A Laboratory Investigation of Flow Resistance in Wide Channel

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Hasanzadeh Vayghan Vahid; Mohammadi Mirali

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Journal: Modares Civil Engineering journal Year:2018 | Volume:18 | Issue:6 Page(s): 73-82

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Title

A Laboratory Investigation of Flow Resistance in Wide Channel

Author(s)

Hasanzadeh Vayghan Vahid | Mohammadi Mirali | Issue Writer Certificate

Keywords

Wide ChannelQ1

Physical ModelQ2

Stage-DischargeQ1

Flow ResistanceQ1

Manning’s roughnessQ1

nQ1

Abstract

The Stage-Discharge relationship is a type of resistance to flow evaluation that is used to determine the depth and hydraulic radius in open channels, if the flow discharge, channel cross-sectional shape and the properties of bed materials are specific. Wide Channels as well as plane bed rivers, due to having the higher ratios of width to depth, b/h, they have specific hydraulic characteristics than that of the normal open channels. In this research work, the hydraulic characteristics of widening long and Wide Channels including flow pattern, Stage-Discharge relationship and Flow Resistance, by using a Physical Model of rigid boundary with 60m length, 1. 5m wide and a longitudinal chanel bed slope of 1 in 1000 (0. 001) that has b/h ratios range of 12 to 56 are experimentally investigated. The construction material of channel model is concrete bed and concrete block walls were used. To insulate the channel bed and walls, a thick layer under the concrete was also used. Due to its wide width and length, the Physical Model of this study has low scale effects and the obtained results are closer to the normal open channels as well as the plain bed rivers. Based on the values obtained for the Froude, Reynolds and Shear Reynolds numbers in model, it was found that the flow regime is subcritical and turbulent. According to the results of model, Stage-Discharge-Tailgate relationship is shown plotted and it is found that as the flow rate increases, the Tailgate height that required at the downstream end of the channel to produce a normal depth, increases. On the basis of normal depths obtained in a widen channel model, a reliable Stage-Discharge relationship is presented. The results show that this relationship has a higher coefficient than that of a natural channel Stage-Discharge relationship. Results, also reveals that between the calculated and measured Manning’ s roughness coefficient, n, in the Wide Channel model, a difference (about 10%) is observed. The results show that, for discharges greater than 35 lit/s, the measured Manning roughness coefficient, n is very close to the n values presented in literature. However, for the discharges less than 35 lit/s, the measured values of Manning’ s n is 15% higher than the amounts provided in literature. The results of the present research show that by increasing the ratio of hydraulic radius to the roughness height of the bed (Rh/ks), the Manning roughness, n, decreases linearly. Also, based on the results, it was found that by increasing flow depth, The Manning roughness, n, decreases and by increasing Reynolds number, Re, the Manning n decreases linearly. The results also show that in the Wide Channel model, the Manning roughness coefficient, n, decreases from 0. 022 to 0. 016 by increasing Froude number, Fr, from 0. 26 to 0. 4, In this research, the wide to depth ratio, b/h, was considered as the main independent variable in the determination of n, and using the coding, a reliable relation was obtained between them, which can be used for Wide Channels. According to the results, it is clear that with increasing b/h ratio, the Manning roughness coefficient, n, also increases, but this trend changes in b/h ratios larger than 43 and has a decreasing trend.

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APA: Copy

Hasanzadeh Vayghan, Vahid, & Mohammadi, Mirali. (2018). A Laboratory Investigation of Flow Resistance in Wide Channel. MODARES CIVIL ENGINEERING JOURNAL, 18(6 ), 73-82. SID. https://sid.ir/paper/256719/en

Vancouver: Copy

Hasanzadeh Vayghan Vahid, Mohammadi Mirali. A Laboratory Investigation of Flow Resistance in Wide Channel. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2018;18(6 ):73-82. Available from: https://sid.ir/paper/256719/en

IEEE: Copy

Vahid Hasanzadeh Vayghan, and Mirali Mohammadi, “A Laboratory Investigation of Flow Resistance in Wide Channel,” MODARES CIVIL ENGINEERING JOURNAL, vol. 18, no. 6 , pp. 73–82, 2018, [Online]. Available: https://sid.ir/paper/256719/en

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