地形效應與風應力影響綠島尾流之數值試驗

Numerical Experiments of Green Island Wakes by Topographic Effect and Wind Stress

侯典轟(Tien-Hung Hou) ； 蕭士俊(Shih-Chun Hsiao) ； 蔡加正(Chia-Cheng Tsai) ； 許泰文(Tai-Wen Hsu)

《海洋工程學刊》 18卷3期 (2018/11) Pp. 191-203

摘要

本文以普林斯頓海洋模式（Princeton Ocean Model, POM）模擬在風應力與地形效應下綠島尾渦流的特性，分別在不同流速及風速下，藉由雷諾數（Re）以及司特勞克數（St）來分析綠島尾渦流空間尺度之變化。地形效應影響海流流速與流向，島嶼受到強流影響，島嶼後方產生渦漩曳離且有成對渦街；島嶼受到較弱的流速影響時，島嶼後方流不分離無渦漩，但同時直徑較小的海底山產生了尾渦流。在風應力效應的模擬中顯現，綠島後方的流速在吹西南風時較吹東北風來得大。西南風加速了流的速度，強化了原本的尾渦流機制；東北風則尾渦流受風向影響而向西偏移，但渦流漩曳離現象仍顯著，於風應力效應的模擬結果可發現綠島尾渦流明顯受到風場影響。此外，雷諾數及渦流慣性力對綠島尾渦流的空間尺度分析，扮演著重要作用。不同地形效應與風速會造成司特勞克數的變化，高、低雷諾數案例中，發現風應力的影響結果不同。本研究利用數值模式模擬，將有助於了解綠島尾流在不同季節時，尾渦流變動的狀況。

關鍵字

普林斯頓海洋模式 ； 風應力 ； 台灣綠島 ； 島嶼尾流

並列摘要

In this paper, the Princeton Ocean Model (POM) is used to simulate the characteristics of the ocean vortex by wind stress and topographic effect around the Green Island. Moreover, the spatial scale of the Green Island wake is analyzed by Reynolds (Re) and Strouhal (St) numbers for different current and wind velocity. The topographic effect results in oceanic current and the vortex shedding or even vortex street are resulted in the island lee if the oceanic current is strong. On the other hand, no vortex shedding is resulted in the island lee if the oceanic current is weak while vortex shedding can be resulted in the lee side of a seamount which has smaller radius compared to the Green Island. The wind stress can also affect the velocity of the resulted oceanic current. Basically, the current velocity is larger for the southwest wind than the northeast one. For the situation of southwest wind, it tends to increase the current velocity and therefore strengthen the resulted vortex shedding. On the other hand for the situation of northeast wind, the resulted vortex shedding moves westerly. Therefore, the simulation results indicate that the wind stress can affect the Green Island wake significantly. In addition, the characteristics of the oceanic vortex were analyzed by Re and St numbers. Considering two situations of higher and lower Re numbers, the effects of wind stress on the St numbers are different. Overall, the numerical simulations are used to study the Green Island wake affected by topographic effect and wind fields form different seasons.

並列關鍵字

Princeton ocean model ； wind stress ； Green Island ； wake