NASA Technical Reports Server (NTRS) 20160014559: Temperature Mapping of Air Film-Cooled Thermal Barrier Coated Surfaces Using Cr-Doped GdAlO3 Phosphor Thermography

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by  NASA Technical Reports Server (NTRS)

National Aeronautics and Space Administration
Temperature Mapping of Air Film-Cooled Thermal Barrier Coated
Surfaces Using Cr-Doped GdAlO Phosphor Thermography
3
Jeffrey I. Eldridge, Vikram Shyam, Adam C. Wroblewski, and Dongming Zhu
NASA Glenn Research Center, Cleveland, OH
Michael D. Cuy
Vantage Partners, Cleveland, OH
Douglas E. Wolfe
Penn State University, University Park, PA
40th International Conference on Advanced Ceramics & Composites
Daytona Beach, FL
January 25, 2016
Motivation for Evaluating Combined TBC + Air-Film Cooling
• TBC and air film cooling effectiveness usually studied separately.
• TBC and air film cooling contributions to cooling effectiveness are
interdependent and are not simply additive.
• Combined cooling effectiveness must be measured to achieve optimum
balance between TBC thermal protection and air film cooling.
Heat Transfer Through TBC
TBC-centric view
Mainstream Hot Gas Flow
q = h (T -T )
T conv mainstream surface
mainstream
d TBC
TBC
T
TBC
dT k
Heat flux across TBC: qk  TBC T Fixed q drives heat
TBC TBC
dx d
transport.
TBC
1 d
Thermal protection: T T q[  TBC ]
mainstream metal
h k
conv TBC
For d /k >> 1/h , thermal protection linearly increases with d /k
TBC TBC conv TBC TBC
Heat Transfer Through Turbine Blade/Vane
overall heat transfer view
Mainstream Gas Flow
T
mainstream
T
T
air film
surfaceconvection
d TBC T
TBC TBC
d
metal
metal T
metal
T
T backsideconvection
coolant gas
Total heat flux: qU[T T ]UT
mainstream coolant total
1 1 d d 1
  TBC  metal 
Overall heat transfer coefficient:
U h k k h
conv TBC metal backside
Increasing d &
1 d TBC
 TBC decreasing k will
TBC
T T h k have diminishing
Cooling effectiveness:  mainstream metal  conv TBC
T 1 d d 1 returns, especially with
(fraction of T that total  TBC  metal  air film cooling.
total
h k k h
occurs above metal surface) conv TBC metal backside
TBC & Air-Film Contributions to Cooling Effectiveness
TBC contribution: Air film cooling contribution:
d 1
TBC
k heff
  TBC   conv
TBC 1 d d 1 airfilm 1 d d 1
 TBC  metal   TBC  metal 
heff k k h heff k k h
conv TBC metal backside conv TBC metal backside
• Air film cooling greatly • TBC reduces 
airfilm
reduces effective h and • Putting insulator between air
conv
therefore greatly reduces  film and metal decreases
TBC
• Air film cooling greatly effectiveness of air film cooling.
reduces q and therefore T • Air film cooling carries
TBC
• TBC does not carry significant significant penalty for engine
penalty for engine efficiency. efficiency.
•  >  ,  (TBC, air film cooling always beneficial)
overall TBC airfilm
• But returns can be diminishing.
• TBC is better for reducing air film cooling requirements (increasing engine
efficiency) than increasing temperature capability of air film cooled component.
• Experimental measurements of combined TBC + air film cooling effectiveness
are needed to evaluate TBC/air-film-cooling tradeoffs.
Objectives
• Experimentally map (2D) cooling effectiveness of air film cooling of
TBC-coated surfaces.
– Cooling effectiveness at the TBC surface (to be presented today)
– Cooling effectiveness at the metal surface (future)
• Examine changes in cooling effectiveness as a function of:
– Mainstream hot gas temperature
– Blowing ratio (cooling air flow)
• Examine interplay between air film cooling, backside impingement
cooling, and through-hole convective cooling for TBC-coated substrate.
Approach
• Perform measurements in NASA GRC Mach 0.3 burner rig.
– Vary flame temperature and blowing ratio.
• Perform measurements on TBC-coated superalloy plate.
– 200 µm EB-PVD YSZ on Hastelloy X plate with MCrAlY bond coat
• Use scaled-up cooling hole geometry.
• Perform 2D temperature mapping using Cr-doped GdAlO (Cr:GAP)
3
phosphor thermometry.
– GdAlO exhibits orthorhombic perovskite crystal structure: gadolinium aluminum perovskite
3
(GAP).
– Ultrabright Cr:GAP luminescence emission enable surface temperature mapping using
luminescence lifetime imaging by simply broadening the excitation laser beam to cover the
region of interest.

– Unbiased by emissivity changes and reflected radiation.

– Can be utilized for subsurface temperature mapping (future).

– Only applicable to steady state temperatures.
• Convert temperature maps into cooling effectiveness maps.
Cooling Hole Plate Geometry
6.35 mm 30° Side view
3.175 mm
Top view
76.4 mm
9.525 mm
50.8 mm
152.4 mm
30 m Cr:GAP
Coating layers EB-PVD
200 m
YSZ
125 m
MCrAlY
6.35 mm Hastelloy X
Cooling Effectiveness Measurements
Conventional Air Film Burner Rig Air Film
Cooling Effectiveness Cooling Effectiveness
Test Test
Ducted uniform mainstream flow Diverted unducted divergent
mainstream flow
• Uniform mainstream flow (velocity &
temperature)
37°
• Typical surface temperatures: < 100°C
• Divergent mainstream flow
• Pure air film cooling
• Typical temperatures: 600-1100°C
• No heat flux (insulating substrate)
• Air film + backside impingement +
• No backside impingement cooling
• Measure adiabatic air film cooling thru-hole convection
effectiveness,  • Measure overall surface cooling
T Tadiabatic
effectiveness, ’
 mainstream surface
T T T T
mainstream coolant exit  uncooled cooled
•  is a fundamental characterization of T T
uncooled coolant enter
air film cooling effectiveness • ’ is a nonfundamental but realistic
• Measure  as a function of blowing characterization of combined surface
ratio, M  v cooling effects
M  coolant coolant
 v • Measure  as a function of M
mainstream mainstream  v
M coolant coolant
 vmax
mainstream mainstream
Demonstrating Temperature Measurement Capability
Time-Averaged Luminescence Emission from Cr(0.2%):GAP Puck
Temperature Dependence
20C
532 nm excitation
90C
284C
)
s
t 385C
i
n
u 484C
.
b
r 587C
a
(
y 686C
t
i
s 780C
n
e
880C
t
n
I 977C
bandpass
550 600 650 700 750 800 850
Wavelength (nm)