Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

Liu, Caixi; Tang, Shuai; Shen, Lian; Dong, Yuhong

doi:10.1007/s10409-017-0646-y

Cited by 17 publications

(14 citation statements)

References 43 publications

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“…As a result, the droplets are accumulated along the shear layer, with their vertical velocity being positive. There are more droplets of r = 100 µm than those of r = 400 µm near the shear layer (Figure 3(f3)), indicating that small droplets follow the airflow better than large droplets, which is as expected and is consistent with the conclusion drawn from previous studies on the motion of solid particles in other types of flows [76,77]. Figure 4a shows the time history of the total number of droplets in the air, N, in Case A55.…”

Section: Resultssupporting

confidence: 78%

“…For example, the results analysis in the present simulation is limited by the unsteadiness of wave breaking. We cannot perform time-averaging as has been done in many studies for other types of flows with simpler configurations [38][39][40]77] to define turbulence statistics. In the future, it is important to perform multiple runs with the same wave geometry and wind profile, but different instantaneous turbulence fluctuations to define turbulence statistics based on the ensemble-averaging over different runs.…”

Section: Discussionmentioning

confidence: 99%

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Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves

et al. 2017

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Sea spray droplets play an important role in the momentum, heat and mass transfer in the marine atmospheric boundary layer. We have developed a new direct numerical simulation method to study the generation and transport mechanisms of spume droplets by wind blowing over breaking waves, with the wave breaking process taken into account explicitly. In this new computational framework, the air and water are simulated as a coherent system on fixed Eulerian grid with the density and viscosity varying with the fluid phase. The air-water interface is captured accurately using a coupled level-set and volume-of-fluid method. The trajectories of sea spray droplets are tracked using a Lagrangian particle-tracking method. The generation of droplets is captured by comparing the fluid particle velocity of water and the phase speed of the wave surface. From the simulation data, we obtain for the first time a detailed description of the instantaneous distribution of droplets at different stages of wave breaking. Furthermore, the time histories of the droplet number and its generation and disappearance rates are analyzed. Simulation cases with different parameters are performed to study the effects of wave age and wave steepness. The flow and droplet fields obtained from simulation provided a detailed physical picture of the problem of interest. It is found that plunging breakers generate more droplets than spilling breakers. Droplets are generated near the wave crest at young and intermediate wave ages, but at old wave ages, droplets are generated both near and behind the wave crest. It is also elucidated that the large-scale spanwise vortex induced by the wave plunging event plays an important role in suspending droplets. Our simulation result of the vertical profile of sea spray concentration is consistent with laboratory measurement reported in the literature.

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Section: Resultssupporting

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves

et al. 2017

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“…Rayleigh-Bénard convection (RBC) is commonly used to study natural convection due to the simplicity of its configuration and the richness of its flow regimes. In this system, fluid is filled in a closed cell, heated on the bottom and cooled on the top, with adiabatic side no-slip wall [1,2,3]. The control parameters are the Rayleigh number Ra = gβ∆H 3 /(νκ), the Prandtl number, Pr = ν/κ, and the aspect ratio Γ = L/H, where ν is the kinematic viscosity, κ the thermal diffusivity, H the height of the sample, L its width, g the gravitational The boundary layer (BL) in RBC exhibits a transition from laminar to turbulent regime when Ra exceeds a critical value, Ra c .…”

Section: Introductionmentioning

confidence: 99%

Boundary layer structure in turbulent Rayleigh–Bénard convection in a slim box

et al. 2019

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The logarithmic law of mean temperature profile has been observed in different regions in Rayleigh-Bénard turbulence. However, how thermal plumes correlate to the log law of temperature and how the velocity profile changes with pressure gradient are not fully understood. Here, we performed three-dimensional simulations of Rayleigh-Bénard turbulence in a slim-box without the front and back walls with aspect ratio, width : depth : height = L : D : H = 1 : 1/6 : 1 (respectively corresponding to x, y and z coordinates), in the Rayleigh number Ra = [1 × 10 8 , 1 × 10 10 ] for Prandtl number Pr = 0.7. To investigate the structures of the viscous and thermal boundary layers, we examined the velocity profiles in the streamwise and vertical directions (i.e. U and W) along with the mean temperature profile throughout the plume-impacting, plumeejecting, and wind-shearing regions. The velocity profile is successfully quantified by a two-layer function of a stress length,, as proposed by She et al. (She 2017), though neither a Prandtl-Blasius-Pohlhausen type nor the log-law is seen in the viscous boundary layer. In contrast, the temperature profile in the plume-ejecting region is logarithmic for all simulated cases, being attributed to the emission of thermal plumes. The coefficient of the temperature log-law, A can be described by composition of the thermal stress length * θ0 and the thicknesses of thermal boundary layer z * sub and z * bu f , i.e. A z * sub / * θ0 z * bu f 3/2 . The adverse pressure gradient responsible for turning the wind direction contributes to thermal plumes gathering at the ejecting region and thus the log-law of temperature profile. The Nusselt number scaling and local heat flux of the present simulations are consistent with previous results in confined cells. Therefore, the slim-box RBC is a preferable system for investigating in-box kinetic and thermal structures of turbulent convection with the large-scale circulation on a fixed plane.

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“…As concerns turbulent mutiphase flows, numerical algorithms coupling the heat and mass transfer are often challenging. Hence, in the first attempts, researchers used DNS only for the hydraulic characteristics of the flow and modelled the energy or mass transport equation (Namburu et al, 2009;Chang et al, 2011;Bu et al, 2013;Liu et al, 2017). Among earlier studies, Avila and Cervantes (1995), used a Lagrangianstochastic-deterministic model (LSD) to show that high mass loadings of small particles increases the heat transfer rate, while at low mass loadings, the heat transfer rate decreases.…”

Section: Heat Transfermentioning

confidence: 99%

Regimes of heat transfer in particle suspensions

Yousefi,

Ardekani,

Picano

et al. 2020

Preprint

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We present results of interface-resolved simulations of heat transfer in suspensions of finite-size neutrallybuoyant spherical particles for solid volume fractions up to 35% and bulk Reynolds numbers from 500 to 5600. An Immersed Boundary-Volume of Fluid method is used to solve the energy equation in the fluid and solid phase. We relate the heat transfer to the regimes of particle motion previously identified, i.e. a viscous regime at low volume fractions and low Reynolds number, particle-laden turbulence at high Reynolds and moderate volume fraction and particulate regime at high volume fractions. We show that in the viscous dominated regime, the heat transfer is mainly due to thermal diffusion with enhancement due to the particleinduced fluctuations. In the turbulent-like regime, we observe the largest enhancement of the global heat transfer, dominated by the turbulent heat flux. In the particulate shear-thickening regime, however, the heat transfer enhancement decreases as mixing is quenched by the particle migration towards the channel core. As a result, a compact loosely-packed core region forms and the contribution of thermal diffusion to the total heat transfer becomes significant once again. The global heat transfer becomes, in these flows at volume fractions larger than 25%, lower than in single phase turbulence.

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Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

Cited by 17 publications

References 43 publications

Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves

Numerical Study on the Generation and Transport of Spume Droplets in Wind over Breaking Waves

Boundary layer structure in turbulent Rayleigh–Bénard convection in a slim box

Regimes of heat transfer in particle suspensions

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