Film cooling in the hot gas path of a gas turbine engine can protect components from the high temperature main flow, but it generally increases the heat transfer coefficient h partially offsetting the benefits in reduced adiabatic wall temperature. We are thus interested in adiabatic effectiveness η and h which are combined in a formulation called net heat flux reduction (NHFR). Unsteadiness in coolant flow may arise due to inherent unsteadiness in the external flow or be intentionally introduced for flow control. In previous work it has been suggested that pulsed cooling flow may, in fact, offer benefits over steady blowing in either improving NHFR or reducing the mass flow requirements for matched NHFR. In this paper we examine this hypothesis for a range of steady and pulsed blowing conditions. We use a new experimental technique to analyze unsteady film cooling on a semicircular cylinder simulating the leading edge of a turbine blade. The average NHFR with pulsed and steady film cooling is measured and compared for a single coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. We show that for moderate blowing ratios at blade passing frequencies, steady film flow yields better NHFR. At higher coolant flow rates beyond the optimum steady blowing ratio, however, pulsed film cooling can be advantageous. We present and demonstrate a prediction technique for unsteady blowing at frequencies similar to the blade passing frequency that only requires the knowledge of steady flow behavior. With this important result, it is possible to predict when pulsing would be beneficial or detrimental.

References

References
1.
Sen
,
B.
,
Schmidt
,
D. L.
, and
Bogard
,
D. G.
, 1996, “
Film Cooling With Compound Angle Holes: Heat Transfer
,”
ASME J. Turbomach.
,
118
, pp.
800
806
.
2.
Rutledge
,
J. L.
,
King
,
P. I.
, and
Rivir
,
R.
, 2010, “
Time Averaged Net Heat Flux Reduction for Unsteady Film Cooling
,”
ASME J. Eng. Gas Turbines Power
,
132
,
121901
.
3.
Abhari
,
R. S.
, 1996, “
Impact of Rotor-Stator Interaction on Turbine Blade Film Cooling
,”
ASME J. Turbomach.
,
118
, pp.
123
133
.
4.
Haldeman
,
C. W.
,
Mathison
,
R. M.
,
Dunn
,
M. G.
,
Harral
,
J. W.
, and
Heltland
,
G.
, 2008, “
Aerodynamic and Heat Flux Measurements in a Single-Stage Fully Cooled Turbine—Part II: Experimental Results
,”
ASME J. Turbomach.
,
130
(
2
),
021016
.
5.
Gompertz
,
K.
,
Pluim
,
J.
,
Bons
,
J.
, 2009, “
Separation Control Authority of Vortex Generating Jets in a Low-Pressure Turbine Cascade With Simulated Wakes
,”
47th AIAA Aerospace Sciences Meeting, AIAA Paper No. 2009-377
.
6.
Rutledge
,
J. L.
,
King
,
P. I.
, and
Rivir
,
R.
, 2008, “
CFD Predictions of Pulsed Film Cooling Heat Flux on a Turbine Blade Leading Edge
,”
ASME International Mechanical Engineering Congress and Exposition, ASME Paper No. IMECE2008-67276.
7.
Ekkad
,
S. V.
,
Ou
,
S.
, and
Rivir
,
R. B.
, 2006, “
Effect of Jet Pulsation and Duty Cycle on Film Cooling From a Single Jet on a Leading Edge Model
,”
ASME J. Turbomach.
,
128
, pp.
564
571
.
8.
Rutledge
,
J. L.
, 2009, “
Pulsed Film Cooling on a Turbine Blade Leading Edge
,” Ph.D. dissertation, Department of Aeronautics and Astronautics, Air Force Institute of Technology, Wright-Patterson AFB, OH.
9.
Kays
,
W. M.
and
Crawford
,
M. E.
, 1993,
Convective Heat and Mass Transfer
,
3rd ed.
,
McGraw-Hill
,
New York
.
10.
Mick
,
W. J.
and
Mayle
,
R. E.
, 1988, “
Stagnation Film Cooling and Heat Transfer Including Its Effect Within the Hole Pattern
,”
ASME J. Turbomach.
,
110
, pp.
66
72
.
11.
Kline
,
S. J.
and
McClintock
,
F. A.
, 1953, “
Describing Uncertainties in Single Sample Experiments
,
Mech. Eng.
,
75
, pp.
3
8
.
12.
Rutledge
,
J. L.
,
King
,
P. I.
, and
Rivir
,
R.
, 2009, “
Experimental Flow Visualization of Pulsed Film Cooling on a Turbine Blade Leading Edge
,”
45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, AIAA Paper No. 2009-5104.
13.
Giedt
,
W. H.
, 1949, “
Investigation of Variation of Point Unit Heat-Transfer Coefficient Around a Cylinder Normal to an Air Stream
,”
Trans. ASME
,
71
, p.
375
.
14.
Mayhew
,
J. E.
,
Baugh
,
J. W.
, and
Byerley
,
A. R.
, 2001, “
The Effect of Freestream Turbulence on Film Cooling Heat Transfer Coefficient
,”
ASME Paper No. GT-2002-30173.
15.
Rutledge
,
J. L.
,
King
,
P. I.
, and
Rivir
,
R.
, 2009, “
CFD Predictions of the Frequency Dependence of Pulsed Film Cooling Heat Flux on a Turbine Blade Leading Edge
,”
47th AIAA Aerospace Sciences Meeting, AIAA Paper No. 2009-680.
You do not currently have access to this content.