Acoustic Pressure Estimation Using Euler Model and Laser Velocimetry
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Solution Overview
Problem
Current methods for estimating acoustic pressure in fluid flows, particularly in wind tunnels, face limitations due to the inability to measure in 3-dimensional spaces effectively, leading to inaccurate sound source localization and noise measurement disturbances from turbulent boundary layers and microphone placement.
Innovation Solution
The use of Euler's propagation model instead of Galbrun's, allowing direct measurement of acoustic pressure at a point without displacement calculations, enabling 3-dimensional acoustic pressure estimation and source localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Galbrun's propagation model is used to estimate acoustic pressure from particle displacement vectors, then measurement precision may be improved through integration of velocity vectors along trajectories, but device complexity and calculation time increase significantly due to requiring many velocity measurements along line segments
Solution Approach 1:
The patent extracts the integration calculation step from the measurement process by directly measuring acoustic pressure using Euler's model, eliminating the need to integrate velocity vectors along particle trajectories. This removes the complex computational burden while retaining acoustic pressure estimation capability.
Solution Approach 2:
The patent replaces the mechanical integration process (integrating velocity vectors along trajectories) with a direct measurement approach using Euler's propagation model. This substitution eliminates the need for complex trajectory tracking and integration calculations.
2Adaptability or versatility
If 3-dimensional velocity vector measurements are performed to enable trajectories other than parallel to flow direction, then measurement versatility is improved, but productivity decreases due to the large number of measurement points required for volume-wide acoustic pressure estimation
Solution Approach 1:
The patent extracts the need for extensive 3D velocity measurements by directly measuring acoustic pressure at points using Euler's model. This eliminates the requirement for numerous velocity measurements along multiple trajectories while maintaining the ability to handle arbitrary measurement directions.
3Reliability
If microphones are placed behind porous Kevlar film in wind tunnel walls, then protection from turbulent boundary layers is improved, but measurement precision deteriorates due to distance from acoustic wave sources causing obscuration
Solution Approach 1:
The patent uses laser velocimetry with seeding particles as an intermediary measurement technique. Instead of placing microphones close to sources where they would be obscured, the laser system measures particle velocities in the flow field, which are then used with Euler's model to derive acoustic pressure without requiring physical proximity to sound sources.
4Ease of operation
If measurement grid is made independent of acoustic wavelength using Euler's model, then ease of operation is improved, but measurement precision may be compromised compared to wavelength-dependent grids
Solution Approach 1:
The patent changes the fundamental parameter from which acoustic pressure is derived - instead of integrating velocity along trajectories (Galbrun), it directly uses the Euler propagation model with measured velocity fields. This parameter change enables wavelength-independent grid configurations while maintaining measurement accuracy through the direct relationship between velocity and pressure in Euler's equations.
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 approach reduces the number of measurement points needed, allows for accurate 3-dimensional acoustic pressure and intensity measurement, and determines sound source direction, overcoming previous limitations in 2-dimensional models.
Implementation Method 1
a source (16) of the laser type, capable of emitting light beams of wavelengths different for the three measurement channels (18, 20, 22)
Implementation Method 2
The detector (24) detects the light beams reflected by a succession of particles (12), moving in the fluid (2)
Implementation Method 3
a source of acoustic waves (6), capable of generating acoustic waves having a stationary frequency spectrum
Data Source
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AI summary
The invention relates to a method for estimating the acoustic pressure of a fluid generated by sound waves, including the following steps: seeding (40) the fluid with particles; measuring (42) at least one reference signal correlated with sound waves; for every direction of a reference mark: emitting (44) light beams by means of a source and receiving the diffused light beams, measuring (44) a speed signal of the particles in a predefined volume using laser Doppler velocimetry having fringes, calculating (58) the correlation between the measured speed signal and the measured reference signal, estimating (60) spatial components of the speed of the fluid generated by means of the sound waves; and calculating (64) the acoustic pressure in a macroscopic volume (36) using three-dimensional Euler equations and spatial components of the speed.