Three-Stream Gas Turbine Engine Packaging With Unducted Fan
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Solution Overview
Problem
Conventional turbofan engine designs face challenges in increasing fan diameter to improve fuel efficiency while maintaining propulsive efficiency and overcoming installation difficulties due to the presence of an outer nacelle, which can become weight prohibitive and cause excessive drag.
Innovation Solution
A three-stream gas turbine engine design is implemented, featuring an unducted primary fan and a ducted secondary fan, with a third stream airflow, reducing the core engine axial length and eliminating the outer nacelle, and utilizing a core cowl diameter and length ratios to optimize packaging and accessibility for engine components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fan diameter is increased to improve fuel efficiency, then propulsive efficiency improves, but installation difficulty increases due to outer nacelle constraints
Solution Approach 1:
The patent removes the outer nacelle from the conventional turbofan configuration, extracting the constraint that limited fan diameter. By eliminating this structural component, the design achieves larger fan diameters that improve fuel efficiency without the installation difficulties previously imposed by the nacelle.
Solution Approach 2:
The patent divides the fan system into two separate fans: a primary unducted fan and a secondary ducted fan. This segmentation allows each fan to be optimized independently, with the primary fan having larger diameter for fuel efficiency while the secondary fan handles thrust requirements, resolving the contradiction between size and installability.
2Ease of repair
If outer nacelle is used to accommodate engine accessories, then accessibility for maintenance improves, but weight increases and drag increases
Solution Approach 1:
The patent extracts and removes the outer nacelle entirely, eliminating the weight and drag penalties associated with this structure. Engine accessories are redistributed to the core engine structure and pylon, achieving maintenance accessibility without the harmful effects of the nacelle.
Solution Approach 2:
The patent relocates engine accessories from the radial dimension (nacelle housing) to the axial and longitudinal dimensions (core engine structure and pylon mounting). This dimensional relocation provides accessibility for maintenance while avoiding the weight and drag of the traditional nacelle configuration.
3Loss of energy
If fan diameter is increased to improve fuel efficiency, then propulsive efficiency improves, but drag increases due to outer nacelle presence
Solution Approach 1:
By removing the outer nacelle, the patent eliminates the drag penalty associated with this structural component. The larger primary fan operates without the aerodynamic interference and parasitic drag that would result from nacelle presence, achieving improved fuel efficiency without the harmful drag effects.
Solution Approach 2:
The patent segments the thrust generation into two independent fan systems, allowing the primary unducted fan to operate at optimal, larger diameters for fuel efficiency without the drag constraints imposed by a unified nacelle structure. The secondary ducted fan provides supplemental thrust while maintaining minimal drag.
Data Source
AI summary
A gas turbine engine includes an unducted primary fan and an engine core having a combustor casing that defines an outer surface. A fastening assembly, a mounting assembly, or both are located between a core cowl that surrounds the core engine. In a radial direction, an outer surface of the core cowl defines a peak cowl diameter (D), and the outer surface of the combustor casing defines a maximum combustor casing diameter (d). A core cowl diameter ratio (CDR) is the peak cowl diameter (D) divided by the maximum combustor casing diameter (d) and is between 2.7 and 3.5. In an axial direction, the core engine defines an overall core axial length (L) and an under-core cowl axial length (L1). A core cowl length ratio (CLR) is the under-core cowl axial length (L1) divided by the overall core axial length (L) and is between 0.25 and 0.50.