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Deformation and vibration of twig-connected single leaf in wind is investigated experimentally. Results show that the Reynolds number based on wind speed and length of leaf blade is a key parameter to the aerodynamic problem. In case the front surface facing the wind and with an increase of Reynolds number, the leaf experiences static deformation, large amplitude and low frequency sway, reconfiguration to delta wing shape, flapping of tips, high frequency vibration of whole leaf blade, recovery of delta wing shape, and twig-leaf coupling vibration. Abrupt changes from one state to another occur at critical Reynolds numbers. In case the back surface facing the wind, the large amplitude and low frequency sway does not occur, the recovered delta wing shape is replaced by a conic shape, and the critical Reynolds numbers of vibrations are higher than the ones corresponding to the case with the front surface facing the wind. A pair of ram-horn vortex is observed behind the delta wing shaped leaf. A single vortex is found downstream of the conic shaped leaf. A lift is induced by the vortex, and this lift helps leaf to adjust position and posture, stabilize blade distortion and reduce drag and vibration.

A narrow strip has been introduced as a control element to suppress vortex shedding from a cylinder. The strip is set parallel to the cylinder axis, and the key parameter of control in this study is the strip position, which is determined by the angle of attack of the strip and the distance between the strip and the cylinder axis. A circular cylinder and a square cylinder were tested respectively. Flow visualization and hot-wire measurement were performed in a low turbulence wind tunnel in the range of Reynolds number R Re = 4.0 × 10 3 ~ 2.0 × 10 4 . Test results show that, vortex shedding from both sides of the cylinder can be effectively suppressed if the strip is located in a certain zone in the wake. The effective zones in circular cylinder wakes at different Reynolds numbers have been found out, and the mechanism of the suppression has been discussed.

Small circular, square, and thin-strip cross-sectional elements are used to suppress vortex shedding from a square cylinder at Reynolds numbers in the range of 1:12 10 4 -1:02 10 5 . The axes of the element and cylinder are parallel. The element's size, position, and angle of attack are varied. Measurements of the fluctuating surface pressures and wake velocities, together with smoke flow visualization, show that vortex shedding from both sides of the cylinder is suppressed and the mean drag and fluctuating lift on the cylinder is reduced if the element is installed in an effective zone downstream of the cylinder. The effective zone of the circular element is shown to be much smaller than those of the other elements. The effects of Reynolds number and blockage ratio are investigated. A phenomenon of monoside vortex shedding is observed. The role of the element's bluffness is investigated and the suppression mechanism is discussed.

A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 × 10 4 to 1.0 × 10 5 . The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.

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