Title: Albatrosses of rivers: Inertial mechanism behind dynamic station holding in fish
Time: 14:00 to 15:00, Wednesday, December.20, 2023
Place: F103, School of Mechanical Engineering
Host: WANG Qian, Assoc. Professor (Institute of Engineering Thermophysics)

Biography
Dr. Petr Denissenko has got an MPhil in Plasma Physics from Novosibirsk State University (Russia) in 1996. He started PhD studies at Hong Kong UST in 1997 and acquired a PhD in Applied Mathematics from Hull University (UK) in 2004. After postdoctoral experience in subjects from micro-swimmers to wave turbulence, in 2007 Petr moved to Warwick University, where he currently is an Associate Professor. Dr. Denissenko is a broad range experimentalist in Fluid Dynamics with interests including wind energy harvesting, microorganism motility, waves, two-phase flows, and dispersion in porous media. As a side project, he is involved in human-powered submarine student competitions.

Abstract
Animals are inherently lazy, trying to conserve energy whenever possible. Most of us have observed that in rivers fishes stay in wakes behind stones, but few know that they can choose a faster part of a stream if there are vortices to “push off” from. We investigate the swimming dynamics of rainbow trout in the wake of a thrust-producing oscillating hydrofoil. Despite the higher flow velocities in the inner region of the vortex street, some fish stays there, seemingly “dancing”. Estimates of energy expenditure indicate savings when compared to regular swimming. By examining the accelerations of the fish, an explanation of the mechanism by which energy is harvested from the vortices is proposed. Similarly to dynamic soaring by albatross, the mechanism can be linked to non-equilibrium hydrodynamic forces produced when fish encounter the cross-flow velocity generated by the vortex street.