Jet Engine Afterburner Noise Reduction via Exhaust Density Control

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Solution Overview

Problem

Jet engines equipped with afterburners produce undesirably high levels of noise due to the mixing and shock noise generated by the high velocity exhaust gases, particularly during supersonic operations.

Innovation Solution

A method that involves heating the exhaust gas flow using the afterburner while simultaneously reducing power to the core engine, thereby reducing the pressure and density of the exhaust gas in the nozzle area while maintaining constant exhaust gas velocity, which decreases engine noise. This can be supplemented by altering the afterburner flames to create an inverted exhaust velocity profile.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the afterburner is used to increase thrust by increasing exhaust gas velocity, then thrust is improved, but noise increases due to mixing noise and shock noise

Engineering Contradiction:

ImprovethrustVSAvoidnoise

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent changes the physical parameters of the exhaust gas by heating it with the afterburner to reduce density, and adjusts the nozzle area to maintain velocity while reducing pressure. This allows thrust to be maintained through the relationship Thrust = mass flow rate × velocity, while the reduced density and pressure decrease the noise-generating factors.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a variable area nozzle that dynamically adjusts its cross-sectional area to accommodate changes in exhaust gas density caused by afterburner heating. This dynamic adjustment maintains optimal exhaust velocity and thrust while enabling the noise-reducing low-density flow regime.

Inventive Principle:

Principle #15Dynamics

2Object-generated harmful factors

If the afterburner heats the exhaust gas to reduce density while maintaining velocity, then noise is reduced, but engine power consumption increases

Engineering Contradiction:

ImprovenoiseVSAvoidfuel consumption

Core Design Contradiction:

Object-generated harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent applies partial afterburner heating rather than full heating, sufficient only to reduce exhaust gas density to the level needed for noise reduction while maintaining thrust. This partial application of energy minimizes fuel consumption while achieving the noise reduction objective.

Inventive Principle:

Principle #16Partial or excessive action

3Power

If the variable area nozzle opens wider to accommodate reduced density exhaust gas, then thrust is maintained, but the complexity of the nozzle system increases

Engineering Contradiction:

ImprovethrustVSAvoidnozzle configuration

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

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 method effectively reduces jet engine noise while maintaining thrust levels, as demonstrated by the proportional relationship between noise, exhaust gas density, and thrust, allowing for quieter operation during afterburner use.

Implementation Method 1

using the afterburner to heat the exhaust gas flow while simultaneously reducing power to the core engine. Together these two operations reduce the pressure (and density) of the exhaust gas in the nozzle area while holding the exhaust gas velocity constant

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 2

The ignited fuel produces a blowtorch effect, increasing the temperature and velocity of the exhaust gas shooting through the nozzle, which increases thrust

Methodology Applied

Scientific EffectCombustion: Combustion

Implementation Method 3

Mixing noise is a result of the mixing of the jet exhaust gas with the surrounding ambient air (and caused by the difference in shear), and generally increases as nozzle exhaust gas velocity increases

Methodology Applied

Scientific EffectMixing:

Implementation Method 4

Shock noise is caused by shock waves generated in the engine exhaust plume of jets operating at supersonic speeds

Methodology Applied

Scientific EffectShock wave: Shock Wave

Data Source

PatentUS9140214B2Method of using an afterburner to reduce high velocity jet engine noise

Publication Date: 2015.09.22 RTX CORP

AI summary

A system and method of reducing noise caused by jet engines is provided. The method comprises the steps of using the afterburner to heat the exhaust gas flow while simultaneously reducing power to the core engine. Together these two operations reduce the pressure of the exhaust gas in the nozzle area while holding the exhaust gas velocity constant, which maintains engine thrust while decreasing engine noise. The method may be supplemented by altering the location of the afterburner flames to create an inverted exhaust velocity profile, thereby decreasing engine noise even further.