垂直式海流渦輪機流場計算研究

INVESTIGATIONS OF DIFFERENT METHODS FOR COMPUTING THE VERTICAL AXIS MARINE CURRENT TURBINE FLOW FIELD

In this paper, both the momentum methods and the viscous flow RANS method are adopted to compute the flow around a vertical axis marine current turbine. The momentum method includes the single stream-tube and the multiple stream-tube models, and the RANS method used here is the commercial software SC/Tetra. The results from each method are discussed and compared to the experimental data. The momentum methods though over-predict the power generated by the turbine, both models provide reasonable predictions. The multiple stream-tube model is slightly better between two models. For the RANS methods, the commercial CFD software SC/Tetra is used, and the grid number, time-step sizes and turbulence models are investigated. In general, it is very time consuming using RANS to compute the flow around the vertical axis turbine since it is an unsteady flow problem. Computational results of a Darrieus straight-blade marine current turbine are presented in the paper, and results from different methods will be compared to each other and to the experimental data. The computational results show that reasonable accuracy and physics of flow details can be obtained through the computations. The RANS method not only can provide the flow details, but also give a better prediction of the power generated. 垂直軸洋流渦輪機為獲得海洋能源的常見裝置之一，相較於水平軸洋流渦輪機則有結構簡單及入流方向不受限等優點。本文以三種數值方法計算垂直軸洋流渦輪機之水動力性能與流場情況，計算的方法包括單流管模型、多流管模型及黏性流之RANS方法，並將計算結果與實驗值比對，驗證各方法的正確度與可應用性。文中簡單介紹所使用之實驗模型數據，並介紹三種數值方法的物理假設及限制。除此之外，本文亦探討RANS方法應用在商業計算流力軟體上的各種影響參數，包括計算域大小、網格疏密、時間步長大小以及紊流模型的使用等，最後比較各種計算結果，並呈現其流場狀況。