Adjustable Nozzle Exit Area for Turbofan Compressor Stability

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Solution Overview

Problem

Turbofan engines face challenges in maintaining aerodynamic stability of the low pressure compressor during throttle transients, particularly due to increased pressure ratio during deceleration, which reduces the stability margin and leads to non-optimal performance.

Innovation Solution

A turbofan engine control system that adjusts the nozzle exit area in response to unstable stability margins by monitoring low pressure compressor pressure ratio, spool speed, and throttle position, using a controller to actuate flaps and alter the nozzle exit area to prevent stall or surge conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the nominal low pressure compressor operating line is set to maintain sufficient stability margin during deceleration throttle transients, then the stability margin is preserved, but the low pressure compressor operates at non-optimal performance conditions

Engineering Contradiction:

Improvestability marginVSAvoidperformance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies dynamics by making the nozzle exit area adjustable rather than fixed. The controller dynamically changes the nozzle exit area in response to detected stability margin conditions, allowing the system to adapt between stability prioritization and performance optimization based on real-time operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the physical parameter of nozzle exit area to resolve the contradiction. By decreasing the nozzle exit area during deceleration transients, the system temporarily optimizes stability margin, and by increasing it during steady-state operation, the system optimizes performance, thus resolving the trade-off between these two parameters.

Inventive Principle:

Principle #35Parameter changes

2Stress or pressure

If the low pressure compressor pressure ratio is increased during deceleration, then the stability margin is reduced, but the high spool pressurizes the low pressure compressor

Engineering Contradiction:

Improvepressure ratioVSAvoidstability margin

Core Design Contradiction:

Stress or pressureVSReliability

Solution Approach 1:

The nozzle exit area acts as an intermediary parameter that mediates between the high spool pressurization effect and the low pressure compressor stability requirement. By adjusting the nozzle exit area, the system controls the backpressure on the turbofan and low pressure compressor, effectively managing the pressure ratio impact on stability margin.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The controller detects the incoming deceleration transient and preemptively decreases the nozzle exit area before the pressure ratio increase fully impacts the stability margin. This preliminary anti-action prevents the harmful effect of reduced stability margin from fully developing.

Inventive Principle:

Principle #9Preliminary anti-action

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 system effectively maintains a desired operating line for the low pressure compressor, ensuring sufficient stability margin and optimal performance throughout the flight envelope by reducing the pressure ratio and preventing stall or surge conditions during engine deceleration.

Implementation Method 1

A controller is programmed to effectively change the nozzle exit area in response to an undesired low pressure compressor stability margin

Methodology Applied

Scientific EffectFlow control through nozzle area adjustment:

Implementation Method 2

The low pressure compressor operating characteristics are set to maintain a sufficient stability margin for the compressor at all operating conditions

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 3

During a deceleration, the high spool pressurizes the low pressure compressor while the turbofan and low pressure compressor depressurize

Methodology Applied

Scientific EffectPressurization: Pressurisation

Data Source

PatentUS8601786B2Operational line management of low pressure compressor in a turbofan engine

Publication Date: 2013.12.10 RTX CORP

AI summary

A turbofan engine control system is provided for managing a low pressure compressor operating line. The engine includes a low spool having a low pressure compressor housed in a core nacelle. A turbofan is coupled to the low spool. A fan nacelle surrounds the turbofan and core nacelle and provides a bypass flow path having a nozzle exit area. A controller is programmed to effectively change the nozzle exit area in response to an undesired low pressure compressor stability margin which can result in a stall or surge condition. In one example, the physical nozzle exit area is decreased at the undesired stability condition occurring during engine deceleration. A low pressure compressor pressure ratio, low spool speed and throttle position are monitored to determine the undesired stability margin.