كليدواژه :
ظرفيت آبگذري , ديوارهاي هادي جريان , ضريب آبگذري , كارآيي , سرريز كنگره‌اي قوسي
چكيده فارسي :
استفاده از سرريزهاي كنگره‌اي بعنوان يك راه مؤثر و اقتصادي جهت افزايش ظرفيت آبگذري مطرح مي‌باشد. قرارگيري سيكل‌هاي سرريز كنگره‌اي بر روي قوسي از يك دايره مي‌تواند بهبود جهت‌گيري سيكل‌هاي سرريز نسبت به جريان ورودي و نيز افزايش طول تاج بازاي يك عرض معين را سبب گردد. اين تحقيق به بررسي آزمايشگاهي اثرات ديوارهاي هادي جريان بر عملكرد سرريزهاي كنگره‌اي قوسي مي‌پردازد. ضمن بررسي اثرات پارامترهاي نسبت بار هيدروليكي به ارتفاع سرريز (Ho/P)، زاويه ديوار جانبي سرريز (α) و زاويه انحنا (Θ) بر ضريب آبگذري و كارآيي سرريزهاي كنگره‌اي قوسي، اثرات زاويه بين ديوارهاي هادي جريان (Θ′) نيز بر اين مهم مورد تحقيق قرار گرفته است. نتايج نشان مي‌دهد كه قوسي‌كردن سرريز كنگره‌اي مي‌تواند بهبود كارآيي آن را سبب گردد. علي‌ايحال با افزايش بار هيدرويكي، كارآيي سرريزهاي كنگره‌اي قوسي كاهش مي‌يابد. در مقادير پايين زاويه انحنا، انتخاب مناسب زاويه بين ديوارهاي هادي جريان مي‌تواند تا حدود 20 درصد كارآيي سرريز را بهبود بخشد. ليكن اثرات اين پارامتر در مقادير بالاي زاويه انحنا قابل صرف‌نظر كردن مي‌باشد.
چكيده لاتين :
Labyrinth weir is one of the approaches to increase the discharge capacity. An arced configuration improves the orientation of the labyrinth weir cycles to the approach flow and increases the weir crest length for a given width. In this study, the effects of the entrance flow conditions on the hydraulic performance of the arced labyrinth weirs is studied experimentally. The effects of the angle between the entrance channel walls (Θ′) on the discharge coefficient and the efficiency are investigated for different values of the headwater ratio (Ho/P), the downstream sidewall angle (α), and the weir arc angle (Θ). Experiments were conducted in a recirculating flume which is 10 m long, 2 m wide, and 0.9 m deep at Tarbiat Modares University. To simulate the reservoir conditions, a specific setup was added to the flume, known as the reservoir simulator. The flume was launched from its two ends by two pipelines. The inflow passes from underneath of the reservoir simulator and enters into it through a semi-circular opening in its horizontal wall. After moving
over the horizontal wall, the flow comes up through the gap between the vertical wall. Finally, it flows on the platform and moves towards the downstream channel. All the plates (including the platform and the simulator walls) have a semicircular plan-view with a porosity equal to zero. The weirs were mounted on the platform at the entrance of the downstream channel. Totally 132 experiments were conducted to investigate the effects of the mentioned parameters on hydraulic performance of arced labyrinth weirs.
Due to the nappe interference, the local submergence forms in the downstream of the labyrinth weirs. The size of local submergence regions increase by increasing the headwater ratio and the arc angle. However, vice versa trend occurs with the downstream sidewall angle. In addition, for low values of the arc angle, the lateral flow from the side cycles to their adjacent cycles produces the surface turbulences. The results indicate that the discharge coefficient decreases by increasing the headwater ratio and the downstream sidewall angle. For low values of the headwater ratio, the discharge coefficient increases when the arc angle increases. However, a decreasing trend is observed in high head conditions. By increasing the arc angle and decreasing the downstream sidewall angle, the efficiency of a labyrinth weir can be increased. However, the efficiency gains diminish by increasing the headwater ratio. The efficiency of a labyrinth weir can slightly be increased by projecting of the cycles into a reservoir for low values of Ho/P, α, and Θ. However, in the wide range of the research domain, the efficiency decreases ween the angle between the entrance channel walls increases. According to the results of this research, the efficiency of a labyrinth weir can be increased up to 20% by channelizing abutments in high head conditions. However, the effect of Θ′ is insignificant for higher values of Θ. In addition, as α decreases, the benefits and the losses of decreasing Θ′ become more severe at higher and lower values of Ho/P, respectively.
