Handbook of Turbomachinery Second Edition Revised - Ventech!

lade-row spacings, and initial blade shapes are among the characteristics
determined during preliminary design. The process is highly iterative, due to
the large number of component and flow-path features that must be
optimized, through the analysis of many configurations.
In contrast, the detailed design process focuses on one or a small
number of design configurations that offer the optimum combination of
features, and the best match with aerodynamic performance objectives,
based on the analyses of the preliminary design. The objective of the detailed
design process is to predict, as realistically as possible, those characteristics
of the flow that are critical to the aerodynamic performance of the
turbomachinery component being analyzed. Such characteristics would
include tip clearance flows, shock–boundary-layer interactions, blade–endwall
interactions, flow separations, wakes, and any other regions of high
loss.
The level of detail and capability required of a particular flow model
will be determined by the phase of the design process to which it is applied.
During the preliminary design process, simplifying assumptions are typically
made that allow the flow to be modeled in less detail. Once the overall
characteristics of a particular design have been established using these
simple tools, then the detailed behavior of the flow for that configuration
must be determined, using the full capabilities of the available CFD analysis
tools.
Flow Modeling for the Preliminary Design Process
Because the preliminary design process is typically performed over many
iterations, to optimize the component design, the analysis tools used must
not only provide adequate insight into the flow behavior but also require a
minimum of computation time. Therefore, the level of flow modeling
employed during preliminary design is, to some extent, limited by the
performance of the computer hardware and the modeling software.
Traditionally, simple flow models such as streamline curvature, radial
equilibrium analyses, and blade-to-blade analyses, combined with appropriate
loss models, have provided adequate information to perform an
efficient preliminary design of flow-path shape and blade shape. However,
although they offer speed of computation, such 2D design tools do not
provide insight into three-dimensional flow behavior.
Because of recent rapid increases in computer speed, it is now possible
to include 3D inviscid analyses in the earlier stages of the design process.
Transonic Euler solutions for a single blade row can now be performed
within minutes on many platforms and can therefore be utilized in a highly
iterative design environment. Access to a 3D transonic Euler analysis at this
Copyright © 2003 Marcel Dekker, Inc.