Handbook of Turbomachinery Second Edition Revised - Ventech!

analysis, in order to provide accurate life prediction for the components.
When a component design is completed, its specific geometries are
determined by the particular constraints of the overall engine design. The
new design may differ sufficiently from reference existing design with proven
operating experience to warrant model testing of specific new design features
and, if necessary, hot cascade and/or engine testing.
External Heat-Transfer Measurements and Cooling
Validation Techniques
Direct measurements of the turbine airfoil external heat transfer (or local
heat-flux values) in a stator–rotor interacting system, even when only timeaveraged
data are recorded, are known to be quite complex and require very
sophisticated experimental rigs. Such rigs are usually configured as lowspeed,
long-duration or near-full-speed, short-duration (blowdown, shocktunnel,
or light piston) facilities. Heat-transfer measurements are often
performed in these rigs using a thin-film heat-flux measuring gauge. The
thin-film gauge is a device consisting of a thin metal element having a very
small heat capacity bonded to the surface of an insulator that is mounted in
the studied component. Some examples of these facilities and measurements
can be found in a recent Scholar Lecture presented by Dunn [121].
Takeishi et al. [122] report the results of a study for which the filmcooling
effectiveness was measured for the same scaled model blades
mounted either in a two-dimensional, low-speed stationary cascade or in a
high-speed air turbine rotating rig. The specific application was for a
stationary power plant turbine. The turbine stage consisted of 32 vanes and
72 blades. Two of the blades were configured so that heated or cooled air or
CO2 could be injected through them. Film-cooling effectiveness was
determined based on surface temperature measurements and by using gas
chromatography to analyze the relative amounts of CO2 collected at
selected locations along the blade surface. The authors used engine
hardware, but were not able to reproduce the proper density ratio (density
ratio is known to have an influence on film effectiveness) for the operating
conditions.
More often, especially for turbine nozzle vanes, the heat-transfer
measurements are performed in stationary cascades using traditional massheat-transfer
analogy techniques such as naphthalene, liquid crystal, or
other physical methods. When film-cooling effectiveness has to be measured,
a higher spatial resolution technique needs to be applied. A recently
developed application of pressure–sensitive paint for these measurements
has demonstrated significant benefits for obtaining qualitative as well as
quantitative results.
Copyright © 2003 Marcel Dekker, Inc.