Refuging rainbow trout selectively exploit flows behind tandem cylinders

Abstract

Fishes may exploit environmental vortices to save in the cost of locomotion. Previous work has investigated fish refuging behind a single cylinder in current, a behavior termed the Kaŕmań gait. However, current-swept habitats often contain aggregations of physical objects, and it is unclear how the complex hydrodynamics shed from multiple structures affect refuging in fish. To begin to address this, we investigated how the flow fields produced by two D-shaped cylinders arranged in tandem affect the ability of rainbow trout (Oncorhynchus mykiss) to Kaŕmań gait. We altered the spacing of the two cylinders from l/D of 0.7 to 2.7 (where l=downstream spacing of cylinders and D=cylinder diameter) and recorded the kinematics of trout swimming behind the cylinders with high-speed video at Re=10,000-55,000. Digital particle image velocimetry showed that increasing l/D decreased the strength of the vortex street by an average of 53% and decreased the frequency that vortices were shed by ∼20% for all speeds. Trout were able to Kaŕmań gait behind all cylinder treatments despite these differences in the downstream wake; however, they Kaŕmań gaited over twice as often behind closely spaced cylinders (l/D=0.7, 1.1, and 1.5). Computational fluid dynamics simulations show that when cylinders are widely spaced, the upstream cylinder generates a vortex street that interacts destructively with the downstream cylinder, producing weaker, more widely spaced and less-organized vortices that discourage Kaŕmań gaiting. These findings are poised to help predict when fish may seek refuge in natural habitats based on the position and arrangement of stationary objects.

Accelerating fishes increase propulsive efficiency by modulating vortex ring geometry

“…To more closely investigate the kinematics and hydrodynamics of acceleration, we chose a generalized teleost fish, the rainbow trout (Oncoryhnchus mykiss). The swimming kinematics of this species have been studied in great detail for steady swimming and other behaviors but not for acceleration (5,13,(47)(48)(49)(50)(51)(52)(53)(54). Like those in other species tested in this study, the body amplitudes of trout are higher during acceleration than during steady swimming ( Fig.…”

Heat Transfer in Non-Newtonian Flows by a Hybrid Immersed Boundary–Lattice Boltzmann and Finite Difference Method

“…This model has been extensively used to study fish behaviors in a street wake [17,[59][60][61]. Simulations are performed at l/D = 3.0, m s = 0, and Re = 100.…”

Behavior, Electrophysiology, and Robotics Experiments to Study Lateral Line Sensing in Fishes

“…The results from these experiments have been summarized in Liao and Akanyeti (2017). Briefly: (1) fish reduced muscle activity and consume less oxygen during K arm an gaiting than steady swimming (Liao 2004;Taguchi and Liao 2011); (2) depending on body size, there was a range of flow speeds and cylinder diameters that increase the probability of K arm an gaiting (Akanyeti and Liao 2013a); (3) fish were typically one-two body lengths downstream from the cylinder while K arm an gaiting (in this region, vortices are strong, and the average flow speed is significantly lower than the incoming flow speed); (4) K arm an gait kinematics were closely related to flow parameters, and could be modeled with a traveling wave equation (Akanyeti and Liao 2013b); (5) fish also K arm an gait behind tandem cylinders (i.e., two cylinders placed one after another) when downstream spacing between the cylinders was appropriate (Stewart et al 2016); and (6) both vision and lateral line system played active roles during K arm an gaiting (Liao 2006).…”