The importance of flow and turbulence characteristics for hydrokinetic energy development on the Tanana River at Nenana, Alaska

Abstract

The site selection for the installation of hydrokinetic devices along a river reach is an issue of fundamental importance. While it is acknowledged that multiple factors such as accessibility, navigation, safety, and hydraulics, among many others, must be considered in the final decision, this article focuses on the influence of river morphology on turbulence flow parameters. Specifically, continuous high-resolution velocity measurements from a hydrokinetic resource assessment on the Tanana River near Nenana in the interior of Alaska are analysed to estimate, kinetic energy (KE), turbulent kinetic energy (TKE) as well as KE partition at particular locations. To accomplish these tasks, two different methods used to rotate the coordinate systems into the main flow direction are correlated and compared in order to extract the turbulent parameters from the main flow. The coordinate system methods include the streamline coordinate rotation and the extraction of statistical fluctuations from the average flow. The streamline coordinate rotation method is chosen to extract the TKE in temporal series. The calculated TKE was up to 30 per cent of the total flow KE in measurements located in pools and dissipated downstream, beyond the highly turbulent locations of bathymetric depressions and river bends. The overall KE increased over a bed free of major macro-obstacles and reduced depth, where the TKE fraction accounted for only 2 per cent of the total KE. The visualizations of the KE and TKE are compared with the river morphology, leading to identification of helical flow, flow separation, and turbulent flow structures along the river bend and in pools to help the decision-making process in hydrokinetic planning.