Flow mixing enhancement by crossflow induced oscillations of an open semicircular cylinder

Abstract

Flow-induced vibrations of a rigid prism with an open semicircular cross section, supported elastically, were experimentally studied in a free-surface water channel. The objective of the study was to explore the prism’s potential to promote flow mixing in its wake and simultaneously harvest mechanical energy from the incoming flow. The mechanical dimensionless parameters, namely the mass ratio and damping, were kept constant, focusing primarily on the influence of flow speed (or reduced velocity $U^{\ast }$) on mixing efficiency and energy extraction. The following findings were obtained: (i) a clear correlation exists between the efficiency of mixing and the efficiency of energy extraction, (ii) mixing efficiency is higher in the near wake and gradually decreases downstream, and (iii) mixing efficiency scales with $A^{\ast }{(f^{\ast }/U^{\ast })}^2$, where $A^{\ast }$ and $f^{\ast }$ represent the dimensionless amplitude and frequency of the prism’s oscillation, respectively. This indicates that flow mixing is directly influenced by the transverse acceleration of the prism and the unperturbed flow speed. Then, maximum mixing efficiency is expected to be achieved when high oscillation amplitudes occur at low reduced velocities which suggest that synchronization of vortex shedding contributes to enhance flow mixing.