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 v****ideo 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.