Boundary Layer Ingesting Blade Root Twist
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Solution Overview
Problem
Propellers designed under ideal inflow conditions degrade in performance when placed in the wake of a body, such as a fuselage or wing, due to increased local inflow angles and non-ideal airfoil loading.
Innovation Solution
A boundary layer ingesting (BLI) blade with a root section having a greater local twist up to 70% span location than the tip section, optimizing twist distribution and geometry to adjust angles of attack and efficiently operate in the wake-induced boundary layer, enhancing propeller efficiency by up to 3%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a propeller is designed under ideal inflow conditions with uniform and constant free stream airflow velocity, then the propeller achieves optimal performance and efficiency, but the propeller performance degrades when placed in the wake of a body where non-uniform inflow conditions exist
Solution Approach 1:
The propeller blade is designed with non-uniform twist distribution along its span, with the root section having a greater local twist than the tip section. This creates different local angles of attack in different regions of the blade, allowing the root section to effectively operate in the boundary layer region with higher local inflow angles while the tip section operates in the free stream flow. This local differentiation resolves the contradiction by optimizing each section for its specific operating conditions.
Solution Approach 2:
The invention changes the geometric parameters of the propeller blade, specifically the twist angle distribution, to adapt to non-ideal inflow conditions. By increasing the local twist at the root section relative to the tip section, the blade modifies its angle of attack distribution to compensate for the non-uniform velocity field in the wake region, thereby maintaining propeller efficiency in boundary layer ingesting conditions.
2Ease of operation
If the propeller operates in the wake of a body, then the propeller can be positioned downstream of the fuselage or wing, but the local inflow angles increase and airfoil loading becomes non-ideal, degrading performance
Solution Approach 1:
The blade design applies different twist characteristics to different sections: the root section has greater local twist to handle the boundary layer conditions with higher local inflow angles, while the tip section has lesser twist for free stream operation. This local differentiation allows the propeller to maintain thrust generation efficiency despite the non-ideal wake conditions.
Solution Approach 2:
The invention converts the harmful effect of the wake-induced boundary layer into a beneficial operating condition. By designing the root section with greater local twist, the propeller blade intentionally operates in the boundary layer region, adjusting local angles of attack to extract useful thrust from the non-uniform flow, thereby converting the previously harmful wake effect into a productive operating regime.
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 BLI blade design improves propeller efficiency by optimizing thrust generation and load transfer from the boundary layer to free stream inflow, providing increased performance and efficiency benefits in non-ideal operating conditions.
Implementation Method 1
boundary layer region defined in and around the root section
Data Source
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AI summary
A boundary layer ingesting (BLI) blade having a span is provided and includes a root section connectable to a hub, a tip section disposable at a distance from the hub and having a pitch and a body extending in a spanwise dimension from the root section to the tip section. The root section has a local pitch from the root section to about a 70% span location, which is less than the pitch at the tip section, to thereby reduce local angles of attack in a boundary layer region defined in and around the root section.