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Accuracy of Numerical Simulation in Asymmetric Compound Channels

Abstract

In the recent years, compound channels received more attention in hydraulic engineering for their role in estimating and calculating the hydraulic parameters of natural rivers. Usually, for determination of the hydraulic parameters of compound channels, physical models are used which have cost and time assumption. According to the wide usage of numerical modeling in hydraulic engineering, this paper aims to evaluate the accuracy of numerical models in compound channels by simulating the hydraulic parameters in nine different types of compound channels and to compare them with experimental data. These simulations can show the interaction between velocity and vorticity and other hydraulic parameters by using contours and graphs along the channel length which help to have more and better understanding about their changes. Numerical simulations were performed using the renormalization-group turbulence model and volume-of-fluid free surface model for determining the level of fluid. Values of convergence ratio and the grid convergence index were calculated for evaluating the extrapolated values from numerical modeling and the sensitivity of the model solution to the numerical discretization, respectively, which indicates a proper validation of grid spacing and refinement selection for optimizing the calculation process. The comparison between numerical and experimental results shows a good agreement. The extracted numerical results show that by changing the floodplain width and depth, the water surface level changes 4–20% and 5–34%, respectively. Moreover, the numerical results show an increment of 20 and 145% in Froude and Weber numbers in floodplains, respectively, because of increment of velocity in floodplain.

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Abbreviations

A :

The fractional area open to flow

B :

Width of main channel

B o :

Width of upstream channel

B f :

Width of floodplain

D :

Hydraulic diameter

f i :

The result corresponding to the different mesh sizes

F SOR :

The time rate of change of the volume fraction of fluid associated with the mass source for fluid

Fr :

Froude number

f x , f y and f z :

Viscous accelerations

g :

Earth gravity

G x , G y and G z :

Body accelerations

H :

Main channel water depth

K :

The turbulence kinetic energy

Q 1 :

Mean main channel volumetric flow rate

Q 2 :

Mean floodplain volumetric flow rate

Q 3 :

Mean full cross-sectional volumetric flow rate

R :

Refinement factor

R :

The center of mass of a body

R c :

The convergence ratio

R DIF :

A turbulent diffusion term

R SOR :

A mass source

u w, v w and w w :

The velocity of source component

u s, v s and w s :

The velocity of the fluid at the surface of the source relative to the source itself

V :

Mean cross-sectional velocity

V F :

The fractional volume open to flow

We :

Weber number

x, y and z :

Coordinate directions

u, v and w :

Velocity components

Y f :

Floodplain water depth

Y r :

The ratio of floodplain water depth and main channel water depth

Z :

Step height

θ 1 :

Entrance angles

θ 2 :

Entrance angles

ρ :

The fluid density

ε i + 1,i :

The relative deviation

ε :

Dissipation rate

v t :

Eddy viscosity

v :

The kinematic viscosity

Δh :

The grid spacing

σ :

Surface tension

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Correspondence to Hamed Sarkardeh.

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Sajjadi, SAH., Sajjadi, SH. & Sarkardeh, H. Accuracy of Numerical Simulation in Asymmetric Compound Channels. Int J Civ Eng 16, 155–167 (2018). https://doi.org/10.1007/s40999-016-0113-3

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Keywords

  • Compound channel
  • Numerical simulation
  • RNG
  • VOF
  • Hydraulic engineering
  • Physical models