On the wake dynamics of a cylinder with flexible splitter plate

Abstract

An experimental investigation is carried out to study the effect of a flexible splitter plate on the wake dynamics of a circular cylinder. Several regimes of foil motion are imaged and identified in the range of free stream velocities 1e4 < Re < 1e5. Based on the amplitude and the span-wise coherence of the plate motion, the regimes are classified into 4 categories: low oscillations, resonance, chaotic, and bi-stable. Wind-tunnel experiments are conducted on the resonant and chaotic regimes to further explore the cylinder-plate flow. Object surface and flow tracers are tracked by a volumetric Particle Image Velocimetry system based on four high speed cameras and LED illumination. The images are analysed with Lagrangian Particle Tracking techniques and the flow tracers and surface markers are separated based on the different properties of their images. A statistical analysis of the stream-wise and transverse velocity components on the cross-sectional plane compares the pure cylinder flow to the cylinder with the trailing splitter plate. Proper Orthogonal Decomposition is applied to study the most dominant modes from each flow. Results show two different coupling mechanisms pertaining to different aeroelastic regimes. In the resonant regime, the first bending mode of the flexible plate is excited by the shedding frequency. Overall, the results showed a one-way coupling between the flow and the plate, meaning that the motion of the structure was driven by the dominant features of the flow, whereas the flow was mostly unaffected by the presence of the flexible plate. The chaotic regime is an example of full interaction, i.e. 2-way coupling between flow and structure, where the addition of the plate disrupts the shedding structures of the cylinder wake flow. The three-dimensional motion of the flexible plate enhanced the span-wise flow oscillations and so, the three-dimensional features of the wake.