In order to minimize the number of iterations to a turbine design, reasonable choices of the key parameters must be made at the preliminary design stage. The choice of blade loading is of particular concern in the low pressure (LP) turbine of civil aero engines, where the use of high-lift blades is widespread. This paper considers how blade loading should be measured, compares the performance of various loss correlations, and explores the impact of blade lift on performance and lapse rates. To these ends, an analytical design study is presented for a repeating-stage, axial-flow LP turbine. It is demonstrated that the long-established Zweifel lift coefficient (Zweifel, 1945, “The Spacing of Turbomachine Blading, Especially with Large Angular Deflection” Brown Boveri Rev., 32(1), pp. 436–444) is flawed because it does not account for the blade camber. As a result the Zweifel coefficient is only meaningful for a fixed set of flow angles and cannot be used as an absolute measure of blade loading. A lift coefficient based on circulation is instead proposed that accounts for the blade curvature and is independent of the flow angles. Various existing profile and secondary loss correlations are examined for their suitability to preliminary design. A largely qualitative comparison demonstrates that the loss correlations based on Ainley and Mathieson (Ainley and Mathieson, 1957, “A Method of Performance Estimation for Axial-Flow Turbines,” ARC Reports and Memoranda No. 2974; Dunham and Came, 1970, “Improvements to the Ainley-Mathieson Method of Turbine Performance Prediction,” Trans. ASME: J. Eng. Gas Turbines Power, July, pp. 252–256; Kacker and Okapuu, 1982, “A Mean Line Performance Method for Axial Flow Turbine Efficiency,” J. Eng. Power, 104, pp. 111–119). are not realistic, while the profile loss model of Coull and Hodson (Coull and Hodson, 2011, “Predicting the Profile Loss of High-Lift Low Pressure Turbines,” J. Turbomach., 134(2), pp. 021002) and the secondary loss model of (Traupel, W, 1977, Thermische Turbomaschinen, Springer-Verlag, Berlin) are arguably the most reasonable. A quantitative comparison with multistage rig data indicates that, together, these methods over-predict lapse rates by around 30%, highlighting the need for improved loss models and a better understanding of the multistage environment. By examining the influence of blade lift across the Smith efficiency chart, the analysis demonstrates that designs with higher flow turning will tend to be less sensitive to increases in blade loading.

References

1.
Smith
,
SF.
,
1965
, “
A Simple Correlation of Turbine Efficiency
,”
J. R., Aeronaut. Soc.
,
69
,
pp.
367
370
.
2.
Zweifel
,
O.
,
1945
, “
The Spacing of Turbomachine Blading, Especially with Large Angular Deflection
Brown Boveri Rev.
,
32
(
1
),
pp.
436
444
.
3.
Ainley
,
D. G.
, and
Mathieson
,
G. C. R.
,
1957
, “
A Method of Performance Estimation for Axial-Flow Turbines
,”
ARC Reports and Memoranda Paper No. 2974
.
4.
Dunham
,
J.
, and
Came
,
P. M.
,
1970
, “
Improvements to the Ainley-Mathieson Method of Turbine Performance Prediction
,”
Trans. ASME:, J. Eng. Gas Turbines Power
, July,
pp.
252
256
.
5.
Kacker
,
S. C.
, and
Okapuu
,
U.
,
1982
, “
A Mean Line Performance Method for Axial Flow Turbine Efficiency
,”
J. Eng. Power
,
104
,
pp.
111
119
.10.1115/1.3227240
6.
Coull
,
J. D.
, and
Hodson
,
H. P.
,
2011
, “
Predicting the Profile Loss of High-Lift Low Pressure Turbines
,”
J. Turbomach.
,
134
(
2
),
pp.
021002-1
021002-14
.10.1115/1.4002961
7.
Traupel
,
W
,
1977
,
Thermische Turbomaschinen
,
Springer-Verlag
,
Berlin
.
8.
Haselbach
,
F.
,
Schiffer
,
H. P.
,
Horsman
,
M.
,
Dressen
,
S.
,
Harvey
,
N.
, and
Read
,
S.
