Low pressure turbines typically operate in the low Reynolds number regime. Depending on the loading of the blade, they may exhibit detached flow with associated reattachment in the rear part of the suction surface. Additionally, the flow is highly time-dependent due to the sequence of rotating and stationary blade rows. The work presented in this paper covers experimental efforts taken to investigate this type of flow in detail. Typical low pressure turbine flow conditions have been chosen as baseline for the experimental work. A pressure distribution has been created on a flat plate by means of a contoured upper wall in a low speed wind tunnel. The distribution matches the one of the Pak-B airfoil. Unsteadiness is then superimposed in two ways: A specific unsteadiness was created by using a rotating flap (RF) downstream of the test section. This results in almost sinusoidal periodic unsteady flow across the plate, simulating the interaction between stator and rotor of a turbine stage. Furthermore, pulsed blowing by vortex generating jets (VGJ) upstream of the suction peak was used to influence the transition process and development of the separation bubble. Measurements have been performed with hot-wire anemometry. Experimental results are presented to compare both forcing mechanisms. In sinusoidal unsteady main flow, the transition occurs naturally by the breakdown of the shear layer instability, which is affected by periodic changes in the overall Reynolds number and thus pressure gradient. In opposition, active flow control (AFC) by VGJ triggers the transition process by impulse and vorticity injection into the boundary layer, while maintaining a constant Reynolds number. The flow fields are compared using phase averaged data of velocity und turbulence intensity as well as boundary layer parameters, namely shape factor and momentum thickness Reynolds number. Finally, a model to describe the time mean intermittency distribution is refined to fit the data.

References

References
1.
Curtis
,
E. M.
,
Hodson
,
H. P.
,
Banieghbal
,
M. R.
,
Denton
,
J. D.
, and
Howell
,
R. J.
,
1996
, “
Development of Blade Profiles for Low Pressure Turbine Applications
,”
Proceedings of the International Gas Turbine and Aeroengine Congress and Exposition
, Paper No. 96-GT-358.
2.
Hodson
,
H. P.
, and
Howell
,
R. J.
,
2005
, “
The Role of Transition in High-Lift Low-Pressure Turbines for Aeroengines
,”
Prog. Aerosp. Sci.
,
41
, pp.
419
454
.10.1016/j.paerosci.2005.08.001
3.
Praisner
,
T. J.
,
Grover
,
E. A.
,
Knezevici
,
D. C.
,
Popovic
,
I.
,
Sjolander
,
S. A.
,
Clark
,
J. P.
, and
Sondergaard
,
R.
,
2008
, “
Toward the Expansion of Low-Pressure-Turbine Airfoil Design Space
,”
ASME
Paper No. GT2008-50898.10.1115/GT2008-50898
4.
Hourmouziadis
,
J.
,
1989
, “
Aerodynamic Design of Low Pressure Turbines
,”
AGARD Lect. Ser.
,
167
, pp.
8-1
8-40
.
5.
Mayle
,
R. E.
,
1991
, “
The Role of Laminar-Turbulent Transition in Gas Turbine Engines
,”
ASME J. Turbomach.
,
113
(
10
), pp.
509
536
.10.1115/1.2929110
6.
Sharma
,
O. P.
,
Ni
,
R. H.
, and
Tanrikut
,
S.
,
1994
, “
Unsteady Flows in Turbines—Impact on Design Procedure
,”
AGARD Lect. Ser.
,
195
, pp.
5-1
5-27
.
7.
Hatman
,
A.
, and
Wang
,
T.
,
1999
, “
A Prediction Model for Separated-Flow Transition
,”
ASME J. Turbomach.
,
121
(
7
), pp.
594
602
.10.1115/1.2841357
8.
Muti Lin
,
J. C.
, and
Pauley
,
L. L.
,
1996
, “
Low-Reynolds-Number Separation on an Airfoil
,”
AIAA J.
