Modeling Strategies for Air Flow Through Perforated Tiles in a Data Center

Raised-floor data centers supply cold air to server racks through perforated tiles; hence, designing an efficient air delivery scheme requires better understanding of flow features through the tiles. Computational fluid dynamics (CFD) have been established as an important tool for examining the overall flow fields in data centers. The generally used model for air flow through the perforated tiles, the porous jump model, specifies a step pressure loss across the tile surface without affecting the velocity field across the tile. A recently proposed improvement in the porous jump model, the body force model, includes an additional momentum source above the tile surface to account for the acceleration of the flow through the pores. In both these models, geometrical details of the tile such as pore size, location, and shape are not included, which results in a significantly lower computational effort. However, to improve the solution accuracy, it is important to consider the geometrical details due to complex flow behavior through the tiles, such as flow acceleration through pores, jet-jet interactions, and downstream flow development, which simplified models may fail to capture. In this paper, we present a systematic approach to perforated tile flow modeling, with focus on consideration of geometrical details of the tile. First, different turbulence models are compared for the prediction of flow field through a sharp-edged orifice that is representative of a single pore of the tile. Comparison with the published experimental results suggests that a realizable k-ε model is more appropriate for modeling flow through pores, as compared to the generally used standard k-ε model. Flow characteristics through a single pore are analyzed next, and the balance between solution accuracy and grid coarsening is discussed. Subsequently, a full-scale tile model is presented, and it is observed that the elimination of plenum from the model significantly a- ters the flow field prediction. Body force model is compared with the full-scale tile model, and it shows promise for capturing the major features of flow-through tiles, with scope for further improvement.