Microjet Ring Noise Reduction for Jet Engine Exhaust
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Solution Overview
Problem
Existing noise reduction systems for jet engines, such as Chevron Nozzles and oscillating jets, suffer from pressure loss, complexity, and difficulty in maintaining precise injection angles, leading to inefficient noise reduction and potential damage to components.
Innovation Solution
A noise reduction system utilizing a microjet ring with injection pipes formed in a circumferential direction at regular intervals, injecting compressed air into the jet flow at the throat of the main nozzle, which increases rigidity and maintains injection angle stability, reducing pressure loss and additional noise sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Chevron Nozzle is used to reduce noise, then noise reduction is achieved, but pressure loss occurs due to velocity difference
Solution Approach 1:
The invention divides the single large nozzle into multiple smaller nozzles arranged circumferentially. This segmentation allows each micro-nozzle to maintain lower velocity and reduce pressure loss while collectively achieving noise reduction through distributed injection points along the jet flow path.
Solution Approach 2:
The invention applies noise reduction injection locally at multiple circumferential positions around the jet flow rather than using a single Chevron structure. This local quality approach enables targeted noise reduction at specific confluence zones without creating velocity differences across the entire nozzle, thereby avoiding pressure loss.
2Duration of action of moving object
If oscillating jet channel is made thin to guide oscillating flow, then oscillating flow is achieved, but pressure loss in the channel becomes large
Solution Approach 1:
Instead of using a thin channel to guide oscillating flow (which causes pressure loss), the invention inverts the approach by directly injecting compressed air through multiple circumferential nozzles. This eliminates the need for a guiding channel and its associated pressure losses while still achieving oscillating flow effects through the distributed injection pattern.
3Reliability
If additional devices (flow control valve, flow stabilizer) are attached to the oscillating flow channel, then oscillating flow control is improved, but device complexity and number of components increase
Solution Approach 1:
The invention extracts and eliminates the need for additional control devices by integrating the oscillating flow generation function directly into the circumferential nozzle arrangement. The distributed nozzle structure inherently provides flow stability and control without requiring separate valves or stabilizers, thereby reducing device complexity while maintaining reliability.
4Object-affected harmful factors
If pipe is used to guide compressed air for microjet injection, then microjet injection is achieved, but pipe expansion by heat and damage is possible
Solution Approach 1:
The invention merges the compressed air supply system with the nozzle structure by directly integrating the air supply into the circumferential nozzle assembly. This eliminates the need for separate pipes that could expand due to heat, and the merged structure allows for better thermal management and material selection resistant to high-temperature jet engine environments.
5Object-affected harmful factors
If multiple nozzles are installed around main nozzle for microjet injection, then noise reduction is achieved, but assembling workability deteriorates due to precision requirements
Solution Approach 1:
The circumferential nozzle structure serves multiple functions simultaneously: it provides structural support, defines injection angles, positions multiple micro-nozzles, and guides compressed air flow. This multi-functionality reduces the number of separate components and assembly steps, improving assembling workability while maintaining precise injection geometry for noise reduction.
Solution Approach 2:
The invention uses a circumferential (curved) nozzle arrangement that naturally accommodates the cylindrical geometry of jet engines. This curved configuration allows uniform distribution of multiple injection points around the engine while maintaining consistent injection angles relative to the jet flow, simplifying the assembly process compared to linear or irregular arrangements.
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 reduces noise by ensuring stable microjet injection without altering the injection angle, minimizing pressure loss, and preventing component damage, while simplifying assembly and improving aerodynamic performance.
Implementation Method 1
the Coanda effect, an adhering effect of a fluid to a surface, is utilized, and thereby the microjets are injected along the jet flow surface
Implementation Method 2
the jet flow and the bypass flow are properly mixed by the swirl generated by the microjet
Data Source
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AI summary
A noise reduction system includes: a microjet ring (16) provided at an exhaust side peripheral edge of a main nozzle of a jet engine, and has a plurality of injection pipes (26) formed in a circumferential direction thereof at regular intervals; and a supply path configured to take part of compressed air in from a flow path in an upstream side of a combustor in the jet engine, and to guide the part of compressed air to the plurality of injection pipes (26), wherein the plurality of injection pipes (26) is configured to inject the part of compressed air to a jet flow.