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DOI:10.22059/jwim.2022.342521.986

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A numerical simulation of overlay effect of rigid vegetation in a straight open channel by OpenFOAM

Komeil Samet¹, Mirali Mohammadi^2*, Khosrow Hosseini³, Saeed Farzin³

1. Ph.D. Student, Department of Water Eng., & Hydraulic Structures, Faculty of Civil Engineering, Semnan University, Semnan, Iran.

2. Associate Professor, Department of Civil Engineering (Water and Hydraulic Structures), Faculty of Engineering, Urmia University, Urmia, Iran, (corresponding author)

3. Associate Professor, Department of Water Eng., & Hydraulic Structures, Faculty of Civil Engineering, Semnan University, Semnan, Iran.

Received: May 03, 2022 Accepted:August 21, 2022 Abstract

In order to understand the mechanism of flow patterns in vegetated channels, the flow located in a rectangular channel was numerically investigated by using OpenFOAM software. Firstly, two solvers of that software (i.e. icoFoam and pimpleFoam) were used to calculate the velocity profiles in both longitudinal and cross-sectional directions for four selected sections in a rectangular channel with a square cylinder. By comparing the simulation results with the available data, the icoFoam solver with a better performance (six Percent Error) was selected for the next developed model. A new model was then created with two tandem square cylinders with spacing ratios of two and a half and five. Flow patterns, velocity distribution and pressure characteristics in the channel with different inlet flow velocities were investigated for two cases. It was observed that a flow field disturbance occurred in all simulations and the current changed from steady state to unsteady one at a critical velocity. This instability occurred in a distance between the cylinders for the spacing ratio of five at an average Reynolds number of eight, while for the ratio of two and a half it is occurred at an average Reynolds number of 32. The maximum values of longitudinal and transverse velocity timelines in a period of 200 seconds for four states (including two Reynolds numbers and two different spacing ratios) were plotted in two spatial ranges and fully investigated. According to the results, it can be said that the overlap has an important role on the flow characteristics in tandem arrangements and by increasing the distance ratio between the cylinders by 55 percent, the critical velocity value decreases by 74 percent.

Keywords: Critical Velocity, Numerical Modelling, OpenFOAM, Spacing Ratio, Straight Channel, Tandem Rigid Vegetation.

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Figure 5. Timelines of velocity profiles in longitudinal direction at four cases while considering the area between two tandem cylinders

Figure 6. Timelines of velocity profiles in lateral direction at four cases while considering the area between two tandem cylinders

0 0.5 1 1.5 2

0 25 50 75 100 125 150 175 200

velocity (m/s)

time (s)

first case second case third case forth case

0 0.5 1 1.5 2 2.5

0 25 50 75 100 125 150 175 200

velocity (m/s)

time (s)

first case second case third case forth case

) 7"/

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& L L .

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& L A+ , 7 / iDL )/

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7 (

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'I 1 A8

&8 & @ A= A+ , S , - ), .A, )1 01 3 +

(a)

(b)

Figure 7. Timelines of velocity profiles at longitudinal a) and, lateral b) directions at four cases while considering a section in the middle of two cylinders

0 0.5 1 1.5 2

0 25 50 75 100 125 150 175 200

Ux (m/s)

0 0.5 1 1.5

0 25 50 75 100 125 150 175 200

Uy (m/s)

time (s) first case

second case third case forth case

<

A= A+ , 7b 2 Y 2 ) & @

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Table 2. Maximum and minimum amounts of pressure, velocity in X and Y directions at the Re of

100 in both states (section and area)

Section Ux Uy P

Max 1.842 1.425 0.609

Min -1.715 -1.516 -1.782

Area Ux Uy P

Max 1.695 2.050 1.498

Min -1.715 -1.918 -1.816

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Anjum &

Tanaka (2019)

-

Wu et al.

(2020)

-

Diwivedi et al.

(2022)

-

Wang et al.

(2022) Wang et al.

(2021)

& 5 & 5 .

3 + u 1

50 100 ! >

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&

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, L L 3 +

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5 / 2

; ,

& V H .

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& -x GQ ![cH & !. / A1 . Q!) H

&. &G=

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& 'I 1 A8 01 ] .

! >

& - '!, 'I 1 A8 A+ , H

A+ ,

H

&8 & @ A=

- ] A,

! >

A 9

! . A+ , < ![cH H

5& 1

1. Computational Fluid Dynamics 2. Drag coefficient

3. Blockage ratio 4. Reynolds number 5. Wake

6. Lattice Boltzmann Method 7. Overlay effect

8. Tandem 9. Viscous flow

10. Dirichlet Boundary Condition 11. Law of wall

12. Overtake

13. Courant-Friedrichs-Lewy 14. Courant number

15. Kinematic viscosity 16. Strouhal number

17. Vortex shedding frequency 18. Fast Fourier Transform 19. Time history

20. Lift coefficient 21. Navier–Stokes

22. Pressure Implicit with Splitting of Operators 23. Semi-Implicit Method for Pressure Linked

Equations

24. Finite Volume Method 25. Streamline direction 26. Cross-sectional direction 27. Percentage Error 28. Velocity timelines

6 7 "#

‹!

. W, H ;1 u BH .

.

6

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