Christian Santoni

Large Eddy Simulation for an array of turbines with Extremum Seeking Control

Large Eddy Simulations of the flow past an array of three aligned turbines have been performed using two different control strategies: constant torque gain and the Extremum Seeking Control. An off-design tip speed ratio has been chosen as initial condition for each turbine. It is shown that the turbines controlled with constant torque gain do not reach their optimum tip speed ratio. On the other hand, turbines controlled with ESC reach, to a close approximation, the tip speed ratio which maximizes their power production. The power produced by the array controlled with ESC is about 10% larger than that obtained with constant torque gain. Power spectral densities of the wind velocity in the wake of the turbines are presented to discuss how to select the proper dithering frequency.

Development of a high fidelity CFD code for wind farm control

In this paper we describe an effort recently completed at UT Dallas to develop a high-fidelity computational fluid dynamics code to test and develop control algorithms aimed at maximizing power production and load mitigation. Preliminary results of three aligned turbines operating at different tip speed ratios (TSRs) are discussed to show the wealth of details available from the present code. The finer solution of the flow physics allows to gain a better understanding of how control algorithms should be designed and implemented in practical configurations. The paper includes a detailed analysis of the power and loads for optimal TSRs obtained by applying dynamic programming to a low-fidelity analytical model.

Towards reduced order modelling for predicting the dynamics of coherent vorticity structures within wind turbine wakes

The dynamics of the velocity field resulting from the interaction between the atmospheric boundary layer and a wind turbine array can affect significantly the performance of a wind power plant and the durability of wind turbines. In this work, dynamics in wind turbine wakes and instabilities of helicoidal tip vortices are detected and characterized through modal decomposition techniques. The dataset under examination consists of snapshots of the velocity field obtained from large-eddy simulations (LES) of an isolated wind turbine, for which aerodynamic forcing exerted by the turbine blades on the atmospheric boundary layer is mimicked through the actuator line model. Particular attention is paid to the interaction between the downstream evolution of the helicoidal tip vortices and the alternate vortex shedding from the turbine tower. The LES dataset is interrogated through different modal decomposition techniques, such as proper orthogonal decomposition and dynamic mode decomposition. The dominant wake dynamics are selected for the formulation of a reduced order model, which consists in a linear time-marching algorithm where temporal evolution of flow dynamics is obtained from the previous temporal realization multiplied by a time-invariant operator. This article is part of the themed issue ‘Wind energy in complex terrains’.

Effects of the Subgrid-Scale Modeling in the Large-Eddy Simulations of Wind Turbines

The increased demand for wind energy had led to a continuous increase in the size of wind turbines and as a consequence in the size of wind farms.