,
34
, pp.
1570
1577
.10.2514/3.13273
9.
Gaster
,
M.
,
1969
, “
The Structure and Behaviour of Laminar Separation Bubbles
,” Ministry of Technology, Aeronautical Research Council, London, Reports and Memoranda No. 3595.
10.
McAuliffe
,
B. R.
, and
Yaras
,
M. I.
,
2008
, “
Numerical Study of Instability Mechanisms Leading to Transition in Separation Bubbles
,”
ASME J. Turbomach.
,
130
(
4
), pp.
1
8
.10.1115/1.2750680
11.
Volino
,
R. J.
, and
Hultgren
,
L. S.
,
2001
, “
Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions
,”
ASME J. Turbomach.
,
123
(
4
), pp.
189
197
.10.1115/1.1350408
12.
Dähnert
,
J.
,
Lyko
,
C.
, and
Peitsch
,
D.
,
2013
, “
Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions
,”
ASME J. Turbomach.
,
135
(
1
), p.
011007
.10.1115/1.4006393
13.
Malkiel
,
E.
and
Mayle
,
R. E.
,
1996
, “
Transition in a Separation Bubble
,”
ASME J. Turbomach.
,
118
(
10
), pp.
752
759
.10.1115/1.2840931
14.
Emmons
,
H. W.
,
1951
, “
The Laminar-Turbulent Transition in a Boundary Layer—Part I
,”
J. Aeronaut. Sci.
,
18
, pp.
490
498
.10.2514/8.2010
15.
Dhawan
,
S.
, and
Narasimha
,
R.
,
1957
, “
Some Properties of Boundary Layer Flow During the Transition From Laminar to Turbulent Motion
,”
J. Fluid Mech.
,
3
, pp.
418
436
.10.1017/S0022112058000094
16.
Walker
,
G. J.
,
1993
, “
The Role of Laminar-Turbulent Transition in Gas Turbine Engines: A Discussion
,”
ASME J. Turbomach.
,
115
(
4
), pp.
207
217
.10.1115/1.2929223
17.
Gostelow
,
J. P.
, and
Thomas
,
R. L.
,
2005
, “
Response of a Laminar Separation Bubble to an Impinging Wake
,”
ASME J. Turbomach.
,
127
(
1
), pp.
35
42
.10.1115/1.1829729
18.
Gostelow
,
J. P.
, and
Thomas
,
R. L.
,
2006
, “
Interactions Between Propagating Wakes and Flow Instabilities in the Presence of a Laminar Separation Bubble
,”
ASME
Paper No. GT2006-91193.10.1115/GT2006-91193
19.
Schulte
,
V.
, and
Hodson
,
H. P.
,
1994
, “
Wake-Separation Bubble Interaction in Low Pressure Turbines
,”
Proceedings of the 30th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
, Indianapolis, IN, June 27–29,
AIAA
Paper No. 94-2931.10.2514/6.1994-2931
20.
Martinstetter
,
M.
,
Schwarze
,
M.
,
Niehuis
,
R.
, and
Hübner
,
N.
,
2008
, “
Influence of Inflow Turbulence on Loss Behavior of Highly Loaded LPT Cascades
,”
Proceedings of the 46th AIAA Aerospace Sciences Meeting and Exhibit
, Reno, NV, January 7–10,
AIAA
Paper No. 2008-82.10.2514/6.2008-82
21.
Mahallati
,
A.
, and
Sjolander
,
S. A.
,
2013
, “
Aerodynamics of a Low-Pressure Turbine Airfoil at Low Reynolds Numbers—Part 2: Blade–Wake Interaction
,”
ASME J. Turbomach.
,
123
, p.
011010
.10.1115/1.4006320
22.
Haselbach
,
F.
,
Schiffer
,
H.-P.
,
Horsman
,
M.
,
Dressen
,
S.
,
Harvey
,
N. W.
, and
Read
,
S.
