Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 15 Definition of film-cooling hole geometry.
Arts and Heider) [50, 51]. It was concluded also that the heat transfer
depends on the operational Mach number and Reynolds number. The
observed differences were related to the changes in the spanwise pressure
distribution, conditions of the inlet boundary layer, and the blade-to-blade
loading of the turbine. It was concluded that results of the annular cascade
heat-transfer data are well representative of an actual engine and can be
applied as a basis for cooling design. At larger Reynolds numbers a high
heat-transfer region migrates upstream of the trailing edge along the inner
end wall and is centered midway between pressure and suction sides. For the
outer end wall the high heat transfer is usually found near the pressure side
closer to the trailing edge. At low Re, the high heat-transfer region moves
toward the trailing edge, also near the pressure side. The effect of Mach
number is found to be much less significant than that of Reynolds number.
Two cooling techniques have been used for nozzle end walls: backside
convective (often impingement) cooling and film cooling. Significant
pressure losses associated with the backside impingement cooling usually
exclude its combination with film cooling at upstream locations near the
leading edge of the end wall. This requires discharging the spent cooling air
further downstream, resulting in significant performance penalties. A similar
negative effect is observed when film cooling is introduced in the vicinity of
end wall next to the nozzle throat.
Copyright © 2003 Marcel Dekker, Inc.