Comparative CFD study of the effect of the presence of downstream turbines on upstream ones using a rotational speed control system

S-P Breton,C Masson,L Dufresne,S Ivanell,K Nilsson,H Olivares-Espinosa

doi:10.1088/1742-6596/555/1/012014

Abstract

The effect of a downstream turbine on the production of a turbine located upstream of the latter is studied in this work. This is done through the use of two CFD simulation codes, namely OpenFOAM and EllipSys3D, which solve the Navier-Stokes equations in their incompressible form using a finite volume approach. In both EllipSys3D and OpenFoam, the LES (Large Eddy Simulation) technique is used for modelling turbulence. The wind turbine rotors are modelled as actuator disks whose loading is determined through the use of tabulated airfoil data by applying the blade-element method. A generator torque controller is used in both simulation methods to ensure that the simulated turbines adapt, in terms of rotational velocity, to the inflow conditions they are submited to. Results from both simulation codes, although they differ slightly, show that the downstream turbine affects the upstream one when the spacing between the turbines is small. This is also suggested to be the case looking at measurements performed at the Lillgrund offshore wind farm, whose turbines are located unusually close to each other. However, for distances used in today's typical wind farms, this effect is shown by our calculations not to be significant.

Highlights

As larger wind turbine farms are being built, much effort is put into understanding the dynamics of the wake development downstream of turbines
In region 3, which corresponds to rotational velocity values equal to and above rated value, power should be kept constant through the use of a pitch control system, making the generator torque inversely proportional to the generator speed
The incoming flow velocity is constant at 10m/s, and the initial rotational velocity given to the two turbines is 9 RPM

Summary

Introduction

As larger wind turbine farms are being built, much effort is put into understanding the dynamics of the wake development downstream of turbines. This is done by performing CFD simulations using two different codes, i.e. EllipSys3D and OpenFoam, into which turbine rotors are modelled as actuator discs, and whose results will be compared.

Results

Conclusion