# Natural Convection Boundary Conditions, tips or advise needed !

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 September 27, 2010, 18:44 Natural Convection Boundary Conditions, tips or advise needed ! #1 Member   Logan Page Join Date: Sep 2010 Posts: 38 Rep Power: 11 Hi I am masters engineering student and I'm currently trying to recreate the first part of results from a journal article: "Constructal multi-scale cylinders with natural convection" by T. Bello-Ochenda and A. Bejan, in FLUENT. Simple put its a row of parallel, horizontal, cylinders (diameter Do) with a constant wall temperature (Tw) cooled by natural convection analyzed in 2D. The current computation domain that i have setup for FLUENT is made up of: 1) a symmetry plane/edge on the left cutting through the middle of a cylinder 2) a symmetry plane/edge on the right cutting through the middle of the spacing (So) between 2 of the cylinders 3) a pressure inlet at the bottom edge (P = 0, T = 0) 4) a pressure outlet at the top edge (P = 0, T = 0) 5) and a cylinder wall (no slip, no penetration, Tw = 1) The governing equations have been non-dimentionalised and the input parameters for a Rayleigh Number of 1000 for FLUENT are as follows: - Do: 1 - Fluid density: 37.268 (boussinesq approximation) - Fluid Cp: 0.72 - Fluid thermal conductivity: 1 - Fluid viscosity: 1 - Fluid thermal exp. coeff.: 1 - Operating pressure: 0 - Gravity: -1 (Y dir) - Operating temp.: 0 - Specific operating density: 37.268 Using this model, FLUENT converges nicely for a given upstream (Hu) and downstream (Hd) length from the cylinder, but when i do a grid independence study i find that as i increase the downstream length (Hd) the heat transfer density rate continues to increase (ie there is a chimney effect created). Does anyone have any suggestions / ideas on how to modify the boundary conditions to eliminate this effect? montazar likes this.

 Tags boundary conditions, cylinders, natural convection