scholarly journals Effects of radiation in turbulent channel flow: analysis of coupled direct numerical simulations

2014 ◽  
Vol 753 ◽  
pp. 360-401 ◽  
Author(s):  
R. Vicquelin ◽  
Y. F. Zhang ◽  
O. Gicquel ◽  
J. Taine
Keyword(s):  
Heat Flux ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Temperature Fluctuations ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Flux ◽  
Direct Numerical Simulations ◽  
Turbulent Heat Transfer ◽  
Radiative Energy ◽  
Turbulent Heat

AbstractThe role of radiative energy transfer in turbulent boundary layers is carefully analysed, focusing on the effect on temperature fluctuations and turbulent heat flux. The study is based on direct numerical simulations (DNS) of channel flows with hot and cold walls coupled to a Monte-Carlo method to compute the field of radiative power. In the conditions studied, the structure of the boundary layers is strongly modified by radiation. Temperature fluctuations and turbulent heat flux are reduced, and new radiative terms appear in their respective balance equations. It is shown that they counteract turbulence production terms. These effects are analysed under different conditions of Reynolds number and wall temperature. It is shown that collapsing of wall-scaled profiles is not efficient when radiation is considered. This drawback is corrected by the introduction of a radiation-based scaling. Finally, the significant impact of radiation on turbulent heat transfer is studied in terms of the turbulent Prandtl number. A model for this quantity, based on the new proposed scaling, is developed and validated.

scholarly journals Application of higher-order heat flux model for predicting turbulent methane-air combustion

2019 ◽  
pp. 415-415
Author(s):  
Ali Ershadi ◽  
Mehran Rajabi-Zargarabadi
Keyword(s):  
Heat Flux ◽  
Stokes Equations ◽  
Eddy Diffusivity ◽  
Turbulent Heat Flux ◽  
Higher Order ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Generalized Gradient ◽  
No Emission ◽  
Turbulent Reactive Flows

The present study addresses a new effort to improve the prediction of turbulent heat transfer and NO emission in non-premixed methane-air combustion. In this regard, a symmetric combustion chamber in a stoichiometric condition is numerically simulated using the Reynolds averaged Navier-Stokes equations. The Realizable k-? model and Discreate Ordinate are applied for modeling turbulence and radiation, respectively. Also, the eddy dissipation model is adopted for predicting the turbulent chemical reaction rate. Zeldovich mechanism is applied for estimating the NO emission. Higher-order generalized gradient diffusion hypothesis (HOGGDH) is employed for predicting the turbulent heat flux in turbulent reactive flows. Results show that the HOGGDH model is capable of predicting temperature distribution in good agreement with the available experimental data. Comparison of the results obtained by the simple eddy diffusivity (SED) and HOGGDH models shows that applying the HOGGDH significantly improves the over-prediction of NO emission. Finally, the average turbulent Prandtl number for the non-premixed methane-air combustion has been calculated.

Budgets of Reynolds Stresses and Turbulent Heat Flux for Hypersonic Turbulent Boundary Layers Subject to Pressure Gradients

2022 ◽  
Author(s):  
Gary L. Nicholson ◽  
Junji Huang ◽  
Lian Duan ◽  
Meelan M. Choudhari ◽  
Bryan Morreale ◽  
...  
Keyword(s):  
Heat Flux ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Pressure Gradients ◽  
Reynolds Stresses

Turbulent heat and momentum transport on a rotating disk

2000 ◽  
Vol 402 ◽  
pp. 225-253 ◽  
Author(s):  
CHRISTOPHER J. ELKINS ◽  
JOHN K. EATON
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Boundary Layers ◽  
Outer Region ◽  
Temperature Fluctuations ◽  
Rotating Disk ◽  
Transport Processes ◽  
Turbulent Heat ◽  
Two Dimensional ◽  
The Mean

Measurements in the turbulent momentum and thermal boundary layers on a rotating disk with a uniform heat flux surface are described for Reynolds numbers up to 106. Measurements include mean velocities and temperatures, all six Reynolds stresses, turbulent temperature fluctuations, and three turbulent heat fluxes. The mean velocity profiles have no wake region, but the mean temperature profiles do. The turbulent temperature fluctuations have a large peak in the outer layer, and there is a third turbulent heat flux in the cross-flow direction. Correlation coefficients and structure parameters are not constant across the boundary layer as they are in two-dimensional boundary layers (2DBLs), and their values are lower. The turbulent Prandtl number agrees with 2DBL values in the lower part of the outer region but is reduced from the 2DBL values higher in the boundary layer. In the outer region of the boundary layer, the transport processes differ significantly from what is observed in two-dimensional turbulent boundary layers: ejections dominate the transport of momentum while both ejections and sweeps contribute to the transport of the passive scalar.

