Hydrodynamic considerations for multiple fin interactions in rapid maneuvers

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Jumping by any organism requires high bursts of power and muscular coordination. Aquatic water-to-air jumpers must produce enough thrust to account for the drastic drop in fluid density, and thus force-producing ability, when exiting the water. Jumps represent short burst maneuvers in a restricted space (a single body length) with finite duration (until the body has exited the water). This work will investigate multi-fin interactions during short distance, confined space, rapid jumping and swimming maneuvers in archer fish. The archer fish is a unique fish species that uses multiple fins in concert to rapidly jump out of the water from a stationary aiming position. The analysis of jumping behaviors, in a controlled laboratory environment, and comparison with in-water maneuvers, can yield valuable hydrodynamic insight into multi-fin interactions for a range of rapid swimming behaviors. Coordinated fin motions are thought to enhance thrust, increase stability and aid in aiming during rapid maneuvers. Understanding complex multi-fin swimming strategies can help inform bio-inspired swimming robot designs ? where multiple fins could be employed to increase vehicle maneuverability in tight spaces or allow for controlled water-exit maneuvers. Synergistic multi-propulsor relationships identified herein could be paradigm-shifting for the design of future bioinspired aquatic and aerial-aquatic vehicles. Several key hypotheses will be considered: (1) tail kinematics during archer fish jumping are tuned for specific jump heights; (2) secondary fins significantly enhance jump thrust and body stability during rapid maneuvers; (3) jumping is an energetically viable prey capture strategy in competitive environments. High-speed imaging of fin motions and fluid flows will be used to develop a hydrodynamic model for the relationship between thrust production during a jump and maximum animal jump height, which is a controllable performance variable in the laboratory. Synthetic aperture particle image velocimetry, a quantitative three-dimensional imaging technique for flow field velocimetry, will measure the near body velocity fields. Archer fish are a model fish species to investigate, as they use multiple fins in concert to rapidly jump out of the water without any upwards velocity at jump initiation. The archer fish jump allows us to look at propulsive forces and momentum generated by the fish, as well as the hydrodynamic energetics ? specifically the kinetic energy required to reach the final jump height (i.e. potential energy) ? to better understand the unexplored paradigm of sea-to-air exit. The unique morphology of the archer fish, with larger aft fins (dorsal and anal fins) just in front of the caudal tail, potentially adds both to the overall propulsive efficiency and thrust production. Jump maneuvers and in-water maneuvers can be compared for further understanding of the overarching role of multiple fin wake interactions in rapid and unsteady swimming behaviors. The characterization of fin-fin interactions during rapid burst jumping helps the organismal and evolutionary biology communities better understand multi-fin function in fish swimming. The proposed STEM outreach activities engage students in fluid physics and bioinspired design, through programming and hands-on experimental data processing; these activities are scalable and portable to the larger K-12 STEM community. Results of the project will be disseminated in peer-reviewed journals and at conferences in both the fluid dynamic and organismal biology communities.