Time-Average Velocity and Turbulence Measurement Using Wireless Bend Sensors in an Open Channel with a Rough Bed
Publication: Journal of Hydraulic Engineering
Volume 139, Issue 7
Abstract
This paper is motivated by the need to develop low cost, wireless velocity sensors for hydraulic research and application in streams. A velocity bend sensor (VBS) is a flexible plastic polyimide substrate sheet with an electronic resistor connected to a voltage divider. Drag of a moving fluid bends the sensor, changes the electronic resistance, and produces a voltage drop that can be related to the time-averaged freestream velocity of the fluid. VBSs were tested in a recirculating hydraulic flume with a gravel bed. The VBSs show transition from rigid to elastic bending with increasing freestream velocity, which can be described using dimensionless fluid and beam-bending properties. The relationship between stream velocity and voltage drop across the circuit is nonlinear. A semitheoretical approach to estimate time-averaged streamwise velocity from the voltage drop based on fluid drag, elastic member bending, and circuit principles is applied and shows good agreement with experimentally derived calibration curves. The triple decomposition theorem and spectral analysis are performed on VBS and acoustic Doppler velocimeter (ADV) time series. Results show that the VBS captures low-frequency characteristics of macroturblence present within the turbulent open channel flow but is unable to measure smaller-scale characteristics of eddy shedding for these hydraulic conditions. Turbulent intensity calculated using VBS data is 12% of that from the ADV attributed to the lack of detection of shedding-sized eddies. But, the linear fit between turbulent intensity from the VBS and ADV suggests that the VBS can be used as a proxy for more detailed turbulent measurements when applied in streams.
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Acknowledgments
The authors would like to thank Alex Thompson, Bill Ford, Ben Zinninger, Thomas Lawrence, and Cory Franklin for building the VBS and for their help with data collection. They thank Prof. Sean Bailey, Mechanical Engineering at the University of Kentucky and Mark Miller for use of, and assistance with, the water tunnel. The authors acknowledge support from National Science Foundation Award No. 0918856. They thank two anonymous reviewers and the associate editor, whose comments helped improve the quality of this paper.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 139 • Issue 7 • July 2013
Pages: 696 - 706
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Mar 12, 2012
Accepted: Dec 19, 2012
Published online: Dec 21, 2012
Published in print: Jul 1, 2013
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