VIV and galloping response of a circular cylinder with rigid detached splitter plates

Researches about the response of a circular cylinder fitted with splitter plates have been performed previously to control VIV. Galloping, as a structure instability has been found under some conditions, which is of great interest recently. However, the mechanism of response for a circular cylinder in the presence of splitter plates has rarely been clarified. In the present study, different vibration characteristics have been observed for a circular cylinder with detached splitter plates (0.4 ≤ L/D ≤ 5.0) (where L is the length of splitter plates, D is the external diameter of cylinder) in a wind tunnel. Combined with previous study for galloping in square cylinders, the patterns were comprehensively described. There exist four kinds of response for different lengths of splitter plates: VIV, which lies in a discrete range of wind velocity (such as L/D = 0.4, 0.5); the interaction between galloping and VIV was also found (such as L/D = 1.0, 1.5); a combination of the velocity-restricted excitation (which occurs before VIV onset velocities) and interaction of VIV and galloping, where there exists separate branches in the response (such as L/D = 2.0, 2.5, 3.0); a combination of the velocity-restricted excitation and pure classical galloping (such as L/D = 4.0, 5.0). Besides, it was discovered that the built-up time needed for pure galloping to reach a steady amplitude is much less than that when is related to VIV. Furthermore, the hysteresis loop was found in cases above. FFT spectrums of the streamwise velocity show the appearance of multiple harmonics.