Study of three LES subgrid-scale turbulence models for predictions of heat and mass transfer in large-scale compartment fires

2016 ◽  
Vol 69 (11) ◽  
pp. 1223-1241 ◽  
Author(s):  
A. C. Y. Yuen ◽  
G. H. Yeoh ◽  
V. Timchenko ◽  
S. C. P. Cheung ◽  
T. Chen
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Turbulence Models ◽  
Subgrid Scale ◽  
Compartment Fires ◽  
Scale Turbulence

A T-RANS/VLES Approach to Indoor Climate Simulations

2002 ◽  
Author(s):  
S. Kenjeresˇ ◽  
K. Hanjalic´ ◽  
S. B. Gunarjo
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Single Point ◽  
Ventilation System ◽  
Convective Motion ◽  
Wall Friction ◽  
Indoor Climate ◽  
Thermal Buoyancy ◽  
Order Of Magnitude

For accurate prediction of flow, scalar transport and wall heat and mass transfer in complex building space we propose a time-dependent RANS (T-RANS) approach which resolves in time and space the large-scale convective motion and associated deterministic eddy structure. The residual (“subscale”) turbulence is modeled by a single-point closure. The method can be regarded as Very Large Eddy Simulations (VLES) since the deterministic and modeled contribution to the turbulence moments are of the same order of magnitude. The modeled part becomes dominant in the near-wall regions where there are no large eddies and the proper choice of the subscale model is especially important for predicting wall friction and heat transfer. We use an ensemble-averaged 〈k〉 - 〈ε〉 - 〈θ2〉 algebraic stress/flux/concentration closure as the subscale model which can provide information about the stress and heat/species flux anisotropies. The method is especially advantageous for predicting flows driven or affected by thermal buoyancy, for which the conventional eddy-viscosity/diffusivity RANS models and gradient transport hypotheses are known to fail even in simple generic configurations. The approach was validated in a series of buoyancy-driven flows for which experimental, DNS and LES data are available. Examples of full-scale application include computational simulations of real occupied and furnished residential or office space in which the furniture elements and persons are treated as passive blocking elements. The simulation showed that the T-RANS approach can be used as a reliable tool for a variety of applications such as optimization of heating and ventilation system, building space insulation, indoor quality, safety measures related to smoke and fire spreading, as well as for accurate wall heat and mass transfer predictions.

Modeling the Impact of Convective Entrainment on the Tropical Tropopause

2006 ◽  
Vol 63 (3) ◽  
pp. 1013-1027 ◽  
Author(s):  
F. J. Robinson ◽  
S. C. Sherwood
Keyword(s):  
Heat Flux ◽  
Large Scale ◽  
Small Scale ◽  
Entrainment Rate ◽  
Subgrid Scale ◽  
Turbulence Parameterization ◽  
Tropical Tropopause ◽  
Scale Turbulence ◽  
Cold Point ◽  
The Impact

Abstract Simulations with the Weather Research and Forecasting (WRF) cloud-resolving model of deep moist convective events reveal net cooling near the tropopause (∼15–18 km above ground), caused by a combination of large-scale ascent and small-scale cooling by the irreversible mixing of turbulent eddies overshooting their level of neutral buoyancy. The turbulent cooling occurred at all CAPE values investigated (local peak values ranging from 1900 to 3500 J kg−1) and was robust to grid resolution, subgrid-scale turbulence parameterization, horizontal domain size, model dimension, and treatment of ice microphysics. The ratio of the maximum downward heat flux in the tropopause to the maximum tropospheric upward heat flux was close to 0.1. This value was independent of CAPE but was affected by changes in microphysics or subgrid-scale turbulence parameterization. The convective cooling peaked roughly 1 km above the cold point in the background input sounding and the mean cloud- and (turbulent kinetic energy) TKE-top heights, which were all near 16.5 km above ground. It was associated with turbulent entrainment of stratospheric air from as high as 18.25 km into the troposphere. Typical cooling in the experiments was of order 1 K during convective events that produced order 10 mm of precipitation, which implied a significant contribution to the tropopause energy budget. Given the sharp concentration gradients and long residence times near the cold point, even such a small entrainment rate is likely consequential for the transport and ambient distribution of trace gases such as water vapor and ozone, and probably helps to explain the gradual increase of ozone typically observed below the tropical tropopause.

