Handbook of Turbomachinery Second Edition Revised - Ventech!

their color when exposed to higher temperatures. The color transition is
sensitive to both temperature and time at the temperature. This technique
provides a very representative map of surface temperatures with resolution
of + 50 8F, although highly trained operators can interpret results with an
accuracy of + 20 8F. The thermal paint technique has become an important
tool for the final qualification of cooled turbine components before
production parts are fabricated. Slight variations in the geometry of the
cooling passages can be produced with the application of rapid prototyping.
This allows for the testing of ‘‘rainbow’’ configurations of the component in
a single thermal paint test, thus qualifying the best configuration for future
production. Further improvements in the technique include an automatic
computer color-recognition method. This method provides fast, accurate
nonsubjective color recognition when an object is properly illuminated.
Proper assessment of experimental uncertainties should be performed
during all stages described in the above section. Moffat [136] provides good
guidance to evaluation of experimental uncertainties.
Thermal paint testing usually completes the development cycle for
advanced airfoil cooling. After that, the selected design is ready for extended
gas turbine endurance testing and production.
MULTIDISCIPLINARY CONSIDERATIONS IN SELECTION OF
TURBINE COOLING SYSTEM
Advancements in modern high-efficiency and high specific power gas turbine
engines are typically measured by the increases in overall pressure ratio and
operating temperature. This trend results in the operating gas temperature
significantly exceeding acceptable material capability limits, relying on
application of cooling for various engine hot section components.
Introduction of turbine cooling air further downstream of the combustor
in an air-based open-cycle cooling system increases its negative impact on
cycle performance. At the same time, reduction of the amount of the air
available for the combustor makes the liner cooling task and emission
control more difficult. This results in a major challenge for the designer of
cooling system: select a system that requires minimal amount of cooling air
and produces the smallest negative impact on engine durability, performance,
weight (particularly for aero engines), emission (particularly for
industrial engines), cost, and fabrication complexity. Such a task can benefit
significantly from a multidisciplinary optimization effort, with each
discipline effectively contributing to a successful design.
The traditional step-by-step engine hot section design process that has
been following the sequential loop of thermodynamic cycle analysis–
Copyright © 2003 Marcel Dekker, Inc.