On the Accuracy of Three-Dimensional Actuator Disc Approach in Modelling a Large-Scale Tidal Turbine in a Simple Channel

Abstract

To date, only a few studies have examined the execution of the actuator disc approximation for a full-size turbine. Small-scale models have fewer constraints than large-scale models because the range of time-scale and length-scale is narrower. Hence, this article presents the methodology in implementing the actuator disc approach via the Reynolds-Averaged Navier-Stokes (RANS) momentum source term for a 20-m diameter turbine in an idealised channel. A structured grid, which varied from 0.5 m to 4 m across rotor diameter and width was used at the turbine location to allow for better representation of the disc. The model was tuned to match known coefficient of thrust and operational profiles for a set of validation cases based on published experimental data. Predictions of velocity deficit and turbulent intensity became almost independent of the grid density beyond 11 diameters downstream of the disc. However, in several instances the finer meshes showed larger errors than coarser meshes when compared to the measurements data. This observation was attributed to the way nodes were distributed across the disc swept area. The results demonstrate that the accuracy of the actuator disc was highly influenced by the vertical resolutions, as well as the grid density of the disc enclosure.

Numerical study of ducted turbines in bi-directional tidal flows

“…Table 2 shows the details of the simulation scheme. The turbine is treated as an actuator disc with the wake swirl and discrete blade effects neglected (Belloni, 2013;Fleming & Willden, 2016;Rahman et al, 2018;Shives & Crawford, 2011). In the numerical model, the axial resistance induced by the actuator disc was represented by a pressure drop p across the disk,…”

Review of tidal turbine wake modelling methods

“…Modelling of a full size (20m) turbine via an AD method was found to be very sensitive to mesh and grid density. Further work is needed, but such a method could be applied in a larger scale model to examine regional flow effects on turbine performance, where fully-resolved geometry would be computationally unfeasible [56].…”

Modelling dynamic loadings of a tidal stream turbine in combined wave-current-turbulence environment

“…It is also known that the fluctuating flow acting on the TST, caused by the turbulence and wave flow, will contribute to the fatigue of a TST. The importance of incorporating the turbulence effects in turbine simulations to accurately predict both power production and turbine loading has been addressed by previous studies in both site measurements [3,10,11] and numerical simulations [12,13,14].…”