Application of flow network modeling and CFD to computer system design

This paper describes the air flow design of a computer system using commercially available flow network modeling (FNM) and computational fluid dynamics (CFD) software and proposes a new Hybrid approach that combines the best features of both. The basis of the proposed approach lies in the recognition that air flow within different regions of a computer system can be divided into two categories. One category, consisting of regions or subsystems through which the flow direction is well defined (e.g. Channels formed between card arrays, power supplies, an array of disk drives etc.) is well modeled using a flow impedance component in a FNM representation whereas the second type of region where the flow pattern is poorly defined (e.g. Air flow plenums) and highly dependent on the characteristics of adjoining subsystems requires CFD to model adequately. The FNM model of the sample design problem provides quick results and allows many design alternatives to be assessed but at the inevitable cost of oversimplifying the second type of region. The full system CFD model is large in size, requires a large computational time and significant post processing effort to understand the results. These issues are addressed by the Hybrid method whose key attributes and implementation within FNM and CFD codes is described. A CFD model is used to illustrate the proposed approach and demonstrate that, for the specific design problem used here, the method yields good accuracy while achieving 14× reduction in model size and 30× reduction in simulation time compared to the full CFD model