Handbook of Turbomachinery Second Edition Revised - Ventech!

physics can be modeled more accurately, providing a much more realistic
picture of the flow behavior before critical design decisions are made.
CFD analysis tool performance improvements can be achieved
through both software and hardware. Solution acceleration algorithms
can provide a significant reduction in computation time. However, a major
source of analysis tool performance improvement today comes from the
rapidly improving speed of the platforms themselves. It has been estimated
that the processor speed of computers doubles every 12 to 18 months
(Moore’s law). Thus, to minimize the computation time for a CFD analysis
tool, both software and hardware aspects of performance need to be
considered.
Software-based performance improvements are dependent upon the
numerical solution technique employed in the analysis. For time-marching
methods applied to the solution of the time-dependent Navier–Stokes
equations, a multigrid technique offers significant reduction in the time
required to achieve convergence. In a multigrid algorithm, the solution is
performed at each time step on a series of grids of increasing coarseness, to
reduce the low-frequency errors in the solution. This convergence
acceleration technique is described by Jameson and Baker [66] and has
been applied to many analysis methods, including that of Dawes [77].
Multigrid schemes are ideally suited to structured grids, because the coarser
grids can be easily generated by combining cells from the denser grid.
However, a multigrid technique has recently been applied to an
unstructured grid analysis, as described by Smith [78].
Additional performance benefits are being achieved through consistent
and dramatic reductions in computational speed. These reductions are
occurring as a result of improvements in computer hardware due to such
technologies as RISC architecture, vector processing, and parallel processing.
Much of this technology has been implemented in workstations, to the
extent that their performance is rapidly approaching that of supercomputers,
but at much more affordable prices. As a result, these
computational speed improvements are readily accessible in the design
environment, permitting more widespread use of CFD analysis tools.
In particular, parallel processing offers an opportunity for significant
performance improvements. Parallel processing allows a problem to be split
among two or more processors that operate together, such that each of them
executes different instructions within the same program. At the lowest level,
parallel processing may be applied on workstations that have multiple
processors. The compilers with such platforms automatically perform a
basic level of parallelization of the software, using an autotasker. The
autotasker enables the compiler to identify independent segments of the
Copyright © 2003 Marcel Dekker, Inc.