Variable Area Fan Nozzle for Gas Turbine Engine In-Flight Restart
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Gas turbine engines face challenges in starting at higher aircraft speeds, where traditional starters are ineffective, and existing windmilling methods do not adequately increase windmilling speed to facilitate efficient engine restart in flight conditions.
Innovation Solution
A control system that positions a variable inlet guide vane upstream of the low pressure compressor and a variable fan nozzle to maximize airflow, combined with the use of a starter when possible, to enhance windmilling speed during engine startup, particularly in flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional starter is used to start the engine in the air, then the engine can be started at lower aircraft speeds, but the starter becomes ineffective at higher aircraft speeds
Solution Approach 1:
The fan nozzle area is made variable and adjustable during different phases of operation. During engine start in flight, the nozzle area is increased to enhance windmilling speed. This dynamic adjustment allows the same engine starting system to effectively handle both low-speed (with starter) and high-speed (windmilling only) conditions, resolving the contradiction between starter effectiveness and adaptability across flight conditions.
2Adaptability or versatility
If windmilling is relied upon at higher aircraft speeds, then the engine can be started without a starter, but the windmilling speed is insufficient without additional measures
Solution Approach 1:
The fan nozzle area parameter is changed during engine start to optimize windmilling performance. By increasing the nozzle area opening, the system changes the airflow parameters to maximize the windmilling effect at high aircraft speeds, enabling sufficient rotor acceleration without mechanical starter assistance.
3Speed
If the fan nozzle area is increased to enhance windmilling speed, then engine restart in flight is facilitated, but airflow distribution must be optimized to maximize benefit
Solution Approach 1:
The control system merges the adjustment of multiple components (fan nozzle area and inlet guide vane angle) into a coordinated action. This combined approach optimizes airflow distribution across the engine while enhancing windmilling speed, achieving the speed improvement goal while managing system complexity through integrated control.
4Productivity
If the inlet guide vane angle is adjusted to maximize airflow, then windmilling efficiency is improved, but additional control mechanisms are required
Solution Approach 1:
The inlet guide vane serves multiple functions: normal operation airflow control and windmilling enhancement during engine start. By making the inlet guide vane angle adjustable, the same component performs both routine airflow management and critical windmilling optimization, improving productivity without proportionally increasing device 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 solution effectively increases windmilling speed and airflow, enabling more efficient engine restarts, even when traditional starters are not viable, by optimizing the position of the inlet guide vane and fan nozzle based on aircraft altitude and speed signals.
Implementation Method 1
A control system is provided which controls the position of the variable area fan nozzle to maximize airflow across the fan, and which controls the position of the variable inlet guide vane to maximize airflow across the low pressure compressor
Implementation Method 2
At higher speeds so called 'windmilling' is relied upon at startup. Windmilling typically occurs as the compressor and fan rotors are driven by the air being forced into the core engine, and the bypass duct, as the aircraft continues to move
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A gas turbine engine includes a variable inlet guide vane positioned forwardly of a low pressure compressor. The angle of the inlet guide vane is controlled at startup to increase airflow into the compressor. This is particularly useful when the gas turbine engine is being restarted while an associated aircraft is in the air, and is relied upon to increase windmill speed of the compressor and turbine rotors. A method and nozzle are also disclosed.