船模支架對尾流發展的影響研究

ANALYSIS OF SUPPORT-STING INTERFERENCE ON THE WAKE DEVELOPMENT IN SHIP MODEL TESTS

水下載具在進行模型試驗時，必須以支架固定在水槽中，而不同的支架幾何及連接位置都會對結果產生大小不一的干擾和影響，本論文探討上側支架對模型尾流的影響。本研究係以國立臺灣海洋大學大型空蝕水槽擬進行的長球體實驗為標的進行探討，此長球體之長軸與直徑比為6:1(長軸4.5 m，直徑0.75 m)，以前後兩根支架固定在水槽中，其中前支架係包覆在類似帆罩的結構體內(長215 mm，寬52 mm)，後支架(長380 mm，寬15 mm)則暴露在水流中。我們採用計算流體力學的研究方式，來探討後支架幾何對尾流場的影響，計算域大小與水槽測試段一致(長10 m，寬2.6 m，高1.5 m)，且入流流速設定相同，若以長球體長軸為特徵長度，雷諾數約為2.37×107。研究中所運用的計算流體力學軟體為Ansys Fluent，在流場的網格建置上，我們採用非結構性網格，並使用SST k-w紊流模型。我們比較不同幾何截面支架對水下載具尾流的影響，以圖降低支架在試驗中所造成干擾，結果顯示傳統使用的平板式支架對流場的干擾最大，而對稱、厚度呈拋物線分布的支架影小最小。

In model tests of underwater vehicles, the test model must be fixed in the testing tank using support stings, and different sting geometries and attachment locations introduce varying degrees of interference to the flow field and, hence, the test results. This study investigates the influence of an upper sting on the wake of the model. The target of this investigation is a prolate spheroid experiment planned for the large cavitation tunnel at National Taiwan Ocean University. The spheroid has a length-to-diameter ratio of 6:1 (length 4.5 m, diameter 0.75 m) and is fixed in the facility using forward and aft stings. The forward sting is enclosed within a sub-marine sail-like structure (length 215 mm, width 52 mm), while the aft sting (length 380 mm, width 15 mm) is directly exposed to the incoming flow.
Computational fluid dynamics (CFD) is employed to examine the effect of the aft sting geometry on the wake field. The computational domain matches the dimensions of the test section of the large cavitation tunnel (10 m in length, 2.6 m in width, and 1.5 m in height), and the inflow velocity is set identical to the experimental condition. Using the spheroid’s major axis as the characteristic length, the Reynolds number is approximately 2.37×10⁷. The CFD software used in this study is Ansys Fluent. An unstructured mesh is adopted for grid generation, and the SST k–ωturbulence model is applied.
We compare the effects of different sting cross-section geometries on the wake of the underwater vehicle in order to reduce experimental interference caused by the stings. The results show that the commonly used flat-plate sting produces the greatest disturbance to the flow, whereas a symmetric sting with a parabolic thickness distribution causes the least interference.