On Passive Control Of Transition To Galloping Of A Circular Cylinder Undergoing Vortex Induced Vibration Using Thick Strips

Experiments exploring modifications to a circular cylinder to enhance vortex-induced vibrations (VIV) and incite galloping oscillations are conducted in the Reynolds number range, 1.5×10³ < Re < 3×10⁴. These measurements, bound within the TrSL2 (Transition in Shear Layer) Reynolds number regime, complement studies by Michael Bernitsas and group spanning the TrSL3 Reynolds number regime.  Pairs of smooth rectangular strips varying in thickness from 1.6% to 31% of the cylinder diameter were attached to a circular cylinder at 60º from the frontal stagnation point. Amplified VIV and galloping oscillations were observed for all strip thicknesses tested, except the least thickness, where reduced VIV amplitudes at the lower flow velocities and high amplitude galloping oscillations at the higher flow velocities were noticed. It was evident that thicker strips led to higher VIV and galloping amplitudes, accompanied by increased steadiness within the transition regime. Thicker strips also led to the earlier initiation of galloping, indicating the potential 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 in all cases tested.