UC Berkeley

The design, calibration, and testing of a borescopic quantitative imaging profiler (BQuIP) system, suitable for the insitu measurement of two components of the instantaneous velocity in high sediment concentration flows, are presented. Unlike planar quantitative imaging techniques, BQuIP has a concentration-dependent field of view, requiring detailed calibration. BQuIP is demonstrated in unidirectional sheet flow in an open channel flume with a narrow-graded sand with median diameter 0.25 mm. Acoustic velocity measurements are made in the suspension region above the BQuIP measured region yielding a continuous measurement of velocity and turbulent stress from the immobile bed to just below the free surface. The temporal history at a point reveals the sheet flow sediment velocities to be highly intermittent, and the spectra reveal a broad range of temporal scales close to −5/3 in slope for the streamwise velocity component. At its core BQuIP is a quantitative imaging technique giving it significant flexibility in terms of both the spatial and temporal analysis parameters (e.g., interrogation subwindow size and Δt, the time between images in a pair to be analyzed), allowing it to have tremendous dynamic range in terms of the velocities that can be measured.