Handbook of Turbomachinery Second Edition Revised - Ventech!

shroud static pressure and the exit flow distribution were compared with the
actual measurements to validate the computation.
They found that the turbine exit flow showed a substantial
nonuniformity, with a wake region of high loss and high absolute flow
angle near the shroud, between the suction surface and the midpitch, and a
jet located near the pressure surface. Comparison of measurements and
numerical predictions indicated that the wake and the observed nonuniform
flow at the exit of the turbine were due, in part, to secondary flows
accumulating low-momentum fluid near the shroud-suction corner, but the
tip-leakage flow also contributed significantly to the process by feeding lowmomentum
fluid on the shroud into the wake.
As with other radial and axial components, the flow structures typical
of radial turbines are highly complex, three-dimensional, and viscous. To
design such components to achieve minimum loss requires a thorough
understanding of the behavior of the flow and the means to accurately
predict it.
MODELING OF TURBOMACHINERY FLOW FIELDS
The preceding sections of this chapter have emphasized the complexity of
flows that occur in typical turbomachinery components. Clearly, in order to
successfully design such devices, the analysis tools used must be capable of
adequately modeling those complex flow fields, in order to determine their
influence on component performance.
The current section examines the requirements for flow analysis tools
at different stages in the component design process and then focuses on the
capabilities of state-of-the-art computational fluid dynamics (CFD) analysis
tools, which can be employed in the later stages of turbomachinery
component design, to model the details of complex flow fields.
Levels of Modeling as Related to the Design Process
The goal of the aerodynamic design process, for turbomachinery
components, is to minimize losses and maximize aerodynamic performance,
within the geometric, physical, and economic constraints placed on the
component. This goal is accomplished through a process that consists of two
primary phases: preliminary design and detailed design. These two phases
differ, according to their specific purposes.
The preliminary design phase establishes the overall characteristics of
the component, such that it will satisfy the requirements and constraints of
the overall engine design. Basic flow-path configurations, blade counts,
Copyright © 2003 Marcel Dekker, Inc.