Abstract
The present study is on periodic three-dimensional biological flow during batlike flapping as well as fishlike undulation based spanwise symmetric three-dimensional (3D) kinematics and propulsion of batoid fish. For a single parameter based unified study on various types of real and hypothetical batoid fish, a 3D unified-kinematics model is proposed here. Using our immersed interface method based in-house code, the present numerical study is on the effect of various wavelengths (of the wavy undulation of a hydrofoil-shaped lateral cross section) and aspect ratios (of the elliptical span of the body)—corresponding to various types of batoid fishlike locomotion—at a constant nondimensional frequency of 0.5. Furthermore, for Dasyatis and a hypothetical batoid fish, the effect of various nondimensional frequencies is studied at an aspect ratio of 1. The study is done at a maximum nondimensional amplitude of 0.15 of the pitching/undulation and a Reynolds number of 10 000. A 3D vortex structure demonstrates a spanwise symmetric double row of vortex structure at the various wavelengths while a larger wavelength also results in a horseshoe type of vortices with multiple vortex rings. For propulsive performance, the maximum thrust force (propulsive efficiency) is obtained at an intermediate (smaller) wavelength. Further, with increasing aspect ratio, an increase in the thrust force and the propulsive efficiency are found for various wavelengths. A single-row (double-row) vortex structure leading to smaller (larger) thrust force is obtained at a smaller (larger) nondimensional frequency. Using the more realistic 3D kinematics, as compared to the 2D kinematics used earlier, more realistic flow structures and the associated propulsive performance parameters are presented that can be used for the efficient design of underwater vehicles.
12 More- Received 25 July 2019
- Accepted 28 January 2020
DOI:https://doi.org/10.1103/PhysRevFluids.5.023101
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