Stepped Vortex Generator for HAWT Blade Stalling
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Solution Overview
Problem
Conventional vortex generators mounted on the proximal end region of lift-based HAWT rotor blades tend to produce a single vortex that detaches early, allowing a thick boundary layer to form behind it, leading to stalling and reduced lift.
Innovation Solution
A vortex generator with a progressively upwardly stepped upper margin is designed to generate multiple vortices, which bind together and remain attached to the blade surface, effectively energizing the boundary layer and preventing stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional vortex generators are mounted on the proximal end region of the blade, then the boundary layer mixing is initiated, but the single vortex detaches early and allows a thick boundary layer to form, leading to stalling and reduced lift
Solution Approach 1:
The vortex generator is segmented into multiple sections along its length, with each section generating a separate vortex. This segmentation ensures that multiple vortices are produced instead of a single detached vortex, maintaining boundary layer stability and preventing stalling while preserving lift generation capability
Solution Approach 2:
The vortex generator incorporates a stepped configuration that extends in multiple dimensional levels. The steps create additional vortex generation surfaces, transforming a single-dimensional vortex structure into a multi-dimensional system that produces multiple bound vortices, thereby preventing early detachment and maintaining boundary layer attachment
2Device complexity
If the vortex generator produces a single vortex, then the structure is simple, but the vortex detaches early and allows thick boundary layer formation behind it
Solution Approach 1:
The vortex generator is divided into multiple segments or steps along its length, with each segment contributing to vortex generation. This segmentation increases device complexity slightly but ensures multiple vortices are produced that remain bound to the blade surface, preventing boundary layer separation and improving reliability
Solution Approach 2:
The stepped configuration creates a dynamic vortex generation system where each step produces a vortex that interacts with the flow and blade surface. This dynamic interaction ensures the vortices remain attached and energetic, maintaining boundary layer stability without requiring overly complex structures
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
The use of stepped vortex generators effectively suppresses stalling over a large portion of the blade, increasing lift and maintaining a stable boundary layer from the root to the trailing edge.
Implementation Method 1
The aerofoil profile is shaped to generate a pressure differential between the downwind (lower pressure or 'suction') side of the blade and the upwind (higher pressure or 'pressure') side of the blade
Implementation Method 2
The pressure differential across the blade appears as a force acting on the blade in a direction perpendicular to the direction of the relative airflow, referred to as lift
Implementation Method 3
Vortex generators are typically small, triangular projections which are mounted on aerofoils to mix faster flowing air into the boundary layer at the blade surface so as to mitigate stalling
Implementation Method 4
Stalling means the separation of the high speed airflow from the surface of the aerofoil in advance of the trailing edge
Implementation Method 5
A vortex generator with a progressively upwardly stepped upper margin is designed to generate multiple vortices, which bind together and remain attached to the blade surface
Implementation Method 6
The upper and lower concavities open at different sides of the vortex generator. In use, it is found that a cushion of pressurised air will tend to develop in the concavity opening at the pressure side of the VG, while a reduced pressure develops in the concavity opening at the suction side of the VG
Data Source
AI summary
A vortex generator 10, 10′ is arranged oblique to the flow direction DF on the surface 8 of the radially inward portion 1 of a HAWT rotor blade. The vortex generator has an upwardly stepped free edge 12 and defines, proximate its trailing end 14, a lower convexity 23 opposite a lower concavity 23′, and an upper convexity 24 opposite an upper concavity 24′. The upper and lower concavities 24′, 23′ open at opposite sides 15, 16 of the vortex generator.