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars,the Ministry of Education(Grant No.1685[2014])the State Key Laboratory of Ocean Engineering(Shanghai Jiao Tong University)(Grant No.1312)China
文摘A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number(Re=300) placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise-and-counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry(PIV) technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and timeaveraged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed.The effects of four rotation angle and frequency ratios F r(F r=f n/f v, the ratio of the forcing frequency f n to the natural vortex shedding frequency f v) on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤F r≤1.0.
基金supported by the National Natural Science Foundation of China (Grant No. 10832001)the Innovation Foundation of BUAA for PhD Graduates
文摘Particle Imaging Velocimetry(PIV) is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail.At the same oscillation frequency and amplitude,the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length.Meanwhile,the longer the flexible tail is,the larger its deformation is.In order to study the influence of flexible tail length on the wake pattern of the experimental model,the relationships between the swirling strength Λ ci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed.Moreover,the convection tracks and the Λci of vortex cores for different flexible tails are discussed.
