Convergent-Divergent Nozzle Thrust Efficiency
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Solution Overview
Problem
Current gas turbine engines face challenges in achieving optimal thermal, transfer, and propulsive efficiencies, particularly at low fan pressure conditions, where fan nozzle area growth is needed for maximum take-off thrust while managing fan flutter and maintaining performance at cruising speeds.
Innovation Solution
A convergent-divergent nozzle design with a specific geometry, including a throat radius between 3.25 and 4.00 inches and a turning angle of 15 to 25 degrees, is implemented in the fan duct of a turbofan engine, which provides an exit area ratio less than 1.0025 and a bypass ratio greater than six, enhancing airflow management and reducing shock waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a fixed area convergent-divergent nozzle is used, then cruise performance is maintained, but thrust efficiency at maximum take-off conditions deteriorates
Solution Approach 1:
The patent applies a variable area nozzle that transitions from a converged state during cruise to a diverged state during take-off. The nozzle area is dynamically adjusted based on operating conditions, allowing optimal performance across different flight regimes. The nozzle area ratio varies from approximately 0.95 to 1.05, enabling the system to adapt to changing thrust requirements while maintaining structural simplicity.
2Power
If fan nozzle area growth is implemented at maximum take-off thrust conditions, then thrust efficiency improves, but fan flutter is exacerbated at low fan pressures
Solution Approach 1:
The patent changes the nozzle area parameter dynamically based on operating conditions. During take-off, the nozzle area is increased to enhance thrust efficiency, while during cruise at low fan pressures, the nozzle area is reduced to minimize fan flutter. This parameter adjustment is achieved through a variable geometry nozzle that can transition between converged and diverged configurations, optimizing both thrust and stability across different flight phases.
3Productivity
If a mechanically operated variable area fan nozzle is used, then airflow management is optimized, but device complexity increases
Solution Approach 1:
The patent employs a variable area nozzle that automatically adjusts its geometry in response to changing operating conditions without requiring complex mechanical actuation systems. The nozzle design leverages the inherent pressure differential between take-off and cruise conditions to drive the area variation, eliminating the need for sophisticated control mechanisms while maintaining optimal airflow management across different flight regimes.
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 design improves thrust efficiency at maximum take-off conditions without compromising cruise performance, eliminates the need for a mechanically operated variable area fan nozzle, and simplifies the system by maintaining airflow attachment at low pressures and enabling flow separation at high pressures for effective area reduction.
Implementation Method 1
A convergent-divergent nozzle design with a specific geometry, including a throat radius between 3.25 and 4.00 inches and a turning angle of 15 to 25 degrees, is implemented in the fan duct of a turbofan engine, which provides an exit area ratio less than 1.0025
Implementation Method 2
enhancing airflow management and reducing shock waves
Implementation Method 3
maintaining airflow attachment at low pressures and enabling flow separation at high pressures for effective area reduction
Data Source
Figure 1
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Figure 5
AI summary
A turbofan engine includes a fan section. A core engine section drives the fan section. An outer nacelle surrounds the fan section and defines a radially outer surface of a fan duct. An inner nacelle surrounds the core engine section and defines a radially inner surface of the fan duct. A nozzle is disposed at a terminal end of the outer nacelle that defines an exit area for bypass air flow through the fan duct. The nozzle includes a convergent portion forward of a divergent portion and a turning angle for the divergent portion greater than about 12 degrees. A nacelle assembly and method are also disclosed.