,
2002
, “
The Application of Ultra High Lift Blading in the BR715 LP Turbine
,”
ASME J. Turbomach.
,
124
, pp.
45
51
.10.1115/1.1415737
23.
Miller
,
J. A.
, and
Fejer
,
A. A.
,
1964
, “
Transition Phenomena in Oscillating Boundary-Layer Flows
,”
J. Fluid Mech.
,
3
, pp.
438
449
.10.1017/S0022112064000325
24.
Obremski
,
H. J.
, and
Fejer
,
A. A.
,
1967
, “
Transition in Oscillating Boundary Layer Flows
,”
J. Fluid Mech.
,
29
, pp.
93
111
.10.1017/S0022112067000655
25.
Lou
,
W.
,
Willer
,
L.
,
Gündogdu
,
Y.
,
Ücgül
,
E.
, and
Hourmouziadis
,
J.
,
1999
, “
Experimentelle Untersuchung der Stationären und Periodischen Plattengrenzschichten mit Ablöseblase
,” German Air and Space Conference 1999, DGLR Annual Meeting, Berlin, September 27–30, Paper No. DGLR-JT99-077.
26.
Lou
,
W.
, and
Hourmouziadis
,
J.
,
2000
, “
Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions
,”
ASME J. Turbomach.
,
122
, pp.
634
643
.10.1115/1.1308568
27.
Talan
,
M.
, and
Hourmouziadis
,
J.
,
2002
, “
Characteristic Regimes of Transitional Separation Bubbles in Unsteady Flow
,”
J. Flow, Turbul. Combust.
,
69
, pp.
207
227
.10.1023/A:1027355105017
28.
Talan
,
M.
,
Meyer
,
A.
, and
Hourmouziadis
,
J.
,
2003
, “
Kelvin–Helmholtz Type Vortices in Unsteady Separation Bubbles
,” 16th International Symposium on Air Breathing Engines, Cleveland, OH, August 31–September 5, ISABE Paper No. 1085.
29.
Lyko
,
C.
,
Dähnert
,
J.
, and
Peitsch
,
D.
,
2011
, “
Transition Mechanisms in Laminar Separated Flow Under Unsteady Main Flow Conditions—Part 1: Steady Flowfield
,”
Proceedings of the International Gas Turbine Congress
, Osaka, Japan, November 13–18, Paper No. IGTC2011-0254.
30.
Lyko
,
C.
,
Dähnert
,
J.
, and
Peitsch
,
D.
,
2011
, “
Transition Mechanisms in Laminar Separated Flow Under Unsteady Main Flow Conditions—Part 2: Unsteady Flowfield
,”
Proceedings of the International Gas Turbine Congress
, Osaka, Japan, November 13–18, Paper No. IGTC2011-0255.
31.
Tiedemann
,
C.
,
Heinrich
,
A.
, and
Peitsch
,
D.
,
2012
, “
A New Linear High Speed Compressor Stator Cascade for Active Flow Control Investigations
,”
Proceedings of the 6th AIAA Flow Control Conference
, New Orleans, LA, June 25–28,
AIAA
Paper No. 2012-3251.10.2514/6.2012-3251
32.
Bons
,
J. P.
,
Sondergaard
,
R.
, and
Rivir
,
R. B.
,
1999
, “
Control of Low-Pressure Turbine Separation Using Vortex Generator Jets
,”
Proceedings of the 37th Aerospace Sciences Meeting and Exhibit
,
Reno
,
N
V
, January 11–14,
AIAA
Paper No. 99-0367.10.2514/6.1999-367
33.
Sondergaard
,
R.
,
Rivir
,
R. B.
, and
Bons
,
J. P.
,
2002
, “
Control of Low-Pressure Turbine Separation Using Vortex-Generator Jets
,”
J. Propul. Power
,
18
, pp.
889
895
.10.2514/2.6014
34.
