Improved Computational Fluid Dynamics Model for Open-Aisle Air-Cooled Data Center Simulations

Abstract

There is a need in the IT industry for CFD models that are capable of accurately predicting the thermal distributions in high power density open-aisle air-cooled data centers for use in the design of these facilities with reduced cooling needs. A recent detailed evaluation of a small data center cell equipped with one high power rack using current CFD practice showed that the CFD results were not accurate. The simulation results exhibited pronounced hot/cold spots in the data center while the test data were much more diffused, indicating that the CFD model under-predicted the mixing process between the cold tile flow and the hot rack exhaust flow with the warm room air. In this study, a parametric study was carried out to identify CFD modeling issues that contributed to this error. Through a combined experimental and computational investigation, it was found that the boundary condition imposed at the perforated surfaces (e.g., perforated tiles and rack exhaust door) as fully open surfaces was the main source of error. This method enforces the correct mass flux but the initial jet momentum is under-specified. A momentum source model proposed for these perforated surfaces is found to improve the CFD results significantly. Another CFD modeling refinement shown to improve CFD predictions is the inclusion of some large-scale geometrical features of the perforated surfaces (e.g., lands/gaps) in the CFD model, but this refinement requires the use of grids finer than those typically used in practice.

Impact of aisle containment on energy performance of a data center when using an integrated water-side economizer

“…9, the thermal management performance of each architecture was evaluated based on two metrics: RTI and RCI HI (Eqs. (9) and (10)). With the uncontained architecture, bypass airflow is observed (RTI: 94.3%), while recirculation airflow is observed with the contained architecture (RTI: 104.4%).…”

“…While this method is acceptable in terms of mass balance, it does not correctly account for the momentum conservation of airflow across the tile. A few researchers have pointed out this limitation in the conventional modeling strategy [9,10], and went on to improve the conventional method by adding an artificial momentum box region above the tile (referred to as the body force model). This study adopted the modified body force model [22] for perforated tile modeling.…”

“…3). In previous researches [8,9,22,42], the researchers measured all the temperature distribution of the space in a data center since their goal is to validate their CFD modeling method and boundary conditions such as turbulence model and tile modeling. However, from the previous research [16], it was indicated that little temperature gradient is observed when the aisle containment is installed with sufficient airflow, so measuring the temperature of whole space is not necessary.…”

“…In the black box model, when cold air is introduced into the box, the air is discharged from the back of the box after its temperature has been increase by a specified amount. To take rack porosity into consideration, the rack inlet and outlet were modeled as four large openings, and the open areas of which are equivalent to the overall rack porosity (60%) [9,22]. The measured heat generation rate of the rack and the mass flow rate of the supply air to the rack were used as boundary conditions for the CFD simulation (Table 1).…”

“…The rack was modeled as an empty black box by using the recirculation boundary condition in Fluent [33], as is normal in data center modeling [8,9,22]. In the black box model, when cold air is introduced into the box, the air is discharged from the back of the box after its temperature has been increase by a specified amount.…”