Interface-resolved simulations of dense particulate flows: Studies on sedimentation and slurry pipe flow

Dense suspension flows, both in the natural environment and industrial settings, are complex phenomena with significant implications. From rivers shaping landscapes to industrial processes involving slurry transport, these flows hold a prominent position in numerous sectors. This thesis delves into a specific facet of these intricate flows:...

Dynamic wind farm flow control using free-vortex wake models

In the current state of model-based wind farm flow control, the implementation of yaw-based wake steering based on steady-state models has demonstrated potential for improving wind farm power production. However, for realistic, time-varying wind directions, the dynamics of wake propagation may impact the effectiveness of wake redirection. This...

Dynamics of the Pitch-able VAWT: A Study of the Dynamics of the Vertical Axis Wind Turbine with Individual Pitch Control

Society is finally entering a new age of renewable energy development. For the first time it is truly conceivable to power a vast majority of global energy use with a combination of wind, solar, and other forms of low carbon, renewable power. The rise of electrification and so called ”Power to X”, where renewable energy is used to create other...

Advances in actuation techniques for wind farm flow control

Offshore wind farms suffer substantial energy losses due to the interference of wind turbine wakes, with estimates indicating losses of approximately 10%. This thesis aims to advance the state of the art of wind farm flow control techniques for maximizing wind farm power performance. Wind farm flow control can be divided into three categories:...

Wake and wind farm aerodynamics of vertical axis wind turbines

The development of offshore wind energy, especially the steps towards deep water and/or higher density wind farms, revives the prospects of vertical axis wind turbines (VAWTs). Because VAWTs may reduce the cost of floating structures, there is a potential to lower energy costs. However, VAWTs are often assumed to be less efficient and less...

Pitch control for wind turbine load mitigation and enhanced wake mixing: A simulation and experimental validation study

The dissertation discusses different wind turbine control strategies that use pitch actuation to decrease the Levelized Cost of Energy (LCoE) of wind farms. This is achieved by either mitigating the loads experienced by individual turbines, or by enhancing wake mixing in turbines located within a wind farm. The latter strategy exploits the fact...

Aerodynamic advances in vertical-axis wind turbines

As wind farms tend to move towards deeper waters with better wind resources, the classical top-heavy horizontal-axis wind turbines (HAWTs) become particularly challenging. This raises the question whether other concepts could be more suitable and compatible with the deep-sea floating conditions. Hence, the interest in vertical-axis wind turbines...

Closing the loop in model-based wind farm control

Open-loop wake steering inconsistently improves the energy yield of wind farms in field experiments in the literature. This thesis matures wind farm control technologies for power maximization in a model-based closed-loop framework towards real-world practical applicability. Firstly, open-loop wake steering is evaluated on a commercial onshore...

A single wake oscillator model for coupled cross-flow and in-line vortex-induced vibrations of marine structures

Vortex-induced vibration (VIV) is awell-known phenomenon for civil and offshore structures. Currently, the prediction of this type of vibration in practice currently mainly relies on the force-decomposition method. However, the limitations of this method have restricted the applicability of the method, and alternative models are therefore needed...

The wake of an unsteady actuator disc

Blade Element Momentum (BEM) is the most important aerodynamic analysis method for wind turbines. BEM is derived assuming stationary conditions, which limits its ability to model the unsteady aerodynamic effects. This becomes increasingly relevant for the flexible blades of current large-scale turbines, and the employment of passive and active...

On the Turbulent Mixing in Horizontal Axis Wind Turbine Wakes

The wake flow of a horizontal axis wind turbine is characterised by lower wind speed and higher turbulence than the free-stream conditions. When clustered in large wind farms, wind turbines regularly operate inside the wake of one or more upstream machines. This is a major cause of energy production loss and a source of higher fatigue loads on...

Data-driven wind plant control

Each wind turbine in a cluster of wind turbines (a wind power plant) can influence the performance of other turbines through the wake that forms downstream of its rotor. The wake has a reduced wind velocity, since the turbine extracts energy from the flow, and the obstruction by the wind turbine rotor causes increased turbulence. If another...

Computation of Rotorcraft Wake Geometry using NURBS

This thesis contains the results of research in the area of rotorcraft aerodynamics with a focus on method development related to the vortical wake generated by rotor blades. It is applied to a vortex tube representation of the wake (using a single NURBS surface) and a simplified filament wake model where only the tip vortices are taken into...

Mobility-based Time References for Wireless Sensor Networks

Wireless Sensor Networks require small low-cost radios to enable communication among its nodes. Since those radios must be fully integrated to reduce cost and size, integration is required also for their on-board time references, which are needed to achieve synchronization with the other nodes. To deal with the lower accuracy of integrated...

Wind turbine aerodynamics in yaw: Unravelling the measured rotor wake

Adaptive image interrogation for PIV: Application to compressible flows and interfaces

As an experimental tool, Particle Image Velocimetry has quickly superseded traditional point-wise measurements. The inherent image processing has become standardized though the performances are strongly dependent on user experience. Moreover, the arduously selected image interrogation parameters are applied uniformly throughout the image...