Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds numbers. Compared to steady flow, a reduction of total pressure loss coefficient over a broad range of Reynolds numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading. Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane. Unsteady flow causes the transition on the surface of the suction side of a low-pressure turbine blade to move upstream whenever an incoming wake is present on the surface; moreover, a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot wire data acquisition system is required. Due to the fact that hot wires give a good insight into boundary layer development, a new hot-wire data acquisition system has been set up. The anemometry system can acquire four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilized for a once-per-revolution trigger. The once-per-revolution trigger is used to start the measurement of one data block. Using the well-established ensemble-averaging technique, 300 ensembles each consisting of five wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction. The adaptation of this new hot-wire anemometry data acquisition system to the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen is pointed out. First, results on unsteady periodic boundary layer development of a highly loaded low-pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from $x/lax=0.82$ to $x/lax=0.99$ (suction side), at steady and unsteady inlet flow conditions $Ubar=10 m/s$ at an outlet Reynolds number of $Re2th=100,000$ have been conducted. [S0889-504X(00)00204-X]

1.
Schulte, V., 1995, “Unsteady Separated Boundary Layers in Axial-flow Turbomachinery,” PhD thesis, Cambridge University.
2.
Schulte
,
V.
, and
Hodson
,
H. P.
,
1998
, “
Unsteady Wake-Induced Boundary Layer Transition in High Lift LP Turbines
,”
ASME J. Turbomach.
,
120
, pp.
28
35
.
3.
Hodson, H. P., 1998, “Blade Row Interference Effects in Axial Turbomachinery Stages: Bladerow Interactions in Low Pressure Turbines,” VKI Lecture Series 1998-02.
4.
Mayle
,
Robert Edward
,
1991
, “
The 1991 IGTI Scholar Lecture: The Role of Laminar–Turbulent Transition in Gas Turbine Engines
,”
ASME J. Turbo-mach.
,
113
, pp.
590
537
.
5.
,
D. E.
,
Wisler
,
D. C.
,
Okiishi
,
T. H.
,
Walker
,
G. J.
,
Hodson
,
H. P.
, and
Shin
,
H.-W.
,
1997
, “
Boundary Layer Development in Axial Compressors and Turbines: Part 3 of 4—LP Turbines
,”
ASME J. Turbomach.
,
119
, pp.
225
237
.
6.
Schulte
,
V.
, and
Hodson
,
H. P.
,
1998
, “
Prediction of the Becalmed Region for LP Turbine Profile Design
,”
ASME J. Turbomach.
,
120
, pp.
839
846
.
7.
Curtis
,
E. M.
,
Hodson
,
H. P.
,
Banieghbal
,
M. R.
,
Howell
,
R. J.
, and
Harvey
,
N. W.
,
1997
, “
Development of Blade Profiles for Low-Pressure Turbine Applications
,”
ASME J. Turbomach.
,
119
, pp.
531
538
.
8.
Harvey, N. W., Cox, J. C., Schulte, V., Howell, R., and Hodson, H. P., 1999, “The Role of Research in the Aerodynamic Design of an Advanced Low Pressure Turbine,” ImechE Conference Transactions/Vol. A: 3rd European Conference on Turbomachinery, C557/043, pp. 123–132.
9.
Brunner, S., Fottner, L., Schulte, V., and Kappler, G., 1999a, “Investigation of Wake-Induced Transition on a Highly Loaded Low-Pressure Turbine Cascade,” ImechE Conference Transactions/Vol. A: 3rd European Conference on Turbomachinery, C557/068, p. 231 ff.
10.
Schro¨der, Th., 1991, “Investigations of Blade Row Interaction and Boundary Layer Transition Phenomena in a Multistage Aero Engine Low-Pressure Turbine by Measurements With Hot-Film Probes and Surface-Mounted Hot-Film Gauges,” Von Karman Institute for Fluid Dynamics, Lecture Series 1991-06.
11.
Arndt
,
N.
,
1993
, “
Blade Row Interaction in a Multistage Low-Pressure Turbine
,”
ASME J. Turbomach.
,
115
, pp.
137
146
.
12.
Banieghbal, M. R., Curtis, E. M., Denton, J. D., Hodson, H. P., Huntsmann, I., and Schulte, V., 1995, “Wake Passing in LP Turbine Blades,” AGARD CP 571, Paper 23.
13.
Acton, P., and Fottner, L., 1996, “The Generation of Instationary Flow Conditions in the High Speed Cascade Wind Tunnel,” 13th Symposium on Measuring Techniques.
14.
Sturm, W., Fottner, L., 1985, “The High-Speed Cascade Wind-Tunnel of the German Armed Forces University Munich,” 8th Symposium on Measuring Techniques.
15.
Pfeil, H., and Eifler, J., 1979, “Turbulenzverha¨ltnisse hinter rotierenden Zylindergittern,” Forschung im Ingenieurwesen, 42.
16.
Brunner, S., and Fottner, L., 1999, “Untersuchungen zum Einfluß der Rotor–Stator Interaktion auf die saugseitige Transition eines hochbelassteten ungeku¨hlten Niederdruck-Turbinengitters,” DGLR-JT99-078.
17.
Amecke, J., 1967, “Auswertung von Nachlaufmessungen an ebenen Schaufelgittern,” Bericht 67A49, AVA Go¨ttingen.
18.
Ganzert, W., and Pottner, L., 1996, “WINPANDA—an Enhanced PC-Based Data Acquisition System for Wake and Profile Distribution,” 13th Symposium on Measuring Techniques.
19.
Wolff, S., 1999, “Konzeption, Programmierung and Erprobung eines PC-gesteuereten Meßsystems zur Aufnahme und Auswertung von 1-D and 3-D-Hitzdraht-Signalen am Hochgeschwindigkeits-Gitterwindkanal als Ersatz des HP-Systems,” Institute Report WOIB9909.
20.
Brunner, S., Teusch, R., Stadtmu¨ller, P., and Fottner, L., 1998, “The Use of Simultaneous Surface Hot Film Anemometry to Investigate Unsteady Wake Induced Transition in Turbine and Compressor Cascades,” 14th Symposium on Measuring Techniques.