串列式雙振動翼仿生推進器之流體動力研究

Abstract

近年，自主式水下滑翔機已迅速發展成探測海洋的利器，它們已經被成功證明是可以應用在探測廣大海洋與採樣的工具。自主式水下滑翔機使用浮力引擎調整浮力和重心，並結合翼板產生的上升與下沉力，作為水下滑翔機前進的動力。其中，它的運動軌跡為上升與下降的鋸齒狀軌跡。因此，水下滑翔機受限於運動軌跡，只能進行基本的海洋探測與採樣，對於在特定水平深度的偵搜能力，則無法做到。本研究目的即開發水下滑翔機水平移動的推進裝置，且為了保有自主式水下滑翔機長航程低耗能的優勢，提出仿生推進器設計概念應用在串列式雙振動翼推進裝置上，研究振動翼在水平推進的能力。串列式雙振動翼推進裝置採用前翼當作渦產生器和主翼當作渦控制器。串列式雙振動翼與過去單一振動翼文獻相比，推力與效率皆有明顯提升，增加振動翼推進裝置使用水下載具的可能性。 本研究透過計算流體動力分析軟體FLUENT，模擬雙振動翼在起伏縱搖耦合運動之流體動力對振動翼之影響，並確認前翼與主翼的影響對推進性能的貢獻。結果顯示，最佳雙振動翼運動條件下，前翼對振動翼整體增加了推進效率與跡流渦街的增強。在雙振動翼最佳推力與最佳效率條件下與單振動翼相比，分別增加了26%的推力，其推力係數為1.26與增加20%的效率，其效率可高達80%。

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.