Handbook of Turbomachinery Second Edition Revised - Ventech!

The story of turbomachinery research over the last approximately 50
years is one of advances in both theory and experiment that have
continually reduced development costs. New theory and, in particular,
computational methods, have now developed to the point where fully threedimensional,
time-accurate (unsteady) numerical simulations are, if not
routine, certainly possible in the design of a turbine.
In this chapter we will make an attempt to summarize the progress in
just one part of a very large body of research and discovery. We have limited
our discussion to external turbine heat transfer, and then to only that part
that does not include film cooling. But even then it has been difficult to write
a comprehensive summary that can fit into the practical limits of this
handbook. Our objective, then, is to highlight major accomplishments in
understanding turbine flow-path heat transfer, both through theory and
experiment, starting at the beginning of the 1950s and continuing through
today. As mentioned above, much of this story deals with the improved fluid
dynamic computational tools, allowing the gas turbine industry to refine
and verify its design systems. The computational tools must, of course, be
verified themselves, and the consequent need for more accurate, more engine
relevant data has led to significant improvements in experimental methods
and instrumentation.
Because of the direct link between fluid boundary-layer skin friction
and heat transfer, our review has been made much easier by the very
comprehensive presentation of turbomachinery fluid dynamics given in
Chapter 2.
What has been the result of all this research and development effort?
An easy way to appreciate the effect that improved understanding of turbine
heat transfer has had is to compare take-off high-pressure turbine inlet
temperature for engines developed in the 1950s through those of today.
Figure 1 shows this comparison for a large number of engines, both
commercial and military. We see that inlet temperature has been nearly
doubled in approximately the last 50 years. Engines of the future may reach
nearly stoichiometric temperatures that would provide the maximum power
output for a given engine overall pressure ratio.
The maximum turbine inlet temperature is a function of many factors,
but primarily it is the more effective cooling schemes plus the higher usage
temperature materials that have allowed the significant increases shown in
the figure. Development of better cooling schemes is due in part to better
understanding of the turbine heat-transfer mechanisms and the heat load
that must be tolerated. This understanding includes knowing the behavior of
the main stream flow and all of the wall boundary layers, wakes, separation
bubbles, vortices, etc. As we shall see, these have been the subjects of many
individual studies of the separate phenomena as well as measurements of all
Copyright © 2003 Marcel Dekker, Inc.