Analysis of the sweeped actuator line method

Nathan, Jörn; Masson, Christian; Dufresne, Louis; Churchfield, Matthew J.

doi:10.1051/e3sconf/20150501001

Cited by 9 publications

(5 citation statements)

References 10 publications

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“…The turbine is modelled using an actuator disk model (ADM) that incorporates airfoil data [46,47]. The forces are calculated at nodes distributed on multiple lines that cover the entire rotor swept area [48,49] and applied to the cells using an isotropic Gaussian convolution kernel. The calculated forces are corrected with the tip correction proposed by Shen [50,51].…”

Section: Rans-openfoammentioning

confidence: 99%

Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements

et al. 2021

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Section: Rans-openfoammentioning

confidence: 99%

Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements

et al. 2021

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“…Equations 2 and 3 define the minimum required number of time steps per rotor revolution as a function of mesh size and are displayed graphically in Figure 3. By comparing the two conditions that apply simultaneously in actuator line simulations, it is clear that the ALM time step constraint imposes a more significant restriction on the allowable time step compared to the constraint due to the streamwise CFL condition, which is a limitation widely acknowledged by the ALM community 28,29 . In fact, for Co 𝑥,𝑚𝑎𝑥 = 1 and 𝜆 = 1 the streamwise CFL condition of Equation 2 reduces to the ALM time step constraint.…”

Section: Relationship Between the Alm Time Step Condition And Streamw...mentioning

confidence: 99%

The effect of flow sampling on the robustness of the actuator line method

Zormpa,

Arcos,

Chen

et al. 2024

Preprint

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The actuator line method (ALM) is a widely-used tool for the modelling of horizontal axis turbines and wind and tidal farm flows. The method uses a virtual blade representation to simulate the dynamics of wind turbines without the computational expense associated with resolving the blade geometry. Within the ALM the flow is first sampled at each blade section, allowing for the calculation of the sectional lift and drag forces that are in turn imposed on the flow domain using a smearing kernel. In this work the effect of the flow sampling method on the robustness of the ALM is discussed. Implementations of two widely-used types of methods for horizontal axis wind turbines are tested: point sampling, where the flow is sampled at or near the collocation point, and volume average sampling where flow field information from multiple points centered at the collocation point is averaged into a representative blade-local velocity vector. A third method, line average sampling, that was initially proposed for sampling flows from blade resolved simulations is adapted for the ALM framework. This method samples the flow symmetrically around a control element in order to eliminate the interference of the bound circulation, thus allowing the inflow velocity at the aerofoil to be determined. When evaluating power and thrust coefficients as well as the flow field at the rotor plane predicted by the ALM, the line average sampling approach is demonstrated to be more robust and converges faster with time step for two different rotors: a small wind rotor and a high solidity tidal rotor. This suggests that carefully selecting the sampling method could be key in alleviating the very strict time step restriction imposed by the ALM, a widely acknowledged limitation of the method. Such an advancement could contribute towards improving the computational efficiency and tractability of the method.

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“…In the actuator disk model, ADM, the forces are instead distributed over the entire rotor swept area. To make an analogy to the ALM, in this work the disk is represented by multiple non-rotating ar-tificial lines (Nathan et al, 2015;Martinez et al, 2012). The idea behind the proposed technique is that there exists a full correspondence between the ADM and the ALM such that the advantage of using generic WT data in the ADM also can be exploited in the ALM.…”

Section: Force Modelingmentioning

confidence: 99%

Actuator line model using simplified force calculation methods

et al. 2023

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Abstract. To simulate transient wind turbine wake interaction problems using limited wind turbine data, two new variants of the actuator line technique are proposed in which the rotor blade forces are computed locally using generic load data. The proposed models, which are extensions of the actuator disk force models proposed by Navarro Diaz et al. (2019a) and Sørensen et al. (2020), only demand thrust and power coefficients and the tip speed ratio as input parameters. In the paper the analogy between the actuator disk model (ADM) and the actuator line model (ALM) is shown, and from this a simple methodology to implement local forces in the ALM without the need for knowledge of blade geometry and local airfoil data is derived. Two simplified variants of ALMs are proposed, an analytical one based on Sørensen et al. (2020) and a numerical one based on Navarro Diaz et al. (2019a). The proposed models are compared to the ADM using analogous data, as well as to the classical ALM based on blade element theory, which provides more detailed force distributions by using airfoil data. To evaluate the local force calculation, the analysis of a partial-wake interaction case between two wind turbines is carried out for a uniform laminar inflow and for a turbulent neutral atmospheric boundary layer inflow. The computations are performed using the large eddy simulation facility in Open Source Field Operation and Manipulation (OpenFOAM), including Simulator for Wind Farm Applications (SOWFA) libraries and the reference National Renewable Energy Laboratory (NREL) 5 MW wind turbine as the test case. In the single-turbine case, computed normal and tangential force distributions along the blade showed a very good agreement between the employed models. The two new ALMs exhibited the same distribution as the ALM based on geometry and airfoil data, with minor differences due to the particular tip correction needed in the ALM. For the challenging partially impacted wake case, both the analytical and the numerical approaches manage to correctly capture the force distribution at the different regions of the rotor area, with, however, a consistent overestimation of the normal force outside the wake and an underestimation inside the wake. The analytical approach shows a slightly better performance in wake impact cases compared to the numerical one. As expected, the ALMs gave a much more detailed prediction of the higher-frequency power output fluctuations than the ADM. These promising findings open the possibility to simulate commercial wind farms in transient inflows using the ALM without having to get access to actual wind turbine and airfoil data, which in most cases are restricted due to confidentiality.

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Analysis of the sweeped actuator line method

Cited by 9 publications

References 10 publications

Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements

Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements

The effect of flow sampling on the robustness of the actuator line method

Actuator line model using simplified force calculation methods

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