Flow-Driven Oscillating Acoustic Attenuator for Cavity Resonance
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Solution Overview
Problem
Existing methods for mitigating acoustic resonance caused by fluid flow over cavities, such as those found in aircraft and piping systems, are limited by their narrow operating range, require external energy sources, and incur weight and power penalties, making them unsuitable for efficient noise reduction in dynamic environments.
Innovation Solution
The use of flow-driven oscillating acoustic attenuators, comprising flaps mounted upstream of the cavity that oscillate independently due to fluid flow, disrupting the shear layer and reducing acoustic energy through self-actuated vortex generation, which is designed to resonate with cavity frequencies and attenuate sound pressure levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If active control systems with external energy sources are used to mitigate cavity resonance, then acoustic energy reduction is achieved, but weight and power consumption increase
Solution Approach 1:
The passive control system utilizes the kinetic energy already present in the fluid flow to drive the oscillating elements, eliminating the need for external power sources. The flow itself provides the energy needed to generate vortices that disrupt the shear layer and reduce acoustic resonance, making the system self-sufficient without adding weight of power supplies or actuators.
Solution Approach 2:
The patent replaces active mechanical control systems (which require motors, power supplies, and control electronics) with a passive mechanical system that uses flow-induced oscillations. The oscillating elements are driven purely by aerodynamic forces from the fluid flow, substituting complex active mechanical systems with simpler passive mechanics.
2Object-affected harmful factors
If stationary passive control devices are used to mitigate cavity resonance, then device complexity is reduced, but operating range becomes limited
Solution Approach 1:
The patent employs dynamically oscillating elements that respond to varying flow conditions rather than stationary fixed structures. The oscillating flaps or plates adjust their motion characteristics based on the incoming flow velocity and pressure conditions, enabling the system to maintain effectiveness across a broader range of operating conditions compared to static geometries.
Solution Approach 2:
The control mechanism utilizes periodic oscillations of the passive elements that are naturally induced by the flow. This periodic motion creates time-varying vortex structures that can adapt to different flow rates and cavity resonance frequencies, extending the effective operating range compared to continuous stationary configurations.
3Weight of moving object
If flow-driven oscillating attenuators are used to mitigate cavity resonance, then weight and power consumption are minimized, but device complexity increases
Solution Approach 1:
The patent divides the control function into multiple distributed oscillating elements (flaps, plates, or similar structures) positioned at strategic locations upstream of the cavity. Each element independently responds to local flow conditions and contributes to the overall noise reduction, distributing the functional complexity across multiple simple components rather than requiring a single complex active system.
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
This solution effectively reduces sound pressure levels without external power, maintains efficiency across varying flow conditions, and minimizes weight and power consumption, providing a self-sustaining mechanism for noise mitigation in complex fluid dynamics scenarios.
Implementation Method 1
disrupting the shear layer and reducing acoustic energy through self-actuated vortex generation
Implementation Method 2
a shear layer SL between the free-stream flow U∞ above the cavity and the slower flow inside the cavity. The shear layer, which is an unstable, turbulent flow region
Implementation Method 3
the oscillation of each flap is driven solely by the flow independent of an actuation mechanism
Data Source
AI summary
An apparatus for attenuating acoustic resonance generated by flow over a cavity in a surface comprises a plurality of flat flaps proximate to an upstream edge of the cavity. The flaps are disposed in an array spaced in a width direction of the cavity edge, and are oscillated by the flow in two degrees of freedom solely by the flow, independent of an actuation mechanism. Each flap includes a first hinge generally coextensive with the surface for enabling oscillation in a first degree of freedom and a second hinge orthogonal to the first hinge and forming a tab for enabling oscillation in a second degree of freedom. The hinges are constructed with torsional spring constants that provide predetermined oscillation frequencies and magnitudes. The apparatus can include a deployment mechanism for moving each flap between a stowed position wherein it is generally flush with the surface and a deployed position wherein the flap can be oscillated by the flow.