Schlieren Optical Jet Noise Source Localization
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Solution Overview
Problem
Current methods for measuring noise caused by jet flows, especially supersonic jets, are invasive and ineffective in identifying noise sources within the jet flow, leading to difficulties in reducing noise pollution and potential damage to aircraft structures.
Innovation Solution
A non-invasive acoustic measurement device using an optical system with a laser beam and high-speed photo sensor to measure brightness fluctuations, converting data into frequency and amplitude information, and applying Abel inversion to obtain density gradient information, allowing for visualization of noise sources within the jet flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an intrusive method such as a microphone is used to measure noise, then the noise can be detected, but the jet flow is blocked by wind noise caused when the jet interferes with the microphone
Solution Approach 1:
The patent uses a Schlieren optical system as an intermediary to measure noise. Instead of placing a microphone directly in the jet flow where it would be blocked by wind noise, the optical system measures density gradients in the jet flow, which serve as a proxy for noise detection. This intermediary approach allows non-intrusive measurement while avoiding the harmful wind noise interference that would occur with direct microphone placement.
Solution Approach 2:
The patent replaces the mechanical microphone system with an optical measurement system. Instead of using a mechanical microphone that physically interacts with the jet flow and generates wind noise, the system uses optical methods (Schlieren imaging) to detect density gradients caused by sound waves in the jet flow. This substitution eliminates the mechanical interference problem while maintaining noise measurement capability.
2Loss of information
If the source of noise is not identified, then no targeted reduction method can be developed, but identifying the noise source requires intrusive measurement tools that block the jet flow
Solution Approach 1:
The Schlieren optical system acts as an intermediary that enables non-intrusive identification of noise sources. By measuring density gradients in the jet flow, the system can locate sound sources without physically blocking the jet. This allows the jet flow to remain unobstructed while still providing detailed information about noise source locations and characteristics.
Solution Approach 2:
The patent replaces intrusive mechanical measurement tools with an optical system to identify noise sources. The optical method detects density gradients caused by sound waves without requiring physical contact with the jet flow, thereby avoiding blockage while enabling precise localization of noise sources for targeted reduction strategies.
3Object-generated harmful factors
If aerodynamic tabs are used to reduce noise, then noise reduction can be achieved, but the thrust of the jet engine is reduced
Solution Approach 1:
The patent employs feedback control using the Schlieren optical measurement system. By continuously measuring density gradients and identifying noise sources in real-time, the system provides feedback information that enables dynamic adjustment of jet engine parameters. This allows noise reduction through controlled modification of jet flow characteristics without the thrust penalty associated with fixed aerodynamic tabs, as the adjustments can be made optimally based on actual noise conditions.
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
Enables accurate, non-invasive measurement and analysis of noise across a wide speed range from subsonic to supersonic jets, effectively identifying noise sources and reducing noise pollution without impacting thrust.
Implementation Method 1
an optical system is employed, and a light beam is passed through a jet flow. The brightness of the light beam is converted into an electrical signal
Implementation Method 2
The brightness of the light beam is converted into an electrical signal, and the electrical signal is subjected to a sampling process
Implementation Method 3
converted by an Abel inversion section into density gradient information of the jet flow at a radial position from the center of the jet flow
Data Source
AI summary
In a schlieren optical system, a laser beam is passed through the jet flow and the ambient around the jet flow, and a high speed sampling is performed using a high speed photo sensor while displacing measurement points. The value obtained by sampling represents a result of the optical path caused curved by a density gradient generated in an arc-shape from the center of the jet flow. The value is subjected to a high speed discrete Fourier transform and decomposed into frequency components which constitute the noise. Thereafter, Abel inversion is performed on data belonging to a particular frequency to obtain a density gradient in the radial direction from the center of the jet flow. The obtained density gradient is visualized in a graph display, so that the position of the sound source and the state of the jet flow can be accurately grasped.