شبيه سازي انتقال رسوب در كانال مستقيم و آبگيرجانبي

Simulation of Sediment Transport at Straight Channel and Lateral Intake

در اين مقاله حركت ذرات رسوب در كانال مستقيم و آبگير‌جانبي بر اساس ديدگاه لاگرانژي شبيه‌سازي شده است. هدف از اين مطالعه بررسي عملكرد مدلDPM در شبيه سازي مسير حركت ذرات رسوب و همچنين برآورد نسبت رسوب انحرافي (نسبت بار ‌بستر ورودي به آبگير به كانال اصلي) با استفاده از اين روش است. خصوصيات جريان با استفاده از مدل آشفتگي تنش‌هاي رينولدز در نرم افزار فلوينت شبيه‌سازي شده است. مطالعات شامل دو بخش كلي است: در بخش اول به منظور بررسي صحت عملكرد مدل، مسير حركت ذره در كانال مستقيم شبيه‌سازي‌ شد. مقايسه نتايج عددي حاصل با داده‌هاي آزمايشگاهي كه به همين منظور برداشت شده است، صحت شبيه‌سازي عددي را تاييد مي‌كند. در بخش دوم الگوي حركت رسوبات در آبگير جانبي از مسير مستقيم به صورت كيفي و كمّي ‌بررسي شد و نتايج با داده‌هاي آزمايشگاهي موجود مقايسه شد. بررسي الگوي حركت رسوبات، نشان‌دهنده تشكيل ناحيه‌اي گوه‌اي‌شكل در دهانه آبگير مي‌باشد. همچنين نسبت رسوب انحرافي در مدل‌سازي عددي به صورت دست‌بالا تخمين زده شده است.

Abstract: In this paper, the Lagrangian tracking of individual particles was performed at the straigh channel and the lateral intake. The CFD software package Fluent (Fluent Inc.) is used to solve the governin equations. This study is conducted to research the performance of Discrete Phase Model (DPM) fo simulation of tracking of individual sediment particles and estimation of the rate of bed load at the entranc of lateral intake. For flow field simulation, the Reynolds Averaged Navier - Stokes (RANS) equations wer solved. The Reynolds stress transport model (RSM) was used evaluating the turbulent ?ow characteristics The simulation results were compared with the available experimental data. The study was conducted i two parts. In the first part, the particle movement was simulated in the straight channel to evaluate model performance The comparison of numerical results (predicted) and experimental data (measured), which were done for thi purpose, confirmed numerical simulation results. Based on the experimental and numerical results, under th same flow conditions, particle with greater diameter has a shorter trajectory than smaller one, because o increasing weight and increasing drag force. In modeling of particle trajectory, the effects of drag force, lif force, added mass and particle weight are considered. A deterministic approach was used for simulation o tracking of individual sediment particles. The particle was released from water level and its trajectory wa studied before approaching the bed. Experimental studies conducted for two diameters (particle density 1065 kg/ m3, particle diameter=2.5 and 4 mm) in a rectangular straight channel. To consider the stochasti behavior due to turbulent effect, each experiment was repeated three times. In the second part, sediments movement pattern in lateral intake from straight channel was investigate from quantitative and qualitative views and were compared with available experimental data. The intak channel was installed at right angle to the main channel. In numerical model, one hundred sand particle (sand density = 2650 kg/ m3, particle diameter =1 mm) were released uniformly, near the bed (0.02m abov bed level) across the whole width of the main channel (2m) upstream of intake, so they move at the entranc of intake as bed load. The effect of changing number of particles was studied using a sensitivity analysis Increasing number of particles show no effect on results. The qualitative analysis of sediments movement showed a shape of wedge like sand bar forms by bed load a the entrance of lateral intake. The quantitative comparison of the predicted and measured Qs (ratio of the bed load discharge in latera intake to the bed load in main channel) shows that the predicted values were more than the measured one Maybe this matter is related to simplifications and assumptions that were used in modeling. In this study, th interaction between particles was ignored, because of the inability of numerical model. At the entrance o lateral intake, compaction of particles is more than the main channel so it seems particle - particl interactions are more important than main channel. It is necessary to perform further studies on this proble to achieve proper results.