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Modeling of Fan Failures in Networking Enclosures
Keywords: Fan Failures , Thermal Management, Simulations
Modeling of fan failures in networking chassis is a challenging task. There is not enough data or literature available to accurately model fan failures. This paper embarks on a study consisting of both modeling and experimental cases to investigate how to accurately model fan failures. The study will include CFD simulations in different ways to model fan failures and also real life experimental measurements to verify the simulation concepts. Recommendations will then be made about the exact and accurate ways of modeling fan failures. Normally the fans have been modeled as a two dimensional entity. The fan curve measured by the vendor is used in the fan during modeling. The problem that arises with this kind of a fan modeling especially during fan failures is that the three dimensional effect of the rotor and stator blades of the fan is not taken into account. In reality, the fan blades provide a big obstruction to the flow reversal that happens due to pressure imbalance during fan failures. In this paper, we start with modeling a single fan in an AMCA wind tunnel. The complete rotor and stator geometry of the fan is modeled. We run a MRF model (Multiple Reference Frame) to generate the fan curve for the fan and compare it with the experimental fan curve. After we validate the fan curve in an AMCA model for a single fan, the paper discusses three different set of temperature and flow data 1) Temperature and flow data in a real system with four fans modeled with two dimensional fans. 2) Temperature and flow data in a real system with four fans modeled with MRF fans ( full three dimensional rotor and stator blade geometry 3) Experimental Comparisons with the simulated data. This study also focuses on analyzing fan failures in Pull and Push Systems analyzed in both Front to Back and Back to Front Airflows as applied to a Data Center. Conclusions will be drawn based on this modeling and experimental data about accurate ways of modeling fans during fan failures in real systems.
Susheela Narasimhan, Technical Leader
Cisco Systems Inc.
San Jose, CA

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