The interaction between flow-induced vibration mechanisms of a square cylinder with varying angles of attack

• Published in: Journal of fluid mechanics Vol. 710; pp. 102 - 130
• Main Authors: Nemes, András, Zhao, Jisheng, Lo Jacono, David, Sheridan, John
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.11.2012; Cambridge University Press (CUP)
• Subjects: Amplitudes; Angle of attack; Cylinders; Engineering Sciences; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Fluids mechanics; Fundamental areas of phenomenology (including applications); Galloping; Mechanics; Oscillations; Oscillators; Physics; Rotational flow and vorticity; Separated flows; Solid mechanics; Structural and continuum mechanics; Vibration; Vibration analysis; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Vortex-induced vibrations; wakes; wake–structure interactions; vortex shedding; Vortex shedding; Swirling flow; Pitch angle; Frequency response; Fluid structure interaction; Oscillating cylinder; Experimental study; Square section; Intermittency; Wakes; Wake-structure interactions
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2012.353

This study examines the influence of angle of attack of a square section cylinder on the cylinder’s flow-induced vibration, where the direction of the vibration is transverse to the oncoming flow. Our experiments, which traversed the velocity–angle of attack parameter space in considerable breadth and depth, show that a low-mass ratio body can undergo combinations of both vortex-induced vibration and galloping. When the body has an angle of attack that makes it symmetric to the flow, such as when it assumes the square or diamond orientation, the two mechanisms remain independent. However, when symmetry is lost we find a mixed mode response with a new branch of vortex-induced oscillations that exceeds the amplitudes resulting from the two phenomena independently. The oscillations of this higher branch have amplitudes larger than the ‘upper branch’ of vortex-induced vibrations and at half the frequency. For velocities above this resonant region, the frequency splits into two diverging branches. Analysis of the amplitude response reveals that the transition between galloping and vortex-induced vibrations occurs over a narrow range of angle of incidence. Despite the rich set of states found in the parameter space the vortex shedding modes remain very similar to those found previously in vortex-induced vibration.