هيدروليك جريان بر روي سرريز گابيوني عريض در شرايط عملكرد آزاد و مستغرق

Classification of surface regimes over broad-crested gabion weir

پژوهش حاضر براي بررسي آزمايشگاهي الگوي جريان روي سرريز گابيوني عريض در ابعاد مختلف طرح‌ريزي شده است. آزمايش‌ها جمعاً براي 12 مدل با سه طول 100، 200 و 300 ميلي‌متر و دو ارتفاع 100 و 200 ميلي‌متر و دو دانه‌بندي گابيون 31/1 و 93/2 ميلي‌متر انجام پذيرفته است. ابتدا با ايجاد شرايط آزاد جريان پايين‌دست سرريز، ضريب دبي براي سرريزهاي لبه‌پهن گابيوني و صلب مقايسه شد. پس از حصول اطمينان از صحت آزمايش‌ها، با افزايش عمق پايين‌دست به منظور مستغرق ساختن سرريز گابيوني، رفتار جريان در استغراق‌هاي مختلف بررسي شده است. چهار وضعيت هيدروليكي براي سرريز گابيوني بر اساس عدد فرود جريان در روند آزمايش‌ها تشخيص داده شد. وضعيت‌ها عبارت‌اند از: جريان آزاد، جريان با پرش پايين‌دست، جريان با فرم موجي بر سطح آب در پايين‌دست و جريان كاملاً مستغرق. نتايج نشان دادند با تغيير جريان از حالت آزاد به مستغرق پيش‌بيني مي‌شود جريان درون‌گذر از گابيون كاهش يابد و جريان از روي سرريز عبور كند. اين بدين معناست با افزايش عمق پايين‌دست جريان، رفتار هيدروليكي سرريز گابيوني عريض تغيير مي‌كند و از سرريز گابيوني به سرريز لبه‌پهن تغيير وضعيت مي‌دهد. در انتها، با استفاده از ميزان درجه‌ي استغراق و عدد فرود بالادست، معادله‌يي براي تعيين محدوده‌ي هيدروليكي رژيم‌هاي جريان ارائه شده است.

The present study investigate 12 experimental broad-crested gabion models. In order to investigate the flow regimes over this structure, hydraulic characteristics were measured under different submergence conditions. A comparison of coefficient discharge values showed that a significant increase in these values was observed between the broad-crested and broad-crested gabion weirs. It seemed that the passed flows through gabion weir could raise the discharge coefficient values versus the same values with same hydraulic condition for solid broad-crested weir. To predict the discharge values over this weir, reduction factor has been calculated for the experiments in different submerged ratio. By considering the submergence ratio, an equation has been proposed to calculate these values. Three regimes have been introduced to measure the water surface profiles as free flow, (I) surface jump regime, (II) surface wave regime, (III) Deeply submerge regime. Due to increase the tail water height, water surface profile was measured as proposed regimes. The surface jump regime was defined as a downstream hydraulic jump which was developed from downstream location of channel to the weir crest. Additionally, the water surface turn to the series of downward waves which is called surface wave regime. By increasing the submerged ratio, the surface wave regime was vanished as the deeply submerged condition. The submerged ratio 0.18 has been proposed to region the surface jump regime and surface wave regime. Also, based on submerged ratio, an equation has been proposed to separate the surface wave regime and deeply submerge regime. The longitudinal velocity has been measured by ADV probe at the downstream broad-crested weir over the longitudinal section. Comparing between measured longitudinal velocity and color injection illustrates that increasing the submergence ratio causes the flow within gabion weir has marginally decreased and this flow is dependent on submergence ratio. The color injection results show the passed the performance of gabion weir in deeply submerged regime is same as broad-crested weir and the flow with in gabion will be negligible over the developed deeply submerged regime.