Analysis of factors affecting selection and design of air-cooled single-stage turbines for turbojet engines 4: coolant-flow requirements and performance of engines using air-cooled corrugated-insert blades Page: 4 of 47

                                
KACA EM E55C09

The purpose of this report, which concludes a series, is to present
the estimated minimum cooling requirements and the resulting changes in
performance of engines with single-stage turbines with air-cooled
corrugated-insert blades. The possible limitations of this blade are also
presented. A range of turbine-inlet temperatures from 20000 to 35000 R,
turbine blade tip speeds of 1100 and 1700 feet per second (actual tip
speeds as used throughout), and turbine hub-tip radius ratios of 0.60 and
0.75 were considered for a flight Mach number of 2.0 at a 50,000-foot
altitude.  In addition, typical variations in the corrugation geometry
2 and coolant flows with flight Mach number, altitude, stress-ratio factor,
pressure losses in cooling-air ducting and turbine rotor disk, and outside
heat-transfer coefficients are presented.
ANALYTICAL PROCEDURES
General Considerations
The analytical procedures used to evaluate the cooling requirements
of air-cooled turbines with corrugated-insert blades are presented in
detail in references 3 and 4. Figures 1(b) and (c) show a cross-sectional
view of a corrugated-insert blade and a typical corrugated section. The
principal dimensions of the corrugation that may be varied in the selec-
9 tion of corrugation geometry are indicated in figure 1(c). These dimen-
sions are the corrugation amplitude Y, the corrugation spacing   m, and
the corrugation thickness T. References 2 and 8 present a general dis-
cussion of the procedures for computing the performance of turbojet en-
gines equipped with single-stage air-cooled turbines and the turbine
operating conditions required in evaluating the cooling requirements.
Detailed procedures are given in reference 9.  In addition, references 2
and 8 tabulate the engine performance and many of the operating conditions
for the complete range of turbine design specifications considered in
this analysis.
Schematic drawings of the turbojet engine and the turbine rotor
cooling-air impeller are shown on figure 2.  In some cases, three compres-
sor bleed points were considered for the rotor blade cooling-air supply
and two compressor bleed points for the stator blades. The relative po-
sitions of these bleed points are shown on figure 2(a). The exact loca-
tions actually vary for each engine design specification. Only one com-
pressor bleed point was considered in the analysis for the engine
performance results of reference 2. However, as shown in reference 1,
the effect of cooling-air bleed point on engine performance is small.
For this reason, the engine performance results of reference 2 were used
herein, even though the compressor bleed point did differ somewhat for
many of the cases studied.

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