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2004 SCIENCE NEWS
08.25.04 Computer Simulations Assess Columbia Cooling System
A high-fidelity simulation of the air flow in the main computer room housing the Columbia system was performed by members of the Applications Branch in the NASA Advanced Supercomputing (NAS) Division. The purpose of the simulation was to assess whether the current air handling/conditioning system will be adequate for the full 10,240-processor computer. The team (Jasim Ahmad, William Chan, Shishir Pandya, and Neal Chaderjian) utilized the in-house Chimera Grid tools software package to generate a geometric model of the computer room, and used the OVERFLOW-2 code to perform the airflow simulations. The simulations verified that the air handling system is adequate, as all temperatures in the room are within specifications for normal computer operation, and the simulations did not indicate any significant short-cycling; that is, air from the hot (back) side of the computer rack returning directly to the cold (front) side. Furthermore, the team identified areas of low air circulation and recommended modifications to eliminate them. Modified cooler intakes were also modeled to assess whether such modifications provide better airflow characteristics.
Computer simulations of the main floor of the computer room at the NASA Advanced Supercomputing (NAS) Facility at Ames Research Center were performed to assess the adequacy of the air handling/conditioning system. Of special interest were the following issues:
- High-temperature build-up in certain regions of the room
- Areas of low air circulation in the room
- Short-cycling
- Air from the hot aisle feeding directly to the cold-aisle intake
- Cold air from the perforated floor tiles returning directly to the cooler intake instead of being directed to the central processing units (CPUs)
In order to report preliminary results in a three-week time frame and final results is six weeks, some engineering approximations were made. First, a two-dimensional simulation of the sub-floor region was performed to assess the change in flow rates in the perforated floor tiles, with distance from a cooler. The team concluded that it is reasonable to assume that the cooler flow rate is evenly distributed among all the perforated floor tiles, for the purpose of the main-floor simulation. The simulation was performed in three dimensions and is comprised of two parts: Part 1 is the geometric modeling and Part 2 is the flow/thermal simulation. The geometric model was developed as a template, so the present model can be easily modified to accommodate any changes in room shape and size, and changes in the sizes and locations of the CPUs and/or disk racks, coolers, power distribution units, or the mass storage system. The team created this template using a scripting method developed in-house under the Chimera Grid Tools project. The flow/thermal simulation was performed using OVERFLOW-2.
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