Heat Transfer Modulation by Inertial Particles in Particle-Laden Turbulent Channel Flow

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Caixi Liu ◽  
Shuai Tang ◽  
Yuhong Dong ◽  
Lian Shen
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Flux ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Inertial Particles ◽  
Thermal Feedback ◽  
Heat Transfer Modulation

We study the effects of particle-turbulence interactions on heat transfer in a particle-laden turbulent channel flow using an Eulerian–Lagrangian simulation approach, with direct numerical simulation (DNS) for turbulence and Lagrangian tracking for particles. A two-way coupling model is employed in which the momentum and energy exchange between the discrete particles and the continuous fluid phase is fully taken into account. Our study focuses on the modulations of the temperature field and heat transfer process by inertial particles with different particle momentum Stokes numbers (St), which in a combination of the particle-to-fluid specific heat ratio and the Prandtl number results in different particle heat Stokes numbers. It is found that as St increases, while the turbulent heat flux decreases due to the suppression of wall-normal turbulence velocity fluctuation, the particle feedback heat flux increases significantly and results in an increase in the total heat flux. The particle thermal feedback effect is illustrated using the instantaneous structures and statistics of the flow and temperature fields. The mechanisms of heat transfer modulation by inertial particles are investigated in detail. The budget of turbulent heat flux is examined. Moreover, by taking advantage of the ability of numerical simulation to address different momentum and heat processes separately, we investigate in detail the two processes of particles affecting heat transfer for the first time, namely the direct effect of particle thermal feedback to the fluid (i.e., heat feedback) and the indirect effect of the modulation of turbulent velocity field induced by the particles (i.e., momentum feedback). It is found that the contribution of heat transfer from turbulent convection is reduced by both heat and momentum feedback due to the decrease of the turbulent heat flux. The contribution of heat transfer from particle transport effects is barely influenced by the momentum feedback, even if St is large and is mainly affected by the heat feedback. Our results indicate that both heat and momentum feedback are important when the particle inertia is large, suggesting that both feedback processes need to be taken into account in computation and modeling.

Spanwise Heat Transport in Turbulent Channel Flow With Prandtl Numbers Ranging From 0.025 to 5.0

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Koji Matsubara ◽  
Atsushi Sakurai ◽  
Takahiro Miura ◽  
Takuya Kawabata
Keyword(s):  
Heat Flux ◽  
Prandtl Number ◽  
Heat Transport ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Flux ◽  
Spanwise Direction ◽  
Uniform Heat Flux ◽  
Turbulent Heat ◽  
Algebraic Models ◽  
Prandtl Numbers

The near-wall turbulent heat transport of the three orthogonal directions was directly solved for the Prandtl numbers ranging from 0.025 to 5.0 to validate the algebraic models of the turbulent heat flux. Two kinds of thermal situations were considered in the low Reynolds number turbulent flow: (a) the case with a uniform heat flux in the spanwise direction (UHF) and (b) the case with the mean spanwise temperature gradient (STG). Among the turbulent heat flux models tested, the model of Rogers preferably predicted over the treated range of the Prandtl numbers, but it failed to reproduce the low Prandtl number effects very accurately. This paper revealed that the coefficient of the Rotta model can be modified to include the low Prandtl number effects by means of the correlation between the exact coefficient suggested by DNS and the Prandtl number.

Heat Transfer Scaling Close to the Wall for Turbulent Channel Flows

2013 ◽  
Vol 65 (3) ◽  
Author(s):  
Chiranth Srinivasan ◽  
Dimitrios V. Papavassiliou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbulent Flow ◽  
Turbulent Heat Flux ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Mean Temperature ◽  
Scaling Parameters ◽  
The Mean

This work serves a two-fold purpose of briefly reviewing the currently existing literature on the scaling of thermal turbulent fields and, in addition, proposing a new scaling framework and testing its applicability. An extensive set of turbulent scalar transport data for turbulent flow in infinitely long channels is obtained using a Lagrangian scalar tracking approach combined with direct numerical simulation of turbulent flow. Two cases of Poiseuille channel flow, with friction Reynolds numbers 150 and 300, and different types of fluids with Prandtl number ranging from 0.7 to 50,000 are studied. Based on analysis of this database, it is argued that the value and the location of the maximum normal turbulent heat flux are important scaling parameters in turbulent heat transfer. Implementing such scaling on the mean temperature profile for different fluids and Reynolds number cases shows a collapse of the mean temperature profiles onto a single universal profile in the near wall region of the channel. In addition, the profiles of normal turbulent heat flux and the root mean square of the temperature fluctuations appear to collapse on one profile, respectively. The maximum normal turbulent heat flux is thus established as a turbulence thermal scaling parameter for both mean and fluctuating temperature statistics.

DNS Based Analysis and Modeling of the Turbulent Heat Transfer by Natural Convection in Liquid Lead-Bismuth

2005 ◽  
Author(s):  
I. Otic´ ◽  
G. Gro¨tzbach
Keyword(s):  
Heat Flux ◽  
Pressure Gradient ◽  
Correlation Method ◽  
Turbulent Heat Flux ◽  
Turbulent Heat Transfer ◽  
Liquid Lead ◽  
Suitable Model ◽  
Turbulent Heat ◽  
Standard Pressure ◽  
Total Temperature

Results of a direct numerical simulation for Rayleigh-Be´nard convection with Pr = 0.025 are used to analyze the transport equations for the turbulent heat flux. These results show the importance of the pressure diffusion and of the pressure scrambling term in the budget of turbulent heat flux equations. Analysis using the two-point correlation method shows, that a suitable model for the pressure scrambling term may give good approximation of the total temperature pressure gradient correlation, if the flow field is locally dominated by small structures. DNS results show, that a standard pressure scrambling model predicts the total temperature pressure gradient correlation acceptably well for this type of flow. DNS based analysis of the standard pressure scrambling model indicates, that an application of the mixed time scale may improve the model and reduce the number of empirical coefficients.

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