||Betz analysis of a single flapping foil power generator
Young, John ,
Tian, Fang-Bao ,
Lai, Joseph C.S. ,
Young, John ,
田, 方宝Lai, Joseph C.S.
宇宙航空研究開発機構特別資料=JAXA Special Publication: Proceedings of the First International Symposium on Flutter and its Application
494 , 2017-03-15 , Japan Aerospace Exploration Agency (JAXA) , 宇宙航空研究開発機構(JAXA)
The Betz limit for extraction of power from a flowing fluid is based upon an assumption of steady flow, and effects from viscosity and non-uniform pressures are ignored. Flapping foils used for power generation involve inherently highly unsteady flows, and operate most effectively when there is significant vortex shedding from the foil leading edge. This work conducts an analysis of the theoretical limits of efficiency for such an unsteady system, for the first time. Analysis of the magnitude and impact of the unsteady effects shows that the action of shed vortices as they convect downstream entrains a significant amount of momentum and kinetic energy into the wake of the foil. This entrainment is likely insufficient to render the Betz limit invalid for a single foil, however it is promising for a tandem foil system where the downstream foil benefits from this re-energisation of the upstrem foil wake, and suggests a mechanism by which the Betz limit for such a system (64%) might theoretically be exceeded.
Meeting Information: First International Symposium on Flutter and its Application (May 15-17, 2016. Mielparque-tokyo), Minato-ku, Tokyo, Japan
Physical characteristics: Original contains color illustrations