Satellite-tracked drifting buoy data and altimetry data are used to study the active vortex field to the west of Big Island. A pair of vortexes were observed at the trajectory of buoy in 1995. The westward propagation...Satellite-tracked drifting buoy data and altimetry data are used to study the active vortex field to the west of Big Island. A pair of vortexes were observed at the trajectory of buoy in 1995. The westward propagation of the vortex pair is studied in detail by reproducing the loops of each vortex. The orbital period and radius of the pair of vortex are determined to be 10-11 d and 58-68 km. Two arrays of contra-rotating vortices are displayed in the average sea surface height anomaly (SSHA) field to the west of Big Island. Based on the calculation of the fluid dynamical parameter, the 'von Karman vortex street' is proved to be generated to the west of Big Island as the North Equatorial Current impinges upon Big Island from the east. Finally, the analysis of the buoy trajectories in a decade contributes to the conclusion of the pattern of VKVS in a statistical view.展开更多
To control the Karman vortex street formed behind a thin airfoil at a certain incidence, a control cylinder was placed at the suction side apart from the airfoil in the downstream region. Both smoke visualization and ...To control the Karman vortex street formed behind a thin airfoil at a certain incidence, a control cylinder was placed at the suction side apart from the airfoil in the downstream region. Both smoke visualization and hot-wire measurements confirmed that the Karman vortex street was completely suppressed. The mechanism for suppression of the vortex street was examined with a hot-wire survey.展开更多
The purpose of this study was to clarify grid convergence property of three-dimensional measurement-integrated (3D-MI) simulation for a flow behind a square cylinder with Karman vortex street. Measurement-integrated (...The purpose of this study was to clarify grid convergence property of three-dimensional measurement-integrated (3D-MI) simulation for a flow behind a square cylinder with Karman vortex street. Measurement-integrated (MI) simulation is a kind of the observer in the dynamical system theory by using CFD scheme as a mathematical model of the system. In a former study, two-dimensional MI (2D-MI) simulation with a coarse grid system showed a fairly good result in comparison with a 2D ordinary (2D-O) simulation, but the results were degraded with grid refinement. In this study, 3D-MI simulation and three-dimensional ordinary (3D-O) simulation were performed with three grid systems of different grid resolutions, and their grid convergence properties were compared. As a result, all 3D-MI simulations reproduced the vortex shedding frequency identical to that of the experiment, and the flow fields obtained were very close, within 5% difference between the results, while the results of the 3D-O simulations showed variation of the solution under convergence. It is shown that the grid convergence property of 3D-MI simulation is monotonic and better than that of 3D-O simulation, whereas those of 2D-O and 2D-MI simulations for streamwise velocity fluctuation are divergent. The solution of 3D-MI simulation with a relatively coarse grid system properly reproduces the basic three-dimensional structure of the wake flow as well as the drag and lift coefficients.展开更多
Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimen...Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimental kinematic results, a 2-d panel method was used to calculate the forces acting on the filament. The experiment and numerical results revealed that different from that in free stream, the filament in Karman vortex street flapped at the same frequency as the vortex street, and with smaller amplitude and larger curvature. The filament suffered an evident thrust in Karman vortex street, while a drag appeared in the case of free stream. The dependence of the drag coefficient on the phase relation between the movement of the filament and the Karman vortex street was also studied.展开更多
In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the S...In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500 Hz to 1250 Hz. It was experimentally proved that the influence of the Karman vortex street on the noise in the domains of high and low frequencies did not exist when the distribution of the estimated sound pressure level corresponded to the measured broadband noise.展开更多
文摘Satellite-tracked drifting buoy data and altimetry data are used to study the active vortex field to the west of Big Island. A pair of vortexes were observed at the trajectory of buoy in 1995. The westward propagation of the vortex pair is studied in detail by reproducing the loops of each vortex. The orbital period and radius of the pair of vortex are determined to be 10-11 d and 58-68 km. Two arrays of contra-rotating vortices are displayed in the average sea surface height anomaly (SSHA) field to the west of Big Island. Based on the calculation of the fluid dynamical parameter, the 'von Karman vortex street' is proved to be generated to the west of Big Island as the North Equatorial Current impinges upon Big Island from the east. Finally, the analysis of the buoy trajectories in a decade contributes to the conclusion of the pattern of VKVS in a statistical view.
文摘To control the Karman vortex street formed behind a thin airfoil at a certain incidence, a control cylinder was placed at the suction side apart from the airfoil in the downstream region. Both smoke visualization and hot-wire measurements confirmed that the Karman vortex street was completely suppressed. The mechanism for suppression of the vortex street was examined with a hot-wire survey.
文摘The purpose of this study was to clarify grid convergence property of three-dimensional measurement-integrated (3D-MI) simulation for a flow behind a square cylinder with Karman vortex street. Measurement-integrated (MI) simulation is a kind of the observer in the dynamical system theory by using CFD scheme as a mathematical model of the system. In a former study, two-dimensional MI (2D-MI) simulation with a coarse grid system showed a fairly good result in comparison with a 2D ordinary (2D-O) simulation, but the results were degraded with grid refinement. In this study, 3D-MI simulation and three-dimensional ordinary (3D-O) simulation were performed with three grid systems of different grid resolutions, and their grid convergence properties were compared. As a result, all 3D-MI simulations reproduced the vortex shedding frequency identical to that of the experiment, and the flow fields obtained were very close, within 5% difference between the results, while the results of the 3D-O simulations showed variation of the solution under convergence. It is shown that the grid convergence property of 3D-MI simulation is monotonic and better than that of 3D-O simulation, whereas those of 2D-O and 2D-MI simulations for streamwise velocity fluctuation are divergent. The solution of 3D-MI simulation with a relatively coarse grid system properly reproduces the basic three-dimensional structure of the wake flow as well as the drag and lift coefficients.
基金Supported by the National Natural Science Foundation of China (Grant No. 10832010)Innovation Project of Chinese Academy of Sciences (Grant No. KJCX2-YW-L05)
文摘Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimental kinematic results, a 2-d panel method was used to calculate the forces acting on the filament. The experiment and numerical results revealed that different from that in free stream, the filament in Karman vortex street flapped at the same frequency as the vortex street, and with smaller amplitude and larger curvature. The filament suffered an evident thrust in Karman vortex street, while a drag appeared in the case of free stream. The dependence of the drag coefficient on the phase relation between the movement of the filament and the Karman vortex street was also studied.
文摘In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500 Hz to 1250 Hz. It was experimentally proved that the influence of the Karman vortex street on the noise in the domains of high and low frequencies did not exist when the distribution of the estimated sound pressure level corresponded to the measured broadband noise.
