Large eddy simulations of the flow past wind turbines: actuator line and disk modeling

Abstract

Large eddy simulations of the flow through wind turbines have been carried out using actuator disk and actuator line models for the turbine rotor aerodynamics. In this study, we compare the performance of these two models in producing wind turbine wakes. We also examine parameters that strongly affect the performance of these models, namely, grid resolution and the way in which the actuator force is projected onto the flow field. The proper choice of these two parameters has not been adequately addressed in previous works. We see that as the grid is coarsened, the predicted power decreases. As the width of the body force projection function is increased, the predicted power increases. The actuator disk and actuator line models produce similar wake profiles and predict power within 1% of one another when subject to the same uniform inflow. The actuator line model is able to generate flow structures near the blades such as root and tip vortices which the actuator disk model does not, but in the far wake, the predicted mean wakes are very similar. In order to perform validation against experimental data, the actuator line model output was compared with data from the wind tunnel experiment conducted at the Norwegian University of Science and Technology, Trondheim. Agreement between measured and predicted power, wake profiles, and turbulent kinetic energy has been observed for most tip speed ratios; larger discrepancies in power and thrust coefficient, though, have been found for tip speed ratios of 9 and 12. Copyright © 2014 John Wiley & Sons, Ltd.

Gravity Waves and Wind-Farm Efficiency in Neutral and Stable Conditions

“…ADM avoids full resolution of the wind-turbine blade geometry and is therefore well-suited to study large wind farms (see, e.g., Calaf et al 2010;Meyers and Meneveau 2010;Goit and Meyers 2015;Allaerts and Meyers 2017). The performance of ADM has been investigated by several authors (Wu and Porté-Agel 2011;Meyers and Meneveau 2013;Martínez-Tossas et al 2015;Lignarolo et al 2016), and it is generally accepted that ADM provides an accurate representation of the turbine far wake and the wake mixing.…”

Full Downwind Turbine Simulations Using Actuator Line Method

“…Moreover, compared with other simplified methods (actuator disk), actuator line provides information about the dynamics of the flow and allows a more detailed study of wake structures and tip and root vortices [9,12]. However, boundary layer phenomena like flow separation and dynamic stall cannot be properly captured by the model since there is no surface and the boundary layer over the surface of the blades is not resolved.…”

“…This technique has been used to predict wind turbine power production and compared to actuator disk it has deployed good agreement; additionally, good practices of its use were attempted to be achieved [9]; numerical tests to determine mesh density and force distribution (important parameters in the method) guidelines using an infinite and finite span wing have been done [10]. All those studies have proven the accuracy of the AL model for wake analysis and its satisfactory performance [11,12] as it resolves the wake velocity profiles.…”

“…Furthermore, it is needed to analyze the tower and nacelle implementation and their effect on the turbine's predicted power, forces, and wake profiles [12].…”

Analysis of the sweeped actuator line method

“…This is done in order to avoid the occurence of spurious oscillations in the flow field, which are generated when the flow exhibits high velocity gradients and the discretization is done by pure central differencing. This can also be avoided by applying a hybrid scheme which blends between central differencing and a scheme with upwind character as done by Troldborg [10] and Martínez-Tossas [11]. This reduction of accuracy guarantees more physical results.…”