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Numerical Modeling of Compound Channels for Determining Kinetic Energy and Momentum Correction Coefficients Using the OpenFOAM Software

Mehranfar Nariman, Ghanbari-Adivi Elham

Archives of Hydro-Engineering and Environmental Mechanics

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2022

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Vol. 69, nr 1

27--43

EN

The non-uniformity of the flow velocity distribution in each section of compound channels and in the main channel-floodplain interface area causes errors in estimating water surface profile, flood routing, pollution transfer, and so on. To reduce the impacts of non-uniformity on the exact calculation of kinetic energy and momentum, α and β correction coefficients are used, respectively. However, the determination method of these coefficients is a challenging issue in river engineering. This study used the OpenFOAM Software to determine these coefficients numerically for two laboratory models of compound open channels of which the data are available, using the single-phase pimpleFoam solver to do modeling in the mentioned software and the k-ωSST turbulence model to calculate the flow characteristics. Based on the results, the highest difference (13%) between the results estimated by the software and those obtained from the lab experiments was seen in the low flow depth where the flow left the main channel and entered the floodplain of a very shallow depth, possibly due to the grid generation of this area. This difference decreased as the flow depth increased, and its average was 6.65% for α coefficient and 2.32% for β coefficient in all cases, which means the results of numerical modeling and the experimental data conformed well, and the OpenFOAM software can be successfully used in flow modeling and analyzing flow characteristics in compound channels.

2

Compound Channel’s Cross-section Shape Effects on the Kinetic Energy and Momentum Correction Coefficients

Ghanbari-Adivi Elham

Archives of Hydro-Engineering and Environmental Mechanics

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2020

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Vol. 67, nr 1-4

55--71

EN

Since accurate estimation of the flow kinetic energy (α) and momentum (β) is not easily possible in compound channels, determining their accurate correction coefficients is an important task. This paper has used the “flood channel facility (FCF)” data and the “conveyance estimate system (CES)” model (which is 1D, but considers a term related to the secondary flow) to study how the floodplain width and the main channel wall slope and asymmetry affect the values of α and β. Results have shown that their maximum values at the highest floodplain width are, respectively, 1.36 and 1.13 times of those at the lowest case; an increase in the slope increased their maximum values by 1.05 and 1.01 times, respectively. The mean of error values showed that the CES model estimated the values α and β more accurately than the flow discharge. The maximum differences between the estimated and experimental values were 12.14% for α and 4.3% for β; for the flow discharge, it was 24.4%.

3

Scales of Turbulent Eddies in a Compound Channel

Kozioł A.

Acta Geophysica

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2015

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Vol. 63, no. 2

514--532

EN

Experimental research was undertaken to investigate the changes in scales of turbulent eddies (macro- and microeddies) in a compound channel and the influence of rigid, emergent floodplain vegetation on scales of turbulent eddies. The results of eight tests for different roughness conditions (smooth bed, rough bed) and with a tree system on the floodplains from two earlier studies are presented. The increase of the channel roughness resulted in a decrease of longitudinal sizes of macroeddies in the whole channel. Trees on the floodplains resulted in disintegration of the sizes of macroeddies, making values of sizes more uniform. A more significant decreasing influence on sizes of macroeddies in the whole channel was exerted by an increase of the main channel sloping bank roughness, having a higher effect than a twofold decrease in the floodplain trees density. The microeddies’ sizes are larger in the main channel centreline than on the floodplains and the smallest ones were present in the main channel/floodplain interface.

4

Measurements of 3D turbulence structure in a compound channel

Czernuszenko W., Kozioł A., Rowiński P. M.

Archives of Hydro-Engineering and Environmental Mechanics

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2007

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Vol. 54, nr 1

55-73

EN

The paper describes some turbulence measurements carried out in an experimental compound channel with flood plains. The surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed with terrazzo. Instantaneous velocities were measured be means of a three-component acoustic Doppler velocity meter (ADV) manufactured by Sontek Inc. This article presents the results of measurements of primary velocity, the distribution of turbulent intensities, Reynolds stresses, autocorrelation functions, turbulent scales, as well as the energy spectra.

5

Warunki przepływu w rzekach z kieszeniami zalewowymi - badania laboratoryjne

Mazurczyk A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2006

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Vol. 15, No. 1

21--28

EN

Contemporary rules o f controlling rivers suggest leaving vegetation on the floodplains for the sake of its environmental functions. After years of constructing channels with simple geometry and free of obstruction, like floodplain vegetation, the trend to promote restoration of river valleys appeared. Due to the problem s with natural re-shaping of already canalised rivers along their whole lengths, the idea of building of a side-pocket within a shorter reach of a floodplain by shifting the existing dikes further front the main chamtel has appeared. The main aim of the study was the examination of the influence of the occurrence and density of stiff woody vegetation in a floodplain-pocket upon the velocity distributions and flow capacity in a com pound channel in a Iaboratory flume. Vertical and horizontal velocity distributions in a floodplain-pocket and in the main channel and change of water level caused by occurrence of vegetation and the geometry of the pocket by different density of vegetation were investigated. Water flow in the channel with floodplain-pocket is too complicated to be treated like a one-dintensional process. Velocities in the main channel are visibly higher than in the floodplain-pockct. Vegctation reduccs the velocities on the floodplain, but also reduces the effect of geometry of the pocket. The inerease in water stages is observed above and within the pocket. Water stages down the channel remain constant independently of the existence of the pocket and the vegetation.

6

Modelowanie migracji cząstek stałych w korycie o dwudzielnym przekroju

Krukowski M.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2006

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Vol. 15, No. 2

99--112

EN

The aim of my work was definition and analysis elementary charakteristic spread floating solid particles at small dimension in compound cross-section channel. It was carry out position of solid particles (simulate passive pollution) on water surface and definition characteristic spread particles subject to diffrent points batching in channel and intensity of flow. It was also analysis coefficients of turbulent diffusion characteristic transporting capacity of flux and intensity spread particles.

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Analiza wyników obliczeń przepustowości doliny rzecznej w warunkach występowania roślinności wysokiej

Kozioł A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2005

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Vol. 14, No. 1

49--57

EN

The influence of shrubs and trees growing on the floodplain was based on results of the discharge calculation. The discharges in described examples were calculated assuming the decrease of shrubs’ surface and concentration of vegetation. Ali the calculations of discharges were based on the guidelines of hydraulic applied by Union of Engineers of Water Management and Engineering Environment in German (DVWK 220).