نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشجوی کارشناسی ارشد سازه های آبی، دانشگاه بیرجند، ایران
2 هیأت علمی گروه علوم و مهندسی آب دانشگاه بیرجند
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and Objective: Hydraulic jump occurs in an open channel when supercritical flow exists upstream and subcritical flow downstream, resulting in significant energy dissipation. This study proposes a novel method for determining hydraulic parameters such as conjugate depths and jump length, utilizing the characteristics of a fast, free rectangular water jet and bottom roughness to influence the jump’s characteristics and position. The interaction of the jet with the jump and the transfer of momentum impacts the jump’s features and location.
Materials and Methods: In this study, a series of laboratory experiments were conducted in a rectangular channel with glass walls, length 12 meters , width 0.3 meters, and height 0.5 meters. The length and depth of the jump were measured using both direct and indirect methods. In the direct method, the jump depth and length were measured using a fabric meter attached to the channel walls, while in the indirect method, a high-resolution camera and Grapher software were used to measure the flow depth. To evaluate the effects of discharge, jet angle, and bottom roughness on the hydraulic jump characteristics, by three different jet discharges of 2, 2.5, and 3 liters per second were tested at minimum and maximum jet deflection angles and jet impact angles at the beginning of the hydraulic jump. Additionally, two roughness heights and two distances were tested.
Results: This research indicates that at a specific angle of jet impact on the hydraulic jump, no displacement occurs, referred to as the "ineffective angle." As the jet angle increases, the jump moves upstream until a certain angle is reached, beyond which no further upstream movement occurs, termed the "maximum displacement angle." Changes in jet angle and discharge led to variations in jump length, secondary depth, relative energy loss, jump length, and bed shear force. The use of a jet with the lowest Froude number (6.5), a maximum angle of 129 degrees, a discharge of 3 liters per second, and triangular roughness resulted in a 21 percent increase in secondary depth, the location of initial jet impact, and the ratio compared to the condition without a jet and with a smooth bed. Using a 3-liter-per-second jet with a 63-degree angle and the lowest Froude number increased the secondary depth by 20.96 percent compared to the condition without a jet and with a smooth bed. Employing a 3-liter-per-second jet, with the maximum Froude number and an angle greater than the ineffective angle of 145 degrees, resulted in a 30.16% reduction in relative jump length compared to a smooth bed and without a jet. At a 60-degree angle with the maximum Froude number, a 3-liter-per-second jet discharge reduced the relative energy loss by 22.4 percent. The maximum relative energy loss occurred with the minimum jet discharge, the minimum Froude number, and a 64-degree angle, showing a 20 percent reduction compared to the smooth bed condition without roughness and jet. Finally, using a jet with an angle smaller than the ineffective angle and larger than the ineffective angle resulted in a decrease and increase in the bed shear force coefficient, respectively.
Conclusion: Applying a jet to the hydraulic jump with an angle greater than the ineffective angle increases energy loss, reduces jump length, and decreasing in the conjugate depth ratio and bed shear forces in the channel
کلیدواژهها [English]
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