In this paper, the detailed steady and unsteady numerical investigations of a 1.5-stage axial flow turbine are conducted to determine the specific influence of interplatform steps in the first stator—as caused by deviations in manufacturing or assembly. A basic first stator design and a design consisting of a bow and endwall contours are compared. Apart from step height, the position and geometry of the interplatform border are varied for the basic design. To create the steps, every third stator vane was elevated, together with its platforms at hub and shroud, such that the flow capacity is only little affected. The results show that the effects of steps on the platform borders in front and aft of the first stator can be decoupled from those occurring on the interplatform steps. For the latter, being the main contributor to the additional loss, the intensity of recirculation zones and losses increase substantially when the platform border is located close to the suction side. Using a relative step height of 1.82% span, the entropy production doubles when compared to a position close to the pressure side, which can be explained by differences in local flow velocity level. Regarding a circular-arc-shaped platform, the losses can be more than halved—mainly due to lower included angles between step and endwall flow streamlines. The findings can be explained by a nondimensional relation of the local entropy production using local values for step height and characteristic flow quantities. Furthermore, a reduction in step height leads to an attenuation of the otherwise linear relationship between step height and entropy production, which is mainly due to lower local ratio of step height and boundary layer thickness. In the case of laminar or transitional flow regions on the endwall, typical for turbine rigs with low inlet turbulence and low-pressure turbines under cruise conditions, the steps lead to immediate local flow transition and thus substantially different results.

References

References
1.
Sieverding
,
C. H.
,
1985
, “
Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages
,”
ASME J. Eng. Gas Turbines Power
,
107
(
2
), pp.
248
257
.
2.
Langston
,
L. S.
,
2001
, “
Secondary Flows in Axial Turbines—A Review
,”
Ann. N. Y. Acad. Sci.
,
934
, pp.
11
26
.
3.
Grewe
,
R. P.
,
Miller
,
R. J.
, and
Hodson
,
H. P.
,
2014
, “
The Effect of Endwall Manufacturing Variations on Turbine Performance
,”
ASME
Paper No. GT2014-25326.
4.
Colban
,
W. F.
,
Thole
,
K. A.
, and
Zess
,
G.
,
2002
, “
Combustor Turbine Interface Studies—Part 1: Endwall Effectiveness Measurements
,”
ASME
Paper No. GT2002-30526.
5.
Colban
,
W. F.
,
Lethander
,
A. T.
,
Thole
,
K. A.
, and
Zess
,
G.
,
2003
, “
Combustor Turbine Interface Studies—Part 2: Flow and Thermal Field Measurements
,”
ASME J. Turbomach.
,
125
(
2
), pp.
203
209
.
6.
Chyu
,
M. K.
,
Hsing
,
Y. C.
, and
Bunker
,
R. S.
,
1998
, “
Measurements of Heat Transfer Characteristics of Gap Leakage Around a Misaligned Component Interface
,”
ASME
Paper No. 98-GT-132.
7.
Zhang
,
L.
, and
Moon
,
H. K.
,
2004
, “
Turbine Nozzle Endwall Inlet Film Cooling: The Effect of a Back-Facing Step and Velocity Ratio
,”
ASME
Paper No. IMECE2004-59117.
8.
Cardwell
,
N. D.
,
Sundaram
,
N.
, and
Thole
,
K. A.
,
2006
, “
Effect of Midpassage Gap, Endwall Misalignment, and Roughness on Endwall Film-Cooling
,”
ASME J. Turbomach.
,
128
(
1
), pp.
62
70
.
9.
Cardwell
,
N. D.
,
Sundaram
,
N.
, and
Thole
,
K. A.
,
2007
, “
The Effects of Varying the Combustor-Turbine Gap
,”
ASME J. Turbomach.
,
129
(
4
), pp.
756
764
.
10.
Hada
,
S.
, and
Thole
,
K. A.
,
2011
, “
Computational Study of a Midpassage Gap and Upstream Slot on Vane Endwall Film-Cooling
,”
ASME J. Turbomach.
,
133
(
1
), p.
011024
.
11.
Ranson
,
W. W.
,
Thole
,
K. A.
, and
Cunha
,
F. J.
,
2005
, “
Adiabatic Effectiveness Measurements and Predictions of Leakage Flows Along a Blade Endwall
,”
ASME J. Turbomach.
,
127
(
3
), pp.
609
618
.
12.
Piggush
,
J. D.
, and
Simon
,
T. W.
,
2005
, “
Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage and Assembly Features
,”
ASME
Paper No. GT2005-68340.
13.
de la Rosa Blanco
,
E.
,
Hodson
,
H. P.
, and
Vazquez
,
R.
,
2005
, “
Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade
,”
ASME
Paper No. GT2005-68938.
14.
Kluxen
,
R.
,
Terstegen
,
M.
,
Behre
,
S.
,
Jeschke
,
P.
, and
Guendogdu
,
Y.
,
2014
, “
Effects of Platform Misalignment in a 3D Designed 1.5 Stage Axial Turbine
,”
ASME
Paper No. GT2014-26378.
