Negative Hub Angle Boundary Layer Ingestion Fan
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Solution Overview
Problem
Current aircraft propulsion systems face inefficiencies due to downstream wake and jet mixing losses, particularly in conventional tube-and-wing aircraft, where fuselage boundary layer ingestion (BLI) is the most feasible but requires aerodynamic design improvements to enhance propulsive efficiency without adding weight or drag.
Innovation Solution
A boundary layer ingestion fan system is designed with a nacelle and fan located aft of the fuselage, featuring a negative hub angle and specific blade geometries to prevent flow separation and optimize propulsive efficiency by reducing dissipation losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional engine inlet is used with vi=v∞, then the propulsive efficiency is limited to ≤1, but adding BLI capability requires aerodynamic design improvements and may add weight or drag
Solution Approach 1:
The patent applies parameter changes by modifying the hub angle parameter to a negative value (γ < 0), which fundamentally alters the flow patterns and pressure distribution in the fan inlet. This parameter change enables the system to exploit boundary layer ingestion effects, reducing wake and jet mixing losses while maintaining propulsive efficiency ≤1, thus resolving the contradiction between efficiency improvement and design complexity.
2Loss of energy
If fuselage boundary layer is ingested to reduce wake losses, then propulsive efficiency increases, but flow separation may occur upstream of the fan
Solution Approach 1:
The patent changes the hub angle parameter to negative values, which fundamentally alters the flow patterns and pressure distribution in the fan inlet. This parameter change enables the system to exploit boundary layer ingestion effects, reducing wake and jet mixing losses while maintaining propulsive efficiency ≤1, thus resolving the contradiction between efficiency improvement and design complexity.
Solution Approach 2:
The negative hub angle configuration is designed in advance to preemptively control flow separation. By establishing the correct pressure gradient and flow direction before the boundary layer reaches the fan inlet, the design prevents flow separation from occurring in the first place, thereby maintaining reliability while achieving energy loss reduction.
3Force
If a finite propulsor size is used to produce thrust, then thrust is generated, but jet velocity cannot match inlet velocity exactly
Solution Approach 1:
The patent changes the hub angle parameter to negative values, which fundamentally alters the flow patterns and pressure distribution in the fan inlet. This parameter change enables the system to exploit boundary layer ingestion effects, reducing wake and jet mixing losses while maintaining propulsive efficiency ≤1, thus resolving the contradiction between efficiency improvement and design complexity.
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 system increases propulsive efficiency by preventing dissipation that would otherwise occur in the wake, achieving efficiencies beyond unity by maintaining flow attachment and reducing drag, thus enhancing aircraft performance.
Implementation Method 1
Boundary layer ingestion (often abbreviated to BLI) is a technique that may be used to improve aircraft propulsive efficiency by reducing downstream wake and jet mixing losses
Implementation Method 2
This prevents flow separation of the boundary layer upstream of the fan
Data Source
AI summary
A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle defining a duct, and a fan located within the duct. The fan comprises a hub arranged to rotate around a rotational axis and a plurality of blades attached to the hub, each of which has a span from a root at the hub defining a 0 percent span position (rhub) to a tip defining a 100 percent span position (rtip) and a plurality of span positions therebetween (r∈[rhub, rtip]). The hub has a negative hade angle (γ) with respect to the rotational axis at an axial position coincident with the leading edge of the blades.