Handbook of Turbomachinery Second Edition Revised - Ventech!

selected locations in the flow path. Particles are then released from these
rakes, and their paths are determined by integrating through time, given the
local velocity vector distribution.
Among other features of value in a postprocessor is the ability to
compute additional functions or flow properties for display, using the
standard set of dependent variables typically calculated in a CFD analysis.
In some types of displays, the ability to overlay results from multiple
datasets can facilitate the comparison and evaluation of component designs.
Animation can also be extremely valuable as a visualization tool. The ability
to display color contour plots or vector plots on a series of cutting planes
sweeping through the flow path can provide significant insight into the
behavior of a highly three-dimensional flow.
Software packages offering many of these pre- and postprocessing
capabilities are available commercially or have been developed by NASA.
Much of the necessary surface modeling capability may be found in
commercial CAD packages. Grid generation is also available in some CAD
packages and is often included within CFD packages themselves, along with
postprocessing functions. Additional standalone postprocessors for CFD
applications are available from several commercial companies, as well as
NASA.
The FAST (Flow Analysis Software Toolkit) package, developed by
NASA Ames Research Center, provides many of the desired features of a
CFD postprocessor. FAST utilizes a mouse-driven graphical user interface
to produce displays of shaded surfaces, function-mapped surfaces, flow-field
vectors, particle traces, isosurfaces, and displays on arbitrary surfaces. In
addition, more traditional two-dimensional plots can also be produced.
NASA-Ames has also produced similar software packages specifically
for unsteady flow simulations. PLOT4D has many of the features of the
FAST package, with the added capability of depicting unsteady flow via
animation techniques. STREAKER generates streaklines in a manner
similar to the steady-flow particle traces found in FAST.
Analysis Tool Selection
When establishing the specifications for a CFD analysis tool, prior to its
acquisition or development, it is important not to restrict the program’s
capabilities unnecessarily. In most cases, the component designers will soon
find applications for the tool that go beyond those limits. Demands will be
placed on the program to analyze more complex geometries and a wider
range of flow conditions than were originally intended by the program’s
specifications. Thus, to avoid the problem of rapidly ‘‘outgrowing’’ the
analysis tool, due to its limitations, it is advisable to define the tool’s
Copyright © 2003 Marcel Dekker, Inc.