Within a European research project the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Gottingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built
up, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline pattern (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D Particle Image Velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer mainly occur when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horse-shoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.
[1]
R. P. Roy,et al.
Prediction and Measurement of the Flow and Heat Transfer Along the Endwall and Within an Inlet Vane Passage
,
2002
.
[2]
R. J. Goldstein,et al.
Measurements in Heat Transfer
,
1976
.
[3]
F. Haselbach,et al.
Aerothermal Investigations on Turbine Endwalls and Blades (AITEB)
,
2004
.
[4]
M. F. Blair,et al.
An Experimental Study of Endwall and Airfoil Surface Heat Transfer in a Large Scale Turbine Blade Cascade
,
1980
.
[5]
Howard P. Hodson,et al.
Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade
,
2005
.
[6]
Friedrich Kost,et al.
Film-Cooled Turbine Endwall in a Transonic Flow Field: Part I—Aerodynamic Measurements
,
2001
.
[7]
E. R. G. Eckert,et al.
Analysis of Film Cooling and Full-Coverage Film Cooling of Gas Turbine Blades
,
1984
.
[8]
L. S. Langston,et al.
Crossflows in a Turbine Cascade Passage
,
1980
.
[9]
F. Kost,et al.
A new test facility for probe calibration offering independent variation of Mach and Reynolds number
,
2000
.
[10]
H.-J. Rehder,et al.
DLR Rig Instrumentation -European Research Project AITEB-
,
2004
.
[11]
Sunao Aoki,et al.
An Experimental Study of Heat Transfer and Film Cooling on Low Aspect Ratio Turbine Nozzles
,
1990
.
[12]
R. Goldstein,et al.
Turbulent Transport on the Endwall in the Region Between Adjacent Turbine Blades
,
1987
.
[13]
P. Safarik,et al.
Data Reduction of Wake Flow Measurements with Injection of an Other Gas
,
1995
.
[14]
C. H. Sieverding,et al.
Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages
,
1985
.
[15]
T. V. Jones,et al.
Film Cooling in the Presence of Mainstream Pressure Gradients
,
1990
.
[16]
Howard P. Hodson,et al.
Three-Dimensional Flow in a Low-Pressure Turbine Cascade at Its Design Condition
,
1986
.
[17]
S. Standard.
GUIDE TO THE EXPRESSION OF UNCERTAINTY IN MEASUREMENT
,
2006
.
[18]
Markus Raffel,et al.
Particle Image Velocimetry: A Practical Guide
,
2002
.