波浪通過沙漣時底部邊界層流之特性

Boundary Layer Flows Induced by Waves Propagating over Rigid Rippled Beds

陳志欣(Chih-Hsin Chen) ； 林劭權(Shao-Chuan Lin) ； 黃清哲(Ching-Jer Huang)

《海洋工程學刊》 8卷2期 (2008/12) Pp. 169-192

https://doi.org/10.6266/JCOE.2008.0802.04

摘要

本文應用數值方法，在貼壁座標系統中，求解二維時變的Navier-Stokes方程及完整的邊界條件，探討波浪通過剛性沙漣時底部邊界層流之特性。數值計算結果經與Marin(2004)的實驗結果比較相當一致。在確認模式的正確性後，本文探討不同波高與漣高下，沙漣底床附近流場特性、渦流的生成與消散、及邊界層內流體速度特性。本文數值結果顯示，波峰通過沙漣漣峯時，會在向岸漣背上形成一順時針方向之渦流。相反的，當波谷通過漣峯時，則會在離岸漣背上形成一逆時針方向之渦流。隨著入射波高增加，渦流的大小與強度也會增加。此外，隨著波高增加，因渦流而形成的回流(reverse flow)使得沙漣向岸漣背、漣谷及離岸漣背上方邊界層流體速度超射現象減弱，甚至在底床附近有回流的現象。在相同波浪條件下，漣高越大，底床上方流體速度受到回流抵銷的效果也越明顯。

關鍵字

波浪 ； 沙漣 ； Navier-Stokes方程 ； 渦流 ； 邊界層

並列摘要

In this study the unsteady 2-D Navier-Stokes equations and the complete boundary conditions in a body-fitted coordinates system were solved numerically to investigate the bottom boundary layer flow induced by waves propagating over rigid rippled beds. The accuracy of the numerical scheme was verified by comparing the numerical velocity profile within the boundary layer near the rippled bed with the experimental data obtained by Marin (2004).Effects of wave height and ripple height on the flow field, the vortex shedding and the boundary layer flow near the rippled bed were discussed systematically. Our numerical results reveal that as wave crest passes over the ripple crest clockwise vortices are formed at the onshore side of the ripple; on the contrary, the propagation of wave trough over the ripple crest induces counter-clockwise vortices at the offshore side of the ripple. Both the size and strength of the vortices increase with the incident wave height. The reverse flow due to the vortices reduces the overshooting of the velocity profile within the boundary layer. In some cases, this reverse flow may dominate the boundary layer flow near the rippled beds. The effect of the reverse flow due to the vortices seems to increases with the ripple height.

並列關鍵字

waves ； rippled bed ； Navier-Stokes equations ； vortex ； boundary layer