Details of the cooling air ducts in first stage rotor blades are shown in figures 6. In fact two cooling air circuits
exist with a common supply at the blade root. The front circuit serves the cooling of the forward 20 percent of
the blade. The cooling air enters duct 2, separated from the front duct 1 by a perforated wall. Duct 1 contains
five orifice rows (b – f) that provide film cooling to the leading edge. The air jets from the perforations in the
wall between duct 1 and 2 provide a mix of internal impingement cooling and enhancement of the turbulence
level and therewith the heat transfer in duct 1. Orifice rows c-e provide showerhead film cooling of the blade
leading edge near the stagnation point with spanwise orientation rather than streamwise orientation of the
orifices to improve film coverage.
The rear cooling circuit starts with duct 7 from where part of the cooling air is passing to parallel ducts 8 and 9.
Ducts 7 and 8 have each a row of cooling orifices i and j respectively) and cooling air in duct 9 passes through a
slot (k) slightly ahead of the trailing edge to cool the trailing edge at the pressure side. Between ducts 7, 8 and 9
the turbulence level is enhanced by the openings between these ducts resembling a pin cooling configuration.
The remaining cooling air at the end of duct 7 near the blade tip returns its direction and passes the serpentine
cooling ducts 6 - 3 where duct 5 has a row of cooling orifices at the pressure side of the airfoil (row h) and duct
3 has a row of orifices at the pressure side (row g) as well at the suction side (row a). The serpentine cooling
duct walls have small strips at 2.5 mm intervals perpendicular to the flow that increase the turbulence level and
as a result the internal heat transfer.