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

A Study of Bulk Modulus, Entrained Air, and Dynamic Pressure Measurements in Liquids

[+] Author and Article Information
Adam M. Hurst

Kulite® Semiconductor Products, Inc.,
One Willow Tree Road,
Leonia, NJ 07605
e-mail: adamh@kulite.com

Joe VanDeWeert

Kulite® Semiconductor Products, Inc.,
One Willow Tree Road,
Leonia, NJ 07605

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 March 22, 2016; final manuscript received March 23, 2016; published online April 26, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(10), 101601 (Apr 26, 2016) (9 pages) Paper No: GTP-16-1109; doi: 10.1115/1.4033215 History: Received March 22, 2016; Revised March 23, 2016

Accurate static and dynamic pressure measurements in liquids, such as fuel, oil, and hydraulic fluid, are critical to the control and health monitoring of turbomachinery and aerospace systems. This work presents a theoretical and experimental study of the frequency response of pressure transducers and pressure measurement systems in liquid media. First, we theoretically predict the frequency response of pressure transducers based upon a lumped-parameter model. We then present a liquid-based dynamic pressure calibration test apparatus that validates this model by performing several critical measurements. This system first uses a vibrating liquid column to dynamically calibrate and experimentally determine the frequency response of a test pressure transducer, measurement system or geometry. Second, this calibration system experimentally extracts the bulk modulus of the fluid and the percent of entrained and/or dissolved air by volume. Bulk modulus is determined by measuring the speed of sound within the liquid and through static pressure loading while measuring the deflection of the liquid column. Bulk modulus and the entrained/dissolved gas content within the liquid greatly impact the observed frequency response of a pressure transducer or geometry. Gases, such as air, mixed or dissolved into a fluid can add substantial damping to the dynamic response of the fluid measurement system, which makes measurement of the bulk modulus and entrained and/or dissolved air critical for accurate measurement of the frequency response of a system when operating with a liquid media. All experimental results are compared to theoretical predictions.

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Figures

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Fig. 1

Typical tube and volume cavities construction internal to a pressure transducer for liquid media operation

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Fig. 2

IFAS model of theoretical bulk modulus versus pressure for Dow Corning 510 50 cSt fluid with an assumed accepted bulk modulus of 0.75 GPa

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Fig. 3

Lumped-parameter model of frequency response of tube-volume cavity geometry

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Fig. 4

Piezoelectric-driven vibrating liquid column, dynamic pressure calibration apparatus

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Fig. 5

Top view of piezoelectric-driven vibrating liquid column dynamic pressure calibration apparatus

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Fig. 6

Validation of flat frequency response of vibrating liquid column test platform

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Fig. 7

(Top plot) Pressure versus time generated by piezoelectric-driven vibrating liquid column. (Bottom plot) Peak-to-peak pressure dynamic pressure as a function of frequency.

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Fig. 8

Measurement of bulk modulus as well as entrained and dissolved air by static loading of liquid column using piezoelectric actuator

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Fig. 9

Bulk modulus versus pressure, comparison of experimental data to theoretical predictions (IFAS model)

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Fig. 10

Comparison of theoretical IFAS model and experimental results from static loading of liquid column

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Fig. 11

Transfer function comparing the reference transducers 1 and 2, at the top and the base of the cylinder. Time delay accurately measured.

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Fig. 12

(a) Pressure measurements versus time. (b) Strain measurement and resulting displacement of the piezoelectric actuator. (c) Strain measurement and resulting deflection of the piston.

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Fig. 13

Theoretical and experimental frequency response of sample tube-volume cavity geometry with Dow Corning 510 fluid at various levels of entrained air

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