Meeting Abstract
We investigated the kinematics and preference of rainbow trout (Oncorhynchus mykiss, n= 4, body length = 18.9±0.52 cm mean ± SEM) to Karman gait behind two, 5cm diameter D cylinders arranged in tandem at Reynolds numbers ranging from 10,000-55,000. We used Digital Particle Image Velocimetry and computational fluid dynamics modeling to reveal that cylinder spacing strongly affects the overall strength and structure of the downstream flow field. For example, increasing L/D from 0.7 to 2.7 (where L = downstream spacing of cylinders and D = cylinder diameter) decreased the strength of the vortex street by an average of 53% for all speeds investigated. Likewise, for all speeds an L/D of 2.7 resulted in a 30% increase in the wake wavelength and a 20% decrease in the vortex shedding frequency as compared to a single cylinder. We found that trout Karman gait with similar kinematics across a wide range of L/D values. However, fish did not equally prefer all six of our cylinder spacing arrangements. For example, 73% of Karman gaiting occurred behind an L/D of 0.7, 1.1, and 1.5, while only 4% of Karman gaiting occurred at an L/D = 2.7. Flow visualization reveals that the strong and organized vortices produced by single cylinders or closely-spaced cylinders are what lead trout to prefer these environments. When L/D > 1.5, the upstream cylinder generates a vortex street that interacts destructively with the wake of the downstream cylinder, leading to the establishment of a co-shedding regime that produces weaker, more widely-spaced, and less organized vortices that discourages Karman gaiting.
