以水槽試驗及數值模式分析垂直軸水動力渦輪機轉動效率之研究

Abstract

氣候變遷對環境影響日益加劇，能源轉型與綠色能源發展成為國際趨勢。水力發電因高能源轉換效率與穩定發電量等因素，自90年代以來持續作為最大的可再生能源。近年來，由於生態與社會問題，傳統大壩式水力發電開發減緩，取而代之的是具有環境衝擊小與成本低廉等優勢的水動力能量轉換系統。然而，水動力能量轉換系統仍處於早期發展階段，因此在渦輪機設計和導流裝置等領域仍存在諸多研究缺口。 本研究旨在結合水槽試驗及數值模式模擬，探討導流板設計的關鍵參數，以提升垂直軸水動力式渦輪機發電效率。研究選擇NACA-0015翼型，設計一架固性為0.398，縱橫比為1.0之升力式垂直軸水動力渦輪機。實體成品經由3D列印技術製成，並透過水槽試驗量測其轉速與扭矩，評估原始渦輪機的功率係數。而後將水槽實驗量測之流量與水位分別作為FLOW-3D上下游邊界條件進行模擬，以評估不同網格解析度之準確性，並進行FLOW-3D之參數率定、模式驗證。決定網格解析度後，針對導流板長度、角度與兩板之間距離設計18組不同配置方案，並透過FLOW-3D進行模擬，以觀察渦輪機三維細部速度場與壓力場變化，並分析導流板對於流場之影響。最後，綜合分析與討論18組方案的角速度、扭矩、功率和功率係數，找出導流板配置的關鍵參數，並評估其對渦輪機性能提升的效果。 本研究流場分析結果表明，除渦輪機本身之阻塞作用外，導流板的束縮亦會增加水位差異，產生更大的上下游壓力差。此外，導流板引導接近板面的水流流向，提升其流速，使渦輪機葉片內外側產生更大的流速差，進而增加升力與提高渦輪機效率。渦輪機效率分析結果顯示，渦輪機原始功率係數為0.057，加裝導流板後，隨著導流板越靠近渦輪機，功率係數從0.1提高到0.335左右，提升幅度約為66%到450%。此外，渦輪機功率隨角度之變化呈現明顯的三葉瓣狀，且隨導流板越靠近渦輪，其功率峰值逐漸從60°/180°/300°轉移到90°/210°/330°左右。表明導流板設置不僅能提高速度差，增加渦輪機功率係數，亦會改變流場分布，導致最佳葉片角度位置組合發生變化。最終結果顯示，兩板之間距離對渦輪機周圍流場的影響顯著大於導流板長度和導流板角度。因此它對渦輪機效率的提升也遠高於其他兩個參數。

The impact of climate change on the environment is intensifying, leading to an international trend towards energy transition and the development of green energy. Hydropower has remained the largest renewable energy source since the 1990s due to its high energy efficiency. In recent years, the development of traditional dam-based hydropower has slowed down due to ecological and social issues. Instead, hydrokinetic energy conversion systems, which offer advantages such as minimal environmental impact and low cost, have gained attention. Nonetheless, hydrokinetic energy conversion systems are still in the early stages of development, leaving many research gaps in areas such as turbine design and deflector devices. This study aims to enhance the power efficiency of vertical-axis hydrokinetic turbines by investigating crucial parameters in deflector device design through a combination of flume experiments and CFD model simulations. The research focuses on a lift-based vertical-axis hydrokinetic turbine designed with a NACA-0015 airfoil, a solidity of 0.398, and an aspect ratio of 1.0. The flow conditions and relevant parameters investigated from the flume experiment were utilized as boundary conditions and validation processes for FLOW-3D simulations to evaluate the accuracy of different mesh resolutions and validate the FLOW-3D model. After determining the mesh resolution, 18 different configurations of deflector devices were designed, varying in length, angle, and width between the plates. These configurations were simulated using the verified FLOW-3D to observe the changes in the turbine's three-dimensional detailed velocity and pressure fields and analyze the impact of the deflector devices on the flow field. Finally, a comprehensive analysis and discussion of the angular velocity, torque, power, and power coefficient of the 18 configurations were conducted to identify the critical parameters of the deflector device design and evaluate their effects on improving turbine performance. The flow field analysis results indicate that, in addition to the turbine's blockage effect, the contraction caused by the deflector devices also increases the water elevation difference, leading to a larger pressure difference between upstream and downstream. Additionally, the deflector devices direct the flow close to their surfaces, increasing the flow velocity. This causes a greater velocity difference on both sides of the turbine blades, enhancing lift and thus improving turbine efficiency. The efficiency analysis of the turbine shows that the original power coefficient was 0.057. With the addition of deflector devices, the power coefficient increased from 0.1 to approximately 0.335 as the deflector devices were placed closer to the turbine, indicating an enhancement ranging from about 66% to 450%. Moreover, the variation in turbine power with blade angles exhibited a distinct three-lobed pattern, with the power peaks gradually shifting from 60°/180°/300° to approximately 90°/210°/330° as the deflector devices approached the turbine. This indicates that the deflector devices not only increase the velocity difference and power coefficient but also alter the flow field distribution, thereby changing the optimal blade angle positions. The final results indicate that the distance between the two plates significantly influences the flow field around the turbine compared to the length and angle of the deflector devices. Therefore, it also contributes significantly more to improving turbine efficiency than the other two parameters.