Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 35 Cost, efficiency, and cooling flows versus TRIT.
But even more importantly, this cross-disciplinary team decision can
provide an opportunity to significantly reduce cooling of downstream
turbine components, avoiding in some cases any stage 2 blade cooling. The
higher stage 1 pressure ratio might also lead to fewer turbine stages,
resulting in a larger gas-path divergence angle. This leads to a larger gaspath
area for the blades, which should be optimized between longer blades
and larger tip diameter, which holds an acceptable AN 2 stress parameter
limit (where A is an annular gas-path area and N is the rotational speed of
the rotor). Longer blades are less sensitive to performance losses associated
with tip leakages for the same tip clearance. This makes the option of a
highly loaded stage 1 with longer and smaller tip diameter blades more
attractive for a single-stage high-pressure turbine provided the rotor speed
can be maintained at a stress-limiting maximum. However, longer blades
with smaller tip and hub diameters have their own, primarily mechanical,
stress limitations associated with smaller circumferential disc spaces
available for the blade fir tree attachments and the disc posts separating
Copyright © 2003 Marcel Dekker, Inc.