Three-Stream Gas Turbine Engine Core Cowl Design
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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 reducing weight, as larger fans require more complex and heavier engine components, and the removal of the outer nacelle complicates accessory storage and installation.
Innovation Solution
A three-stream gas turbine engine design with an unducted primary fan and a ducted secondary fan, which allows for a larger fan diameter without an outer nacelle, reducing the axial length of the core engine and providing sufficient packaging space for accessories, while maintaining high propulsive efficiency and reducing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If fan diameter is increased to improve fuel efficiency, then propulsive efficiency is improved, but engine weight and complexity increase
Solution Approach 1:
The fan system is segmented into two separate fans: a primary unducted fan and a secondary ducted fan. This segmentation allows each fan to be optimized independently for its specific function, enabling larger diameters for improved fuel efficiency while distributing the weight and complexity across two smaller components rather than one large fan
Solution Approach 2:
The patent introduces a third airflow stream through the ducted secondary fan, creating a three-stream configuration. This dimensional addition to the airflow architecture enables improved fuel efficiency by capturing and utilizing previously wasted energy, while the ducted configuration provides structural containment that reduces overall system complexity
2Weight of moving object
If outer nacelle is removed to reduce weight and complexity, then engine weight is reduced, but accessory storage and installation become more difficult
Solution Approach 1:
The patent merges the accessory mounting function into the core cowl structure itself, eliminating the need for a separate outer nacelle. The core cowl is designed with integrated mounting features that accommodate accessories directly, combining the structural and accessory storage functions into a single integrated component
Solution Approach 2:
The core cowl is designed as a multi-functional component that serves both as the structural enclosure for the core engine and as the mounting structure for accessories. This universal design allows the same component to perform multiple functions, reducing the need for separate dedicated accessory storage structures
3Use of energy by moving object
If fan diameter is increased to improve propulsive efficiency, then fuel efficiency is improved, but core engine axial length must be reduced to maintain packaging space
Solution Approach 1:
By segmenting the fan system into primary and secondary fans, the patent distributes the airflow functions across two separate stages. This allows the core engine to be more compact axially while still achieving high propulsive efficiency through the combined action of both fans, each operating at optimized diameters
Solution Approach 2:
The patent resolves the length constraint by adding a radial dimension to the airflow architecture through the ducted secondary fan. This creates a three-dimensional airflow pattern that maintains packaging space while achieving the necessary propulsive efficiency through optimized fan diameters in both axial and radial directions
Data Source
AI summary
A gas turbine engine defines an axial direction and a radial direction and comprises a turbomachine having an unducted primary fan, a core engine a combustor casing enclosing a combustor and defining an outer surface, a core cowl surrounding at least a portion of the core engine. The outer surface of the core cowl defines a peak cowl diameter (D) in the radial direction, and the outer surface of the combustor casing defines a maximum combustor casing diameter (d) along the radial direction. The core engine defines an overall core axial length (L) along the axial direction and an under-core cowl axial length (L1) along the axial direction. The gas turbine engine defines a core cowl diameter ratio (CDR) equal to the peak cowl diameter (D) divided by the maximum combustor casing diameter (d) and a core cowl length ratio (CLR) equal to the under-core cowl axial length (L1) divided by the overall core axial length (L). The CDR is between 2.7 and 3.5 and the CLR is between 0.25 and 0.50.