شبيه‌سازي الگوي جريان در رودخانه هاي پيچانرودي با استفاده از مدل CCHE2D

Numerical Simulation of Flow Pattern in Meandering Rivers Using CCHE2D Model

در اين مقاله مزيت و اهميت يك مدل عددي به منظور پيش بيني و پايش فرايند هاي حاكم بر جريان رودخانه ها مورد بحث قرار گرفته است. به همين منظور و با توجه به اهميت سرعت جريان آب و تنش هاي برشي ناشي از آن بر فرسايش رودخانه‏اي، از يك مدل عددي دو بعدي به نامCCHE2D براي شبيه‏سازي الگوي جريان در بازه اي از پيچانرود طبيعي (رودخانه خشكه رود فارسان- ايران) بهره گرفته شده است. در اين بررسي با بهره گيري از نقشه هاي پستي و بلندي محدوده مورد مطالعه، ابتدا هندسه مدل و شبكه محاسباتي با ابعاد مختلف، تهيه و سپس بر اساس مشخصات اندازه گيري شده جريان رودخانه، مدل هيدروديناميك دو بعدي متوسط عمق، اجرا و نتايجي همچون توزيع عمق و سرعت جريان در خم رودخانه استخراج گرديد. نتايج نشان دادند كه در صورت ورود شبكه محاسباتي استاندارد به مدل، اين مدل در پيش بيني مقادير سرعت جريان از دقت بالايي برخوردار بوده و داده هاي شبيه‏سازي شده در مقايسه با داده هاي حاصل از اندازه گيري صحرايي شباهت زيادي دارند. نتايج حاصله نشان دادند كه بهره گيري از مدل هاي ديناميك سيالات محاسباتي (CFD) براي مدل‌سازي جريان آب، ما را يك گام به پيش بيني هاي كلي تر براي فرايندهاي حاكم بر جريان در رودخانه هاي پيچان‏رودي نزديك‏تر مي كند. همچنين، مدل CCHE2D از قابليت خوبي جهت پيش‌بيني مشخصات جريان در رودخانه‌هاي پيچان برخوردار است.

In the present paper, the advantage and importance of a numerical model to predict and monitor the governing processes in the river flow was investigated. With respect to the importance of flow velocity and shear stress on river bank erosion, a two-dimensional numerical model (CCHE2D) was used to predict the river flow pattern in a meandering reach of Farsan Arid River. The first, we applied topographic maps of studied location and then, made the model geometry and calculation mesh with standard dimensions. Finally, the measured properties of the river flow had been input and the Depth-Average, Two-Dimensional Hydrodynamic Model had been run. Then, the results were obtained from the model, like as depth and flow velocity indicated a well compatibility with observed data of meander river. Within the scope of the test cases, the model simulated water flow pattern processes at an intake, as well as a steady flow regime in a sine-shaped meandering channel by a 90_channel bend, which is the free-forming meander evolution of an initially straight channel. Because of high accuracy of this numerical model and multiple content of its internal parameters the evaluation result of model, as well as confirmed measurement results. Therefore, the parameters that gained of model predicted showed that well accordance to measurement parameters at field cross-section. All results matched well with the measurements. The results also showed that using computational fluid dynamics for modeling water flow is one step closer of having a universal predictor for processes in Meandering Rivers. Various algorithms and parameters were implemented in the model for simulation of two-dimensional flow to gain a comprehensive coverage of the current capabilities. Measurements of velocity in the field were used for model validation. Agreement between numerical results and measurements data showed high applicability of CCHE2D model in prediction of flow pattern in the meandering river.