Numerical investigation of natural convection in an asymmetrically heated inclined channel-chimney systems importance of the choice of artificial inlet-outlet boundary conditions

The present paper is concerned with the results of the numerical investigation of unsteady laminar, natural convection in an asymmetrically heated inclined open channel (i =0, 45, 60 and 75◦) with walls at uniform heat flux (qw = 10, 50, 75 and 100W · m−2). Two methodological approaches have been adopted to in-vestigate the air flow in this case: 2D and 3D DNS, and four sets of inlet-outlet velocity-pressure boundary conditions have been considered. Significant differ-ences are observed in the flow dynamics between 2D and 3D results. The numerical results are compared with the experimental data and a good agreement is obtained when a local pressure boundary condition is applied at the inlet/outlet sections in the 3D case. A generalized correlation for the average Nusselt number is then obtained from numerical results. This correla-tion covers a wide range of the Rayleigh number and aspect ratio values (RaH varying from 5.89 ⇥ 109 to 5.89 ⇥ 1010 and 6.5 < H/b < 12.8).