起伏縱搖耦合串列式雙振動翼之推進性能研究

Abstract

本研究主要目的是希望能夠開發出一水下滑翔機的助推器，其功能為不干擾滑翔且協助水平前進。先前本研究室曾提出串列式雙振動翼之設計，並且進行實體模型的水槽實驗。研究結果顯示該串列式雙振動翼之推進效能並不如預期佳，有許多的改善空間，原因可能是中間的固定翼板所致。之後本實驗室做了進一步的改良，將中間固定翼板移除，流力計算結果顯示在推力與推進效率上有提升，而且確認了前振動翼有提升整體推進效率的效果，但雙振動翼只作縱搖運動，其效率仍有改善的空間。 本研究利用計算流體動力學套裝軟體Fluent，針對二維單振動翼起伏與縱搖耦合運動下之非穩態流場進行模擬計算分析，結果顯示計算所得的推力係數、功率係數、推進效率之結果與實驗結果相近，確認了使用Fluent套裝軟體所發展的流體動力數值計算工具用於振動翼動力分析是有相當的可靠性。 因此，在上述成果之基礎上，本研究持續運用該計算工具，在非穩態流場條件下，以動態網格進行串列式雙振動翼在多種起伏與縱搖耦合運動情況下的流體動力分析，確認前振動翼的效益，並進一步提出串列式雙振動翼之改良設計，探討雙振動翼之配置，各振動翼之振幅、相位差、頻率等參數對於推進性能之效應，並透過流速、渦度分布圖釐清了前翼提升雙振動翼推進效率之力學機制。 本研究藉由數值計算分析探討所獲得的結果，將能作為後續修正實體模型，進行水槽試驗之規劃依據，最終將求促成兼具水平移動與滑翔性能的水下滑翔機之實現。

In view of the fact that an underwater glider is lack of horizontal mobility, a concept design of biomimetic propulsor with two oscillating fins in series was proposed and investigated in the previous study to enhance the horizontal mobility without disturbing gliding. A test apparatus was established and a series of tank tests were carried out for clarifying its hydrodynamic characteristics. However, it was found that the propulsion performance of the proposed design is not as good as expected. Then the fixed intermediate plate was removed from the original design, and CFD calculation confirmed that the propulsion performance of the modified design has been improved. However, it was also concluded that the performance of two oscillating fins in series with simply pitch motion may have further improvement. In the present study, CFD tool of FLUENT is applied to simulate the hydrodynamics of a single oscillating fin with heave-pitch coupled motions, and the results are compared with published experimental data. The validity of FLUENT is confirmed, and then it is applied to the proposed design of two oscillating fins in series with heave-pitch coupled motions. A series of conditions of heave-pitch coupled motions are investigated. In addition, the effects of motion amplitude, phase angle and frequency to the propulsive performance are also clarified. The effects of the fore fin to improve the overall thrust and propulsion efficiency of two oscillating fins in series are confirmed, and the mechanism is clarified via the distribution of velocity and vorticity.