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Vortex-enhanced propulsion

  • LYDIA A. RUIZ (a1), ROBERT W. WHITTLESEY (a2) and JOHN O. DABIRI (a2) (a3)
Abstract

It has been previously suggested that the generation of coherent vortical structures in the near-wake of a self-propelled vehicle can improve its propulsive efficiency by manipulating the local pressure field and entrainment kinematics. This paper investigates these unsteady mechanisms analytically and in experiments. A self-propelled underwater vehicle is designed with the capability to operate using either steady-jet propulsion or a pulsed-jet mode that features the roll-up of large-scale vortex rings in the near-wake. The flow field is characterized by using a combination of planar laser-induced fluorescence, laser Doppler velocimetry and digital particle-image velocimetry. These tools enable measurement of vortex dynamics and entrainment during propulsion. The concept of vortex added-mass is used to deduce the local pressure field at the jet exit as a function of the shape and motion of the forming vortex rings. The propulsive efficiency of the vehicle is computed with the aid of towing experiments to quantify hydrodynamic drag. Finally, the overall vehicle efficiency is determined by monitoring the electrical power consumed by the vehicle in steady and unsteady propulsion modes. This measurement identifies conditions under which the power required to create flow unsteadiness is offset by the improved vehicle efficiency. The experiments demonstrate that substantial increases in propulsive efficiency, over 50 % greater than the performance of the steady-jet mode, can be achieved by using vortex formation to manipulate the near-wake properties. At higher vehicle speeds, the enhanced performance is sufficient to offset the energy cost of generating flow unsteadiness. An analytical model explains this enhanced performance in terms of the vortex added-mass and entrainment. The results suggest a potential mechanism to further enhance the performance of existing engineered propulsion systems. In addition, the analytical methods described here can be extended to examine more complex propulsion systems such as those of swimming and flying animals, for whom vortex formation is inevitable.

