丁壩區之三維流場研究

Abstract

本研究使用三維計算流體力學軟體FLUENT模擬渠道內流經兩支丁壩之流況，藉由軟體模擬流場特性，了解三維流場分布及渦度分布情形。FLUENT數模係採用有限體積法(finite volume method)離散控制方程式，以二階上風法離散對流項，由SIMPLE法耦合速度與壓力，使整個流場符合質量及動量守恆，再由多項流K-ε紊流配合流體體積法處理三維自由液面水流。 本研究中，網格主要由六面體及四面體網格組成之混合網格，總網格數約在20萬個，研究案例依照丁壩長度、丁壩間距與上游流量不同分做三組。經由模擬迴歸得到此三項變因與丁壩迴流長度及壩間流速之關係式，以供後續實驗模擬參考。由FLUENT模擬可以獲得實驗不易量測之局部細微流場。

In this study, three-dimensional computational fluid hydrodynamics software, FLUENT, is adopted to simulate the flow passing through two groynes in a channel. By simulation, we find the flow characteristics and the distribution of three-dimensional flow pattern and vorticity in the spur-dike region. The model applies the finite volume discrete control equation, the second-order upwind scheme discretization advection term and the SIMPLE method coupled velocity and pressure to satisfy the mass conservation and momentum conservation. Also, the model uses the K-ε turbulent model and volume of fluid method to simulate the three-dimensional flow and its free surface, respectively. Using mesh preprocessor, the model has a grid system composed of hexahedron and tetrahedron mixed meshes with total number of cells approximate 200 thousand are generated in this study. The model simulates three cases with different conditions of groyne length, groyne spacing and inflow velocity. By regression, we obtain the relational formula between three variables and both vortex length and distribution of velocity around groyne. Using FLUENT model, we can obtain the local phenomenon that is difficult to measure.