Research Papers

Measurement Uncertainty Analysis in Determining Adiabatic Film Cooling Effectiveness by Using Pressure Sensitive Paint Technique

[+] Author and Article Information
Blake Johnson

Department of Aerospace Engineering,
Iowa State University,
2271 Howe Hall, Room 1200,
Ames, IA 50011-2217

Hui Hu

Fellow ASME
Department of Aerospace Engineering,
Iowa State University,
2271 Howe Hall, Room 1200,
Ames, IA 50011-2217
e-mail: huhui@iastate.edu

1Present address: Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 18, 2015; final manuscript received April 15, 2016; published online June 14, 2016. Assoc. Editor: David G. Bogard.

J. Turbomach 138(12), 121004 (Jun 14, 2016) (11 pages) Paper No: TURBO-15-1180; doi: 10.1115/1.4033506 History: Received August 18, 2015; Revised April 15, 2016

While pressure sensitive paint (PSP) technique has been widely used to measure adiabatic film cooling effectiveness distributions on the surfaces of interest based on a mass transfer analog to traditional thermal-based measurements, very little can be found in literature to provide a comprehensive analysis on the uncertainty levels of the measured film cooling effectiveness distributions derived from PSP measurements. In the present study, a detailed analysis is performed to evaluate the effects of various associated uncertainties in the PSP measurements on the measured film cooling effectiveness distributions over the surfaces of interest. The experimental study is conducted in a low-speed wind tunnel under an isothermal condition. While airflow is used to represent the “hot” mainstream flow, an oxygen-free gas, i.e., carbon dioxide (CO2) gas with a density ratio of DR = 1.5 for the present study, is supplied to simulate the “coolant” stream for the PSP measurements to map the adiabatic film cooling effectiveness distribution over a flat test plate with an array of five cylindrical coolant holes at a span-wise spacing of three diameters center-to-center. A comprehensive analysis was carried out with focus on the measurement uncertainty and process uncertainty for the PSP measurements to determine the film cooling effectiveness distributions over the surface of interest. The final analysis indicates that the total uncertainty in the adiabatic film cooling effectiveness measurements by using the PSP technique depends strongly on the local behavior of the mixing process between the mainstream and coolant flows. The measurement uncertainty is estimated as high as 5% at the near field behind the coolant holes. In the far field away from the coolant holes, the total measurement uncertainty is found to be more uniform throughout the measurement domain and generally lower than those in the near field at about 3%.

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Fig. 1

Schematic layout for PSP calibration setup

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Fig. 2

PSP calibration curves in the range applicable for the film cooling effectiveness measurements

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Fig. 3

Experimental setup for the film cooling measurements by using PSP technique

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Fig. 4

Mean intensity maps of the four ensemble-averaged image intensity maps. Units are in terms of image intensity counts, which is a multiple of electrons freed by photons incident upon the CCD array. (a) Ib, (b) Iref, (c) Iair, (d) Igas.

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Fig. 5

Confidence interval maps of the intensity distributions of the four acquired images. Units are in terms of image intensity counts, which is a multiple of electrons freed by photons incident upon the CCD array. (a) ΔIb, (b) ΔIref (c) ΔIair, (d) ΔIgas.

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Fig. 6

Image intensity ratios and their corresponding uncertainty. (a) I*air, (b) ΔI*air, (c) I*gas, (d) ΔI*gas.

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Fig. 7

Uncertainty propagation through the PSP calibration curve. Bounding curves are determined by the error bars (uncertainty) of the discrete calibration data points.

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Fig. 8

Uncertainty in the PSP pressure measurement; ΔP*/P* is a function of I* with ΔI* as a parameter

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Fig. 9

Measurement uncertainties of normalized pressure measurements. (a) ΔP*air, (b) ΔP*gas, (c) Δ(P*air/P*gas).

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Fig. 10

Measured film cooling effectiveness distribution and measurement uncertainty map. (a) The film cooling effectiveness measurement result under analysis and (b) Measurement uncertainty in the film cooling effectiveness.

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Fig. 11

Sensitivity analysis of the film cooling effectiveness to the pressure ratio. (a) The sensitivity of the film cooling effectiveness to the pressure ratio and (b) The pressure ratio measurement, with line contour indicating the region where DR does not affect uncertainty.

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Fig. 12

Process uncertainty maps made by discrete derivative estimation for the test cases with different bowling ratios. (a) M = 0.60, (b) M = 0.85, and (c) M = 1.00.

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Fig. 13

The total uncertainty in effectiveness Δηtotal, accounting for both process and measurement uncertainty

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Fig. 14

Uncertainty in the laterally averaged film cooling effectiveness




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