A numerical study of turbulent mixed convection in an enclosure with heated rectangular elements

Abstract

By means of direct numerical simulations (DNS), we investigate instantaneous and statistical characteristics of turbulent mixed convection in parallelepiped convective cells with heated parallelepiped obstacles inside. Cold air enters the cell through thin ducts located at the side walls close to the top, and warmer air leaves the cell through the outlet ducts located also at the side walls but close to the bottom. The considered Reynolds numbers, based on the velocity of the inlet flow and the width of the inlet ducts, are and 79 (or 2.37×10⁴ and 1.18×10⁴ if based on the height of the cell) and the Grashof number equals . The results obtained for mixed and forced convection reveal different large-scale circulations of air inside the domain, although the geometry and the Reynolds numbers are the same. The different sense of rotation of the large-scale circulation is attributed to the dominance of buoyancy over inertia in the considered mixed convection cases. The heat flux at the surfaces of the obstacles is determined by the fluid currents around them; therefore, its distribution depends on the orientations of the obstacle surfaces (vertical or horizontal) and their locations within the domain.

Keywords:

• mixed convection
• forced convection
• indoor ventilation
• direct numerical simulations (DNS)

Acknowledgment

The authors are grateful to Professors H. Herwig, J. Schumacher and A. Thess for useful discussions, to the Deutsche Forschungsgemeinschaft (DFG) for supporting the project WA/1510-8 and to the Leibniz Supercomputing Centre (LRZ) for providing the computational resources.