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

An Experimental and Theoretical Investigation of Wave Propagation in Teflon and Nylon Tubing With Methods to Prevent Aliasing in Pressure Scanners

[+] Author and Article Information
Adam M. Hurst

e-mail: adamh@kulite.com

Joe VanDeWeert

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

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 27, 2013; final manuscript received July 3, 2013; published online September 6, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(10), 101602 (Sep 06, 2013) (7 pages) Paper No: GTP-13-1196; doi: 10.1115/1.4025004 History: Received June 27, 2013; Revised July 03, 2013

Accurate static and dynamic pressure measurements provide the feedback needed to advance gas turbine efficiency and reliability as well as improve aircraft design and flight control. During turbine testing and aircraft flight testing, flush mounting pressure transducers at the desired pressure measurement location is not always feasible and recess mounting with connective tubing is often used as an alternative. Resonances in the connective tubing can result in aliasing within pressure scanners even within a narrow bandwidth and especially when higher frequency content dc to ∼125 Hz is desired. We present experimental results that investigate tube resonances and attenuation in 1.35 mm inner diameter (I.D.) (used on 0.063 in. tubulations) and 2.69 mm I.D. (used on 0.125 in. tubulations) Teflon and Nylon tubing at various lengths. We utilize a novel dynamic pressure generator, capable of creating large changes in air pressure (<1 psi to 10 psi, <6.8 kPa to 68.9 kPa), to determine the frequency response of such tubing from ∼1 Hz to 2800 Hz. We further compare these experimental results to established analytical models for propagation of pressure disturbances in narrow tubes. While significant theoretical and experimental work relating to the frequency response of connective tubing or transmission lines has been published, there is limited literature presenting experimental frequency response data with air as the media in elastic tubing. In addition, little progress has been made in addressing the issue of tubing-related aliasing within pressure scanners, as the low sampling rate in scanners often makes postprocessing antialiasing filters ineffective.

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References

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Figures

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Fig. 1

Example of pressure signal amplification and phase shift from a 1 m long pressure transmission tube (data presented above was taken using the dynamic pressure generator presented herein)

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Fig. 2

Experimental demonstration of aliasing when making pressure measurements at the end of a 1 m, 2.69 mm diameter Teflon pressure transmission line (tube) (data presented above was taken using the dynamic pressure generator presented herein)

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Fig. 3

Schematic of spinning valve, variable mass based dynamic pressure generator

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Fig. 4

Power spectral density plot of flush mounted reference transducer and the response from the transducer at the end of the 1 m long, 2.69 mm I.D. Teflon tube

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Fig. 5

Comparison of past modeling techniques with experimental results for a 2 m, 2.69 mm diameter Teflon tube

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Fig. 6

Tube with pressure sensor at terminating end

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Fig. 7

Model and measured data for 2.69 mm diameter Teflon tubing at lengths of 1, 2, and 5 m

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Fig. 8

Model and measured data for 1.35 mm diameter Teflon tubing at lengths of 1, 2, and 5 m

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Fig. 9

Model and measured data for 1.45 mm diameter Nylon tubing at lengths of 1, 2, and 5 m

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Fig. 10

Comparison of past modeling techniques with new model for 2.69 mm diameter Teflon tubing 2 m long

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Fig. 11

Model of data taken with and without 3 m of 1.35 mm tubing

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