Femtosecond Laser Electronic Excitation Tagging for Flow Measurement
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Solution Overview
Problem
Current techniques for measuring velocities in turbulent and reacting flows, such as pitot tube pressure measurements and particle imaging velocimetry, have limitations including limited spatial resolution and the need for particle seeding, which can lead to inaccurate and incomplete data.
Innovation Solution
The use of a sub-nanosecond pulsed laser to fragment molecular species in a gaseous fluid, followed by time-gated imaging of the recombining fragments' fluorescence, allowing for precise measurement of fluid velocity without the need for seeding, using the Femtosecond Laser Electronic Excitation Tagging (FLEET) method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If particle imaging velocimetry is used to measure fluid velocity, then velocity measurement capability is provided, but spatial resolution is limited and particle seeding is required which can perturb the flow
Solution Approach 1:
The invention extracts and eliminates the need for particle seeding by directly utilizing molecular species already present in the gas flow. The laser excitation targets specific molecular transitions in the gas molecules themselves, removing the harmful external particles while maintaining the velocity measurement capability through molecular fluorescence tagging.
Solution Approach 2:
The gas molecules themselves serve as the tracers for velocity measurement without requiring external particle seeding. The molecular species in the flow are directly excited by the laser and provide the fluorescence signal, making the flow field self-tagging and eliminating the need for external additives that could perturb the flow.
2Measurement precision
If conventional laser Doppler velocimetry is used, then velocity measurement is achieved, but spatial resolution is limited by probe size and measurement is not continuous
Solution Approach 1:
The invention segments the measurement process into discrete laser pulse excitations followed by time-gated fluorescence detection. Each laser pulse creates a localized tagged region that can be imaged with high spatial resolution, and by sequencing multiple pulses, continuous velocity field mapping is achieved without the spatial averaging limitations of probe-based methods.
Solution Approach 2:
The measurement system uses periodic laser pulsing to continuously tag and track molecular positions over time. The repeated excitation cycles allow for temporal sequencing of velocity measurements across the flow field, providing continuous data without the spatial resolution constraints of stationary probes.
3Measurement precision
If pitot tube pressure measurements are used, then velocity inference is possible, but spatial resolution is limited by probe size
Solution Approach 1:
The invention replaces the mechanical pitot tube probe with a non-contact optical measurement system. Laser excitation and fluorescence detection eliminate the need for physical insertion into the flow, removing the spatial resolution limitation imposed by probe dimensions while maintaining velocity measurement capability through optical tagging and imaging.
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, high-resolution measurement of fluid velocity and flow properties, including turbulent characteristics, without perturbing the flow and over a wide range of pressures and temperatures, providing detailed velocity profiles and transport properties.
Implementation Method 1
a sub nanosecond pulsed laser beam which is focused into the gaseous fluid such that some of the molecular species along the laser path through the focal zone are caused to be fragmented by nonlinear absorption of laser light
Implementation Method 2
the atomic or molecular fragments combine and emit light, thus providing an image of the displacement of the gaseous fluid
Data Source
AI summary
An apparatus for the imaging of gaseous fluid motion is disclosed. The apparatus includes a sub-nanosecond pulsed laser. The sub-nanosecond pulsed laser is configured to cause a particle species to fragment and for the recombining fragments subsequently to fluoresce. The apparatus also includes a gaseous fluid comprised of particle species. The apparatus also includes a time gated camera. The time gated camera configured to capture at least one image of the fluorescence from the recombining particle fragment species displaced after a specific time lapse following the laser pulse. Additionally, a fluid velocity can be calculated from a comparison of the image of the displaced particle species to an initial reference position and the time lapse. A Femtosecond Laser Electronic Excitation Tagging (FLEET) method of using the disclosed apparatus is also disclosed.