Simplified CFD Model for Perforated Tile with Distorted Outflow

Abstract

Most of the perforated tile flow CFD models in the literature so far assume the air velocity coming out of the tile openings (pores) is uniform. However, in typical applications, such as data centers and indoor environments, perforated tile or diffuser outflow can be highly non-uniform due to many reasons (e.g., spatial variation of plenum pressure or varying local tile geometrical patterns). For an ideal (uniform) tile flow velocity that has the same flow rate as the non-uniform tile flow velocity, the tile flow momentum of the latter will always be greater because momentum scales with velocity squared. To illustrate the effect of tile flow velocity distortion, two generic CFD cases (one with uniform velocity and the other with non-uniform velocity) with multiple openings model are presented here. Their CFD results are compared to the momentum source model results and validated against previously published data of an isolated tile flow measurement. The momentum source model is one of the simplest/most practical CFD models that uses a body-force value for correcting the momentum deficit between perforated and fully open areas. Initially, the momentum source model results show good agreement with results of the uniform velocity case only. Thus, due to velocity distortion (non-uniform velocity) in the tile flow, the CFD results presented in this paper show a potential reason to modify the body-force value in the momentum source model with an adjustment factor (C). Several values of C factor are numerically investigated for the present distorted tile flow CFD case, and the best match is found to be at C, equaling approximately 1.6.