Perforated OFV Exhaust Nozzle for Aircraft Cabin Noise Reduction
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Solution Overview
Problem
Existing aircraft pressurization systems face challenges in reducing noise from the outflow valve (OFV) during the discharge of pressurized air, with current solutions either altering the valve's functionality or increasing system pressure loss and weight through the use of vortex generators or acoustic mufflers.
Innovation Solution
An outflow valve exhaust nozzle design featuring a cylindrical upstream section and a frustroconical downstream section with air intake perforations and integrated vortex generators, which reduces noise without modifying the OFV or increasing pressure loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If vortex generators are added to reduce OFV noise, then noise is reduced, but device complexity and pressure loss increase
Solution Approach 1:
The exhaust nozzle is divided into multiple sections: a first section with vortex generators for noise reduction, and a second section with a different geometry for flow management. This segmentation allows each section to perform its specific function optimally without interfering with the other, reducing overall system complexity while maintaining noise reduction effectiveness.
Solution Approach 2:
The noise reduction function is extracted from the main valve body and placed into a separate exhaust nozzle assembly. The vortex generators are positioned in the first section of the nozzle, isolating the noise mitigation mechanism from the valve's primary pressurization control function, thereby reducing device complexity and avoiding interference with control laws.
2Object-affected harmful factors
If acoustic mufflers are added to reduce noise, then noise is reduced, but weight and cost increase
Solution Approach 1:
Instead of adding heavy acoustic mufflers, the invention changes the geometric parameters of the exhaust nozzle - specifically creating a frustroconical shape with varying cross-sectional area and strategic perforation patterns. This geometric parameter change achieves noise reduction through flow manipulation and acoustic path modification without the weight penalty of traditional mufflers.
3Object-affected harmful factors
If acoustic mufflers are added to reduce noise, then noise is reduced, but system pressure loss increases
Solution Approach 1:
The exhaust nozzle features localized perforations in specific regions rather than being uniformly perforated throughout. This local quality approach allows acoustic energy to be managed where it is most effective while maintaining efficient flow paths in other areas, thereby reducing noise without significantly increasing system pressure loss.
4Object-affected harmful factors
If the OFV is modified to reduce noise, then noise is reduced, but cabin pressurization control is affected
Solution Approach 1:
The exhaust nozzle acts as an intermediary component between the OFV and the external environment. It provides noise reduction functionality while allowing the OFV to operate independently without modification to its control laws or pressurization management, thus maintaining reliability while reducing noise.
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 effectively reduces cabin noise levels by up to 3 dB without affecting cabin pressurization or passenger comfort, maintaining the system's performance and comfort standards.
Implementation Method 1
employing vortex generators (VGs) to increase flow turbulence of the discharged pressurized air
Implementation Method 2
increase flow turbulence of the discharged pressurized air
Implementation Method 3
reduce boundary layer flow separation
Implementation Method 4
reduce the effectiveness of acoustic propagation downstream of the OFV
Data Source
AI summary
Exhaust nozzles for outflow valves (OFVs) that are usefully employed in aircraft pressurization systems include an upstream solid (e.g., cylindrical) wall section and a downstream solid exhaust wall section fixed to the upstream solid wall section. The downstream solid exhaust wall section includes a circumferential portion defining a series of air intake perforations. A pair of vortex generators may also be provided upstream of the series of air intake perforations. The air intake perforations and optional vortex generators thereby allow air from the ambient pressure environment to be introduced into the boundary layer of pressurized air discharged by the OFV in the interior of the perforated region of the downstream solid exhaust wall section of the nozzle thereby reducing adverse pressure gradients therewithin which in turn results in a more attached air flow and hence less perceived noise.