Numerical Simulation of Heat and Mass Transfer of Limestone Decomposition in Normal Shaft Kiln

2011 ◽  
Author(s):  
Duc Hai Do ◽  
Eckehard Specht
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Solid Material ◽  
Local Heat ◽  
Operational Parameters ◽  
Calcination Process ◽  
One Dimensional ◽  
Shrinking Core ◽  
Particle Bed

A mathematical model of lime calcination process in normal shafts kiln has been developed to determine the heat and mass transfer between the gas and the solid. The model is one-dimensional and steady state. The transport of mass and energy of the gas and the solid is modeled by a system of ordinary differential equations. A shrinking core approach is employed for the mechanics and chemical reactions of the solid material. The model can be used to predict the temperature profiles of the particle bed, the gas phase along the length of kiln axis. The calcination behavior of the particle bed can be also investigated. The influences of operational parameters such as: energy input, the origin of feed limestone and the lime throughput on the kiln performance including pressure drop are considered. Additionally, the local heat loss through the kiln wall is studied. The results of this study are direct utility for optimization and design of large-scale technical shaft kilns.

scholarly journals Heat and mass transfer enhancement strategies by impinging jets: A literature review

2020 ◽  
pp. 227-227
Author(s):  
Florin Bode ◽  
Claudiu Patrascu ◽  
Ilinca Nastase
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Nozzle Geometry ◽  
Small Scale ◽  
Mixing Enhancement ◽  
Transfer Enhancement

Heat and mass transfer can be greatly increased when using impinging jets, regardless the application. The reason behind this is the complex behavior of the impinging jet flow which is leading to the generation of a multitude of flow phenomena, like: large-scale structures, small scale turbulent mixing, large curvature involving strong normal stresses and strong shear, stagnation, separation and re-attachment of the wall boundary layers, increased heat transfer at the impinged plate. All these phenomena listed above have highly unsteady nature and even though a lot of scientific studies have approached this subject, the impinging jet is not fully understood due to the difficulties of carrying out detailed experimental and numerically investigations. Nevertheless, for heat transfer enhancement in impinging jet applications, both passive and active strategies are employed. The effect of nozzle geometry and the impinging surface macrostructure modification are some of the most prominent passive strategies. On the other side, the most used active strategies utilize acoustical and mechanical oscillations in the exit plane of the flow, which in certain situations favors mixing enhancement. This is favored by the intensification of some instabilities and by the onset of large scale vortices with important levels of energy.

Prediction of transpiration effects on heat and mass transfer by different turbulence models

2008 ◽  
Vol 238 (4) ◽  
pp. 958-974 ◽  
Author(s):  
M. Bucci ◽  
M. Sharabi ◽  
W. Ambrosini ◽  
N. Forgione ◽  
F. Oriolo ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Turbulence Models

Statistical Properties of Subgrid-Scale Turbulence Models

2021 ◽  
Vol 53 (1) ◽  
pp. 255-286
Author(s):  
Robert D. Moser ◽  
Sigfried W. Haering ◽  
Gopal R. Yalla
Keyword(s):  
Turbulent Flows ◽  
A Priori ◽  
Turbulence Models ◽  
Statistical Characteristics ◽  
Scale Model ◽  
Subgrid Scale ◽  
Dissipation Energy ◽  
Eddy Simulation ◽  
Scale Turbulence ◽  
Subgrid Stress

This review examines large eddy simulation (LES) models from the perspective of their a priori statistical characteristics. The most well-known statistical characteristic of an LES subgrid-scale model is its dissipation (energy transfer to unresolved scales), and many models are directly or indirectly formulated and tuned for consistency of this characteristic. However, in complex turbulent flows, many other subgrid statistical characteristics are important. These include such quantities as mean subgrid stress, subgrid transport of resolved Reynolds stress, and dissipation anisotropy. Also important are the statistical characteristics of models that account for filters that do not commute with differentiation and of the discrete numerical operators in the LES equations. We review the known statistical characteristics of subgrid models to assess these characteristics and the importance of their a priori consistency. We hope that this analysis will be helpful in continued development of LES models.

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