Variable-Incidence Discharge Fins for Stable Engine Reverse Thrust
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Solution Overview
Problem
Ultra-high bypass ratio turbine engines face challenges in managing counter-thrust gas flow disturbances due to bleed discharge air in the secondary flow path, which complicates thrust reversal configurations and necessitates larger nacelle dimensions and prevents conventional thrust reversal systems.
Innovation Solution
The use of incidence-controlled discharge fins that adapt their pitch angles to align the discharge air flow with the counter-thrust gas flow direction, whether in normal propulsion or thrust reversal configurations, ensuring axial co-current introduction into the secondary flow path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional discharge fins with fixed incidence angles are used to direct bleed air into the secondary flow path, then the bleed air can be effectively mixed with the secondary flow in normal propulsion configuration, but the counter-thrust gas flow is disturbed in thrust reversal configuration
Solution Approach 1:
The discharge fins are made movable rather than fixed, allowing their incidence angles to be dynamically adjusted between propulsion and thrust reversal configurations. The control system actuates the fins to achieve first acute pitch angles in propulsion mode for optimal bleed air mixing, and second acute pitch angles in thrust reversal mode for co-current flow alignment, thereby resolving the contradiction between fixed-structure reliability and adaptive versatility
Solution Approach 2:
The incidence angle parameter of the discharge fins is changed based on operational mode. By varying the pitch angles between two specific configurations, the system adapts the discharge fin geometry to match the required flow patterns, transforming the fixed-parameter design into a variable-parameter system that maintains gas flow stability across different operational states
2Use of energy by moving object
If ultra-high bypass ratio design is used to reduce fuel consumption and extend operability range, then fuel efficiency improves, but the outer diameter of the turbine engine increases substantially
Solution Approach 1:
The variable-pitch fan serves multiple functions: in propulsion mode it provides high bypass ratio for fuel efficiency, and in thrust reversal mode it reverses flow direction to create counter-thrust. This multi-functionality allows the engine to achieve ultra-high bypass ratio benefits without requiring separate thrust reversal systems, accepting the increased diameter as a trade-off for consolidated system architecture
Solution Approach 2:
The thrust reversal function is merged with the variable-pitch fan system rather than using a separate conventional thrust reversal mechanism. By combining these functions, the patent accepts the larger diameter necessary for the fan system while eliminating the need for additional thrust reversal hardware, thereby managing the diameter constraint through system integration
3Device complexity
If the variable-pitch fan is used to reverse flow direction for counter-thrust, then conventional thrust reversal systems can be eliminated, but the counter-thrust gas flow is disturbed by countercurrent introduction of bleed discharge air
Solution Approach 1:
The discharge fins are dynamically adjusted to different incidence angles in thrust reversal mode, changing from their propulsion configuration to a reversed configuration. This dynamic adaptation allows the fins to direct bleed air in the same axial direction as the counter-thrust gas flow, eliminating countercurrent disturbances while maintaining the simplified single-system architecture
Solution Approach 2:
The discharge fins are positioned in advance to prevent the harmful countercurrent effect. By setting the fins at second acute pitch angles before the counter-thrust gas flow enters the secondary flow path, the system pre-establishes co-current flow alignment, preventing flow disturbances before they can occur rather than correcting them afterward
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
This solution stabilizes the counter-thrust gas flow, enabling efficient thrust reversal and reducing the need for larger nacelle dimensions by minimizing disturbances, thus optimizing engine performance and operation.
Implementation Method 1
discharge fins are provided, having an angle of incidence adapted to direct the bleed air flow with an axial component in the downstream direction, when it is introduced into the secondary flow path
Implementation Method 2
the variable-pitch fan is also used to reverse the direction of the flow of the secondary flow in the secondary flow path, and thus create the counter-thrust in the reverse direction
Implementation Method 3
the reverse flow, essentially located in a top region of the fan, bypasses the lips of the nacelle (corresponding to the air inlet in the conventional propulsion configuration), but flows along the outer surface of the nacelle
Implementation Method 4
thanks to the incidence control of the discharge fins, the assembly according to the invention is capable of discharging the flow from the discharge duct in the same axial direction as the counter-thrust gas flow flowing in the secondary flow path
Data Source
AI summary
An aircraft dual-flow turbine engine assembly includes: an internal shroud for externally delimiting a primary flow path of the turbine engine gases; an external shroud for internally delimiting a secondary flow path of the turbine engine gas; and at least one air discharge duct extending between the internal shroud and the external shroud, the air discharge duct opening into the secondary flow path through an outlet orifice equipped with discharge fins. At least some of the discharge fins are movably mounted so as to be able to be incidence-control between a propulsion position, and a reverse thrust position.