G.E. Lau

Large-Eddy Simulation of Turbulent Natural Convection in Vertical Parallel-Plate Channels

A numerical investigation examining natural convection in a vertical parallel-plate channel with the simultaneous presence of laminar, transitional, and turbulent regimes is conducted using large-eddy simulation. The compressible three-dimensional Favre-filtered mass, momentum, and energy conservation equations are closed using the Smagorinsky and the Vreman subgrid-scale models. A two-stage predictor-corrector numerical methodology for low-Mach-number compressible flows is adopted. Time-averaged wall temperature and field profiles are well captured by the Vreman model, while the Smagorinsky model underpredicts wall behavior considerably. It is demonstrated that the present code is capable of capturing the flow development which is unachievable by conventional Reynolds-averaged Navier-Stokes approaches.

Application of dynamic global-coefficient subgrid-scale models to turbulent natural convection in an enclosed tall cavity

Large-eddy simulations examining natural convection in an enclosed cavity with the simultaneous presence of laminar, transitional, and turbulent flow regimes were conducted. The Rayleigh number based on height of the cavity is 4.6 × 1010. Different dynamic global-coefficient procedures to compute the Vreman [A. W. Vreman, “An eddy-viscosity subgrid-scale model for turbulent shear flow: Algebraic theory and applications,” Phys. Fluids 16, 3670 (2004)] model coefficient were implemented for the subgrid-scale tensors in both the momentum and energy equations. Based on comparison with experimental and existing numerical data, it is shown that the dynamic model derived from the “global equilibrium” hypothesis gives favorable results in the mean flow and turbulence quantities. Nevertheless, because of higher subgrid-scale dissipation, transition to a turbulent flow is postponed when the Vreman model coefficient is either uniform or determined dynamically using the Germano identity approach. This suggests that m...

Effect of heat loss on turbulent buoyancy-driven flow in a rectangular cavity using the large-eddy simulation

ABSTRACT Large-eddy simulations (LESs) investigating the effect of heat loss on buoyancy-driven flow in a tall rectangular cavity are performed. A time-dependent one-dimensional energy balance approach is utilized to model the heat loss at the top wall. Compared with the experimental data and numerical results for a perfectly adiabatic case, allowing heat loss at the top wall alters both the time-averaged and instantaneous flow and the thermal fields and constitutes a delay in the relaminarization process. Intense recirculation flows exist adjacent to both the top and bottom walls, thereby triggering the earlier formation of vortex cores along both the hot and cold walls.

Natural convection in an asymmetrically-heated open-ended channel: A three-dimensional computational study

Buoyancy-driven flows in an asymmetrically heated open-ended channel which occur in facade and roof building-integrated photovoltaic systems were investigated using large-eddy simulation. The channel inclination angle was varied from 30° to 90° to the horizontal, whereas the channel height-to-width aspect ratio remained at 20. In each case, a uniform heat flux was applied along the top wall whereas the bottom wall was assumed to be adiabatic. It is shown that typical dynamics of large-scale structures in the flow and thermal fields of natural convection in the channels are successfully modeled numerically by the use of LES. The effects of varying the inclination angle on the heat transfer in the channel are explored by examining the mean flow fields and in addition, the effects of radiation have been considered. Both experimental and numerical results show that open-ended channels with low inclination angles are characterized by a low chimney effect which leads to a decreased flow rate and a delay in transition to turbulence, thereby decreasing the heat transfer coefficient and leading to higher temperatures on the heated wall. A correlation describing the local Nusselt number in the channel is also developed in order to characterize the global heat transfer behavior.© 2013 ASME