Performance and Wake Characterization of a Model Hydrokinetic Turbine: The Reference Model 1 (RM1) Dual Rotor Tidal Energy Converter

Abstract

The mechanical power and wake flow field of a 1:40 scale model of the US Department of Energy’s Reference Model 1 (RM1) dual rotor tidal energy converter are characterized in an open-channel flume to evaluate power performance and wake flow recovery. The NACA-63(4)-24 hydrofoil profile in the original RM1 design is replaced with a NACA-4415 profile to minimize the Reynolds dependency of lift and drag characteristics at the test chord Reynolds number. Precise blade angular position and torque measurements were synchronized with three acoustic Doppler velocimeters (ADV) aligned with each rotor centerline and the midpoint between the rotor axes. Flow conditions for each case were controlled to maintain a hub height velocity, uhub= 1.04 ms−1, a flow Reynolds number, ReD= 4.4 × 105, and a blade chord length Reynolds number, Rec= 3.1 × 105. Performance was measured for a range of tip-speed ratios by varying rotor angular velocity. Peak power coefficients, CP= 0.48 (right rotor) and CP= 0.43 (left rotor), were observed at a tip speed ratio, λ= 5.1. Vertical velocity profiles collected in the wake of each rotor between 1 and 10 rotor diameters are used to estimate the turbulent flow recovery in the wake, as well as the interaction of the counter-rotating rotor wakes. The observed performance characteristics of the dual rotor configuration in the present study are found to be similar to those for single rotor investigations in other studies. Similarities between dual and single rotor far-wake characteristics are also observed.

A Review of Modeling Approaches for Understanding and Monitoring the Environmental Effects of Marine Renewable Energy

“…By harvesting energy, operating ME devices may modify the direction and magnitude of currents [31], water surface elevations (WSEs) [32,33], turbulence [34,35], and wave height and direction [36] near and downstream of the devices. The nature of the changes varies by device and placement within the environment.…”

A review of commercial numerical modelling approaches for axial hydrokinetic turbine wake analysis in channel flow

“…A more informed understanding of these complex flow effects enables an improvement of the design and installation of HK devices. This also provides more clarity on site selection [16], proper array spacing [17] and other challenges surrounding operations and maintenance.…”

“…Numerical/computational modelling techniques may be used as a tool to assess possible concerns, problem areas and unforeseen hydrodynamic effects in the HK turbine flow field. Laboratory tests are often expensive and prove difficult to accurately scale the flow environment [16]. Inland hydrokinetic turbines or turbine arrays are often placed in constrained flow areas that are only one or two orders of magnitude larger than their energy extraction planes [17], therefore accurate modelling of blockage and free surface effects are important [18].…”

Development of a Hydrokinetic Turbine Backwater Prediction Model for Inland Flow through Validated CFD Models

“…Three different turbines (shown in Table 2) were modelled using CFD and validated with experimental results (a variation of free-surface, wake, and performance measurements). The primary validation case used was the U.S. Department of Energy's Reference Model 1 (RM1) dual-rotor axial flow turbine, which was modelled in the St. Anthony Falls Laboratory (SAFL) at the University of Minnesota [10]. Free-surface measurements allowed validation of the multiphase CFD model and free-surface deformation.…”

“…Previous studies have investigated the hydrodynamic effects of horizontal-axis hydrokinetic turbines (HAHTs) both experimentally (e.g., in canals [5], investigating boundary layers [6] and varying Reynolds numbers [7]) and computationally (e.g., both CFD applications in [4,8]). However, most of the studies are performed under constant operational conditions, and are site-specific (e.g., three-bladed [9] and two-bladed [9,10] turbines under optimal conditions). Some attempts have been made in the past to develop backwater models using roughness values [4] or analytical relationships [11], but the lack of experimental results over a range of turbine designs and operational conditions has resulted in site-specific models.…”