Author(s): Jingmei Zhang; Hongyu Li; Minne Li; Dongzi Pan; Hang Wang
Linked Author(s): Hang Wang
Keywords: Robotic fish; Weir obstacle; Fish swimming; Turbulence; Fish migration
Abstract: The presence of obstacles in waterway may create areas suitable for resting during the upstream migration of fish. Understanding of the fish-flow interplay in this process requires detailed characterization of flow dynamics in the fish swimming circumstance. In this study, a bionic robotic fish is used to provide consistent and repeatable swimming performance in a hydraulic flume. Particle image velocimetry (PIV) is employed to characterize the turbulent velocity field downstream of four types of full-width prismatic obstacles on the flume bottom, namely, the obstacle cross-sectional shape being rectangular, triangular, semicircular, and a thinwalled weir. The shape of the obstacles are critical factors changing the flow structure. The interaction between the swimming fish movement and the turbulent flow structures downstream of the different obstacles is analyzed with comparison to the reference cases in the absence of the fish. Among the tested obstacles, strongest turbulence enhancement is observed for the triangular prism and thin-walled weir. The large-scale turbulence in the wake region causes some irregular tail flapping of the robotic fish, although the dominant tail flapping frequency is not changed. The flow recirculation at the downstream toe of the obstacle may facilitate fish crossing by boosting fish thrust and uplift. Zones of relatively low turbulence intensity and Reynolds stresses are shown on the two sides of the fish body, which may attract fellows by reducing their energy consumption of swimming.