Optical Advances in Laser Transit Anemometry

Smart, Anthony E.; Wisler, D. C.; Mayo, W.

doi:10.1115/1.3230739

Cited by 2 publications

(3 citation statements)

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“…Further improvements to the accuracy and precision can be achieved by increasing δ and by making R 1/0 = 1. ToFA systems often use δ as large as 95, which would improve the precision, and possibly accuracy, by an order of magnitude (Smart et al 1981). Changing R 1/0 can improve the light utilization efficiency from √ η = 0.0635 to as much as √ η = 0.207.…”

Section: Resultsmentioning

confidence: 99%

“…Several beam patterns and pattern generation methods have proven successful. Time-of-flight anemometry (ToFA) is a common class of approaches that was first introduced to measure velocity from smaller aerosols, and closer to walls than the standard approach, laser Doppler anemometry (LDA), could achieve (Smart et al 1981, Albrecht et al 2003. Rather than generate an interference pattern by intersecting two beams as LDA does, ToFA generates fewer but more intense laser sheets or focal points at a given standoff distance from each other.…”

Section: Introductionmentioning

confidence: 99%

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Time-of-flight anemometry using a displacement plate-beamsplitter

Bollt

2023

Meas. Sci. Technol.

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We propose the use of a second surface mirror as a displacement plate-beamsplitter to provide significant simplification and cost reduction of Time-of-Flight Anemometry (ToFA), without sacrificing precision and accuracy. These benefits are most pronounced for long-range applications. Our method's principle benefits are due to the few and simple components it requires as well as low sensitivity to both temperature effects and light source incoherence. We found that precise and accurate results are possible using a common consumer mirror as the main optical element and an inexpensive diode laser as the light source, which could broaden access to laser anemometry and make many industry applications economically feasible. The nature of the design also permits an increase in range for a given laser power since the method can utilize the entire optical area of the focusing lens/mirror independent of other design considerations and the cost of a flat second-surface mirror is usually negligible. To characterize the performance of this method, we develop a Cramer-Rao bound for a general class of ToFA's with multiple Gaussian beams under signal-independent Gaussian white noise. For a given measurement volume, the lowest velocity uncertainty is achieved by creating a standard two-sheet geometry: power-matching the first two beams by adjusting the beamsplitter and blocking the rest of the beams is optimal. However, keeping the higher order beams permits determination of flow direction. Conditions to achieve beam power-matching are given. An anemometer is built using a diode laser with 12mw 405nm beam using a total of just 3 transmitting optical components. Our setup has an accuracy of 99.1\%. The worst-case precision of 96.7\% nearly achieves the Cramer-Rao bound, although optimizing the setup more can lower the bound, and therefore allow increase in the performance by an order of magnitude or more.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time-of-flight anemometry using a displacement plate-beamsplitter

Bollt

2023

Meas. Sci. Technol.

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“…Optical techniques that have been used for flow measurements in turbomachinery include holographic interferometry [8], the gas fluorescence technique [9], the laser-two-focus technique (L2F, also called laser transit anemometry or LTA) [10 and 111, and laser velocimetry or LDV) [4 and 5]. Comparisons between LTA measurements and steady blade-to-blade solutions of the flow in a low speed four stage GE research rotor are given in [14]. Reference [151 gives an early comparison between LA measurements and a steady blade-to-blade solution in a GE transonic fan.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Two and Three Dimensional Flow Computations With Laser Anemometer Measurements in a Transonic Compressor Rotor

Chima

Strazisar

1982

Volume 1: Turbomachinery

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Two and three-dimensional inviscid solutions for the flow within a transonic axial compressor rotor at design speed are compared to laser anemometer measurements at maximum flow and near stall operating points. Computational details of the two-dimensional axisymmetric stream function solution and the three-dimensional full Euler solution are described. Upstream of rotor, the two-dimensional and three-dimensional solutions for radial distribution of relative Mach number and total pressure agree well with the data. Within the bow wave system and the blade row, the axisymmetric two-dimensional solution shows only qualitative agreement with the data.

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Optical Advances in Laser Transit Anemometry

Cited by 2 publications

References 0 publications

Time-of-flight anemometry using a displacement plate-beamsplitter

Time-of-flight anemometry using a displacement plate-beamsplitter

Comparison of Two and Three Dimensional Flow Computations With Laser Anemometer Measurements in a Transonic Compressor Rotor

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