Volumetric Flow Rate Measurement via Surface Imaging Techniques

Abstract:

Volumetric discharge measurements in natural streams are an important metric in a myriad of engineering fields. The most widely-used method discretizes the cross-section of the channel into vertical strips where each strip has a point velocity that is then multiplied by its respective area; the sum of each strip measurement gives the total volumetric discharge. However, in situ measurements can be intrusive to the flow, affecting the accuracy of the results obtained. Surface particle image velocimetry (SPIV) is a powerful tool for visualizing the dynamics of the free surface of a flow. Its strength lies in its unobtrusive nature, which allows for more reliable and cost-effective data collection. Further, it provides spatio-temporally resolved measurements across large regions of space and thus greater insight about the spatially varying dynamics across a stream than can be provided by point measurements.

The purpose of our research is to validate an experimental method developed by Johnson and Cowen (2016) aimed at measuring volumetric discharge in an open channel flume using SPIV techniques combined with turbulent boundary layer analysis to infer the bathymetry and volumetric discharge of the flume. The tests were carried out in an outdoor recirculating concrete flume. Water entered the rectangular channel from two outlets located in the channel head. Wood chips and biodegradable glitter were used as seeding and were manually released upstream of the measurement region, illuminated by natural sunlight . Surface flow dynamics were captured by a downward-facing camera mounted above the streamwise centerline of the flume. A Nortek Vectrino acoustic Doppler velocimeter (ADV) was used to measure single-point, instantaneous velocities. ADV measurements were collected at the flume centerline at the downstream edge of the PIV measurement region to construct velocity profiles. This study aims to obtain the bathymetry and volumetric discharge of an open channel using turbulent metrics from remote measurements, mitigating interference in data acquisition from more intrusive techniques.