Dual-Winglet Rotor Blade for Turbine Wake Management
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Solution Overview
Problem
Conventional horizontal axis fluid turbines face limitations in power extraction due to the Betz limit, where only 16/27 of the total kinetic energy can be captured, and the rotor wake affects intake, leading to reduced energy extraction and increased flow bypass.
Innovation Solution
An annular formation of varying relative pressures on rotor blades with a dual-tip design and a mixing element that injects high-energy bypass flow into the rotor wake, creating a spiral flow to enhance energy output and mixing with bypass flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If energy extraction is increased at the rotor, then power generation is improved, but the rotor wake expands and more fluid flow bypasses the rotor
Solution Approach 1:
The mixing element acts as an intermediary device that introduces high-energy bypass flow into the rotor wake, facilitating energy transfer and reducing wake expansion. This mediator enables continued high power extraction without the usual penalty of excessive wake growth and flow bypass.
Solution Approach 2:
The dual-tip design changes the pressure distribution parameters in the rotor wake, creating an annular formation of varying relative pressures that reduces the pressure coefficient. This parameter change allows for reduced wake expansion and improved flow characteristics while maintaining high power extraction.
2Power
If the rotor wake is allowed to expand, then more power can be extracted, but the upstream area of fluid flow becomes smaller than the rotor area
Solution Approach 1:
The mixing element serves as an intermediary that manages the wake expansion process by injecting high-energy bypass flow, allowing the rotor to operate at higher power extraction levels without the upstream flow area being reduced below the rotor area.
3Power
If conventional rotor design is used, then the Betz limit of 16/27 is achieved, but maximum power extraction is limited
Solution Approach 1:
The rotor blade is segmented into multiple functional sections: the main blade body and the dual-tip structures with mixing elements. This segmentation allows each section to perform specific functions - the main blade for primary energy extraction and the dual-tips with mixing elements for wake management and enhanced power extraction beyond the Betz limit.
Solution Approach 2:
The mixing element acts as an intermediary device that enables the system to surpass the conventional Betz limit by facilitating energy transfer from bypass flow to the rotor wake, thereby increasing overall power extraction efficiency.
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 dual-tip rotor blade design increases power generation by reducing the pressure coefficient in the rotor wake and enhancing mixing with bypass flow, allowing for higher energy extraction without stalling, thus surpassing the Betz limit and improving overall energy output.
Implementation Method 1
A mixing element is designed to provide a spiral flow, following the wake of each rotor blade, of high-energy flow from ambient-flow upstream of the rotor that mixes with the rotor wake-flow downstream of the rotor
Implementation Method 2
as fluid flows from the upstream side of the rotor to the downstream side, the average axial fluid velocity remains constant as the flow passes through the rotor plane. Energy is extracted at the rotor resulting in a pressure drop on the downstream side of the rotor
Implementation Method 3
The high pressure upstream of the rotor deflects some of the upstream air around the rotor. In other words, a portion of the fluid stream is diverted around the open rotor as if by an impediment. As the fluid stream is diverted around the open rotor, it expands, which is referred to as flow expansion at the rotor
Data Source
AI summary
A family of dual-winglet rotor blades are designed to dissipate the low energy flow in the wake of a turbine rotor. In some embodiments a dual-winglet having a first winglet transitioning from the lift surface of a rotor blade and a second winglet transitioning from the pressure surface of the rotor blade creates two distinct streams in the wake of the rotor. In one embodiment the first winglet curving away from the lift surface turns the lift force toward the center of the rotor plane while a second, smaller, winglet curving away from the pressure surface of the rotor blade turns the lift force away from the center of the rotor plane. In other embodiments winglets create a virtual shroud that expands the wake to dissipate the low-energy flow in the turbine wake. In another embodiment a dual winglet combines the aforementioned mixing effect with the wake expansion effect.