پديد آورندگان :
كيان مهر، حميد دانشگاه فردوسي مشهد - گروه علوم و مهندسي آب , خداشناس، سعيدرضا دانشگاه فردوسي مشهد - گروه علوم و مهندسي آب , رستمي، محمد سازمان تحقيقات آموزش و ترويج كشاورزي - پژوهشكده حفاظت خاك و آبخيزداري، تهران
كليدواژه :
اندازه گيري , سازه كنترل , شبكه آبياري , ضريب بده , كانال آبگير
چكيده فارسي :
دريچه هاي كشويي جانبي به‌سبب هندسۀ ساده و قابليت بهره برداري آسان، يكي از متداول ترين سازه هاي كاربردي در شبكه هاي آبياري براي انحراف آب از كانال اصلي و تنظيم ميزان بده عبوري براي آبياري زمين هاي كشاورزي هستند كه به‌رغم اهميت فراوان آنها در بهره برداري و مديريت منابع آب در شبكه هاي آبياري، كمتر بررسي شده اند. براي تعيين مشخصات جريان دريچه هاي جانبي، تحت شرايط رژيم جريان زير بحراني از 107 آزمايش تحقيق حاضر به‌همراه 529 آزمايش ساير محققان استفاده شد. با حل رابطه ديناميكي حاكم بر دريچه هاي جانبي با استفاده از روش عددي رانگ كوتاي مرتبۀ چهارم، نيمرخ سطح آب در طول دريچۀ جانبي محاسبه شد. با مقايسۀ ضريب بده در دو رويكرد حل رابطه جريان متغير مكاني و روش مستقيم حل رابطة بده، مشخص شد مقادير ضريب بده در هر دو رويكرد، تطابق قابل قبولي با هم دارند. با استفاده از تحليل ابعادي و آماري، به‌منظور تخمين ضريب بده رابطههايي پيشنهاد شدند و رويكردي براي تشخيص شرايط جريان آزاد يا مستغرق ارائه شد. نتايج بررسيها نشان داد كه ضريب بده دريچۀ جانبي در شرايط جريان آزاد به نسبت عمق جريان به بازشدگي دريچه و عدد فرود جريان بالا‌دست بستگي دارد و در شرايط مستغرق به نسبت عمق جريان به عمق پاياب كانال آبگير و نسبت عمق جريان به بازشدگي دريچه بستگي دارد. رابطۀ پيشنهادي تخمين ضريب بده در شرايط جريان آزاد و مستغرق به‌ترتيب داراي متوسط خطاي نسبي 2/96 و 5/33 درصد است و دقت قابل قبول رابطۀ پيشنهادي را نشان مي دهد.
چكيده لاتين :
Introduction
A side sluice gate is an underflow and metering diversion device set into the side of a channel with the
purpose of allowing part of the liquid to spill through the side. Review of the literature shows that in spite
of the importance of the side sluice gate, little attention has been given to studying the behaviour of flow
through this device. The available published works on side sluice gates found are those of Panda (1981),
Swamee et al. (1993) and Ghodsian (2003). They related the discharge coefficient of the side sluice gate to
depth of flow and gate opening. For this purpose, the side sluice gates, since flow control devices, are
widely used in the irrigation channels to divert flow from a main channel to a secondary channel. The main
purpose of present study was to determine the water surface profile, gate opening, and flow discharge
through the sharp-crested rectangular side sluice gates in a subcritical flow regime in free and submerged
flow conditions. This study also provides some approaches to differentiate the free or submerged flow
conditions. For this purpose, two approaches of solving spatially varied flow equation in a sub-critical flow
regime and the direct solution of the discharge equation of the side sluice gates in determining the flow
characteristics of the side sluice gates was experimentally investigated.
