On passive control of transition to galloping of a circular cylinder undergoing vortex induced vibration using thick strips

The current experimental work using circular cylinders aims to identify mechanisms that amplify vortex-induced vibrations (VIV) and galloping oscillations, within the Reynolds number range, 1.5 × 103 < Re < 3 × 104. Our experiments fall in the TrSL2 (Transition in Shear Layer) regime and complement studies in the TrSL3 regime (3 × 104 < Re < 1.2 × 105) performed by Bernitsas and his group. Smooth rectangular strip pairs of varying thickness (1.6%-31% of cylinder diameter) were attached to a circular cylinder at 60° from the frontal stagnation point. Amplified VIV and high amplitude galloping oscillations were observed for all configurations with strips, except at the least thickness, where we observed reduced VIV amplitudes compared to the smooth cylinder at the lower flow velocities and high amplitude galloping at the higher flow velocities. Thicker strips led to higher VIV and galloping amplitudes, accompanied by an increase in steadiness within the transition regime. Thicker strips also led to the earlier initiation of galloping, indicating capability for increased energy transfer even at the lower flow speeds. Higher mass-damping led to lower vibration amplitudes and frequencies in both modes, however, the potential of smooth strips to incite galloping was evident even at the higher values tested.