Active Acoustic Damping Cavity for Thermoacoustic Resonance Control
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Solution Overview
Problem
Existing methods for damping acoustic waves, particularly in engines and combustion chambers, are inadequate in effectively reducing thermoacoustic resonances across a wide frequency range, often requiring significant energy and leading to inefficiencies and potential damage from inadequate damping.
Innovation Solution
An apparatus with a cavity enclosed by delimiting surfaces, at least one of which is permeable to fluid, actively excites acoustic waves using sound producers like loudspeakers or aerophonic elements, allowing for damping of acoustic waves independent of their frequency and phase, with energy requirements negligible compared to engine energy availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional passive damping structures (perforated surfaces, honeycomb structures, acoustic materials) are used, then acoustic damping is achieved at specific frequencies, but the damping effectiveness is limited to narrow frequency bands and cannot effectively reduce thermoacoustic resonances across a wide frequency range
Solution Approach 1:
The invention transitions from static passive damping structures to dynamic active damping using sound producers (loudspeakers, aerophonic elements) that generate counter-phase acoustic waves. This dynamic approach allows the damping system to adapt to varying frequency content of thermoacoustic resonances, achieving effective damping across a wide frequency range rather than being limited to narrow bands.
Solution Approach 2:
The invention implements a feedback control mechanism where microphones detect acoustic pressure fluctuations and the signal is processed to drive sound producers that generate counter-phase waves. This closed-loop feedback system continuously adapts to the actual acoustic conditions, enabling effective damping across varying frequencies and intensity levels of thermoacoustic resonances.
2Reliability
If active control systems with feedback mechanisms are implemented, then damping effectiveness across wide frequency ranges is improved, but device complexity and energy consumption increase
Solution Approach 1:
The damping system utilizes the existing acoustic field itself as the control signal source. Microphones detect the acoustic pressure fluctuations, and these detected signals directly drive the sound producers without requiring external complex control systems. The system serves itself by using the problematic acoustic waves as both the input signal and the basis for generating the counteracting waves, thereby reducing overall system complexity.
Solution Approach 2:
The invention replaces complex mechanical damping structures (multiple layers of perforated surfaces, honeycomb structures, acoustic materials) with a simpler electronic-acoustic system consisting of microphones, signal processors, and sound producers. This substitution reduces mechanical complexity while achieving broader frequency range effectiveness.
3Use of energy by moving object
If passive acoustic damping materials and structures are used, then no external energy is required, but the damping capability is insufficient for strong thermoacoustic vibrations and may lead to structural damage
Solution Approach 1:
The invention converts the harmful strong acoustic pressure fluctuations into useful control signals. The microphones detect the damaging thermoacoustic vibrations, and these same signals drive the sound producers to generate counter-phase waves that cancel the harmful vibrations. The harmful acoustic energy is thus transformed into a beneficial control mechanism that protects against structural damage.
Solution Approach 2:
The invention uses mechanical vibration principles by generating acoustic waves at the same frequency as the thermoacoustic resonances but with opposite phase. The sound producers create vibrations that interfere destructively with the harmful vibrations, canceling them out and preventing structural damage while consuming minimal energy compared to the magnitude of the damping effect achieved.
4Use of energy by moving object
If Helmholtz resonators are used for damping, then damping is achieved at the resonator's natural frequency, but the damping is limited to a very narrow frequency band
Solution Approach 1:
The invention replaces the fixed-tuned Helmholtz resonator with a dynamic active control system using sound producers that can operate across a wide frequency range. The electronic control system adjusts the phase and amplitude of the counteracting waves in real-time, allowing effective damping across multiple frequencies rather than being constrained to a single narrow resonant frequency.
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 solution achieves significant damping of acoustic waves across a wide frequency range, reducing energy consumption and preventing damage from thermoacoustic resonances, while maintaining efficiency in engines and gas turbines.
Implementation Method 1
arranged in or at the cavity is at least one sound producer (9) for exciting actively excited acoustic waves (11) in a fluid that is disposed in the cavity (8)
Implementation Method 2
at least one of the delimiting surfaces (4-7) being permeable to fluid (44) in order to enable fluid (44) to be exchanged with the volume (3)
Implementation Method 3
the excited acoustic waves (11) being unrelated to the frequency and phase of the acoustic waves (2) to be damped
Data Source
AI summary
An apparatus for damping acoustic waves that includes a volume of fluid having actively excited acoustic waves, an enclosure disposed in the volume of fluid including delimiting surfaces which define a cavity, at least one of the delimiting surfaces being permeable to the fluid, such that fluid may be exchanged between the cavity and the volume, and at least one sound producer disposed proximate the cavity to actively excite the actively excited acoustic waves in the fluid disposed in the cavity such that acoustic waves are damped in the volume.