Time-Average Velocity and Turbulence Measurement Using Wireless Bend Sensors in an Open Channel with a Rough Bed

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 beambending 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.

Outer region scaling using the freestream velocity for nonuniform open channel flow over gravel

“…On the other hand, estimation of U ∞ requires only a single velocity measurement at a location where velocity gradients are small and thus errors introduced by improperly estimating the location of maximum velocity is not likely to have significant impact on estimates or the accuracy of predicted velocity distributions. Further, in the nonuniform case, such measurements could be carried out in pools within gravel bed rivers using velocity sensors, such as inexpensive velocity bend sensors (Stewart et al, 2013), in order to provide a longitudinal velocity distribution within a reach. The ability to accurately estimate U ∞ compared to the friction velocity may provide for the improved collapse of the velocity distributions.…”

Proposition of water meter for buildings based on a thin-film resistive sensor: electromechanical and thermal characterizations

“…However, it is possible to verify some studies that demonstrate the applicability of this type of sensor for this purpose. For example, Fan et al [21] employ the sensor to monitor the airflow velocity in real-time, helping to save energy consumption in a wastewater treatment process; Xu et al [22] report a way to monitor water flow in pipelines using a flexible resistive film; Srinivasan, Sen, Kumar and Sabebu [23] use the sensor as a cantilever beam for flow measurement for moderate flow applications; Stewart, Fox and Harnett [24] developed a velocity sensor using the bend sensor for application in streams; Gonçalves, Medeiros, and Barbosa [25] presented a study of the resistive sensor application to measure the flow of water through the comparison between the results of experimental electromechanical characterization with a computer simulation, and these same authors [26] also proposed an adaptation of the valves commonly present in residential hydraulic systems, using a bend sensor, and demonstrated a new methodology for measuring the volume of water consumed in autonomous units.…”