| The fluid-structure interactions of a single streamwise oscillating circular cylinder and two tandem (including a streamwise oscillating circular cylinder) and side-by-side circular cylinders have been experimentally investigated using methods of LIF (Laser-induced fluorescence) visualization, PIV, laser vibrometer and hot wires.;In the case of a single streamwise oscillating cylinder, the wake mode has been studied at relatively large oscillation amplitudes A/d = 0.5 and 0.67 over a range of frequencies fe/fs = 0∼3.1. Five typical flow structures, referred to as S-I, S-II, A-I, A-III and A-IV modes, respectively, are identified. Their occurrence is dependent on a combination of A/d and fe/f s. The occurrence of the S-II mode has been predicted. The threshold frequency ratio (fe/fs) c for the occurrence of the S-II mode is inversely proportional to A/d and dependent on the Reynolds number Re. The Re effect is negligible for Re > 250. The results are in good agreement with available experimental data.;Interference between a streamwise oscillating cylinder (A/d = 0.5 and 0.67, fe/fs = 0∼2) wake and that of a downstream stationary cylinder with an identical diameter has been experimentally studied. The center-to-center spacing L/d of two cylinders varies from 2.5 to 4.5. Three distinct flow regimes have been identified. For 0.45∼0.5 < fe/fs < 0.8∼1.0 (depends on A/d), a single antisymmetrical vortex street (A-mode) emerges behind the downstream cylinder. For 0.8∼1.0 < fe/fs < (fe/f s)c which depends on A/d and Re, the flow behind the downstream cylinder is characterized by an antisymmetric-antisymmetric complex street (AA-mode) that consists of two outer rows of binary vortices originating from the upstream cylinder, and two inner rows of single vortices shed by the downstream cylinder. For fe/fs > (fe/f s)c, the symmetric-antisymmetric complex street (SA-mode) occurs behind the downstream cylinders, respectively.;Interference between a stationary cylinder wake and that of a downstream streamwise oscillating cylinder (L/d = 2.5∼4.5; A/d = 0.5 and 0.67; fe/fs = 0∼2) has also been studied. Two flow regimes have been identified, i.e., the ‘single-cylinder shedding regime’ at L/d ≤ 3.5 and the ‘two-cylinder shedding regime’ at L/d > 3.5. For the ‘single-cylinder shedding regime’, the upstream cylinder does not appear to shed vortices; vortices are symmetrically formed behind the downstream cylinder as a result of interactions between the shear layers separated from the upstream cylinder and the oscillation of the downstream cylinder. (Abstract shortened by UMI.). |
