Laser Doppler Velocity Field Measurement Using Scattered Light Subtraction
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Solution Overview
Problem
Existing laser Doppler methods for measuring fluid flow velocity fields are influenced by multi-particle scattering and require an additional reference camera for normalization, limiting their dynamic range and sensitivity, especially for low velocities.
Innovation Solution
A method that subtracts normalized spatial light intensity distributions from different scattering directions to eliminate multi-particle scattering effects, using a frequency-to-intensity converter with a symmetric transfer function to normalize the light intensity distributions without a reference camera, and projects the velocity field onto orthogonal coordinate axes, allowing for measurements across a wide dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional laser Doppler methods using gas absorption cells or optical processors are used, then velocity field measurement is achieved, but multi-particle scattering influences the measurement results and reduces measurement precision
Solution Approach 1:
The patent divides the measurement process into multiple scattering direction channels and processes each direction separately. By segmenting the light intensity distribution measurement into different scattering directions and then combining them through mathematical processing, the method eliminates multi-particle scattering effects while maintaining measurement precision.
Solution Approach 2:
The patent introduces normalized spatial light intensity distributions as an intermediary representation that captures scattering direction information without being directly affected by multi-particle scattering. These normalized distributions serve as mediators that are later combined to eliminate scattering effects and retrieve accurate velocity field data.
2Measurement precision
If an additional reference camera is used for normalization, then the converted image can be normalized, but device complexity increases and measurement of low velocities becomes difficult
Solution Approach 1:
The patent enables the measurement system to perform self-normalization by utilizing the scattered light information from different scattering directions itself. Instead of requiring an external reference camera, the system uses its own scattered light measurements to normalize the data, thereby reducing device complexity while maintaining normalization capability.
Solution Approach 2:
The patent makes the scattered light detection system multi-functional by using the same camera and optical path for both velocity measurement and normalization. The scattered light measurements serve dual purposes: capturing velocity information and providing normalization references, eliminating the need for separate reference camera hardware.
3Adaptability or versatility
If the dynamic range is expanded by reducing the quality factor of the optical resonator, then measurement range increases, but sensitivity for low velocities decreases
Solution Approach 1:
The patent transitions from a single-dimension optical resonator quality factor adjustment to a multi-dimensional approach using scattered light distributions from different directions. By incorporating angular dimension information and processing multiple scattering directions, the system achieves both wide dynamic range and high sensitivity without relying on quality factor reduction.
Solution Approach 2:
The patent changes the measurement parameters from relying solely on optical resonator quality factor to using normalized spatial light intensity distributions from multiple scattering directions. This parameter transformation allows the system to maintain sensitivity across a wide velocity range by processing directional scattering information rather than depending on resonator characteristics.
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 effectively eliminates the influence of multi-particle scattering, enables normalization without an additional reference camera, and expands the dynamic range of velocity measurements, improving sensitivity across all velocity ranges, including low velocities.
Implementation Method 1
Methods for visualizing and measuring velocity fields of flows, based on the Doppler frequency shift in the scattered light
Implementation Method 2
scattered light image of a section of a flow irradiated by a laser sheet
Data Source
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AI summary
A laser Doppler method for measuring a velocity field of a fluid flow comprises the steps of: illuminating a light-section (4) extending through the fluid flow with laser light; converting spatial distributions of Doppler frequency shifts of scattered light, which is scattered by particles carried by the fluid flow out of the light-section (4) in different scattering directions, into a spatial light intensity distribution for each scattering direction; normalizing the spatial light intensity distributions in respect of a light intensity distribution of the scattered light; subtracting the normalized spatial light intensity distributions obtained for the different scattering directions in pairs to obtain a spatial light intensity difference distribution for each pair of the different scattering directions; defining coordinate axes by the directions of difference vectors of pairs of wave vectors (k) of the scattered light pointing in the different scattering directions; and quantitatively determining a projection of the velocity field of the fluid flow in the light-section on each coordinate axis (x, y, z) from the corresponding spatial light intensity difference distribution divided by the modulus of the corresponding difference vector.