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

Pinelli, Michele; Herlina, Herlina; Wissink, Jan G.; Uhlmann, Markus

doi:10.1017/jfm.2021.1080

Cited by 8 publications

(22 citation statements)

References 65 publications

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“…Due to impermeability of the free surface, the Reynolds normal stresses of OCFs are highly anisotropic when compared with the CCFs. Specifically on the free surface of OCFs, as the wall-normal Reynolds stress τ + 22 drops to zero with its energy transferring to the wall-parallel components, τ + 11 and τ + almost equally transferred to the streamwise τ + 11 and the spanwise τ + 33 components, in agreement with that observed in Swean et al (1991), Bauer (2015) and Pinelli et al (2022). In addition, for the Re τ considered here, both τ + 11 and τ + 33 on the free surface rise with increasing Re τ , suggesting more energy transfer at higher Re τ .…”

Section: Reynolds Stressessupporting

confidence: 89%

“…(1991), Bauer (2015) and Pinelli et al. (2022). In addition, for the considered here, both and on the free surface rise with increasing , suggesting more energy transfer at higher .…”

Section: Resultsmentioning

confidence: 96%

“…DNS is conducted at four different Reynolds numbers Re τ = 180, 550, 1000 and 2000, based on the frictional velocity u τ and the channel height h. The computational domain size is L x × L y × L z = 8πh × h × 4πh: large enough to accommodate most large-scale structures in OCFs (Pinelli et al 2022). The grid sizes, resolutions and integration times used are listed in table 1.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The computational domain size is : large enough to accommodate most large-scale structures in OCFs (Pinelli et al. 2022). The grid sizes, resolutions and integration times used are listed in table 1.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The OCF is of practical relevance to many civil engineering applications, such as river, lake and ocean flows (Calmet & Magnaudet 2003;Nezu 2005;Chaudhry 2007). During the past decades, significant attention has been given to the study of the OCFs, concerning various aspects, such as heat and mass transfer (Pinelli et al 2022), sediment transportation (López & García 1998;Wu, Rodi & Wenka 2000;Khosronejad & Sotiropoulos 2014) and roughness effects (Qi et al 2018;Aghaei Jouybari, Brereton & Yuan 2019).…”

Section: Introductionmentioning

confidence: 99%

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Direct numerical simulation of turbulent open channel flows at moderately high Reynolds numbers

2022

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Well-resolved direct numerical simulations of turbulent open channel flows (OCFs) are performed for friction Reynolds numbers up to $Re_\tau =2000$ . Various turbulent statistics are documented and compared with the closed channel flows (CCFs). As expected, the mean velocity profiles of the OCFs match well with the CCFs in the near-wall region but diverge notably in the outer region. Interestingly, a logarithmic layer with Kárman constant $\kappa =0.363$ occurs for OCF at $Re_\tau =2000$ , distinctly different from CCF. Except for a very thin layer near the free surface, most of the velocity and vorticity variances match between OCFs and CCFs. The one-dimensional energy spectra reveal that the very-large-scale motions (VLSMs) with streamwise wavelength $\lambda _x>3 h$ or spanwise wavelength $\lambda _z>0.5 h$ contribute the most to turbulence intensity and Reynolds shear stress in the overlap and outer layers (where h is the water depth). Furthermore, the VLSMs in OCFs are stronger than those in CCFs, resulting in a slightly higher streamwise velocity variance in the former. Due to the footprint effect, these structures also have significant contributions to the mean wall shear stress, and the difference between OCF and CCF enlarges with increasing $Re_\tau$ . In summary, the free surface in OCFs plays an essential role in various flow phenomena, including the formation of stronger VLSMs and turbulent kinetic energy redistribution.

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Section: Reynolds Stressessupporting

confidence: 89%

“…(1991), Bauer (2015) and Pinelli et al. (2022). In addition, for the considered here, both and on the free surface rise with increasing , suggesting more energy transfer at higher .…”

Section: Resultsmentioning

confidence: 96%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Direct numerical simulation of turbulent open channel flows at moderately high Reynolds numbers

2022

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Direct Numerical Simulation of Turbulent Open Channel Flow: Streamwise Turbulence Intensity Scaling and Its Relation to Large-Scale Coherent Motions

Bauer,

Sakai,

Uhlmann

2024

Springer Proceedings in Physics

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Direct numerical simulations of bubble-mediated gas transfer and dissolution in quiescent and turbulent flows

Farsoiya

Magdelaine²,

Antkowiak³

et al. 2023

J. Fluid Mech.

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We perform direct numerical simulations of a gas bubble dissolving in a surrounding liquid. The bubble volume is reduced due to dissolution of the gas, with the numerical implementation of an immersed boundary method, coupling the gas diffusion and the Navier–Stokes equations. The methods are validated against planar and spherical geometries’ analytical moving boundary problems, including the classic Epstein–Plesset problem. Considering a bubble rising in a quiescent liquid, we show that the mass transfer coefficient $k_L$ can be described by the classic Levich formula $k_L = (2/\sqrt {{\rm \pi} })\sqrt {\mathscr {D}_l\,U(t)/d(t)}$ , with $d(t)$ and $U(t)$ the time-varying bubble size and rise velocity, and $\mathscr {D}_l$ the gas diffusivity in the liquid. Next, we investigate the dissolution and gas transfer of a bubble in homogeneous and isotropic turbulence flow, extending Farsoiya et al. (J. Fluid Mech., vol. 920, 2021, A34). We show that with a bubble size initially within the turbulent inertial subrange, the mass transfer coefficient in turbulence $k_L$ is controlled by the smallest scales of the flow, the Kolmogorov $\eta$ and Batchelor $\eta _B$ microscales, and is independent of the bubble size. This leads to the non-dimensional transfer rate ${Sh}=k_L L^\star /\mathscr {D}_l$ scaling as ${Sh}/{Sc}^{1/2} \propto {Re}^{3/4}$ , where ${Re}$ is the macroscale Reynolds number ${Re} = u_{rms}L^\star /\nu _l$ , with $u_{rms}$ the velocity fluctuations, $L^*$ the integral length scale, $\nu _l$ the liquid viscosity, and ${Sc}=\nu _l/\mathscr {D}_l$ the Schmidt number. This scaling can be expressed in terms of the turbulence dissipation rate $\epsilon$ as ${k_L}\propto {Sc}^{-1/2} (\epsilon \nu _l)^{1/4}$ , in agreement with the model proposed by Lamont & Scott (AIChE J., vol. 16, issue 4, 1970, pp. 513–519) and corresponding to the high $Re$ regime from Theofanous et al. (Intl J. Heat Mass Transfer, vol. 19, issue 6, 1976, pp. 613–624).

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

Cited by 8 publications

References 65 publications

Direct numerical simulation of turbulent open channel flows at moderately high Reynolds numbers

Direct numerical simulation of turbulent open channel flows at moderately high Reynolds numbers

Direct Numerical Simulation of Turbulent Open Channel Flow: Streamwise Turbulence Intensity Scaling and Its Relation to Large-Scale Coherent Motions

Direct numerical simulations of bubble-mediated gas transfer and dissolution in quiescent and turbulent flows

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