,
2002
, “
The Application of Ultra High Lift Blading in the BR715 LP Turbine,”
ASME J. Turbomach.
124
(
1
),
pp.
45
51
.10.1115/1.1415737
9.
Craig
,
H. R. M.
, and
Cox
,
H. J. A.
,
1971
, “
Performance Estimation of Axial Flow Turbines
,”
Proc. Inst. Mech. Eng.
,
71
,
pp.
1970
1971
.
10.
Coull
,
J. D.
,
Thomas
,
R. L.
, and
Hodson
,
H. P.
, 2010, “
Velocity Distributions for Low Pressure Turbines
,”
J. Turbomach.
,
132
(
4
),
pp.
041006-1
041006-13
.10.1115/1.3192149
11.
Gier
,
J.
,
Franke
,
M.
,
Hübner
,
N.
, and
Schröder
,
T
,
2008
, “
Designing LP Turbines for Optimized Airfoil Lift
,”
ASME Paper No. GT2008-51101
.
12.
Horlock
,
J. H.
,
1966
, “
Axial Flow Turbines: Fluid Mechanics and Thermodynamics
,”
SBN 0-88275-097-6
.
13.
Denton
,
JD
,
1993
, “
Loss Mechanisms in Turbomachines
ASME J. Turbomach.
,
115
(
4
),
p.
621
656
.10.1115/1.2929299
14.
Ainley
,
D. G.
, and
Mathieson
,
G. C. R.
,
1951
, “
An Examination of the Flow and Pressure Losses in Blade Rows of Axial-Flow Turbines
,”
ARC Reports and Memoranda Paper No. 2891
.
15.
Carter
,
ADS
,
1948
, “
Three-Dimensional Flow Theories for Axial Compressors and Turbines
,”
Proc. Inst. Mech. Eng.
,
159
(
1
),
pp.
255
268
.10.1243/PIME_PROC_1948_159_023_02
16.
Thwaites
,
B.
,
1949
, “
Approximate Calculation of the Laminar Boundary Layer
,”
Aeronaut. Q.
,
1
,
pp.
245
280
.
17.
Benner
,
M. W.
,
Sjolander
,
S. A.
, and
Moustapha
,
S. H.
,
2006
, “
An Empirical Prediction Method For Secondary Losses In Turbines – Part II: A New Secondary Loss Correlation
,”
J. Turbomach.
,
128
(
2
),
pp.
281
291
.10.1115/1.2162594
18.
Vera
,
M.
,
Hodson
,
H. P.
, and
Vazquez
,
R.
,
2003
, “
The Effect of Mach Number on LP Turbine Wake-Blade Interaction
9th ISUAAAT
,
Sept.
4–8
,
Lyon, France
19.
Marconcini
,
M.
,
Rubechini
,
F.
,
Pacciani
,
R.
,
Arnone
,
A.
, and
Bertini
,
F.
,
2010
, “
Redesign of High-Lift LP-Turbine Airfoils For Low Speed Testing
ASME Turbo Expo
,
Glasgow, UK
,
14–18
June
,
ASME Paper No. GT2010-23284
.
20.
Praisner
,
T. J.
,
Grover
,
E. A.
,
Knezevici
,
D. C.
,
Popovic
,
I.
,
Sjolander
,
S. A.
,
Clarke
,
J. P.
, and
Sondergaard
,
R.
,
2008
, “
Towards the Expansion of Low-Pressure-Turbine Airfoil Design Space
,”
ASME Paper No. GT2008-50898
.
21.
Hodson
,
H. P.
, and
Dominy
,
R. G.
,
1987
, “
The Off-Design Performance of a Low-Pressure Turbine Cascade
ASME J. Turbomach.
109
(
2
),
pp.
201
209
.10.1115/1.3262086
22.
Vázquez
,
R.
,
Torre
,
D.
,
Partida
,
F.
,
Armañanzas
,
L.
, and
Antoranz
,
A.
,
2011
, “
Influence of Surface Roughness on the Profile and End-Wall Losses in Low Pressure Turbines
,”
ASME Paper No. GT2011-46371
.
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