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Corresponding author
Email address for correspondence: jodabiri@caltech.edu
References
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Batchelor G. K. 2000 An Introduction to Fluid Dynamics. Cambridge University Press.
Binder G. & Didelle H. 1981 Improvement of ejector thrust augmentation by pulsating or flapping jets. Proc. AGARD Conf. Fluid Dynamics of Jets with Applications to V/STOL, Lisbon, Portugal, vol. 308, pp. 1–11.
Blaurock J. 1990 An appraisal of unconventional aftbody configurations and propulsion devices. Mar. Tech. 27, 325336.
Bohl D. G. & Koochesfahani M. F. 2009 MTV measurements of the vortical field in the wake of an airfoil oscillating at high reduced frequency. J. Fluid Mech. 620, 6388.
Breslin J. P. & Andersen P. 1996 Hydrodynamics of Ship Propellers. Cambridge University Press.
Choutapalli I. M., Alkislar M. B., Krothapalli A. & Lourenco L. M. 2005 An experimental study of pulsed jet ejector. AIAA paper 2005-1208.
Cox B. D. & Reed A. M. 1988 Contrarotating propellers: design theory and applications. In Proceedings of the Propellers '88 Symposium, pp. 15.1–15.29.
Dabiri J. O. 2006 Note on the induced Lagrangian drift and added-mass of a vortex. J. Fluid Mech. 547, 105113.
Dabiri J. O. 2009 Optimal vortex formation as a unifying principle in biological propulsion. Annu. Rev. Fluid Mech. 41, 1733.
Dabiri J. O. & Gharib M. 2004 Fluid entrainment by isolated vortex rings. J. Fluid Mech. 511, 311331.
Gharib M., Rambod E. & Shariff K. 1998 A universal time scale for vortex ring formation. J. Fluid Mech. 360, 121140.
Glover E. J. 1987 Propulsive devices for improved propulsive efficiency. Trans. Inst. Mar. Engrs 99, 2329.
Grim O. 1980 Propeller and vane wheel. J. Ship Res. 24, 203226.
Grothues-Spork H. 1988 Bilge vortex control devices and their benefits for propulsion. Intl Shipbuilding Prog. 35, 183214.
Hadler J. B. 1969 Contrarotating propeller propulsion: a state-of-the-art report. Mar. Tech. 6, 281289.
Hill M. J. M. 1894 On a spherical vortex. Phil. Trans. R. Soc. Lond. A 185, 213245.
Hoerner S. F. 1965 Fluid-Dynamic Drag. Hoerner Fluid Dynamics.
Houghton E. L. & Carpenter P. W. 2003 Aerodynamics. Elsevier.
Hussain F. & Husain H. S. 1989 Elliptic jets. Part 1. Characteristics of unexcited and excited jets. J. Fluid Mech. 208, 257320.
Kanso E., Marsden J. E., Rowley C. W. & Melli-Huber J. B. 2005 Locomotion of articulated bodies in a perfect fluid. J. Nonlinear Sci. 15, 255289.
Krieg M. & Mohseni K. 2008 Thrust characterization of a bioinspired vortex ring thruster for locomotion of underwater robots. IEEE J. Ocean. Engng 33, 123132.
Krueger P. S. 2001 The significance of vortex ring formation and nozzle exit over-pressure to pulsatile jet propulsion. PhD thesis, California Institute of Technology.
Krueger P. S., Dabiri J. O. & Gharib M. 2006 The formation number of vortex rings formed in uniform background co-flow. J. Fluid Mech. 556, 147166.
Krueger P. S. & Gharib M. 2003 The significance of vortex ring formation to the impulse and thrust of a starting jet. Phys. Fluids 15, 12711281.
Krueger P. S. & Gharib M. 2005 Thrust augmentation and vortex ring evolution in a fully pulsed jet. AIAA J. 43, 792801.
Linden P. F. & Turner J. S. 2004 ‘Optimal’ vortex rings and aquatic propulsion mechanisms. Proc. R. Soc. Lond. B 271, 647653.
Lockwood R. M. 1961 Interim summary report on investigation of the process of energy transfer from an intermittent jet to secondary fluid in an ejector-type thrust augmenter. Hiller Aircraft Rep. ARD-286.
Maxworthy T. 1972 The structure and stability of vortex rings. J. Fluid Mech. 51, 1532.
Moslemi A. A. & Krueger P. S. 2010 Propulsive efficiency of a bio-inspired pulsed-jet underwater vehicle. Bioinspir. Biomim. 5, 036003.
Narita H., Yagi H., Johnson H. D. & Breves L. R. 1981 Development and full-scale experiences of a novel integrated duct propeller. Trans. SNAME 89, 319346.
Norbury J. 1973 A family of steady vortex rings. J. Fluid Mech. 57, 417431.
Olcay A. B. & Krueger P. S. 2008 Measurement of ambient fluid entrainment during laminar vortex ring formation. Exp. Fluids 44, 235247.
Paxson D. E., Litke P. J., Schauer F. R., Bradley R. P. & Hoke J. L. 2006 Performance assessment of a large scale pulsejet-driven ejector system. NASA Tech. Memo. 2006-214224.
Prandtl L. 1952 Essentials of Fluid Dynamics. Hafner.
Prandtl L. & Tietjens O. G. 1934 Applied Hydro- and Aeromechanics. Dover.
Reynolds W. C., Parekh D. E., Juvet P. J. D. & Lee M. J. D. 2003 Bifurcating and blooming jets. Annu. Rev. Fluid Mech. 35, 295315.
Sachs A. H. & Burnell J. A. 1962 Ducted propellers: a critical review of the state of the art. Prog. Aeronaut. Sci. 3, 85135.
Saffman P. G. 1992 Vortex Dynamics. Cambridge University Press.
Schlichting H. & Gersten K. 2000 Boundary-Layer Theory. Springer.
Shadden S. C., Dabiri J. O. & Marsden J. E. 2006 Lagrangian analysis of fluid transport in empirical vortex ring flows. Phys. Fluids 18, 047105.
Stipa L. 1931 Experiments with intubed propellers. NACA Tech. Rep. TM 655.
Williamson C. H. K. 1996 Vortex dynamics in the cylinder wake. Annu. Rev. Fluid Mech. 28, 477539.
Wu T. Y. 1962 Flow through a heavily loaded actuator disc. Schiffstechnik 9, 134138.
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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
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