Shaped film cooling holes are used as a cooling technology in gas turbines to reduce metal temperatures and improve durability, and they generally consist of a small metering section connected to a diffuser that expands in one or more directions. The area ratio (AR) of these holes is defined as the area at the exit of the diffuser, divided by the area at the metering section. A larger AR increases the diffusion of the coolant momentum, leading to lower average momentum of the coolant jet at the exit of the hole and generally better cooling performance. Cooling holes with larger ARs are also more tolerant of high blowing ratio conditions, and the increased coolant diffusion typically better prevents jet lift-off from occurring. Higher ARs have traditionally been accomplished by increasing the expansion angle of the diffuser while keeping the overall length of the hole constant. The present study maintains the diffuser expansion angles and instead increases the length of the diffuser, which results in longer holes. Various ARs have been examined for two shaped holes: one with forward and lateral expansion angles of 7 deg (7-7-7 hole) and one with forward and lateral expansion angles of 12 deg (12-12-12 hole). Each hole shape was tested at numerous blowing ratios to capture trends across various flow rates. Adiabatic effectiveness measurements indicate that for the baseline 7-7-7 hole, a larger AR provides higher effectiveness, especially at higher blowing ratios. Measurements also indicate that for the 12-12-12 hole, a larger AR performs better at high blowing ratios but the hole experiences ingestion at low blowing ratios. Steady Reynolds-averaged Navier–Stokes simulations did not accurately predict the levels of adiabatic effectiveness, but did predict the trend of improving effectiveness with increasing AR for both hole shapes. Flowfield measurements with particle image velocimetry (PIV) were also performed at one downstream plane for a low and high AR case, and the results indicate an expected decrease in jet velocity due to a larger diffuser.

References

References
1.
Bunker
,
R. S.
,
2005
, “
A Review of Shaped Hole Turbine Film-Cooling Technology
,”
ASME J. Heat Transfer
,
127
(
4
), p.
441
.
2.
Schroeder
,
R. P.
, and
Thole
,
K. A.
,
2014
, “Adiabatic Effectiveness Measurements for a Baseline Shaped Film Cooling Hole,”
ASME
Paper No. GT2014-25992.
3.
Goldstein
,
R. J.
,
Eckert
,
E. R. G.
, and
Burggraf, F.
,
1974
, “
Effects of Hole Geometry and Density on Three-Dimensional Film Cooling
,”
J. Heat Mass Transfer
,
17
(5), pp. 595–607.
4.
Thole
,
K.
,
Gritsch
,
M.
,
Schulz
,
A.
, and
Wittig
,
S.
,
1998
, “
Flowfield Measurements for Film-Cooling Holes With Expanded Exits
,”
ASME J. Turbomach.
,
120
(
2
), pp.
327
336
.
5.
Peterson
,
S.
, and
Plesniak
,
M.
,
2002
, “
Short-Hole Jet-in-Crossflow Velocity Field and Its Relationship to Film-Cooling Performance
,”
Exp. Fluids
,
33
(
6
), pp.
889
898
.
6.
Haven
,
B. A.
, and
Kurosaka
,
M.
,
1997
, “
Kidney and Anti-Kidney Vortices in Crossflow Jets
,”
J. Fluid Mech.
,
352
, pp. 27–64.
7.
Gritsch
,
M.
,
Colban
,
W.
,
Schär
,
H.
, and
Döbbeling
,
K.
,
2005
, “
Effect of Hole Geometry on the Thermal Performance of Fan-Shaped Film Cooling Holes
,”
ASME J. Turbomach.
,
127
(
4
), pp.
718
725
.
8.
Saumweber
,
C.
, and
Schulz
,
A.
,
2012
, “
Effect of Geometry Variations on the Cooling Performance of Fan-Shaped Cooling Holes
,”
ASME J. Turbomach.
,
134
(
6
), p.
061008
.
9.
Colban
,
W. F.
,
Thole
,
K. A.
, and
Bogard
,
D.
,
2011
, “
A Film-Cooling Correlation for Shaped Holes on a Flat-Plate Surface
,”
ASME J. Turbomach.
,
133
(
1
), p.
011002
.
10.
Kohli
,
A.
, and
Bogard
,
D. G.
,
1999
, “Effects of Hole Shape on Film Cooling With Large Angle Injection,”
ASME
Paper No. 99-GT-165.
11.
Kohli
,
A.
, and
Thole
,
K. A.
,
1998
, “Entrance Effects on Diffused Film-Cooling Holes,”
ASME
Paper No. 98-GT-402.
12.
McDonald
,
A. T.
, and
Fox
,
R. W.
,
1966
, “
An Experimental Investigation of Incompressible Flow in Conical Diffusers
,”
Int. J. Mech. Sci.
,
8
(2), pp.
125
130
.
13.
Klein
,
A.
,
1981
, “
Review: Effects of Inlet Conditions on Conical-Diffuser Performance
,”
ASME J. Fluids Eng.
,
103
(2), pp. 250–257.
14.
Wolf
,
S.
, and
Johnston
,
J. P.
,
1969
, “
Effects of Nonuniform Inlet Velocity Profiles on Flow Regimes and Performance in Two-Dimensional Diffusers
,”
J. Basic Eng.
,
91
(
3
), pp.
462
474
.
15.
Leylek
,
J. H.
, and
Zerkle
,
R. D.
,
1994
, “
Discrete-Jet Film Cooling: A Comparison of Computational Results With Experiments
,”
ASME J. Turbomach.
,
116
(3), pp. 358–368.
16.
Thole
,
K. A.
,
Gritsch
,
M.
,
Schulz
,
A.
, and
Wittig
,
S.
,
1997
, “
Effect of a Crossflow at the Entrance to a Film-Cooling Hole
,”
ASME J. Fluids Eng.
,
119
(
3
), pp.
533
540
.
17.
Saumweber
,
C.
, and
Schulz
,
A.
,
2008
, “Comparison the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes With Special Emphasis on the Effect of Internal Coolant Cross-Flow,”
ASME
Paper No. GT2008-51036.
18.
Coletti
,
F.
,
Elkins
,
C. J.
, and
Eaton
,
J. K.
,
2013
, “
An Inclined Jet in Crossflow Under the Effect of Streamwise Pressure Gradients
,”
Exp. Fluids
,
54
(
9
), p. 1589.
19.
Haydt
,
S.
,
Lynch
,
S.
, and
Lewis
,
S.
,
2017
, “
The Effect of a Meter-Diffuser Offset on Shaped Film Cooling Hole Adiabatic Effectiveness
,”
ASME J. Turbomach.
,
139
(
9
), p.
091012
.
20.
Eberly
,
M. K.
, and
Thole
,
K. A.
,
2013
, “
Time-Resolved Film-Cooling Flows at High and Low Density Ratios
,”
ASME J. Turbomach.
,
136
(
6
), p.
061003
.
21.
Figliola
,
R. S.
, and
Beasley
,
D. E.
,
2006
,
Theory and Design for Mechanical Measurements
,
Wiley
,
Hoboken, NJ
.
22.
Schroeder
,
R. P.
, and
Thole
,
K. A.
,
2016
, “
Effect of High Freestream Turbulence on Flowfields of Shaped Film Cooling Holes
,”
ASME J. Turbomach.
,
138
(9), p.
091001
.
You do not currently have access to this content.