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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 2 Generic turbine hot section cooling system: 1. back side cooling in-series<br />

with combustion air, 2. dilution air, 3. liner exit film, 4. nozzle endwall film, 5. nozzle<br />

shower head film, 6. tip clearance control modulated air, 7. nozzle trailing edge<br />

discharge, 8. blade leading edge air, 9. blade tip discharge, 10. blade trailing edge<br />

discharge, 11. preswirled air, 12. disc forward cavity buffer air/blade platform film,<br />

13. interstage buffer air, 14. disc aft cooling air/stage 2 nozzle endwall film.<br />

long-term durability and emission reduction are <strong>of</strong>ten critical targets for<br />

industrial engines.<br />

Stage 1 nozzle vanes operate at the highest cycle gas temperatures and<br />

blades experience a combination <strong>of</strong> high temperatures and centrifugal loads.<br />

Accordingly, cooling them presents the most challenging task in turbine<br />

cooling system design.<br />

Typical thermal loads for the blades (thermal boundary conditions on<br />

the external surfaces) can be presented in a simplified form as a combination<br />

<strong>of</strong> the local heat-transfer coefficients and relative turbine rotor inlet gas<br />

temperatures (TRIT). Internal airfoil cooling is arranged to counterbalance<br />

thermal loads in order to keep the metal temperatures at an acceptable level.<br />

A number <strong>of</strong> sophisticated cooling techniques (Fig. 3) have been<br />

developed to allow gas temperatures <strong>of</strong> nearly 540 8C (1,000 8F) above<br />

material temperature limit. These cooling techniques could be grouped in<br />

three categories:<br />

1. Internal convective cooling, where the cooling is performed by<br />

convection only (without providing further cooling effect by the<br />

spent air). This category can be subdivided into six subgroups:<br />

Copyright © 2003 Marcel Dekker, Inc.

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