Rupert Storey

Modelling Turbine Loads during an Extreme Coherent Gust using Large Eddy Simulation

A group of wind turbines operating in extreme transient wind conditions has been simulated using LES and an actuator model. An extreme wind event is introduced into the simulation domain using transient boundary conditions. The event is based on the extreme coherent gust (ECG) structure from the International Wind Turbine Design Standard IEC61400-1:2005 which consists of a simultaneous gust and wind direction change. Details of the implementation are discussed with regard to adapting the analytical functions described in the standard. A recently developed actuator sector method is used to represent the wind turbines in the simulation. The actuator method is coupled to the aero-elastic wind turbine simulation code FAST to allow dynamic control of the wind turbines based on the ambient flow conditions. Standard baseline controllers are used to regulate generator torque, actuate blade pitch angle and control yaw direction. A span-wise periodic array of turbines operating in a steady atmospheric boundary layer is simulated before the introduction of the ECG structure. The convection of the wind event is analysed, along with the subsequent response of the wind turbines and loading during the wind event is quantified. The simulations demonstrate a methodology for modelling groups of turbines operating in transient wind conditions that can be used to study turbine loads or test new turbine control strategies.

Modeling Gusts Moving Through Wind Farms

A large-eddy simulation code has been used to model the atmospheric boundary layer flowing through a pair of wind turbines. The wind turbines are modeled as actuator discs, with the disc loadings being calculated by a coupled wind turbine simulation code, FAST. In addition to modeling a steady wind, the case of an extreme gust passing through the farm is simulated. The persistence of the gust structure suggests the possibility of designing turbine controllers based partially on upstream information.

A CFD code comparison of wind turbine wakes

A comparison is made between the EllipSys3D and SnS CFD codes. Both codes are used to perform Large-Eddy Simulations (LES) of single wind turbine wakes, using the actuator disk method. The comparison shows that both LES models predict similar velocity deficits and stream-wise Reynolds-stresses for four test cases. A grid resolution study, performed in EllipSys3D and SnS, shows that a minimal uniform cell spacing of 1/30 of the rotor diameter is necessary to resolve the wind turbine wake. In addition, the LES-predicted velocity deficits are also compared with Reynolds-Averaged Navier Stokes simulations using EllipSys3D for a test case that is based on field measurements. In these simulations, two eddy viscosity turbulence models are employed: the k- model and the k--fp model. Where the k- model fails to predict the velocity deficit, the results of the k--fP model show good agreement with both LES models and measurements.

Large Eddy Simulation of Dynamically Controlled Wind Turbines using Actuator Discs

Accurate modelling of wind turbine wakes in a wind farm is an important feature of developing wind farm layouts. This paper discusses a new technique for coupling wind and turbine modelling with an aero-elastic simulation to dynamically model turbine wakes and responses in a wind farm. The advantage of this approach is a turbine model in a simulation domain with the ability to actively respond to transient wind events through the inclusion of a controller. The coupled nature of the aero-elastic/ow simulation also allows recording of load and control data allowing analysis of single and multiple turbine systems. An aero-elastic turbine modelling code and a research LES code were chosen for this work. The research focused on developing a computationally ecient simulation with the ability to model a turbine exhibiting standard baseline control operating in a turbulent Atmospheric Boundary Layer (ABL) such as that observed in an o-shore environment. Multiple wind turbine instances were introduced to a transient ow domain to investigate wake structures and interaction eects between turbines. Results show the successful implementation of a coupled simulation. Preliminary results indicate the signicance of the controller and demonstrate signicant turbine interaction eects in simulations with multiple turbines. This work demonstrates promising techniques to increase the delity of transient modelling of turbulence and wake structures in wind farms for better prediction of load uctuations and power decits.