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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Assessment of Unsteady Pressure Measurement Uncertainty—Part I: Single Sensor Probe

[+] Author and Article Information
Giulia Dell'Era

Turbomachinery and Propulsion Department,
von Kármán Institute for Fluid Dynamics,
72, Chaussée de Waterloo,
Rhode-Saint-Genèse B-1640, Belgium
e-mail: dellera@vki.ac.be

Mehmet Mersinligil

Turbomachinery and Propulsion Department,
von Kármán Institute for Fluid Dynamics,
72, Chaussée de Waterloo,
Rhode-Saint-Genèse B-1640, Belgium
e-mail: mersinli@vki.ac.be

Jean-François Brouckaert

Turbomachinery and Propulsion Department,
von Kármán Institute for Fluid Dynamics,
72, Chaussée de Waterloo,
Rhode-Saint-Genèse B-1640, Belgium
e-mail: jean-francois.brouckaert@cleansky.eu

1Corresponding author.

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 15, 2015; final manuscript received August 10, 2015; published online October 13, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(4), 041601 (Oct 13, 2015) (11 pages) Paper No: GTP-15-1323; doi: 10.1115/1.4031371 History: Received July 15, 2015; Revised August 10, 2015

With the advancements in miniaturization and temperature capabilities of piezoresistive pressure sensors, pneumatic probes—which are the long established standard for flow-path pressure measurements in gas turbine environments—are being replaced with unsteady pressure probes. Any measured quantity is by definition inherently different from the “true” value, requiring the estimation of the associated errors for determining the validity of the results and establishing respective confidence intervals. In the context of pressure measurements, the calibration uncertainty values, which differ from measurement uncertainties, are typically provided. Even then, the lack of a standard methodology is evident as uncertainties are often reported without appropriate confidence intervals. Moreover, no time-resolved measurement uncertainty analysis has come to the attention of the authors. The objective of this paper is to present a standard method for the estimation of the uncertainties related to measurements performed using single sensor unsteady pressure probes, with the help of measurements obtained in a one and a half stage low pressure (LP) high speed axial compressor test rig as an example. The methodology presented is also valid for similar applications involving the use of steady or unsteady sensors and instruments. The static calibration uncertainty, steady measurement uncertainties, and unsteady measurement uncertainties based on phase-locked average (PLA) and ensemble average are presented in this contribution. Depending on the number of points used for the averaging, different values for uncertainty have been observed, underlining the importance of having greater number of samples. For unsteady flows, higher uncertainties have been observed at regions of higher unsteadiness such as tip leakage vortices, hub corner vortices, and blade wakes. Unfortunately, the state of the art in single sensor miniature unsteady pressure probes is comparable to multihole pneumatic probes in size, preventing the use of multihole unsteady probes in turbomachinery environments. However, the angular calibration properties of a single sensor probe obtained via an aerodynamic calibration may further be exploited as if a three-hole directional probe is employed, yielding corrected total pressure, unsteady yaw angle, static pressure, and Mach number distributions based on the PLAs with the expense of losing the time-correlation between the virtual ports. The aerodynamic calibration and derivation process are presented together with the assessment of the uncertainties associated to these derived quantities by the authors in Dell'Era et al. (2016, “Assessment of Unsteady Pressure Measurement Uncertainty—Part II: Virtual Three Hole Probe,” ASME J. Eng. Gas Turbines Power, 138(4), p. 041602). In the virtual three-hole mode, similar to that of a single sensor probe, higher uncertainty values are observed at regions of higher unsteadiness.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

AP1-FP3 fast response total pressure probe head

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Fig. 2

Active compensation amplifier circuit diagram

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Fig. 3

VKI-R4 compressor rig test section

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Fig. 4

Test cross section of the VKI-R4 compressor rig

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Fig. 5

Student's t distribution for 95% confidence interval with respect to degrees-of-freedom

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Fig. 6

Temperature (left) and pressure (right) calibration surface fits–dots indicating actual calibration points

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Fig. 7

Time-averaged pressure distribution along radial traverse. Error bars represent calculated uncertainty values for 95% confidence interval.

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Fig. 8

Pressure data used (blue) and the calculated value of PLA (black) for one class

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Fig. 9

PLA map (left) and RMS of the PLA (right) of the flowfield presented over two blade passages

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Fig. 10

Ensemble average map (left) and RMS of the ensemble average (right) of the flow-field presented for the first two blade passages

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Fig. 11

Skewness (left) and kurtosis (right) maps calculated using PLA values presented over two blade passages

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Fig. 12

Histogram of data acquired at midspan

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Fig. 13

Normal probability plot of data acquired at midspan

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Fig. 14

Histogram of example PLA classes for data acquired at midspan (left) and at tip region (right)

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Fig. 15

Normal probability plot of example PLA classes for data acquired at midspan (left) and at tip region (right)

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Fig. 16

PRMS (left) and expanded uncertainty (right) maps (left) of the PLA presented over two blade passages

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Fig. 17

PRMS (left) and expanded uncertainty (right) maps (left) of the ensemble average presented for the first two blade passages

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