PNNL

Abstract

Energetic river and tidal flow environments feature complex hydrodynamic conditions. Conventional acoustic Doppler profiling instrumentation typically requires assumptions of flow homogeneity to be made over the spatial scales of the divergent beam separation. This has the effect of removing the spatio-temporal variability from measurements. Velocity variability within these spatial scales is often important in the engineering design and optimisation of submerged installations and devices exposed to such flow, informing the expected dynamic and peak hydrodynamic loads. The research presented outlines the development and testing of a novel flow measurement instrument consisting of multiple spatially-separated single beam acoustic Doppler profilers converging on a remote and dynamically adjustable focal point location. This method increases the spatial resolution at which remote field measurements can be made in the energetic flow environments. Field testing of the instrument was conducted in the tidal channel of Sequim Bay Inlet at the Marine Sciences Lab of the Pacific Northwest National Laboratory, Sequim, WA, USA. Results from the multiple beam configurations, targeting a range of focal point locations, are presented and compared with independent reference measurements made by a co-located, motion-corrected acoustic Doppler velocimeter. To the authors’ knowledge, this is the first publication of flow velocity results from non-intrusive acoustic measurements at an off-axis, focal point location that features 3D positional control.