Large eddy simulation of turbulent natural convection between symmetrically heated vertical parallel plates for water Takuma Kogawa a,⇑ , Junnosuke Okajima b , Atsuki Komiya b , Steven Armfield c , Shigenao Maruyama b a Graduate School of Engineering, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan b Institute of Fluid Science, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan c School of Aerospace, Mechatronic Engineering, The University of Sydney, 2006 NSW, Australia article info Article history: Received 20 September 2015 Received in revised form 4 March 2016 Accepted 24 April 2016 Keywords: Vreman model Large eddy simulation Turbulent natural convection Vertical parallel plates Boundary layer interaction abstract The boundary layer interaction effect of the turbulent natural convection in the gap between symmetrically heated vertical parallel plates was evaluated using a numerical simulation in the present study. A large eddy simulation was conducted, and a Vreman model was used as a dynamic subgrid-scale model. The numerical simulation was validated thorough a comparison with the experimental result for the turbulent natural convection adjacent to a single vertical heated plate. The boundary interaction effect was investigated by varying the gap between the parallel plates. The results showed that the flow for vertical parallel plates had a lower heat transfer rate than a vertical plate flow. The boundary layers and vortex structure were evaluated. The heat transfer was reduced as a result of a reduced velocity gradient in the outer region of the velocity boundary layer. The averaged heat transfer was similar to that of the laminar flow. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Natural convection flow occurs in the gap between two heated vertical parallel plates in many mechanical engineering settings. For example, such a flow is used to cool computer motherboards, electrical transformers, spent nuclear fuel, and in many other applications. Recently, such flow has been used to generate electricity and provide ventilation in buildings to reduce energy consumption [1–4]. Therefore, it is important to evaluate the heat and fluid flow characteristics of this type of flow to improve and optimize mechanical devices and building structures. The interaction of the two boundary layers has been of great interest because of its complicated flow structure and key role in determining the heat transfer characteristics. In the past, the laminar natural convection flow associated with heated vertical parallel plates has been precisely studied, with the first experiment conducted by Elenbass [5], where he calculated the average heat transfer rate by introducing the aspect ratio of the vertical parallel plates. Aihara et al. [6–9] numerically simulated parallel plates flows with various aspect ratios and thermophysical fluid properties and obtained a comprehensive average heat transfer rate distribution map. Furthermore, Maruyama [10] numerically simulated the laminar convection in a vertical concentric annular duct and found that the analytical formula for the average heat transfer rate of vertical parallel plates could be available for a vertical concentric annular duct using the characteristic length proposed by Aihara et al. [7]. Additionally, Aihara [11–15] conducted experiments and evaluated the heat transfer rate and temperature boundary layer quantitatively using the Schliren method. The turbulent natural convection flow associated with heated parallel plates has been investigated for many years, using both numerical calculations and experiments. Miyamoto et al. [16] conducted an experiment on the turbulent natural convection of asymmetrically heated vertical parallel plates for air, evaluating the local heat transfer rate distribution at some ranges of vertical locations, while varying the gap between the vertical parallel plates, with a uniform heat flux condition. Yilmaz et al. [17] carried out similar experiments, obtaining details of the turbulent fields under a uniform temperature condition. Furthermore, they compared experimental and numerical results and confirmed that a low Reynolds number k–e model had the ability to predict the turbulent flow qualitatively. Alzwayi et al. [18] analyzed an asymmetrically heated vertical parallel plates flow using a realizable k–e model [19] and they investigated the gap effect of the parallel plates on the turbulent flow. However, two-dimensional calculation may overestimate or underestimate the turbulence because of an incor- rect turbulent viscosity calculation. Recently, a three-dimensional calculation of the turbulent natural convection was evaluated using large eddy simulation (LES). Barhagni et al. [20] investigated the tur- bulent natural convection boundary layer on a vertical cylinder http://dx.doi.org/10.1016/j.ijheatmasstransfer.2016.04.083 0017-9310/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: takuma@pixy.ifs.tohoku.ac.jp (T. Kogawa). International Journal of Heat and Mass Transfer 101 (2016) 870–877 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt