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How to extract energy from turbulence in flight by fast tracking

Bollt, Scott A. and Bewley, Gregory P. (2021) How to extract energy from turbulence in flight by fast tracking. Journal of Fluid Mechanics, 921 . Art. No. A18. ISSN 0022-1120. doi:10.1017/jfm.2021.499.

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We analyse a way to make flight vehicles harvest energy from homogeneous turbulence by fast tracking in the way that falling inertial particles do. Mean air speed increases relative to flight through quiescent fluid when turbulent eddies sweep particles and vehicles along in a productive way. Once swept, inertia tends to carry a vehicle into tailwinds more often than headwinds. We introduce a forcing that rescales the effective inertia of rotorcraft in computer simulations. Given a certain thrust and effective inertia, we find that flight energy consumption can be calculated from measurements of mean particle settling velocities and acceleration variances alone, without the need for other information. In calculations using a turbulence model, we optimize the balance between the work performed to generate the forcing and the advantages induced by fast tracking. The results show net energy reductions of up to approximately 10 % relative to flight through quiescent fluid and mean velocities up to 40 % higher. The forcing expands the range of conditions under which fast tracking operates by a factor of approximately ten. We discuss how the mechanism can operate for any vehicle, how it may be even more effective in real turbulence and for fixed-wing aircraft and how modifications might yield yet greater performance.

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Additional Information:© The Author(s), 2021. Published by Cambridge University Press. Received 4 October 2020; revised 6 May 2021; accepted 1 June 2021. Published online by Cambridge University Press: 30 June 2021. We are grateful to Professors S. Ferrari, E. Fisher and Z. Warhaft. The authors report no conflict of interest.
Subject Keywords:flow-structure interactions, swimming/flying, particle/fluid flow
Record Number:CaltechAUTHORS:20210727-191808194
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Official Citation:Bollt, S., & Bewley, G. (2021). How to extract energy from turbulence in flight by fast tracking. Journal of Fluid Mechanics, 921, A18. doi:10.1017/jfm.2021.499
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110033
Deposited By: Tony Diaz
Deposited On:28 Jul 2021 19:48
Last Modified:28 Jul 2021 19:48

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