Physical modelling of tidal turbines and acoustic imaging of turbidity currents in the Congo submarine canyon
Power output from Tidal Stream Turbines (TST) is more stable and predictable than wind turbines but the take-up of the technology remains slow with the impact on the ocean and sea-poorly understood. To gain a better understanding of the impacts on flow and sediment transport, two model horizontal axis TSTs were deployed in the Total Environment Simulator laboratory flume at the University of Hull. A two-camera, submersible Particle Image Velocimetry (PIV) system was used to measure the detailed 3D fluid flow structure and quantify the bed shear stress downstream from the scaled TST device. Results are presented that show the flow structure and the effect of the distance between the rotor axis and the bed surface on the distribution of flow and bed shear stress.
Seafloor hugging flows, called turbidity currents, transport prodigious volumes of sediment to form the largest sediment accumulations on Earth. Individual currents transport similar volumes of sediment as the largest river systems on the planet. Understanding what controls their duration and basic structure is important because these flows can damage expensive and strategically important seafloor infrastructure severely, such as oil and gas pipelines and telecommunication cables that now carry the majority of global data traffic. Their sediment deposits host numerous petroleum reservoirs, and they play a globally important role in organic carbon burial and supply of nutrients to deep-sea ecosystems. This study is based on the first detailed (sub-minute) acoustic velocity, turbulence and sediment concentration data from turbidity currents in the deep ocean. Flows of up to 6 to 10 day’s duration were observed in the Congo Canyon and the aim of the work at the University of Hull is to understand the basic suspended sediment structure of these turbidity currents through the application of the extensive theory developed for acoustic inversions of suspended sediment backscatter.