Abstract
The wake field of the flexible oscillating caudal fin is investigated using the Digital Particle Image Velocity (DPIV) system. The distributions of the vorticity with different Strouhal numbers are presented, and a self-developed program is used for calculating the velocity circulation of the vortex ring. Quantitative analysis of the wake field such as velocity circulation of the vortex ring, vortex radius, and the center-to-center spacing of vortex pair is presented. A three-dimensional vortex ring chain model of oscillating caudal fin is introduced. A conversion model between velocity circulation and dynamic moment of the vortex ring is presented according to the vortex dynamics theory, and a self-developed program is used for the calculation, in which the conversion of the thrust force based on wake field of oscillating caudal fin is carried out. Comparisons of the results of the two kinds flexible caudal fins thrust force conversion with the result of tricomponent balance system have been done in this paper. The relative errors are 5.86% and 3.44%, respectively. It is shown that the thrust force conversion model of flexible oscillating caudal fin is accurate and reliable, and the method presented in the paper provides an effective model for the quantitative conversion between the flow field and the thrust force of the caudal fin.
Highlights
The formation, evolution, and shedding of vortex are controlled by the oscillating of the fish body, and the caudal fin while fish is swimming
A computational program is developed based on the information of velocity field which is obtained by the test. Quantitative information such as velocity circulation and radius of vortex ring in wake vortex filed are obtained, and a conversion model between the velocity circulation and the dynamic moment of the vortex ring is presented using the Kelvin theory, and a self-developed program is used for the calculation in which the quantitative analysis of the wake vortex field structure, and conversion of the thrust force of the caudal fin is carried out
Tests on the flow field of the oscillating caudal fin are carried out based on the Digital Particle Image Velocity (DPIV) system
Summary
The formation, evolution, and shedding of vortex are controlled by the oscillating of the fish body, and the caudal fin while fish is swimming. Tests and analysis on the information of vortex field structure of the oscillating caudal fin are needed, and a quantitative conversion model between the information of the flow field and the thrust force of the caudal fin is introduced, which is very important on both exploring the inherent character of fish’s highefficiency swimming and designing a high-efficiency bionic propulsion system. A computational program is developed based on the information of velocity field which is obtained by the test Quantitative information such as velocity circulation and radius of vortex ring in wake vortex filed are obtained, and a conversion model between the velocity circulation and the dynamic moment of the vortex ring is presented using the Kelvin theory, and a self-developed program is used for the calculation in which the quantitative analysis of the wake vortex field structure, and conversion of the thrust force of the caudal fin is carried out. Parameters, the information of the flow field, and the propulsion character of the caudal fin
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