The liquid‐gas mass transfer coefficient in open channel flow is correlated to the turbulent kinetic energy at the interface

2020 ◽  
Vol 98 (5) ◽  
pp. 1191-1201
Author(s):  
Fanny Springer ◽  
Lucie Carrera ◽  
Gislain Lipeme Kouyi ◽  
Alejandro Claro‐Barreto ◽  
Pierre Buffiere
Keyword(s):  
Mass Transfer ◽  
Kinetic Energy ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Turbulent Kinetic Energy ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow

The relationship between surface-renewal and bursting motions in an open-channel flow

1989 ◽  
Vol 203 ◽  
pp. 103-123 ◽  
Author(s):  
Satoru Komori ◽  
Yasuhiro Murakami ◽  
Hiromasa Ueda
Keyword(s):  
Mass Transfer ◽  
Methylene Blue ◽  
Free Surface ◽  
Transfer Coefficient ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Liquid Interface ◽  
Surface Renewal ◽  
Buffer Region

Surface-renewal motions in the interfacial region below a gas-liquid interface were experimentally investigated in relation to bursting motions in the wall region. To estimate the frequency of the appearance of surface-renewal eddies, mass-transport experiments with methylene-blue solution, together with velocity measurements, were done in an open-channel flow. The instantaneous concentration of methylene-blue tracer emitted from a point source positioned in the buffer layer was measured at the free surface downstream from the source by an optical probe. Instantaneous streamwise velocity was measured using a laser-Doppler velocimeter at a position in the buffer region. Frequencies of both surface-renewal and bursting events were computed from these concentration and velocity signals using a conditional-averaging method. In order to clarify whether the surface-renewal eddies actually dominate mass transfer across the gas-liquid interface, gas-absorption experiments were added. Carbon dioxide was absorbed into the water flow across the calm free surface and its mass-transfer coefficient on the liquid side was measured under the same flow conditions as used in the above mass-transport experiments. The results show that the surface-renewal motions originate in the bursting motions which vigorously occur in the buffer region. That is, the decelerated fluid which is strongly lifted towards the outer layer by bursting almost always arrives at the free surface and renews the free surface. The frequency of the surface renewal, as well as the bursting frequency, is uniquely determined by the wall variables or the outer-flow variables and the Reynolds number. Mass transfer across the gas-liquid interface is dominated by the large-scale surface-renewal eddies, and the mass-transfer coefficient on the liquid side is proportional to the square-root of the surface-renewal frequency.

Effect of aspect ratio on developing and developed narrow open channel flow with rough bed

2018 ◽  
Vol 45 (9) ◽  
pp. 780-794 ◽  
Author(s):  
Minakshee Mahananda ◽  
Prashanth Reddy Hanmaiahgari ◽  
Ram Balachandar
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Channel Flow ◽  
Open Channel ◽  
Reynolds Shear Stress ◽  
Open Channel Flow ◽  
Flow Region ◽  
Channel Flows ◽  
Open Channel Flows ◽  
Rough Bed

This study attempts to unravel the effect of aspect ratio on the turbulence characteristics in developing and fully developed narrow open channel flows. In this regard, experiments were conducted in a rough bed open channel flow. Instantaneous 3D velocities were acquired using an acoustic Doppler velocimeter at various locations along the centerline of the flume. The variables of interest include the mean components of the flow velocity, turbulence intensity, wall normal Reynolds shear stress, correlation coefficient, turbulence kinetic energy, and anisotropy. A new correlation between the equivalent roughness and velocity shift from the smooth wall logarithmic equation as a function of aspect ratio is proposed. Aspect ratio was found to influence the velocity characteristics throughout the depth in the developing flow region, while the effects are confined to the outer layer for fully developed flows. New equations to describe the variation of turbulence intensities and turbulent kinetic energy are proposed for narrow open channel flows. Reynolds stress anisotropy analysis reveals that level of anisotropy in narrow open channel flow is less than in wide open channel flows. Finally, a linear regression model is proposed to predict flow development length in narrow open channel flows with a rough bed.

scholarly journals Turbulent Kinetic Energy and Budget of Heterogeneous Open Channel with Gravel and Vegetated Beds

2021 ◽  
Vol 3 (2) ◽  
pp. 1-4
Author(s):  
OP Folorunso ◽  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Open Channel ◽  
Open Channel Flow ◽  
Hydraulic Parameters ◽  
Flow Depth ◽  
Turbulent Kinetic Energy Budget ◽  
Rigid Vegetation ◽  
Flexible Vegetation ◽  
Turbulence Production

Turbulent kinetic energy (TKE) and budget are indispensable hydraulic parameters to determine turbulent scales and processes resulting from various and different natural hydraulic features in open channels. This paper focuses on experimental investigation of turbulent kinetic energy and budget in a heterogeneous open channel flow with gravel and vegetated beds. Results indicate the turbulent kinetic energy (TKE) value over gravel region of the heterogeneous bed remains approximately constant with flow depth. The highest turbulent kinetic energy was calculated for flexible vegetation arrangement compared to the rigid vegetation. The estimation of the turbulent kinetic energy budget shows the higher values of turbulence production recorded over the flexible vegetated bed, consequently, the dissipation rate exhibits faster decay of turbulence kinetic energy over the vegetated bed in comparison to the gravel bed.

