Segmented Rotor Blade Wake Diffusion
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Solution Overview
Problem
Horizontal-axis wind turbines experience efficiency losses due to wake effects from neighboring turbines in wind farms, leading to reduced power output, as the slower wind velocity in the wake reduces energy extraction and expands the wake diameter, necessitating increased spacing that limits the number of turbines in a given area.
Innovation Solution
The design of rotor blades with a radially-outer energy-extraction portion and a radially-inner ventilation portion, where the radially-inner portion is shaped to extract less than 2% of the total energy, creating a ventilation effect that increases kinetic energy at the center of the wake, enhancing wake diffusion without significantly decreasing turbine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional rotor blades extract maximum energy from the wind, then individual turbine power output is maximized, but wake velocity decreases and wake diffusion is reduced, causing efficiency losses for downwind turbines
Solution Approach 1:
The rotor blade is segmented into two functional portions: a radially-outer energy-extraction portion that maximizes power extraction, and a radially-inner ventilation portion that promotes wake diffusion by extracting minimal energy. This segmentation allows the rotor to simultaneously optimize individual turbine performance and reduce wake effects on downstream turbines.
Solution Approach 2:
Different portions of the rotor blade are assigned different aerodynamic properties. The radially-outer portion has high energy extraction capability with optimized airfoil sections, while the radially-inner portion has low energy extraction capability designed to ventilate the wake center. This local differentiation resolves the contradiction between maximizing individual power output and enhancing overall farm productivity.
2Productivity
If wind turbines are spaced further apart to reduce wake effects, then downwind turbine efficiency increases, but the total number of turbines in a given area decreases
Solution Approach 1:
The rotor blade design enables each turbine to actively manage its own wake by using the radially-inner ventilation portion to induce turbulent mixing and accelerate wake recovery. This self-service wake management allows turbines to be placed closer together while maintaining efficiency, effectively increasing the quantity of turbines per area without sacrificing downwind turbine performance.
3Power
If the radially-inner portion of the blade extracts more energy, then individual blade power output increases, but wake ventilation is reduced and wake diffusion is suppressed
Solution Approach 1:
The blade design creates a dynamic balance between energy extraction and wake ventilation. The radially-inner portion is specifically designed with low energy extraction characteristics to maintain high velocity gradients and promote turbulent mixing in the wake center, thereby preserving the wake's diffusive structure while the radially-outer portion captures the majority of available energy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration increases wind flow velocity at the center of the wake, leading to increased shear stresses and turbulence, which enhances wake diffusion, allowing for faster dissipation of wakes and potentially increasing wind farm efficiency by up to 3% or enabling higher turbine densities without significant individual turbine efficiency loss.
Implementation Method 1
the radially-inner ventilation portion being shaped to, in use, ventilate a central area of a wake of the rotor by extracting low levels of energy from the wind or imparting additional energy to the central area of the wake
Implementation Method 2
the wind velocity within the wake increases due to the transfer of kinetic energy from the wind surrounding the wake by turbulent mixing. Turbulent mixing occurs naturally due to the velocity difference between the air flowing inside and outside of the wake
Implementation Method 3
the velocity of the wind generates lift on the blades, causing the rotor to rotate, which in turn drives an electric generator
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A blade 20 for a horizontal-axis wind turbine rotor comprises a radially-outer, energy-extraction portion 32 and a radially-inner, ventilation portion 30. The radially-inner ventilation portion 30 is shaped to ventilate a central area 34 of a wake of the rotor during use such that it contains more kinetic energy compared to the wake from a conventional rotor design. The increased wind flow velocity at the centre 34 of the wake generates additional shear stresses, with corresponding turbulence development, which gives rise to increased wake diffusion.