Methodology
The first approach (Solving the Spatially Varied Flow Equation)
The general differential equation of spatially varied flow along a side sluice gate with decreasing discharge
is:
(1)
𝑑𝑦
𝑑𝑥 =
√2(𝐸 − 𝑦)
𝐵√𝑔 (3𝑦 − 2𝐸) (−
𝑑𝑄
𝑑𝑥)
To determine the variation of flow discharge during the side sluice gate, the functional relationship for
discharge equation must be defined. The velocity at each height V of the gate opening section is obtained as
follows:
𝑉 = √2𝑔 (𝐻 − 𝑌) (2)
Considering the discharge dQ passing through an elementary strip of length dx along the side sluice gate
(Fig. 2c), the discharge per unit length of the side sluice gate is given by:
𝑑𝑄 (3)
𝑑𝑥 = −
2 3
𝐶
𝑑 √2𝑔 [𝑦3⁄2 − (𝑦 − 𝑎)3⁄2]
Swamee et al. (1993) and Gill (1987) considered the following relationships for determining the flow
discharge per unit length of side sluice gates, which is the simplified version of Eq. 3.
𝑑𝑄 (Swamee et al. (1993) ) (4)
𝑑𝑥 = −𝐶𝑑 𝑎 √2𝑔 𝑦
𝑑𝑄 (Gill (1987) ) (5)
𝑑𝑥 = −𝐶𝑑 𝑎√2𝑔 (𝑦 − 𝑎 2)
By inserting the Eqs. 3, 4, and 5 in Eq. 1, the governing differential equations were obtained in these types
of flows in different conditions.
The second approach (direct solution of the side sluice gate discharge equation)
In this approach, assuming that the flow discharge variation along the sluice gate is constant and equal to
the upstream water depth y1, the equations for determining the flow discharge through the side sluice gate
(Eq.. 3, 4, and 5) are re-written as follows:
Q = 2 (Present Research) (6)
3 C𝑑 b √2𝑔 [𝑦1 3⁄2 − (𝑦1 − 𝑎)3⁄2]
𝑄 = 𝐶𝑑 𝑎 𝑏 √2𝑔 𝑦1 (Swamee et al. (1993) ) (7)
𝑄 = 𝐶𝑑 𝑎 𝑏 √2𝑔 (𝑦1 − 𝑎 2) (Gill (1987) ) (8)
Experimental Setup
The experiments of the present study were carried out on a physical model with a width of 1.5 m, a length
of 17 m, and the depth of 0.8 m. In order to intake water, a branch channel with a width of 0.6 m and a
length of 2.5 m in a distance of 8 m from the beginning of the main channel was used. In this study, the
experiments were performed for a sluice gate with three different openings of 2, 4, and 7 cm with the width
of 60 cm in two free and submerged flow conditions.
Results and Discussion
In order to determine the discharge coefficient of the side sluice gate, the first step was to study the
variations of the specific energy and water surface profile along the side sluice gate. Then, by choosing the
best relationship for determining the flow discharge of the side sluice gate, the two approaches of solving
the equation of the spatially varied flow and direct solution of the side sluice gate discharge equation were
examined. . Further, some approaches are presented to differentiate the free or submerged flow conditions,
some fitting equations are given in order to estimate the discharge coefficient using various nondimensional variables and step-by-step consideration of their effect
Conclusions
In this study, the central axis of the main channel was introduced as a measuring axis in side sluice gates.
Comparison of experimental profiles and those obtained from the solution of the differential equation
governing the spatially varied flow indicates the proper agreement between experimental results and
numerical solutions. In addition, by examining the results of solving the spatially varied flow equation, Gill
(1987) ’s equation was selected as the best equation for determining the flow discharge through side sluice
gates, due to the simplicity and high precision. By examining the discharge coefficient in two mentioned approaches, it was found that the discharge coefficient obtained from the direct solution of the discharge
equation is well consistent with the solution of the spatially varied flow equation. Next, some approaches
are presented to differentiate the free or submerged flow conditions. It was found that the discharge
coefficient of the side sluice gate in the free flow conditions depends on the ratio of the flow depth to the
side sluice gate opening and upstream Froude number, and in submerged flow conditions depends on ratio
of the flow depth to the tail-water depth at branch channel and the ratio of the flow depth to the side sluice
gate opening.
