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On the Conditions under which Energy can be Extracted from an Air Stream by an Oscillating Aerofoil

Published online by Cambridge University Press:  07 June 2016

N. C. Lambourne
N. C. Lambourne*
Affiliation:
Aerodynamics Division, National Physical Laboratory
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Summary

A simple system is considered in which a two-dimensional aerofoil in an air stream performs a coupled oscillation in pitching and vertical translation. An expression for the energy transferred from stream to aerofoil is derived as a function of the frequency parameter, amplitude ratio and phase difference, and the conditions under which positive energy can be extracted from the stream are investigated. The connection between the case of zero energy transfer, and the critical flutter state is noted.

Attention is confined to the incompressible case and diagrams show the results obtained when the air loads are obtained from (i) vortex sheet theory and (ii) the classical set of constant derivatives.

Vortex sheet theory leads to the conclusion that, provided that the amplitude ratio and phase difference satisfy certain conditions, energy can be extracted from the stream for all values of the frequency parameter. On the other hand, the use of a set of constant derivatives places an upper limit on the values of the frequency parameter for the extraction of energy.

Type
Research Article
Information
Aeronautical Quarterly , Volume 4 , Issue 1 , February 1954 , pp. 54 - 68
Copyright
Copyright © Royal Aeronautical Society. 1954

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References

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