Focused Laser Differential Interferometric Investigation of Turbulent Jet Spectra

Hameed, Ahsan; Parziale, Nick J.

doi:10.2514/1.a35292

Cited by 14 publications

(2 citation statements)

References 21 publications

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“…( 2) for a direct calculation of the density field from the measured optical path difference. However, the amplitude response of the FLDI system can be studied by analyzing generic density fields [3][4][5][6]. The amplitude response is mainly a result of two effects: the fixed beam distance Δx and the averaging over the beam diameter along the optical axis.…”

Section: Resultsmentioning

confidence: 99%

“…First, several coherent structures or turbulent spots arranged side by side within the boundary layer can simultaneously pass through the sensitive volume of the FLDI setup. Second, the assumptions for deriving analytical transfer functions of the FLDI technique [3][4][5][6] are rarely satisfied in real flow situations and therefore cannot be used for data correction. Third, flat plate models pose a particular challenge, because the light cones outside the focal plane are shadowed by the model itself (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Wall-Normal Focused Laser Differential Interferometry

Lunte,

Schülein

2024

AIAA Journal

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A new approach for measuring boundary-layer disturbances with focused laser differential interferometry (FLDI) for planar models is presented. By integrating a glass window into a flat plate, the optical axis was aligned normal to the model surface, and the focal plane was set inside the boundary layer. By determining the extent of the sensitive volume along the optical axis and calculating the analytical transfer function of the setup, the implications of the FLDI properties on the measured data are analyzed. Measurements performed on a flat plate at Mach 6 are used to demonstrate the effects of the laminar–turbulent transition on the spectral distribution of the power density and to explicitly verify the detectability of the expected second-mode instabilities. Advantages and disadvantages of the proposed setup compared to the conventional one are discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wall-Normal Focused Laser Differential Interferometry

Lunte,

Schülein

2024

AIAA Journal

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Hypersonic boundary-layer instability characterization and transition downstream of distributed roughness

Gui,

Zhang,

et al. 2023

Exp Fluids

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Focused laser differential interferometry post-processing methodology for flowfields with circular symmetry

Camillo

Wagner

2023

Review of Scientific Instruments

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An analytic methodology is presented to reconstruct the pressure waveform of flowfields with circular symmetry from the phase shift detected with Focused Laser Differential Interferometry (FLDI). A weak blast wave generated by an electric spark in ambient air is investigated with the proposed approach. Values of separation distance between the differentiating foci of the FLDI Δ x of 76, 120, 175, and 252 μm are employed to probe the flowfield at locations between 3 and 50 mm from the spark source. In a subset of these distances, reference measurements of peak pressure obtained with a surface pressure sensor indicate good agreement with the reconstructed data when small separation distances are used. Further analysis of FLDI reconstructed data is conducted using theoretical correlations for N-waves in terms of the distribution of pressure peak amplitude and compression phase as the wave front propagates. Agreement with theory is verified for all differentiation separation distances except the largest, for which peak pressure comparison shows a 10% loss of measured vs predicted value. A computational FLDI is employed to scrutinize the simplifying hypotheses supporting the waveform reconstruction approach. The direct comparison between experimental and computational FLDI output reveals additional discrepancies for intermediate Δ x values but very good agreement for the smallest Δ x. The proposed methodology is thus verified to be reasonable, upon appropriate minimization of the FLDI differentiation distance. A parametric analysis using computational FLDI indicates the adequate value of FLDI Δ x to be 20% or less of the flowfield characteristic length in terms of density gradient.

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Focused Laser Differential Interferometric Investigation of Turbulent Jet Spectra

Cited by 14 publications

References 21 publications

Wall-Normal Focused Laser Differential Interferometry

Wall-Normal Focused Laser Differential Interferometry

Hypersonic boundary-layer instability characterization and transition downstream of distributed roughness

Focused laser differential interferometry post-processing methodology for flowfields with circular symmetry

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