HyWind

The Hywind is a program specifically dedicated to the wind turbines. It, not only, calculates the optimum wind turbine blade geometry, but also, calculates the time domain loads on wind turbine blades operating in specific environmental conditions along with the performance analysis of wind turbine.

1. Wind Simulation

Simulation of dynamic loads (fatigue load spectra which is then integrated up to fatigue lifetime estimation) is a key step during the design the wind turbine. In order to establish appropriate dynamic loads acts on the wind turbine blade, the wind field incident on the wind turbine blade is a critical first step towards design calculations.

Wind field calculation is usually the most uncertain part of the design process for wind turbines and requires some statistical treatment. It is, however, essential that the model use for wind simulation should be able to predict both the spatial and temporal variations in the wind field.

This section presents a stochastic, turbulent wind field, which is based on power spectral description of turbulence and the coherence between wind speeds at different points in the rotor plane, together with the effect of wind shear and tower shadow.

A simple flow chart for wind simulation is shown in Fig.1.

Figure.1: Wind simulation flow chart

2. Wind turbine blade Geometry

The design calculation of aerodynamically effective wind turbine blade geometry is presented in this section. The modeling is based on well established treatment of aerodynamic Blade Element Momentum (BEM) Theory. More sophisticated models are available for blade geometry but this method has the advantage of being simple and easy to understand.

When using the blade element momentum theory, various modifications to BEM theory are considered as well in the HWTD program, such as effects of tip and hub losses, changes in the wind velocities due to blade rotation, i.e. in terms of flow induction factors which affects the rotor torque, and effect of wake rotation. An initial optimum blade shape is determined. The final blade shape and performance are determined iteratively. The general steps in determining a blade geometric design are also given.

Figure. 2 : Flow Chart for blade geometric design and performance analysis

3. Wind Turbine Loads

The general approach to test whether a structural design is capable of withstanding the loads, which structure may encounter during its lifetime usually 20 years, is to analyze all load cases. Therefore, structural components of wind turbine should be designed to the requirement of resisting the ultimate loads and the fatigue loads, and checks whether the structure meets the requirements, i.e. safe or fails. If the structure fails under a certain load, the initial structure must be redesigned to withstand that load. The boundary between the safe state and the failed state is referred to as limit state. The properly designed structure is, therefore, concerned with how likely it is that the structure will reach a limit state and enter a state of failure.

There are three main types of loads: aerodynamic, gravitational, and inertial loads.