On the onset of wake meandering for an axial flow turbine in a turbulent open channel flow

2014 ◽  
Vol 744 ◽  
pp. 376-403 ◽  
Author(s):  
Seokkoo Kang ◽  
Xiaolei Yang ◽  
Fotis Sotiropoulos
Keyword(s):  
Kinetic Energy ◽  
Shear Layer ◽  
Channel Flow ◽  
Open Channel ◽  
Axial Flow ◽  
Open Channel Flow ◽  
Flow Fields ◽  
Turbulence Kinetic Energy ◽  
Actuator Disk ◽  
Far Wake

AbstractLaboratory experiments have yielded evidence suggestive of large-scale meandering motions in the wake of an axial flow hydrokinetic turbine in a turbulent open channel flow (Chamorro et al., J. Fluid Mech., vol. 716, 2013, pp. 658–670). We carry out a large-eddy simulation (LES) of the experimental flow to investigate the structure of turbulence in the wake of the turbine and elucidate the mechanism that gives rise to wake meandering. All geometrical details of the turbine structure are taken into account in the simulation using the curvilinear immersed boundary LES method with wall modelling (Kang et al., Adv. Water Resour., vol. 34(1), 2011, pp. 98–113). The simulated flow fields are in good agreement with the experimental measurements and confirm the theoretical model of turbine wakes (Joukowski, Tr. Otdel. Fizich. Nauk Obshch. Lyub. Estestv., vol. 16, 1912, no. 1), yielding a near-turbine wake that consists of two layers: the tip vortex (or outer) shear layer that rotates in the same direction as the rotor; and the inner layer counter-rotating hub vortex. Analysis of the calculated instantaneous flow fields reveals that the hub vortex undergoes spiral vortex breakdown and precesses slowly in the direction opposite to the turbine rotation. The precessing vortex core remains coherent for three to four rotor diameters, expands radially outwards, and intercepts the outer shear layer at approximately the location where wake meandering is initiated. The wake meandering manifests itself in terms of an elongated region of increased turbulence kinetic energy and Reynolds shear stress across the top tip wake boundary. The interaction of the outer region of the flow with the precessing hub vortex also causes the rotational component of the wake to decay completely at approximately the location where the wake begins to meander (four rotor diameters downstream of the turbine). To further investigate the importance of turbine geometry on far-wake dynamics, we carry out LES under the same flow conditions but using actuator disk and actuator line parametrizations of the turbine. While both actuator approaches yield a meandering wake, the actuator line model yields results that are in better overall agreement with the measurements. However, comparisons between the actuator line and the turbine-resolving LES reveal significant differences. Namely, in the actuator line LES model: (i) the hub vortex does not develop spiral instability and remains stable and columnar without ever intercepting the outer shear layer; (ii) wake rotation persists for much longer distance downstream than in the turbine-resolving LES; and (iii) the level of turbulence kinetic energy within and the overall size of the far-wake meandering region are considerably smaller (this discrepancy is even more pronounced for the actuator disk LES case) compared with the turbine-resolving LES. Our results identify for the first time the instability mechanism that amplified wake meandering in the experiment of Chamorro et al., show that computational models that do not take into account the geometrical details of the turbine cannot capture such phenomena, and point to the potential significance of the near-hub rotor design as a means for suppressing the instability of the hub vortex and diminishing the extent and intensity of the far-wake meandering region.

Ionic mass transfer in open channel flow

1976 ◽  
Vol 21 (2) ◽  
pp. 143-147 ◽  
Author(s):  
S. Mohanta ◽  
T.Z. Fahidy
Keyword(s):  
Mass Transfer ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Ionic Mass Transfer ◽  
Ionic Mass

scholarly journals Direct numerical simulation of turbulent mass transfer at the surface of an open channel flow

2022 ◽  
Vol 933 ◽  
Author(s):  
Michele Pinelli ◽  
H. Herlina ◽  
J.G. Wissink ◽  
M. Uhlmann
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Channel Flow ◽  
Schmidt Number ◽  
Open Channel ◽  
Open Channel Flow ◽  
Reynolds Numbers ◽  
Transfer Velocity

We present direct numerical simulation results of turbulent open channel flow at bulk Reynolds numbers up to 12 000, coupled with (passive) scalar transport at Schmidt numbers up to 200. Care is taken to capture the very large-scale motions which appear already for relatively modest Reynolds numbers. The transfer velocity at the flat, free surface is found to scale with the Schmidt number to the power ‘ $-1/2$ ’, in accordance with previous studies and theoretical predictions for uncontaminated surfaces. The scaling of the transfer velocity with Reynolds number is found to vary, depending on the Reynolds number definition used. To compare the present results with those obtained in other systems, we define a turbulent Reynolds number at the edge of the surface-influenced layer. This allows us to probe the two-regime model of Theofanous et al. (Intl J. Heat Mass Transfer, vol. 19, 1976, pp. 613–624), which is found to correctly predict that small-scale vortices significantly affect the mass transfer for turbulent Reynolds numbers larger than 500. It is further established that the root mean square of the surface divergence is, on average, proportional to the mean transfer velocity. However, the spatial correlation between instantaneous surface divergence and transfer velocity tends to decrease with increasing Schmidt number and increase with increasing Reynolds number. The latter is shown to be caused by an enhancement of the correlation in high-speed regions, which in turn is linked to the spatial distribution of surface-parallel vortices.

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