Enhancement of energy capture by flow induced motion of a circular cylinder using passive turbulence control: Decoupling strip thickness and roughness effects

Abstract

Passive turbulence control of flow induced motion of a cylinder using strips has been practiced for over 30 years. The two distinct physical characteristics of strips: thickness and roughness, can have coupled effects on altering the flow induced motion. The experimental work discussed here decouples these two effects for augmented energy extraction. Tests with cylinders attached with strips of roughness varying from 0% to 100%, and thickness varying from 0.8% to 8.2% of the cylinder diameter, were performed (5000 < Re < 35600). The dynamic response of the configurations with rough strips was compared to that with smooth strips of same thickness. Mechanical power and energy transfer efficiencies were evaluated to analyze the power extraction potential of different configurations. Power generated by the smooth strip configurations was 1.25–5 times higher depending on the roughness ratio and flow velocity. Smooth strips also provided more operational stability, characterized by smaller values of the coefficient of variation of power and concentrated non-dimensional force-velocity states. These devices are the more efficient adaptation from an energy harvesting perspective at low velocities (<1.0 m/s), a range below the cut-in speed for most hydrokinetic turbines, thereby making energy extraction feasible from shallow rivers and slow-flowing streams.