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Physical Velocity formulation of porous media and PRESTO! pressure scheme diverges

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Old   December 24, 2019, 14:55
Default Physical Velocity formulation of porous media and PRESTO! pressure scheme diverges
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Jamie Levinson
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I am modelling a Steady, 2D data center. There are porous jump boundaries that are used to model the pressure drop due to the perforated plenum tiles and the vent inlets of the ceiling plenum. The inertial resistance term was obtained using relations from Idelchik. Above each porous jump boundary is a momentum source to correct for the momentum of the flow that should increase as the flow moves through the perforated tile. The server racks are adjacent to the momentum sources and are modeled as porous media using the thermal equilibrium model. The permeability and inertial resistance terms for the servers were obtained experimentally. Each server has an energy source term to simulate the heat transfer from the server itself to the air flowing through it. I have 4 velocity inlets with the velocity set to 1.3 m/s and 2 outflow outlets. I have an axial fan at the outlet surface of each rack. The fan curves were obtained experimentally. The walls of the data center are impermeable and adiabatic and the top of each rack is a wall interface. I am using a mesh with an skewness no higher that 0.7 and orthogonality no lower than 0.6. I am using the SIMPLE algorithm and am using the Least Squares Cell-Based Gradient evaluation. All interpolation schemes except the Pressure scheme is set to 2nd order. I can get the simulation to converge when I set the Pressure Interpolation scheme to Body-Force-Weighted and use the superficial velocity formulation for porous media and have obtained strong convergence (Energy residual~10^-9 and all other residuals~10^-6). I have tried to use the physical velocity formulation but every time I do it diverges in under 20 iterations. I have tried letting the superficial velocity formulation converge and then change to the physical velocity formulation but that doesn't make any difference. On the other hand If I use the superficial formulation for porous media and use the PRESTO! scheme the residuals diverge in under 20 iterations as well. Ideally, I would have the porous media using the physical velocity formulation and the Pressure interpolation scheme set to PRESTO!. Does anybody have any Ideas of why this is happening and what I can try to do to fix it?
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divergence, mixed convection, physical velocity, porous media model, presto!

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