Flow-induced oscillations of cylinders in the streamwise direction

An experimental Van der Pol oscillator has been adapted to calculate flow-induced cylinder oscillations in the streamwise direction and approximate model solutions were computed taking into account two inherent time scales. An experiment was carried out to study the effects of reduced velocity, Reynolds number, surface roughness, and free stream turbulence on the stability of a circular cylinder during in-line oscillations. The two test cylinders were 6.5 and 14 inches in diameter, respectively. Springs of various thickness were connected to cables and the cylinders to provide vibrational frequencies, and load cells were connected to the same point to measure the forces on the cylinder. Model estimates were fitted to experimental data in two regions of in-line oscillations with good agreement in the amplitude of the oscillations. It is shown that the occurrence of in-line oscillations may depend on a number of conditions (critical Reynolds number; critical reduced velocity; damping threshold and free-stream turbulence) being met simultaneously. The calculated and measured amplitudes of oscillation are given in a graph.