The effects of jet flow-rate modulation were investigated in the case of a 35 deg inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records, and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.

References

References
1.
Ligrani
,
P. M.
,
Gong
,
R.
,
Cuthrell
,
J. M.
, and
Lee
,
J. S.
,
1996
, “
Bulk Flow Pulsations and Film Cooling-I. Injectant Behavior
,”
Int. J. Heat Mass Transfer
,
39
(
11
), pp.
2271
2282
.10.1016/0017-9310(95)00286-3
2.
Womack
,
K. M.
,
Volino
,
R. J.
, and
Schultz
,
M. P.
,
2008
, “
Combined Effects of Wakes and Jet Pulsing on Film Cooling
,”
J. Turbomach.
,
130
(
4
), p.
041010
.10.1115/1.2812335
3.
Ou
,
S.
,
Han
,
J.-C.
,
Mehendale
,
A. B.
, and
Lee
,
C. P.
,
1994
, “
Unsteady Wake Over a Linear Turbine Blade Cascade With Air and Co2 Film Injection: Part I—Effect on Heat Transfer Coefficients
,”
J. Turbomach.
,
116
(
4
), pp.
721
729
.10.1115/1.2929465
4.
Ekkad
,
S.
,
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
,”
J. Turbomach.
,
128
, pp.
564
571
.10.1115/1.2185122
5.
Coulthard
,
S. M.
,
Volino
,
R. J.
, and
Flack
,
K. A.
,
2007
, “
Effect of Jet Pulsing on Film Cooling-Part I: Effectiveness and Flow-Field Temperature Results
,”
J. Turbomach.
,
129
(
2
), pp.
232
246
.10.1115/1.2437231
6.
Bidan
,
G.
,
Vezier
,
C.
, and
Niktopoulos
,
D. E.
,
2011
, “
Study of Steady and Modulated Inclined Film Cooling Jets Using Proper Orthogonal Decomposition — Part I: Unforced Jets
,”
ASME TurboExpo
,
Vancouver
,
Canada
.
7.
Bidan
,
G.
, and
Nikitopoulos
,
D. E.
,
2011
, “
Fundamental Study of Modulated Transverse Jets From a Film-Cooling Perspective
,”
AIAA J.
,
49
(
7
), pp.
1498
1510
.10.2514/1.J050903
8.
Nikitopoulos
,
D. E.
,
Oertling
,
J.
,
Acharya
,
S.
, and
Muldoon
,
F.
,
2006
, “
On Active Control of Film-Cooling Flows
,”
ASME Turbo Expo
,
Barcelona
,
Spain
, pp.
61
69
.
9.
Ou
,
S.
, and
Rivir
,
R. B.
,
2006
, “
Shaped-Hole Film Cooling With Pulsed Secondary Flow
,”
ASME Turbo Expo
,
Barcelona
,
Spain
, pp.
259
269
.
10.
Johari
,
H.
,
Pacheco-Tougas
,
M.
, and
Hermanson
,
J. C.
,
1999
, “
Penetration and Mixing of Fully Modulated Turbulent Jets in Crossflow
,”
AIAA J.
,
37
(
7
), pp.
842
850
.10.2514/2.7532
11.
Vernet
,
R.
,
Thomas
,
L.
, and
David
,
L.
,
2009
, “
Analysis and Reconstruction of a Pulsed Jet in Crossflow by Multi-Plane Snapshot Pod
,”
Exp. Fluids
,
47
(
4
), pp.
707
720
.10.1007/s00348-009-0730-6
12.
Holmes
,
P.
,
Lumley
,
J. L.
, and
Berkooz
,
G.
,
1996
,
Turbulence, Coherent Structures, Dynamical Systems and Symmetry
,
Cambridge University Press
,
Cambridge, UK
.
You do not currently have access to this content.