كليدواژه :
شكست سد , قوس رودخانه , موج سيلاب , مدل عددي , موج ديناميكي
چكيده فارسي :
در اين مقاله، هيدروديناميك سه بعدي شكست سد در مسيرهاي قوسي بصورت عددي مدلسازي شده و تاثير زاويه و شعاع انحناي قوس بر الگو و نحوه حركت موج سيلاب بررسي شده است. هدف اصلي، بررسي تفاوت ها و تشابه هاي پديده شكست سد در مسيرهاي مستقيم و قوسي مي باشد. نتايج حاصله نشان داد كه در لحظات اوليه شكست سد در مسير مستقم، بخاطر تاثير موج ديناميكي، يك پيك موضعي در هيدروگراف سيلاب رخ مي هد و تا فاصله اي در پائين دست سد اين پديده حفظ مي شود. در حاليكه در بازه هاي قوسي بواسطه نامتعادل شدن موج سيلاب پيش رونده، چنين پديده اي تنها در محل سد رخ داده و به سرعت از بين مي رود. وجود بازه قوسي باعث كاهش شتاب حركت موج سيلاب شده و تاثير قوس بر روند حركت موج سيلاب در امتداد جداره داخلي بسيار بيشتر از جداره هاي خارجي و خط مركزي كانال مي باشد. تغيير شعاع انحنا تاثير بسزايي بر حركت موج سيلاب در امتداد جداره داخلي قوس داشته ولي تاثير اين پارامتر در سرعت حركت موج سيلاب در امتداد جداره بيروني و خط مركزي كانال زياد نمي باشد. مسير قوسي فقط بر شاخه صعودي هيدورگراف سيلاب و مشخصات نقطه پيك تاثير گذار بوده و شاخه نزولي مشابه مسير مستقيم مي باشد.
چكيده لاتين :
In this paper, 3D hydrodynamics of dam break phenomena in curved rivers has been simulated numerically. Effects of curve angle and radius of curvature on the flood wave propagation and unsteady flow features along the curved reach at the downstream of dam has been investigated. The main objective of the research is investigation of similarities and differences between dam break phenomenon in straight and curved reaches. The commercially available CFD program Flow-3D, which utilizes the finite volume scheme for structured meshes was used for solving unsteady Reynolds-averaged Navier-Stokes equations in conjunction with the RNG k-ε closure model. In the utilized software, the Fractional Area/Volume Obstacle Representation (FAVOR) method is used to inspect the geometry in the finite volume mesh. FAVOR appoints the obstacles in a calculation cell with a fractional value between 0 and 1, as obstacle fills in the cell. Geometry of the obstacle is placed in the mesh by setting the area fractions on the cell faces along with the volume fraction open to flow. This approach creates an independent geometry structure on the grid, and then the complex obstacle such as spillways, mechanical parts and domains with natural bed topography can be produced in an easier way. Fluid surface shape is illustrated by volume-of-fluid (VOF) function, F(x,y,z,t). With the VOF method, grid cells are classified as empty, full, or partially filled with fluid. Cells are allocated in the fluid fraction varying from zero to one, depending on fluid quantity. This function displays the VOF per unit volume. FLOW3D solves these semi-implicit equations iteratively using relaxation techniques. In this paper the GMRES technique has been used as pressure implicit solver. Results showed that at the initial instants of the dam break in the straight channel, due to the effects of the dynamic wave, flood hydrographs at the dam location and at a distance downstream of the dam have local peak values. While in the curved channel cases, the flood wave immediately becomes unstable after the dam break and the local peak occurs just at the dam section. The curved reach decelerate the flood wave propagation compared to the straight channel. Effect of channel curvature on the movement of the flood wave along the inner bank is higher than the outer bank and also the centerline of the curved channel. By changing the channel curvature, wave propagation is significantly affected along the inner wall of the channel, while the channel curvature does not have considerable effect on the velocity of the wave propagation along the centerline and outer wall of the curved reach. By decreasing the central radius of the bend, slope of the rising limb of the hydrograph and also the peak discharge attenuates. Furthermore, the peak discharge time reduces. Unlike the effects of the curvature of the bend, increasing the bend angle does not affect the peak discharge. Changing the bend curvature and curve angle has no effect on the falling limb of the flood hydrograph at various stations downstream of the dam.
