V European Conference on Computational Fluid Dynamics ECCOMAS CFD 2010 J. C. F. Pereira and A. Sequeira (Eds) Lisbon, Portugal,14-17 June 2010 NON-OBERBECK-BOUSSINESQ NATURAL CONVECTION IN A TALL DIFFERENTIALLY HEATED CAVITY D. Kızılda˘ g ∗ , J. Ventosa † , I. Rodr´ ıguez † and A. Oliva † ∗† Centre Tecnol` ogic de Transfer` encia de Calor (CTTC), Universitat Polit` ecnica de Catalunya (UPC), ETSEIAT, Colom 11, 08222, Terrassa, Barcelona, Spain. e-mail: cttc@cttc.upc.edu Key words: Natural Convection, Water, Differentially Heated Cavity, Non-Oberbeck- Boussinesq Abstract. Turbulent flow in a water-filled rectangular parallelepiped tank of an inte- grated solar collector is analyzed by means of a set of two and three dimensional simu- lations. The geometry and the working conditions of the prototype yield an aspect ratio of Γ=6.68, Rayleigh number of Ra =2.2 × 10 11 and a Prandtl number of Pr =3.42. Different coarse DNS simulations and LES simulations using the dynamic Smagorinsky SGS and WALE model are presented. Validity of the Oberbeck-Boussinesq approximation is questioned. Heat transfer and first and second order statistics are studied. 1 INTRODUCTION The natural convection flow within enclosures has attracted the attention of many researchers due to its potential to model numerous applications of engineering interest, such as cooling of electronic devices, air flow in buildings, heat transfer in solar collec- tors, among others. The natural convection studies corresponding to the parallelepipedic enclosures can be classified into two elementary classes: i) heating from a horizontal wall (heating from below); ii) heating from a vertical wall. The characteristic example of the former case is the Rayleigh-B´ enard flow, however this work will only focus on the cavities heated from the side. This configuration is referred commonly as the differentially heated cavity. Although the differentially heated cavity configuration represents a simple geometry, the flow gets complex for sufficiently large Rayleigh numbers [1]. The flow undergoes a gradual transition to a chaotic state as the Rayleigh number reaches a critical value. For the situation studied in this work, both laminar, transitional, and turbulent zones are expected to coexist within the domain. Generally the core of the cavity together with the upstream part of the vertical boundary layers remain laminar while at some point in the downstream part of the vertical boundary layers, turbulent fluctuations become 1