Meeting Abstract
One hallmark of fish diversity is the position, number, and structure of the median fins. The role of these fins in both thrust production and maneuverability has been examined previously in a diverse group of fish species. However, assessing the effects of body stiffness, fin function, and fin-fin interactions on the cost of transport is challenging to do in live fish. While several groups of engineers have shown that airfoils in tandem are able to augment performance by recapturing wake energy, none of them have done so in a fish-like undulatory system. We created a set of biomimetic plastic foils with biologically relevant fin-to-body proportions as well as varying dorsal and anal fin position (near, far, or absent) to see if there is any change in performance when the motion and morphology are biologically constrained. Using a leading-edge flapping robot in a recirculating flow tank, we used both pitch and heave of the leading edge to actuate foils of two different stiffnesses at six frequencies (.5-3 Hz). We measured forces produced by the foils, phasing of the dorsal and caudal fins, and visualized water flow around the foils. These force data were used to calculate power consumption and efficiency, and we examined oscillation amplitude of forces during propulsion. Although stiffness had the largest effect on thrust production, there were significant effects of fin positioning at all frequencies. Foil shape also affected power consumption, efficiency, and smoothness of force production, measured as force oscillation amplitude. The relative effects of each fin position were highly dependent on the stiffness of the fin and the flapping frequency. Flow visualization of foils at the highest frequency showed that fin-fin flow interactions differed between foils and altered the angle of attack of flow over the caudal fin.
