A Study on Yaw-Misaligment

A Study on Yaw-Misaligment: Combined Optimization of Wind Farm Power Production and Structural Loading

van Dijk, M.T.

van Wingerden, J.W. (mentor)

Mechanical, Maritime and Materials Engineering

Delft Center for Systems and Control (DCSC)

2016-09-23

Climate change gives incentive for the transition to sustainable energy sources such as wind energy. To make wind energy cost competitive with fossil fuel sources, wind turbines are commonly placed in groups. As wind turbines extract energy from the wind, a wake occurs behind the turbine characterized by reduced a wind speed and increased turbulence. This wake causes downstream turbines to incur decreased power production and increased loading. Due to this aerodynamic interaction between these turbines, the total energy production is sub-optimal. A control strategy to mitigate these losses is by imposing yaw-misalignment with the incoming wind flow. This induces a lateral force which will cause the wake to deflect, with the goal to avoid downstream turbines. A side effect of wake deflection is partial wake overlap which has the potential to increase the fatigue loading of wind turbines. One way to decrease the cost of energy, is to increase the power production without significantly affecting the loads. Therefore, this thesis aims to quantify the load variations due to partial wake overlap and evaluate the benefits of a combined optimization of power and loads over traditional control strategies. For this purpose, we design a computational framework which computes the wind farm power production and the wind turbine rotor loads based on the yaw settings. To investigate the influence of partial wake overlap on the rotor fatigue, the differential flapwise and edgewise bending moments at hub height are computed. FLORIS is used to compute the power and CCBlade to determine the loads, supplemented with an algorithm to find the velocity distributions as hub height. The optimal yaw settings are found using an optimizer. The simulation results show that partial wake overlap can significantly increase asymmetric loading of the rotor and that yaw-misalignment is beneficial in situations where the wake can be sufficiently directed away from the downstream turbines. Furthermore, a combined optimization of power and loads in all wind directions has been found to increase the average power production by 1.53 % and decrease the average differential flapwise and edgwise loads by respectively 42.67% and 45.70% compared to greedy control settings. Although results are promising, further improvements are required to confirm that mixed-objective optimization of power and loads is beneficial. We recommend the use of dynamic models to allow for more accurate load computations, validation of the results using high-fidelity models and investigating the influence of turbulence and Individual Pitch Control.

http://resolver.tudelft.nl/uuid:9bdd375e-a5ee-4d7b-86a8-d74bcb199c9e

2017-01-01

Student theses

master thesis

(c) 2016 van Dijk, M.T.