Interpretation of the flow-induced transverse vibrations of a rectangular cylinder through energy portraits*

The flow-induced vibrations (FIV) of bluff bodies is of research interest due to their importance in many engineering problems, such as energy harvesting and structural design. This study is motivated by the vibrations of precision airdrop suspension lines, which typically operate at Reynolds numbers Re_d, based on the body thickness d, below 10,000. The present study experimentally investigates the transverse oscillations of a rectangular cylinder with a chord to thickness ratio of 2. The separated shear layers of this type of body interact to form a vortex street, making the body susceptible to vortex-induced vibrations. Additionally, unlike circular cylinders, this body is unstable to galloping under certain conditions. In this study, forced transverse sinusoidal oscillations are applied to the body in a water tunnel at Re_d = 2,500 and the fluid-induced forces in the transverse direction are measured over a wide range of frequencies and amplitudes. The motion and measured forces are interpreted through energy portraits, relating the net energy transfer between the fluid and the body. Following the work of Menon & Mital (JFM 2019), the energy portraits are used to help identify various FIV regimes and how they are influenced by different oscillator parameters.