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Keywords: burst-and-coast swimming, undulatory propulsion, speed-power ratio, Cartesian grid method, adaptive mesh refinement, cut cell.

Summary

In this paper, the hydrodynamic characteristics of burst-and-coast swimming of a single fish is studied via a two-dimensional numerical simulation. The numerical method is the previously developed collocated finite volume Cartesian cut cell method with adaptive mesh refinement incorporated to save on mesh numbers [1].

The NACA00xx airfoil shape is used as the top-view contour of the fish body during the coast phase. To model reasonably the lateral motion of the backbone undulation of fish swimming during the burst phase, the camber line oscillates in the form of a wave traveling in the streamwise direction. The amplitude of oscillation is assumed a quadratic polynomial function of distance down the camber line and the polynomial coefficients are fitted by the kinematic data of a steadily swimming saithe.

The simulation of continuous swimming was first performed and compared with previous computation to verify the present method. Then swimming in burst-and-coast style was computed assuming the burst phase is composed of a single tail beat. Using the fish body length and the tail beat period as the characteristic length and time respectively, the effects of Reynolds number and fineness ratio (body length over largest thickness) on swimming performance (speed and speed-power ratio) are studied quantitatively for a fixed dimensionless backbone traveling wavelength.

The results show that the speed-power ratio, or efficiency, can be raised by increasing either the tail beat frequency or the body length, for both continuous and burst-and-coast swimming. Further, the burst-and-coast swimming style is indeed an energy-saving one compared to the continuous one at the same mean swimming speed. Finally, a decrease of the fineness ratio will downgrade the swimming performance.

References

1: M-H. Chung, "Numerical study of rowing hydrofoil performance at low Reynolds numbers", accepted for publication, Journal of Fluids and Structures, 24, 2008. doi:10.1016/j.jfluidstructs.2007.08.008

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 89 PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: M. Papadrakakis and B.H.V. Topping Paper 103 Hydrodynamics and Energetic Advantages of Burst-and-Coast Swimming by Undulatory Propulsion M.H. Chung Institute of Ocean Engineering and Technology, National Kaohsiung Marine University, Taiwan R.O.C. doi:10.4203/ccp.89.103 purchase the full-text of this paper Full Bibliographic Reference for this paper M.H. Chung, "Hydrodynamics and Energetic Advantages of Burst-and-Coast Swimming by Undulatory Propulsion", in M. Papadrakakis, B.H.V. Topping, (Editors), "Proceedings of the Sixth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 103, 2008. doi:10.4203/ccp.89.103 Keywords: burst-and-coast swimming, undulatory propulsion, speed-power ratio, Cartesian grid method, adaptive mesh refinement, cut cell. Summary In this paper, the hydrodynamic characteristics of burst-and-coast swimming of a single fish is studied via a two-dimensional numerical simulation. The numerical method is the previously developed collocated finite volume Cartesian cut cell method with adaptive mesh refinement incorporated to save on mesh numbers [1]. The NACA00xx airfoil shape is used as the top-view contour of the fish body during the coast phase. To model reasonably the lateral motion of the backbone undulation of fish swimming during the burst phase, the camber line oscillates in the form of a wave traveling in the streamwise direction. The amplitude of oscillation is assumed a quadratic polynomial function of distance down the camber line and the polynomial coefficients are fitted by the kinematic data of a steadily swimming saithe. The simulation of continuous swimming was first performed and compared with previous computation to verify the present method. Then swimming in burst-and-coast style was computed assuming the burst phase is composed of a single tail beat. Using the fish body length and the tail beat period as the characteristic length and time respectively, the effects of Reynolds number and fineness ratio (body length over largest thickness) on swimming performance (speed and speed-power ratio) are studied quantitatively for a fixed dimensionless backbone traveling wavelength. The results show that the speed-power ratio, or efficiency, can be raised by increasing either the tail beat frequency or the body length, for both continuous and burst-and-coast swimming. Further, the burst-and-coast swimming style is indeed an energy-saving one compared to the continuous one at the same mean swimming speed. Finally, a decrease of the fineness ratio will downgrade the swimming performance. References 1 M-H. Chung, "Numerical study of rowing hydrofoil performance at low Reynolds numbers", accepted for publication, Journal of Fluids and Structures, 24, 2008. doi:10.1016/j.jfluidstructs.2007.08.008 purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £95 +P&P)
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