Study of hydraulic jump position by using momentum transfer

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ESMAILI K.; maarefdoust r.; Alebuyeh a.

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Journal: IRANIAN WATER RESEARCH JOURNAL Year:2018 | Volume:12 | Issue:1 (28) Page(s): 1-10

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Title

Study of hydraulic jump position by using momentum transfer

Author(s)

ESMAILI K. | maarefdoust r. | Alebuyeh a. | Issue Writer Certificate

Keywords

Energy lossQ1

Hydraulic jumpQ2

Jump lengthQ1

Sensitivity analysisQ1

Water jetQ1

Abstract

Hydraulic jump phenomenon is a rapid variation in flow conditions that occurs during the transition of the flow from supercritical to subcritical conditions. During the Hydraulic jump, flow depth rapidly increases within a short distance. The depth increase is accompanied by a relatively high Energy loss and leads to a sharp decrease in flow velocity. Determination of Hydraulic jump position in the construction of such structures as spillways and lower floodgates in dams, where the Hydraulic jump is formed at the downstream, has particular importance in engineering perspective. Due to the relatively high costs of constructing basins for controlling the Hydraulic jump, many researches have been conducted regarding applied methods for cost reduction, ensuring that the jump occurs at a specific location with the maximum energy dissipation. Controlling the Hydraulic jump via the flow, itself, can be very cost effective. So far, considerable research has been conducted in this regard. The simplest type of Hydraulic jump is the Classic (Type A), which happens in horizontal rectangular channels. The aim of present study is investigating the effect of the momentum transferred from rapid free jet on the Hydraulic jump characteristics. For this purpose, a jet impingement was conducted at six different flow rates and four jet angles. The Hydraulic jump characteristics (i. e., the primary and secondary depths, energy dissipation, and jump displacement) were compared, with and without the jet, at 7 primary Froude numbers. The experiments were conducted inside a laboratory of Mashhad University flume with the following dimensions: length=5 m; width=7. 5 m; and height=17. 5 cm. The flume has an adjustable slope which was set as 0. 0025 in the experiments. The flow rate was determined via the channel measuring system. To eliminate the scaling effect on the obtained results, several experiments were conducted with horizontal bed and rectangular channel to create Hydraulic jumps to obtain the conditions for the control experiment. A control gate was implemented at flume downstream at the distance of 3. 75 meters from the upstream floodgate, in order to control and stabilize the classical Hydraulic jump. The fast Water jet was created via a nozzle installed at the end of the pipe attached to pumping system. The rectangular nozzle was 6. 8 cm long and 1. 5 cm wide. This device was fitted at the distance of 40 cm from the upstream gate. Four angles were considered for the jets with respect to the flume floor: 15, 30, 45, and 60 degrees. Six flow rates were produced for the jet. In the experiments, seven classical Hydraulic jumps at various Froude numbers, namely, 1. 98, 2. 18, 2. 68, 3. 58, 3. 73, and 4. 76 were created and subsequently, fast impinging Water jets were applied to them at different flow rates and angles. Many experiments have been conducted on a small physical model for qualitatively studying the effect of momentum transfer to a Hydraulic jump by a fast jet. Although the results obtained from a small model cannot be generalized to the main prototype, the working process can be very helpful in larger models. By entering the jet into the flow under supercritical conditions, the Hydraulic jump was moved along the upstream of the flow. At a constant jet angle, an increase in the jet flow rate would lead to a corresponding increase in the jump displacement. At constant Froude number and constant angular position of the jet, increasing the jet flow rate would lead to an increase in the secondary Hydraulic jump depth (y2), as well as an increase in the dissipated energy. At constant jet flow rate, increasing the jet angle would decrease the secondary depth (y2) and the dissipated energy. At constant angular position of the fast jet, increasing the jet flow rate would lead to a corresponding increase in the Jump length (Lj). By increasing the jet angle, the Hydraulic jump length (Lj) follows a descending trend. At low Froude numbers, the dissipated energy is greater. At each Hydraulic jump, a different optimum jet angle is obtained (depending on the main channel flow rate and the jet conditions) which shows the correct impingement point. Froude number (effect of gravity in the main channel) variations had the greatest and the jet impinging angle had the least effect on energy dissipation. The impingement point, where the jet hits the flow in the main channel, is significant in the displacement of the Hydraulic jump and also the dissipated energy. At lower Froude numbers, the sensitivity of energy dissipation to Froude number dramatically decreases with increasing Froude number until reaches to the mean value. Thereafter, the sensitivity, once again, increases with a sharp slope.

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APA: Copy

ESMAILI, K., maarefdoust, r., & Alebuyeh, a.. (2018). Study of hydraulic jump position by using momentum transfer. IRANIAN WATER RESEARCH JOURNAL, 12(1 (28) ), 1-10. SID. https://sid.ir/paper/159821/en

Vancouver: Copy

ESMAILI K., maarefdoust r., Alebuyeh a.. Study of hydraulic jump position by using momentum transfer. IRANIAN WATER RESEARCH JOURNAL[Internet]. 2018;12(1 (28) ):1-10. Available from: https://sid.ir/paper/159821/en

IEEE: Copy

K. ESMAILI, r. maarefdoust, and a. Alebuyeh, “Study of hydraulic jump position by using momentum transfer,” IRANIAN WATER RESEARCH JOURNAL, vol. 12, no. 1 (28) , pp. 1–10, 2018, [Online]. Available: https://sid.ir/paper/159821/en

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