Standards provide recommendations for best practice when installing current meters to measure fluid flow in closed conduits. A central guideline requires the velocity distribution to be regular and the flow steady. Because of the nature of the short converging intakes typical of low-head hydroturbines, these assumptions may be invalid if current meters are intended to be used to estimate discharge. Usual concerns are (1) the effects of the number of devices, (2) the sampling location and (3) the high turbulence caused by the presence of fish diversion screens. These three effects were examined in the present study by using 3D simulated flow fields in both steady-state and transient modes. In the process of describing an application at an existing hydroturbine intake at Ice Harbor Dam, the present work outlined the methods involved, which combined computational fluid dynamics, laboratory measurements in physical models of the hydroturbine, and current meter performance evaluations in experimental settings. The main conclusions in this specific application were that a steady-state flow field sufficed to determine the adequate number of meters and their location, and that both the transverse velocity and turbulence intensity had a small impact on estimate errors. However, while it may not be possible to extrapolate these findings to other field conditions and measuring devices, the study laid out a path to conduct similar assessments in other applications.

Accurate modeling of the velocity field in the forebay of a hydroelectric power station is important for both power generation and fish passage, and is able to be increasingly well represented by computational fluid dynamics (CFD) simulations. Acoustic Doppler Current Profiler (ADCP) are investigated herein as a method of validating the numerical flow solutions, particularly in observed and calculated regions of non -homogeneous flow velocity. By using a numerical model of an ADCP operating in a velocity field calculated using CFD, the errors due to the spatial variation of the flow velocity are quantified. The numerical model of the ADCP is referred to herein as a Virtual ADCP (VADCP).Two applications of the VADCP are modeled in the numerical analyses presented. Firstly the virtual measurement error of the VADCP is calculated for a single instrument adjacent to the short converging intake of a powerhouse. Secondly, the flow discharge through the forebay is estimated from a transect of VADCP instruments at different distances from the powerhouse. The influence of instrument location and orientation are investigated for both cases.A velocity error of up to 94% of the reference velocity is calculated for a VADCP modeled adjacent to an operating intake and is shown to decrease with distance from the powerhouse. Qualitative agreement is observed between the calculated VADCP velocities and reference velocities by a horizontal offset distance of 18 m upstream of the powerhouse. (C) 2015 Elsevier Ltd. All rights reserved.

AbstractA method for generating controllable two-dimensional velocity fluctuations using two pitching foils was derived theoretically in a previous companion paper. The present work describes the experimental implementation of the method. The experiments are carried out in a re-circulating water channel optimised to provide low turbulence intensity in the incoming flow. Velocities are measured using an acoustic Doppler velocimeter (ADV). The pitching motions of the foils are position-controlled using a closed-loop control system. Two velocity fluctuation patterns are investigated. They consist of a combination of sinusoidal components. Theoretical predictions and experimental measurements are compared in the time and frequency domain. Although some discrepancies are observed, the agreement is generally good and therefore validates the theoretical method for the conditions investigated.

The directionality of the tidal flow throughout the tidal cycle has important implications for tidal energy capture with respect to turbine performance, capacity factor, and structural loading. There has been a tendency to infer that energetic sites possess near bi-directional flows or that there are sufficient sites with near bi-directional flows such that more omni-directional flow tidal currents can be neglected. This technical note investigates the connection between directionality and the incident kinetic energy density of tidal currents in the Northern United Kingdom. It demonstrates a positive correlation between these flow parameters and quantifies this through the analysis of real tidal velocity data.

This paper presents the research currently being carried out on the potential contribution of hydrofoils to generate additional down-force on seabed fastenings in energetic tidal flows.Firstly, the dynamic lift of a hydrofoil subjected to vertical velocity perturbations was analyzed numerically, showing the reduced response to the fluctuation when unsteady aerodynamic theories are introduced. Secondly, an experimental set-up was developed for the deterministic generation of two-dimension velocity perturbations in a recirculating water flume. This will allow the combined effect of vertical and longitudinal velocity fluctuations on the lift force to be measured.