Numerical investigation of the secondary current pattern in the open channel with different roughness forms on the bed

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Shahbeygi Narjes; PIRZADEH BAHAREH

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Journal: Modares Civil Engineering journal Year:2019 | Volume:19 | Issue:4 Page(s): 97-108

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Title

Numerical investigation of the secondary current pattern in the open channel with different roughness forms on the bed

Author(s)

Shahbeygi Narjes | PIRZADEH BAHAREH | Issue Writer Certificate

Keywords

Secondary currentsQ1

Roughness formQ1

Turbulence intensityQ1

Turbulence kinetic energyQ1

Flow-3DQ1

Abstract

It is important in Hydraulic and river engineering to estimate the mean velocity and Turbulence intensity to identify the presence of Secondary currents, its shape and position. The flow of channels consists of three conponents of velocity, one component in the direction of flow and two components in the transverse direction of the channel. Due to the heterogeneity of the velocity fluctuations, a series of vortex vortices in the channel section to be formed which is called Secondary currents cells. The Secondary currents are dependent on factors such as bed roughness, channel slope and shear stress. The present study investigates the effect of bed Roughness form on the pattern of Secondary currents with numerical modeling in Flow-3D software by using RNG turbulent model. This research has been carried out according to the data of the Negara laboratory model carried out at the Hydraulic Laboratory of Singapore National University. In the results obtained from the mean velocity profile, the mean error for triangular roughness trough was 9. 94% and for roughness crest was 3. 71%. in the case of shear velocity, the error for triangular roughness was obtained at three cross sections x=4, x=5 and x=6 respectively 6. 58%, 6. 86% and 5. 67% which demonstrates the good fit of the numerical model results with the reference laboratory model. The flow conditions in the channel were designed and studied for three types (rectangular roughness, trapezoidal roughness with an internal angle of 80 degrees and trapezoidal roughness with an internal angle of 55 degrees) of roughness that are most used in hydraulic structures. The results of the study on the Turbulence intensity, Secondary currents and Turbulence kinetic energy showed the effect of trapezoidal roughness with an internal angle of 55 degrees relative to the other two forms of roughness. The difference in the Turbulence intensity in trapezoidal roughness with an internal angle of 55 degrees relative to a triangular roughness at a height of 0. 1 meter from the channel bed was obtained at about 4. 54%, which is affected by a sharp roughness. The location of the center of the contour nucleus begins in the depth of about 0. 2 meters, due to channel size B/H=1. 5 of less than 5, the channel is narrow and justifies the presence of vortices in the middle. On the other hand, the tendency of cells to the left and right walls of the canal is also affected by roughness geometry with also different from the deformation of the location of these cells. In trapezoidal roughness with an internal angle of 55 degrees, there is a tendency to both walls. The Turbulence kinetic energy contour with the center of the nucleus begins at the roughness crest with an approximate value of 0. 0002 for all roughness, but its location is different in relation to the roughness geometry. In fact, the Turbulence kinetic energy is the effect of oscillating velocity components that the existence of external rotations is the effect of the redistribution of energy by velocity tensor, which is responsible for the formation of secondary current cells.

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APA: Copy

Shahbeygi, Narjes, & PIRZADEH, BAHAREH. (2019). Numerical investigation of the secondary current pattern in the open channel with different roughness forms on the bed. MODARES CIVIL ENGINEERING JOURNAL, 19(4 ), 97-108. SID. https://sid.ir/paper/256845/en

Vancouver: Copy

Shahbeygi Narjes, PIRZADEH BAHAREH. Numerical investigation of the secondary current pattern in the open channel with different roughness forms on the bed. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2019;19(4 ):97-108. Available from: https://sid.ir/paper/256845/en

IEEE: Copy

Narjes Shahbeygi, and BAHAREH PIRZADEH, “Numerical investigation of the secondary current pattern in the open channel with different roughness forms on the bed,” MODARES CIVIL ENGINEERING JOURNAL, vol. 19, no. 4 , pp. 97–108, 2019, [Online]. Available: https://sid.ir/paper/256845/en

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