Rivir
,
R. B.
,
Sondergaard
,
R.
,
Bons
,
J. P.
, and
Lake
,
J. P.
,
2000
, “
Passive and Active Control of Separation in Gas Turbines
,”
Proceedings of the AIAA Fluids 2000 Conference and Exhibit
,
Denver, CO
, June 19–22,
AIAA
Paper No. 2000-2235.10.2514/6.2000-2235
35.
Bons
,
J. P.
,
Sondergaard
,
R.
, and
Rivir
,
R. B.
,
2001
, “
Turbine Separation Control Using Pulsed Vortex Generator Jets
,”
ASME J Turbomach.
,
123
, pp.
198
206
.10.1115/1.1350410
36.
Bons
,
J. P.
,
Reimann
,
D.
, and
Bloxham
,
M.
,
2008
, “
Separated Flow Transition on an LP Turbine Blade With Pulsed Flow Control
,”
ASME J. Turbomach.
,
130
, p.
021014
.10.1115/1.2751149
37.
Bons
,
J. P.
,
Sondergaard
,
R.
, and
Rivir
,
R. B.
,
2002
, “
The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets
,”
ASME J. Turbomach.
,
124
, pp.
77
85
.10.1115/1.1425392
38.
Volino
,
J. R.
,
2003
, “
Separation Control on Low-Pressure Turbine Airfoils Using Synthetic Vortex Generator Jets
,”
ASME J. Turbomach.
,
125
, pp.
765
777
.10.1115/1.1626686
39.
Schubauer
,
G. B.
, and
Klebanoff
,
P. S.
,
1955
, “
Contributions on the Mechanics of Boundary-Layer Transition
,” NACA Technical Report No. 1289.
40.
Gostelow
,
J. P.
,
Walker
,
G. J.
,
Solomon
,
W. J.
,
Hong
,
G.
, and
Melwani
,
N.
,
1997
, “
Investigation of the Calmed Region Behind a Turbulent Spot
,”
ASME J. Turbomach.
,
119
(
10
), pp.
802
809
.10.1115/1.2841191
41.
Fasel
,
H. F.
,
Balzer
,
W.
, and
Gross
,
A.
,
2008
, “
Investigation of Separation Control for Low-Pressure Turbines Using CFD
,” Proceedings of the 26th Congress of International Council of the Aeronautical Sciences (ICAS 2008), Anchorage, AK, September 14–19, Paper No. ICAS 2008-4.4.2.
42.
Chew
,
Y. T.
,
Shah
,
D. A.
, and
Wan
,
J.
,
1999
, “
An Envelope Method for Detection of Turbulence Intermittency in a Transitional Boundary Layer
,”
Fluid Dyn. Res.
,
24
, pp.
7
22
.10.1016/S0169-5983(98)00012-4
43.
Hedley
,
T. B.
, and
Keffer
,
J. F.
,
1974
, “
Some Turbulent/Non-Turbulent Properties of the Outer Intermittent Region of a Boundary Layer
,”
J. Fluid Mech.
,
64
, pp.
645
678
.10.1017/S0022112074001844
44.
Hourmouziadis
,
J.
,
Buckl
,
F.
, and
Bergmann
,
P.
,
1987
, “
The Development of the Profile Boundary Layer in a Turbine Environment
,”
ASME J. Turbomach.
,
109
(
4
), pp.
286
295
.10.1115/1.3262101
45.
Mayle
,
R. E.
, and
Dullenkopf
,
K.
,
1991
, “
More on the Turbulent-Strip Theory for Wake-Induced Transition
,”
ASME J. Turbomach.
,
113
(
7
), pp.
428
432
.10.1115/1.2927892
46.
Mayle
,
R. T.
, and
Dullenkopf
,
K.
,
1990
, “
A Theory for Wake-Induced Transition
,”
ASME J. Turbomach.
,
112
(
4
), pp.
188
195
.10.1115/1.2927632
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