Application of Focused Laser Differential Interferometry (FLDI) in a Supersonic Boundary Layer

Ceruzzi, Andrew; Callis, Braeden; Weber, Daniel; Cadou, Christopher P.

doi:10.2514/6.2020-1973

Cited by 35 publications

(5 citation statements)

References 23 publications

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“…To determine convective velocities, simultaneous measurements at two adjacent points are essential. Leveraging the design principles from the 2P-FLDI [23,[28][29][30], an additional Wollaston prism (W 0 ) with an increased splitting angle was introduced. This prism precedes the existing Wollaston prism (W 1 ) along the transmit path, effectively dividing the measurement path into two adjacent paths aligned with the flow direction.…”

Section: P-cfldi Systemmentioning

confidence: 99%

Measurement of the Convection Velocities in a Hypersonic Turbulent Boundary Layer Using Two-Point Cylindrical-Focused Laser Differential Interferometer

Huang,

Xue,

2024

Aerospace

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A two-point cylindrical-focused laser differential interferometer (2P-CFLDI) system and a conventional Z-type Schlieren were used to measure the hypersonic turbulent boundary layer on a flat plate at Mach number Ma = 6 and Reynolds number Re = 1.08 × 106 m−1. The boundary layer thickness at the measurement location and the noise radiation angle were obtained by post-processing the Schlieren image. The 2P-CFLDI data underwent cross-correlation analysis to calculate the mean convective velocities at different heights and compared with previous experimental and numerical results. The experimentally measured mean convective velocities agree with the trend of available DNS and experimental results. The mean convective velocity near the wall is significantly larger than the local mean velocity and is the main noise source region. Further filtering treatment shows that the convective velocity of the disturbed structure decreases gradually with the increase in the disturbance scale. The differences between convective velocities at different scales are significantly larger outside the boundary layer than inside the boundary layer, which is in agreement with the findings of the previous hot wire experiments. Near the wall, large-scale disturbances mainly determine the localized mean convective velocity, which are the main source of noise radiation for the hypersonic turbulent boundary layer.

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Section: P-cfldi Systemmentioning

confidence: 99%

Measurement of the Convection Velocities in a Hypersonic Turbulent Boundary Layer Using Two-Point Cylindrical-Focused Laser Differential Interferometer

Huang,

Xue,

2024

Aerospace

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“…Focused-laser differential interferometry (FLDI) has recently become a valuable optical measurement technique for diagnostics of high-speed transitional [1][2][3] and turbulent flows [4,5]. The technique, discussed in detail by several authors [6][7][8][9], provides measurements of the index of refraction changes which are spatially filtered across the beam path by the focusing aspect of the beams.…”

Section: Introductionmentioning

confidence: 99%

“…While FLDI was originally developed in the 1970s by George and Smeets [13], several variations and improvements of the interferometer have been developed to suit modern measurement needs. Jewell et al [14] demonstrated that cross-correlation analyses can be used in tandem with two-point FLDI measurements for measurement of convective velocities, and this work was applied by Ceruzzi et al [5] for measurements of turbulent high-speed boundary layers. Houpt et al [15] and Hopkins et al [16] demonstrated that FLDI could be done with cylindrical lenses instead of the usual spherical lens, which allowed for better measurements of boundary layers on non-axisymmetric geometries.…”

Section: Introductionmentioning

confidence: 99%

Multi-depth focused laser differential interferometer based on chromatic aberration

Webber,

Constantin,

Edwards

et al. 2024

Appl. Opt.

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A modified version of focused laser differential interferometry (FLDI) is demonstrated with adjacent beam pairs distributed along the optical axis. This feature is accomplished using two different wavelengths of light in the interferometer and accounting for the chromatic aberration of the lenses in the optical setup. It is demonstrated that ray trace calculations can be modified to predict the focal points of each of the two different colored beams, and experiments using a tube jet and a laser-induced blast wave show the instrument still has the expected features of an FLDI as well as continued capability for velocimetry. This modification is in effort to allow FLDI to be used for the analysis of three-dimensional flows, especially if combined with other multi-point variations and targeting high-frequency flow content.

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“…Freestream turbulence power spectra, with comparisons to hot-wire anemometry, were made in the Penn State Supersonic Wind Tunnel and AEDC Hypervelocity Wind Tunnel 9 [4,5]. Since then, the FLDI has been applied to several other supersonic and hypersonic ground-testing facilities [6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Focused laser differential interferometer response to shock waves

Lawson

Austin

2021

Meas. Sci. Technol.

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The focused laser differential interferometer (FLDI) can be used to measure rapid density fluctuations non-intrusively in high-speed flow applications. Being a non-imaging shearing interferometer, FLDI response can be accurately modeled using a paraxial ray-tracing scheme. We present the details of a new numerical implementation of this scheme, capable of accepting flow-field input from analytical models, computational fluid dynamics (CFD) results, and experimental data. This implementation has previously been validated for static (laminar jet) and dynamic (ultrasound-generated) changes in index of refraction by Lawson et al. In this work, we examine the FLDI response to shock waves propagating at up to Mach 10, in Caltech’s hypervelocity expansion tube. While the timescale and approximate form of the signal can be recovered using a simple inviscid, planar shock model, it is found that the inclusion of viscous shock effects allows an accurate simulation of both the magnitude and detailed shape of the experimental response. This is a further analytical validation of the FLDI model that extends beyond the results of the existing dynamic validation case. The model implementation is then coupled to a CFD code, and predictions reproduce experimental FLDI response to a complex shock-dominated flow-field.

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Application of Focused Laser Differential Interferometry (FLDI) in a Supersonic Boundary Layer

Cited by 35 publications

References 23 publications

Measurement of the Convection Velocities in a Hypersonic Turbulent Boundary Layer Using Two-Point Cylindrical-Focused Laser Differential Interferometer

Measurement of the Convection Velocities in a Hypersonic Turbulent Boundary Layer Using Two-Point Cylindrical-Focused Laser Differential Interferometer

Multi-depth focused laser differential interferometer based on chromatic aberration

Focused laser differential interferometer response to shock waves

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