Flow Physics of Routine Turns of Koi Carp(Cyprinus Carpio Koi)

Abstract

This paper investigates the flow physics of Koi carp's routine turns with a novel CFD method solving the body-fluid interaction problem, which consists of deforming body dynamics and unsteady fluid dynamics. Firstly, the dynamical equations of the deforming body are presented. Secondly, the coupled equations of body dynamics and fluid dynamics are solved together. The numerical simulation is based on the kinematics data from a video tracking measurement system and the predicted body kinematics and flow visualization are well agreed with the experimental results. Single-beat turn and cruising turn are the basic two turning modes of Koi carp, and the former is the mostly observed. Through comparative studies of the turning maneuverability performance and energetics of these two kinds of turns, their common flow control mechanisms and different features are discovered, such as (1) agility (defined as turning rate) is correlated positively with maneuverability (defined as the reciprocal of the turning radius), (2) the total power appears good linear relation with the turning rate, and (3) single-beat turns are more efficient than cruising turns.

A study on flow physics of burst-and-coast swimming of koi carp (Cyprinus carpio koi) based on measurements and numerical simulations

“…The parameters A max , X 0 , d 0 (X), c 1 , c 2 , t 1 and t 2 in (8) and (9) are determined by fitting the function of (8), where typical parameters are given under…”

“…For body-fluid interaction, the coupled problem of deformable body dynamics (BD) and unsteady fluid dynamics (FD) was solved by the integrated method, on the in-house CFD platform [6,9]. The process of the simulation is as below: given the undulating kinematics from the experiments, the flow field and fluid forces are calculated, following that the whole-body kinematics is predicted, based on FD and BD.…”

“…The CFD platform has been validated and verified by several cases [6,9]. The grid independency has been tested.…”

“…In addition, fluid-body interaction should be considered, as a part of the mechanical chain of fish locomotion. That is to say, the fish should be simulated as an active self-propelled body in the flow [5][6][7][8][9], which is more realistic, comparing to the model of a tethered body [10,11]. To the authors' knowledge, among existing works, almost no simulation-based case of free and self-propelled maneuvering fish has been investigated based on the full Navier-Stokes equations, as follows.…”

“…Kern and Koumoutsakos [7] proposed a better algorithm of body dynamics, while only two kinds of steady anguilliform swimming were investigated. We have built a CFD platform to simulate a selfpropelled freely swimming body [6,9], which is more realistic to study the hydrodynamics of a maneuvering fish. On the platform, built upon the dynamical equations of deforming body, fluid-body interaction induced by the actively deforming body can be simulated properly.…”