Preface

In recent years, with the increasing attention paid to environmental and energy issues in the world, the development and utilization of clean and renewable energy have been greatly valued and developed. Among the potential renewable energy sources, wind energy has become one of the most widely commercialized. However, wind turbines installed in cold regions often experience icing on the surface of their blades. Blade icing can cause many serious impacts on wind turbines and has become an important issue to address. This book focuses on the recent research progress on wind turbine icing. It includes three research reports and three brief reviews.

Investigating the distribution characteristics of icing on the blade surface is the basis for studying wind turbine icing. Numerical simulation is one of the important methods for icing research. In this book, an icing model coupling water film flow with water film evaporation considering airfoil surface roughness is developed to investigate the effect of icing conditions on the icing distribution characteristics of a blade airfoil for vertical-axis wind turbines by numerical simulation. The calculated results are in good agreement with the experimental results. The findings obtained through numerical simulation contribute to the theoretical basis for exploring anti-icing and de-icing methods in wind turbines.

The most direct impact of icing on wind turbines is to reduce their power generation. Accurately predicting the power loss caused by icing conditions on wind turbines is very important. This book provides an overview of power loss estimation in wind turbines due to icing for establishing a foundation for deep research and investigations into the impact of icing on wind turbine power output. Various methodologies available for estimating power loss in wind turbines under icing conditions are collected and compared for analysis. Understanding the magnitude of power loss under icing conditions is crucial for optimizing wind turbine design, operation, and maintenance strategies.

The primary task in solving the problem of wind turbine icing is to accurately predict the occurrence of icing. Therefore, improving wind turbine ice prediction technology can assist wind farms in achieving more precise operation scheduling, avoiding needless shutdowns, and increasing power generation efficiency. This book reviews traditional wind turbine icing prediction methods. Specifically, it gives a detailed introduction to machine learning prediction methods. It provides a comprehensive description of the applicability and accuracy of various machine learning algorithms in wind turbine icing prediction and summarizes the applications and advantages.

The microscopic process of supercooled water droplets freezing on the blade surface is important for exploring the icing mechanism. This book examines the icing process of a single water droplet on a cold aluminum plate surface using a visualized method. The effects of volume and temperature on the icing characteristics are tested and acquired. The profile parameters of iced water droplets are processed and analyzed

via the program, including the contact diameter, maximum diameter and height of iced water droplets, contact angle, and more. These parameters can provide the experimental foundation to study the icing characteristics of wind turbine blades.

To research and develop efficient anti-icing and de-icing technologies, exploring the adhesive properties between the ice and the blade surface is necessary. This book summarizes the main theories of the icing adhesive mechanism, including mechanical theory, electronic theory, and wetting theory. It compares and analyzes the characteristics of several theories, discusses the impact of environmental factors on these theories, and makes suggestions for future research.

At present, there are several types of anti-icing and de-icing methods being developed, including electro-thermal, hot air, microwave, ultrasonic, pneumatic impulse, and other methods. This book introduces the theoretical and experimental studies on the ultrasonic de-icing of wind turbines. It analyzes and decides the de-icing vibration modes of the plate element and an airfoil blade for a wind turbine by simulation method. It tests the icing protection effects of ultrasonic vibration on the iced plate and blade segment. The results show that ultrasonic vibration could decrease the amount and adhesive strength of ice dramatically and have de-icing capability at the frequency of de-icing vibration mode.

Finally, it can be foreseen that with the continuous and rapid development of wind energy utilization and the frequent occurrence of extreme environments, the problem of icing on wind turbine blades will receive increasing attention. In addition, developing more economical and effective anti-icing and de-icing methods will become an important research direction.

> **Yan Li** College of Engineering, Northeast Agricultural University, Harbin, China

**Chapter 1**

*Zhi Xu*

**Abstract**

**1. Introduction**

Numerical Simulation of Icing

Characteristics on a Blade Airfoil

for Vertical-Axis Wind Turbine

under Various Icing Conditions

The phenomenon of icing on wind turbines gives rise to significant liability concerns

in regions characterized by cold and humid climates, especially those with extreme climatic conditions. Accordingly, investigating the icing characteristics is essential for the safety operation of wind turbines. In this chapter, an icing model coupling water film flow with water film evaporation considering airfoil surface roughness is developed to investigate the effect of icing conditions on the icing characteristics of a blade airfoil for vertical-axis wind turbines by numerical simulation. The mechanism of heat and mass transfer under various icing conditions is explored. The results show that the simulated and experimental ice shapes on the airfoil agree well. The ice shape contour fluctuates along the airfoil surface at higher ambient temperature due to water film flow and heat flux variation. A large area of airfoil surface is covered by ice accretion at high wind speed due to an increase in driving force acting on water film and convective cooling between water film and air. The maximum ice thickness changes more significantly at wind speeds of 2–7 m/s than that at wind speeds of 7–12 m/s. This contributes

to theoretical basis for exploring anti/de-icing method in wind turbines.

simulation, heat and mass transfer mechanism

wind turbines is crucial to explore anti/de-icing methods.

**Keywords:** wind turbine blade, icing condition, icing characteristics, numerical

Wind energy is widely used in electricity generation due to huge reserve and cleanness [1, 2]. Owing to the fact that wind turbines are installed in humid and cold regions, ice may accumulate on the wind turbine blades. It causes liability issues such as aerodynamic performance degradation, increased noise, decreased lifetime, ice shedding, and safety risks [3, 4]. Therefore, investigating the icing characteristics on

In the last few decades, numerical simulation methods can provide the insight of flow and heat transfer physics in detail, which is not easily possible using icing wind tunnel [5]. Numerical simulation is therefore reliable-efficient ways to investigate the

## **Chapter 1**
