Experimental investigation of the effect of bed roughness on hydraulic jump characteristics

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ASADI F.; EMADI A.R.; FAZLOULA R.

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Journal: IRANIAN WATER RESEARCH JOURNAL Year:2020 | Volume:13 | Issue:4 (35) Page(s): 39-49

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Title

Experimental investigation of the effect of bed roughness on hydraulic jump characteristics

Author(s)

ASADI F. | EMADI A.R. | FAZLOULA R. | Issue Writer Certificate

Keywords

Energy dissipationQ1

Froude numbersQ1

Relative lengthQ1

Rough bedsQ1

Abstract

The hydraulic jump is one of the important phenomena of water flow in channels that in proportion to the intensity of the jump, faces significant Energy dissipation. True hydraulic jump forms for the Froude numbers greater than 4. 5. Position of steady jump is the least sensitive type to fluctuations in the tail water elevation and forms steadily at the same location. The change of flow state from supercritical to a subcritical state is accompanied by discontinuity in depth of flow, formation of a surface roller, visible air entrainment and two phase flow, significant turbulence, kinetic Energy dissipation, generation of spray and sound. The basic characteristics of a hydraulic jump are defined such as conjugate depth, location of jump, the energy loss in the jump, efficiency of jump, the length of the jump. From the designer's standpoint, hydraulic jump is a powerful Energy dissipation mechanism and due to its erosive potential, is the centroid of scour. In order to take full advantage of the hydraulic jump in apron design, the erosive effect of jump should be confined to the limits of the heavily protected bed surface, hence intensive scour energy would not cause any harm to apron. This is why; hydraulic jump should be in a stilling basin with a fixed location. Turbulent flow over a rough surface is an important problem and it has been subject of diverse fields. Using roughness elements at the bottom of the flow causes increase in resistance to the flow hence accelerate the upstream flow development and increase in amount of kinetic energy, converted into the turbulent energy. Using of Rough beds is an effective factor in reducing costs on Energy dissipation basins. So researchers’ next purpose has been the use of roughness beds in the stilling basins bed and investigation the effect it on hydraulic jump characteristics. In this research, experimental investigation was carried out on the effect of bed roughness on hydraulic jump characteristics. It was done in a flume with length of 12 meters, width of 0. 5 meters and height of 0. 7 meters, in the range of Froude numbers 5. 5 to 9. Also, 24 cubic Rough beds was used with staggered and strip arrangement, different rows and angles. Discharge was measured by a triangular weir with a 90° angle, placed at the end of channel and size of cubic blocks was 0. 05 meters. Point gauges with a sensitivity of ± 0. 1 mm used to measure the depths of flow. To evaluate the effect of roughness, both staggered and strip arrangement were used in the experiments. For creating a hydraulic jump, a sharp sluice gate has been used in the condition which the Rough beds in downstream places. Relative depth and Relative length was obtained as a function of Froude number. The relative depth values on smooth beds obtained in the present study were in good agreement with the data of Belanger classic jump. Relative depth, Relative length and shear force coefficient increase for staggered arrangement, strip arrangement and smooth bed with increasing Froude number. The results showed that in the same Froude number the values of relative depth and Relative length in smooth bed is less than those values on Rough beds whereas shear force coefficient on Rough beds is greater than smooth bed. Equations were obtained with SPSS software for jump relative depth. Results indicated that relative depth and length for staggered arrangement, in compare with strip, have more reducing ratio in smooth bed. Also, they showed, staggered arrangement produced better performance compare with strip arrangement in the ratio of secondary to primary depth and the ratio of length to jump primary depth. Both types arrangement had a better performance compared with jumps formed on smooth beds. For staggered and strip arrangement, the average of length ratio to jump primary depth was obtained 1. 9 and 1. 6 times less than smooth bed, respectively. In the experiments, the ranges of relative for the staggered and strip arrangement were 20. 47 to 39. 04 and 46. 66 to 24. 28, respectively. Shear force coefficient, that is the main factor is in reducing of depth and jump length, calculated 6 percent more of smooth bed in both arrangements. Generally, the experimental results of the current study are matched with the other similar researches on different types of Rough beds. Finally, the equation for estimate of relative depth and Relative length for Froude numbers extracted. By the results, the effects of arrangements in the level of 5 percent were proofed for all beds on relative depth and Relative length.

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APA: Copy

ASADI, F., EMADI, A.R., & FAZLOULA, R.. (2020). Experimental investigation of the effect of bed roughness on hydraulic jump characteristics. IRANIAN WATER RESEARCH JOURNAL, 13(4 (35) ), 39-49. SID. https://sid.ir/paper/159879/en

Vancouver: Copy

ASADI F., EMADI A.R., FAZLOULA R.. Experimental investigation of the effect of bed roughness on hydraulic jump characteristics. IRANIAN WATER RESEARCH JOURNAL[Internet]. 2020;13(4 (35) ):39-49. Available from: https://sid.ir/paper/159879/en

IEEE: Copy

F. ASADI, A.R. EMADI, and R. FAZLOULA, “Experimental investigation of the effect of bed roughness on hydraulic jump characteristics,” IRANIAN WATER RESEARCH JOURNAL, vol. 13, no. 4 (35) , pp. 39–49, 2020, [Online]. Available: https://sid.ir/paper/159879/en

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