15.
Harrison
,
S.
,
1989
, “
Secondary Loss Generation in a Linear Cascade of High-Turning Turbine Blades
,”
ASME
Paper No. 89-GT-47.
16.
Vera
,
M.
,
de la Rosa Blanco
,
E.
,
Hodson
,
H. P.
, and
Vazquez
,
R.
,
2009
, “
Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig
,”
ASME J. Turbomach.
,
131
(
1
), p.
011017
.
17.
Poehler
,
T.
,
Niewoehner
,
J.
,
Jeschke
,
P.
, and
Guendogdu
,
Y.
,
2015
, “
Investigation of Nonaxisymmetric Endwall Contouring and Three-Dimensional Airfoil Design in a 1.5-Stage Axial Turbine—Part I: Design and Novel Numerical Analysis Method
,”
ASME J. Turbomach.
,
137
(
8
), p.
081009
.
18.
Niewoehner
,
J.
,
Poehler
,
T.
,
Jeschke
,
P.
, and
Guendogdu
,
Y.
,
2015
, “
Investigation of Nonaxisymmetric Endwall Contouring and Three-Dimensional Airfoil Design in a 1.5 Stage Axial Turbine—Part II: Experimental Validation
,”
ASME J. Turbomach.
,
137
(
8
), p.
081010
.
19.
Herwig
,
H.
, and
Kock
,
F.
,
2007
, “
Direct and Indirect Methods of Calculating Entropy Generation Rates in Turbulent Convective Heat Transfer Problems
,”
Heat Mass Transfer
,
43
(
3
), pp.
207
215
.
20.
Röber
,
T.
,
Kozulovic
,
D.
,
Kügeler
,
E.
, and
Nürnberger
,
D.
,
2006
, “
Appropriate Turbulence Modelling for Turbomachinery Flows Using a Two-Equation Turbulence Model
,”
New Results in Numerical and Experimental Fluid Mechanics V
,
Springer
,
Berlin
, pp.
446
454
.
21.
Nürnberger
,
D.
, and
Greza
,
H.
,
2002
, “
Numerical Investigation of Unsteady Transitional Flows in Turbomachinery Components Based on a RANS Approach
,”
Flow, Turbul. Combust.
,
69
(
3
), pp.
331
353
.
22.
Kügeler
,
E.
,
Weber
,
A.
, and
Lisiewicz
,
S.
,
2001
, “
Combination of a Transition Model With a Two-Equation Turbulence Model and Comparison With Experimental Results
,”
4th European Turbomachinery Conference
, Florence, Italy, Mar. 20–23, Paper No. ATI-CST-076/01.
23.
Restemeier
,
M.
,
Jeschke
,
P.
,
Guendogdu
,
Y.
, and
Gier
,
J.
,
2013
, “
Numerical and Experimental Analysis of the Effect of Variable Blade Row Spacing in a Subsonic Axial Turbine
,”
ASME J. Turbomach.
,
135
(
2
), p.
021031
.
24.
Langtry
,
R. B.
, and
Menter
,
F. R.
,
2009
, “
Correlation-Based Transition Modeling for Unstructured Parallelized Computational Fluid Dynamics Codes
,”
AIAA J.
,
47
(
12
), pp.
2894
2906
.
25.
Herbst
,
F.
,
Kožulović
,
D.
, and
Seume
,
J. R.
,
2013
, “
Transition Modeling for Vortex Generating Jets on Low-Pressure Turbine Profiles
,”
ASME J. Turbomach.
,
135
(
1
), p.
011038
.
26.
Mayle
,
R. E.
,
1991
, “
The 1991 IGTI Scholar Lecture: The Role of Laminar-Turbulent Transition in Gas Turbine Engines
,”
ASME J. Turbomach.
,
113
(
4
), pp.
509
537
.
27.
Eaton
,
J. K.
, and
Johnston
,
J. P.
,
1981
, “
A Review of Research on Subsonic Turbulent Flow Reattachment
,”
AIAA J.
,
19
(
9
), pp.
1093
1100
.
28.
Denton
,
J. D.
,
1993
, “
Loss Mechanisms in Turbomachines
,”
ASME J. Turbomach.
,
115
(
4
), pp.
621
656
.
29.
Schlichting
,
H.
, and
Gersten
,
K.
,
2006
,
Grenzschichttheorie
, Überarbeitete Auflage, Vol.
10
,
Springer-Verlag
, Berlin, Germany.
30.
Selby
,
G. V.
,
1982
, “
Phenomenological Study of Subsonic Turbulent Flow Over a Swept Rearward-Facing Step
,” Ph.D. thesis, National Aeronautics and Space Administration, Langley Research Center, Hampton, VA.
31.
Hao
,
J.
,
2014
, “
Aeroacoustics of Small Gaps and Steps in Low-Mach-Number Turbulent Boundary Layers
,”
Ph.D. thesis
, University of Notre Dame, Notre Dame, IN.
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