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A simple fluid-flow model of ground effect on hovering

Published online by Cambridge University Press:  19 April 2006

James Lighthill
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Abstract

Hoverming motions, by which an animal (or a helicopter) in stationary fluid generates a downflow to support its weight, entail energy costs that include the induced power (power supplied to that downflow). The simplest classical model for induced power is the actuator-disk model. This paper shows how a relatively insignificant modification can be made to that model to make it aerodynamically self-consistent. The modified simple model of the downflow may be evaluated in fluid that either is unbounded or is bounded below by horizontal ground. Comparison of the calculated induced powers in the two cases (even though made in this paper not for the true axisymmetric flow patterns but for the corresponding two-dimensional flow patterns) appears to give a more satisfactory analysis than was previously available of the observed reduction of induced power associated with proximity to the ground.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 93 , Issue 4 , 29 August 1979 , pp. 781 - 797
Copyright
© 1979 Cambridge University Press

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