Experimental investigation on the role of turbulent buffeting on the dynamics of a flexible filament in airflow

Abstract

This paper documents the results of an experiment conceived to explore and quantitatively assess the role of turbulent buffeting on the dynamics of a flexible filament exposed to airflow. In the experiment, a circular cross-section flexible filament was tested in a wind tunnel where the turbulence level was modified with a square-mesh grid. Measurements were carried out with and without the grid to assess the role of turbulent buffeting on the dynamics of the filament. A hot wire anemometer was used to measure the turbulent airflow, whilst fast video imaging was employed to resolve the filament motion in 3D. The inclusion of the grid and subsequent increase in turbulence level yielded a higher amplitude of motion during the post-flutter regime, thus providing evidence of the role of turbulent buffeting on the flapping dynamics of the filament, hence confirming a conjecture advanced in previous research but not proved yet. Interestingly, the higher amplitude of motion due to turbulent fluctuation was confined only to the vertical plane, suggesting a role of the filament attachment angle in the propagation of disturbances from turbulent fluctuations. No detectable role of turbulent buffeting was observed on the onset of flapping which, based on a comparison with literature data, has been classified as a fluid-elastic instability. Finally, no detectable role of turbulent buffeting was observed in the qualitative dynamics of the filament during flutter and post-flutter.