Experimental and numerical investigations of the VIV-galloping instability of a bluff body Integration internship

Abstract

While VIV and galloping are well investigated separately, their coupled dynamics remain poorly understood. Experimental tests were hence conducted on a square-section cylinder in a wind tunnel to study their interaction at low Scruton numbers. The experimental results were compared to a numerical model that combines both phenomena, making use of the quasi-steady galloping theory and an unsteady fluctuating force. The goal was to assess the model’s capability to capture both steady-state and transient responses across a range of reduced velocities. The amplitudes of oscillations were overestimated close the critical VIV velocity but good agreement was observed between the model and experimental data at higher reduced velocities. In general, the model captured the dominant mechanisms in post-critical flow regimes, while showing limitations near the lock-in region. Regarding the transient behaviour and the build up of oscillations from rest, the model predicted the correct trend for varying airspeed and amplitude but the amplitude-dependent damping ratios were significantly underestimated. The transient trend was associated with the appearance of an even harmonic above a certain amplitude of motion. The numerical excitation force appeared to be overestimated compared to experimental measurements and the discrepancies of the model were attributed to the modeling of the unsteady aerodynamic force. Overall, this work helps to better understand how VIV and galloping interact and how well a simple model can capture that behavior. The results showed where the model agrees with experiments and where it needs improvement.