EFFECTS OF STRAIGHT-CRESTED GRAVEL BED-FORMS AND VEGETATED BANKS ON TURBULENT FLOW CHARACTERISTICS

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DAVARPANAH JAZI SH.; KABIRI SAMANI A.R.; AFZALIMEHR H.

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Journal: Modares Civil Engineering journal Year:2016 | Volume:16 | Issue:2 Page(s): 103-115

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Title

EFFECTS OF STRAIGHT-CRESTED GRAVEL BED-FORMS AND VEGETATED BANKS ON TURBULENT FLOW CHARACTERISTICS

Author(s)

DAVARPANAH JAZI SH. | KABIRI SAMANI A.R. | AFZALIMEHR H. | Issue Writer Certificate

Keywords

GRAVEL BED-FORMQ2

VEGETATED WALLQ2

REYNOLDS STRESSQ2

TURBULENT FLOWQ2

Abstract

Rivers have been always the main source of water for human kind and the basic element of population development. The interaction between river flow structure and the bed-forms is common problem in river engineering that should be considered to better recognition of behavior of the river flows. Moreover, vegetation in natural rivers increases roughness of the main channel and flood plains which affects the geometry of channels, flow structure, bed resistance and consequently the pattern of sediment transport. In general, bed-forms and vegetation significantly influence flow characteristics, thereby result in non-uniformity in flow; variation of the turbulence intensity, increasing the near-wall shear stresses, and modified velocity distributions. To date, limited works on the impacts of the bed-forms and the vegetated banks on flow characteristics has been reported. Considering the role of bed-forms on sediment transport, turbulence production and flow resistance, investigations on details of flow-bed-forms interaction, vegetated banks and flow structure seem to be essential.In this study, the influence of straight crested GRAVEL BED-FORMs and vegetation of the banks of channels on flow turbulent characteristics are investigated based on model experimentation. For this purpose, seven fixed artificial 2-D straight crested bed-forms were built inside a rectangular flume 8 m long, 0.4 m wide and 0.6 m deep. The graded gravel particles used to create the bed-forms had an average diameter of d50 = 10 mm. Johnson grasses with a diameter of 2.8 mm were used to simulate vegetation cover attached to the channel side-walls. Since, the fully developed flow was just observed after the fifth dune, experimental measurements were performed over the fifth and sixth dunes. Overall, three runs were performed over the dunes with a wave length, height, angle of repose and flow depth of 0.96 m, 0.04 m, 28 degrees and 0.28 m, respectively. In the first case 17 velocity profiles and in the second and the third cases 21 velocity profiles were measured. All the tests were performed with a constant discharge of 0.024 m3/s. The instantaneous three-dimensional velocity components were measured using a down-looking Acoustic Doppler Velocimeter ADV. Velocities were recorded point by point with a sampling rate of 200 Hz and the sampling volume of 5 mm. The sampling duration was at least 120 seconds. Overall, about 45400000 velocity data were collected, filtered by WinADV software. Results indicated no negative velocities for both bare and vegetated banks. For no vegetation case (bare bank), the least value of velocity was zero at a small region on the lee side of the dune. Whereas, for the case of vegetating the side-walls, the zero value of velocity was located at the dune's stoss. Negative vertical velocity value in both cases of with and without vegetation along a dune confirmed that separation is not dominant for the case of straight crested dunes compared to the corresponding sharp-crested bed-forms. The REYNOLDS STRESSes increase for the case of vegetating the side-walls compared to the case of without vegetation cover. This is in part due to the increase of flow resistance, while the side-walls are vegetated.

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APA: Copy

DAVARPANAH JAZI, SH., KABIRI SAMANI, A.R., & AFZALIMEHR, H.. (2016). EFFECTS OF STRAIGHT-CRESTED GRAVEL BED-FORMS AND VEGETATED BANKS ON TURBULENT FLOW CHARACTERISTICS. MODARES CIVIL ENGINEERING JOURNAL, 16(2), 103-115. SID. https://sid.ir/paper/256822/en

Vancouver: Copy

DAVARPANAH JAZI SH., KABIRI SAMANI A.R., AFZALIMEHR H.. EFFECTS OF STRAIGHT-CRESTED GRAVEL BED-FORMS AND VEGETATED BANKS ON TURBULENT FLOW CHARACTERISTICS. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2016;16(2):103-115. Available from: https://sid.ir/paper/256822/en

IEEE: Copy

SH. DAVARPANAH JAZI, A.R. KABIRI SAMANI, and H. AFZALIMEHR, “EFFECTS OF STRAIGHT-CRESTED GRAVEL BED-FORMS AND VEGETATED BANKS ON TURBULENT FLOW CHARACTERISTICS,” MODARES CIVIL ENGINEERING JOURNAL, vol. 16, no. 2, pp. 103–115, 2016, [Online]. Available: https://sid.ir/paper/256822/en

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