Hydrodynamics of a Biomimetic Propulsor with Two Flapping Foils in Series
Date Issued
2012
Date
2012
Author(s)
Chien, Yi-Ting
Abstract
Autonomous underwater gliders have rapidly become mature technologies in recent years. They have also been proved to be a successful tool for ocean sampling with an even wider range of future possibilities. An underwater glider is propelled by a buoyancy engine to adjust the difference between buoyancy and weight, combining with the lift induced by the wing. In general, an underwater glider can ascend and descend obliquely on a sawtooth trajectory but it lacks capability to move horizontally. Due to this reason, a concept design of biomimetic propulsor with two serial flapping foils for enhancing the horizontal mobility of an underwater glider was proposed. The propulsor consists of a flapping fore foil acting as a leading edge vortex generator, and a flapping rear foil acting as a vortex manipulator. It was found in the previous paper that both thrust and efficiency can be improved significantly in comparing with the single foil model. However, the propulsion efficiency of the serial foils oscillating with only pitch motion is still not sufficient for practical use; even it has been enhanced by an added fore foil.
Two flapping foils in series with heave-pitch coupled motions are expected to have much higher propulsion efficiency. The investigations on its hydrodynamic characteristics via CFD simulations are conducted in the present paper. The master-foil effects and the fore-foil contributions on propulsive performance are clarified. The optimal flapping modes of the fore foil on enhancing the propulsion efficiency are discussed and their corresponding wake mechanisms are demonstrated. It is known that the optimal thrust coefficient and efficiency of the present two-foil model increase approximately 26% and 20% higher than the single fin model and their magnitudes reach 1.26 and 79.52%, respectively.
Two flapping foils in series with heave-pitch coupled motions are expected to have much higher propulsion efficiency. The investigations on its hydrodynamic characteristics via CFD simulations are conducted in the present paper. The master-foil effects and the fore-foil contributions on propulsive performance are clarified. The optimal flapping modes of the fore foil on enhancing the propulsion efficiency are discussed and their corresponding wake mechanisms are demonstrated. It is known that the optimal thrust coefficient and efficiency of the present two-foil model increase approximately 26% and 20% higher than the single fin model and their magnitudes reach 1.26 and 79.52%, respectively.
Subjects
Hydrodynamic Characteristics
flapping foil
Heave-Pitch Coupled Motions
Underwater Glider
Type
thesis
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