A comparison of actuator disc and BEM models in CFD simulations for the prediction of offshore wake losses

Luca Lavaroni,Malcolm J Cook,Simon J Watson,Mark R Dubal

doi:10.1088/1742-6596/524/1/012148

Luca Lavaroni, Malcolm J Cook + Show 2 more

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https://doi.org/10.1088/1742-6596/524/1/012148

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Abstract

In this paper computational fluid dynamics (CFD) simulations are performed using ANSYS CFX to compare wake interaction results obtained from two rotor modelling methodologies: the standard actuator disc and the blade element momentum model (BEM). The unsteady simulations embed Coriolis forces and neutral stability conditions in the surface layer and stable conditions in the free stream. The BEM method is implemented in the CFD code through a pre-processing set of files that employs look-up tables. The control system for the wind turbines is considered through look-up tables that are constructed based on operational wind farm data. Simulations using the actuator disc and BEM methodologies have been performed using a number of different turbulence models in order to compare the wind turbine wake structure results. The use of URANS and LES numerical methods, coupled with the two different methodologies of representing the turbine, enables an assessment to be made of the details required for varying degrees of accuracy in computing the wake structures. The findings stress the importance of including the rotation of the wake and the non-uniform load on the rotor in LES simulations to account for more accurate turbulence intensity levels in the near wake.

Highlights

The study of wakes in wind farms has been a popular topic of research during the last two decades, gaining momentum from computational fluid dynamics (CFD) methods that allow more complex modelling of the physics of the wake flow than the empirical models
In the present work, numerical simulations are performed of the full scale turbine at high Reynolds number and are carried out with URANS and Large eddy simulation (LES) models using the actuator disc in the cases a) without rotation and constant thrust coefficient over the turbine rotor and b) with the blade element momentum model (BEM) model accounting for rotation of the turbine and uneven thrust
In this work, Unsteady-Reynolds-Averaged Navier-Stokes (RANS) and zonal Large Eddy Simulations have been performed employing two rotor modelling techniques to distribute the force over the turbine rotor: the standard actuator disc without rotation of the flow and the actuator disc with the BEM model that accounts for rotation

Summary

Introduction

The study of wakes in wind farms has been a popular topic of research during the last two decades, gaining momentum from computational fluid dynamics (CFD) methods that allow more complex modelling of the physics of the wake flow than the empirical models. Advanced turbine rotor modelling techniques and turbulence methods have been developed to obtain increased accuracy of the flow in wind farms. Researchers have looked at the flow through wind farms in the atmospheric boundary layer with different methods. Past studies have employed Reynolds-Averaged Navier-Stokes (RANS) [1] [2] showing that the method is unable to model the turbulent propagation of the eddies accurately.

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