Characterization of a Focused Laser Differential Interferometer

Lawson, Joel M.; Neet, Mallory C.; Grossman, Ilan J.; Austin, Joanna

doi:10.2514/6.2019-2296

Cited by 35 publications

(2 citation statements)

References 8 publications

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“…The resulting signals are recorded on an AMOtronics transient recorder with DC coupling and a 100 MHz sampling rate. Conversion of the recorded voltage into the FLDI phase difference is performed following [60]. Prior to each shock tunnel run, the FLDI is adjusted to half the maximum output value, for optimal sensitivity.…”

Section: Methodsmentioning

confidence: 99%

Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

et al. 2023

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This work investigates a hypersonic turbulent boundary layer over a 7° half angle cone at a wall-to-total temperature ratio of 0.1, M∞=7.4 and Re∞m=4.2×106 m−1, in terms of density fluctuations and the convection velocity of density disturbances. Experimental shock tunnel data are collected using a multi-foci Focused Laser Differential Interferometer (FLDI) to probe the boundary layer at several heights. In addition, a high-fidelity, time-resolved Large-Eddy Simulation (LES) of the conical flowfield under the experimentally observed free stream conditions is conducted. The experimentally measured convection velocity of density disturbances is found to follow literature data of pressure disturbances. The spectral distributions evidence the presence of regions with well-defined power laws that are present in pressure spectra. A framework to combine numerical and experimental observations without requiring complex FLDI post-processing strategies is explored using a computational FLDI (cFLDI) on the numerical solution for direct comparisons. Frequency bounds of 160 kHz <f<1 MHz are evaluated in consideration of the constraining conditions of both experimental and numerical data. Within these limits, the direct comparisons yield good agreement. Furthermore, it is verified that in the present case, the cFLDI algorithm may be replaced with a simple line integral on the numerical solution.

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Section: Methodsmentioning

confidence: 99%

Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

et al. 2023

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“…Since the interferometer is adjusted to an infinite fringe configuration, this results in an uniform intensity change after the beams are made to interfere with the polarizer before the photodiode. This approach is present in Lawson et al (2019), only using Wollaston prisms instead of Sanderson. Conversion of voltage produced by the photodetectors into phase difference was also performed following that work.…”

Section: Double-foci Fldimentioning

confidence: 99%

A low-effort and inexpensive methodology to determine beam separation distance of multi-foci FLDI

Camillo

Wagner

2022

Exp Fluids

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A new method is presented to measure the separation distance between probing volumes of closely spaced multi-foci Focused Laser Differential Interferometers (FLDI). The accuracy and precision of this distance measurement directly translate into the quality of convection velocity measurements performed by means of arrays of FLDI. The suggested method is based on the detection of a propagating weak blast wave, generated with a simple and inexpensive apparatus using an automotive spark plug. Demonstration is conducted using an FLDI with two foci (D-FLDI). The generated blast wave is probed at multiple distances from its source to verify its weakening into an acoustic pulse, which offers ideal conditions to the proposed methodology. D-FLDI separation distance measurement using the new approach is compared to measurements using beam profiler images and to the alternative currently established in the literature, based on the FLDI response to a moving weak lens. Tests are made on varying internal configurations of the D-FLDI, while the distance between the two systems is kept constant. Results show the present method to have improved accuracy and robustness in comparison with the moving lens approach, while requiring significantly less effort. Measured separation distances obtained from blast wave detections in a single location are within $$0.5 \%$$ 0.5 % of the reference value measured through the beam profiler. This procedure is therefore a practical and reliable alternative to the measurement using beam profiler imaging, with similar quality. Its advantages concern associated costs, flexibility when measuring in constrained spaces such as in proximity to walls, and applicability to systems in which beam imaging is not an option, such as multi-point line FLDI.

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