Direct Numerical Simulation of Turbulent Velocity, Pressure, and Temperature Fields in Channel Flows

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

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Direct Numerical Simulation of Heat Transfer in Converging–Diverging Wavy Channels

Journal of Heat Transfer ◽

10.1115/1.2717235 ◽

2006 ◽

Vol 129 (7) ◽

pp. 769-777 ◽

Cited By ~ 32

Author(s):

E. Stalio ◽

M. Piller

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

High Temperature ◽

Direct Numerical Simulation ◽

Reynolds Numbers ◽

Temperature Fields ◽

Second Order Statistics ◽

Iterative Procedures ◽

Wavy Channels ◽

Unsteady Problems

Corrugated walls are widely used as passive devices for heat and mass transfer enhancement; they are most effective when operated at transitional and turbulent Reynolds numbers. In the present study, direct numerical simulation is used to investigate the unsteady forced convection in sinusoidal, symmetric wavy channels. A novel numerical method is employed for the simulations; it is meant for fully developed flows in periodic ducts of prescribed wall temperature. The algorithm is free of iterative procedures; it accounts for the effects of streamwise diffusion and can be used for unsteady problems. Results of two simulations in the transitional regime for Reynolds numbers based on average duct height and average velocity of Re=481 and Re=872 are reported. Time averaged and instantaneous velocity and temperature fields together with second-order statistics are interpreted in order to describe the mechanism associated with heat transfer augmentation. Heat flux distributions locate the most active areas in heat transfer and reveal the effects of convective mixing. Slanted traveling waves of high temperature are identified; peak values of Nusselt number are attained when the high-temperature fluid of the waves reaches the converging walls.

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Dissimilarity of Turbulent Fluxes of Momentum and Heat in Perturbed Turbulent Flows

Journal of Heat Transfer ◽

10.1115/1.4023358 ◽

2013 ◽

Vol 135 (5) ◽

Cited By ~ 1

Author(s):

H. D. Pasinato

Keyword(s):

Numerical Simulation ◽

Heat Flux ◽

Direct Numerical Simulation ◽

Turbulent Flows ◽

A Priori ◽

Heat Fluxes ◽

Reynolds Stresses ◽

Interaction Terms ◽

The Difference ◽

Velocity Pressure

The dissimilarity between the Reynolds stresses and the heat fluxes in perturbed turbulent channel and plane Couette flows was studied using direct numerical simulation. The results demonstrate that the majority of the dissimilarity was due to the difference between the wall-normal fluxes, while the difference between the streamwise fluxes was lower. The main causes for the dissimilarity were the production terms, followed by the velocity-pressure interaction terms. Further insights into the importance of the velocity-pressure interaction in the origin of the dissimilarity are provided using two-point correlation. Furthermore, an octant conditional averaged dataset reveals that not only the wall-normal heat flux but also the streamwise heat flux is strongly related to the wall-normal gradient of the mean temperature. A simple Reynolds-averaged Navier–Stokes (RANS) heat flux model is proposed as a function of the Reynolds stresses. A comparison of the direct numerical simulation data with an “a priori” prediction suggests that this simple model performs reasonably well.

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Direct numerical simulation of turbulence in injection-driven plane channel flows

Physics of Fluids ◽

10.1063/1.2963137 ◽

2008 ◽

Vol 20 (10) ◽

pp. 105103 ◽

Cited By ~ 26

Author(s):

Prem Venugopal ◽

Robert D. Moser ◽

Fady M. Najjar

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Plane Channel ◽

Channel Flows

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Direct Numerical Simulation of Particle Heat and Mass Transfer in a Fluidized Bed

Volume 1C, Symposia: Fundamental Issues and Perspectives in Fluid Mechanics; Industrial and Environmental Applications of Fluid Mechanics; Issues and Perspectives in Automotive Flows; Gas-Solid Flows: Dedicated to the Memory of Professor Clayton T. Crowe; Numerical Methods for Multiphase Flow; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes ◽

10.1115/fedsm2014-21319 ◽

2014 ◽

Author(s):

Zhi-Gang Feng ◽

Adam Roig

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Direct Numerical Simulation ◽

Fluidized Bed ◽

Immersed Boundary Method ◽

Fluid Velocity ◽

Temperature Fields ◽

Immersed Boundary ◽

Boundary Method ◽

Study Heat Transfer

We have developed a Direct Numerical Simulation combined with the Immersed Boundary method (DNS-IB) to study heat transfer in particulate flows. In this method, fluid velocity and temperature fields are obtained by solving the modified momentum and heat transfer equations, which result from the presence of heated particles in the fluid; particles are tracked individually and their velocities and positions are solved based on the equations of linear and angular motions; particle temperature is assumed to be a constant. The momentum and heat exchanges between a particle and the surrounding fluid at its surface are resolved using the immersed boundary method with the direct forcing scheme. The DNS-IB method has been used to study heat transfer of 1024 of heated spheres in a fluidized bed. By exploring the rich data generated from the DNS-IB simulations, we are able to obtain statistically averaged fluid and particle velocity as well as overall heat transfer rate in a fluidized bed.

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