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Handbook of Turbomachinery Second Edition Revised - Ventech!

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source code, and to assign each segment to a different processor, in order to<br />

minimize idle processor time. In this way, existing s<strong>of</strong>tware that has not<br />

been optimized for parallel processing can be compiled to achieve<br />

substantial improvements in solution speed. If the source code is modified<br />

to allow for more optimum application <strong>of</strong> parallel processing, then even<br />

better results can be achieved.<br />

To take maximum advantage <strong>of</strong> this particular computer architecture,<br />

it is convenient to utilize multiblock grids when discretizing the computational<br />

space. By defining a number <strong>of</strong> subdomains or grid blocks equal to<br />

the number <strong>of</strong> processors, the solution <strong>of</strong> each subdomain may be assigned<br />

to a particular processor, and the solution time may be reduced by a factor<br />

almost equal to the number <strong>of</strong> processors.<br />

Thus, through the use <strong>of</strong> affordable, state-<strong>of</strong>-the-art hardware,<br />

coupled with appropriate s<strong>of</strong>tware techniques for solution acceleration, it<br />

becomes possible to achieve the performance necessary to utilize CFD<br />

analyses as practical design tools.<br />

Pre- and Postprocessing Considerations<br />

A significant percentage <strong>of</strong> the total time spent on a CFD analysis is<br />

involved in pre- and postprocessing activities. Both the setup for an analysis<br />

and the evaluation <strong>of</strong> results require considerable effort on the part <strong>of</strong> the<br />

component designer. Therefore, the use <strong>of</strong> s<strong>of</strong>tware tools to automate or<br />

facilitate these activities has the potential to substantially reduce the time<br />

required for the analysis and improve the overall efficiency <strong>of</strong> the process.<br />

Both the pre- and postprocessing functions must rely heavily on<br />

interactive computer graphics, due to the need for visualization <strong>of</strong> 3D<br />

objects. Display capabilities such as zooming, rotation, and translation are<br />

required in order to view the flow-path geometry, the computational grid, or<br />

the analysis results within the computational domain. The display <strong>of</strong><br />

multiple images on the screen is also desirable, to allow inspection or<br />

evaluation <strong>of</strong> more than one view at a time. Displays must also be generated<br />

rapidly, to provide utility to the component designer.<br />

A graphical user interface can provide ease <strong>of</strong> use for the pre- and<br />

postprocessors by allowing control, from the screen, for the displays and<br />

functions provided by the tools. Dials, buttons, and menus on the screen can<br />

be mouse-driven by the user. To support pre- and postprocessors with such<br />

capabilities typically requires the use <strong>of</strong> a graphics workstation.<br />

Both pre- and postprocessing can be made more efficient through the<br />

application <strong>of</strong> automation. During the design process, analyses are usually<br />

performed on a number <strong>of</strong> components that are very similar in configuration.<br />

For each <strong>of</strong> these component variations, the initial computational grid<br />

Copyright © 2003 Marcel Dekker, Inc.

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