Expansion Tube Freestream Disturbance Measurements using a Focused Laser Differential Interferometer

Lawson, Joel M.; Austin, Joanna

doi:10.2514/6.2020-1064

Cited by 16 publications

(2 citation statements)

References 6 publications

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“…However, this study is concerned with the transmitted shock itself, so the subsequent details of the HET operation will not be discussed further. An extensive campaign of freestream FLDI measurements were made in HET, with ∆Φ(t) acquired for a sample period spanning the entire start-up and test time [9]. This dataset contains shock velocities in the range 1.8 < U s < 3.6 km s −1 , in air at ambient temperature and pressures between 145 < P 1 < 275 mTorr.…”

Section: Experimental Campaign and Facility Overviewmentioning

confidence: 99%

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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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Section: Experimental Campaign and Facility Overviewmentioning

confidence: 99%

“…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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Measurements and analysis of hypersonic tripped boundary layer turbulence

et al. 2021

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Multi-point line focused laser differential interferometer for high-speed flow fluctuation measurements

et al. 2020

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A multi-point focused laser differential interferometer (FLDI) has been developed to measure density fluctuations at 16 points along a line. A pair of cylindrical lenses on the transmitter side of a conventional single-point FLDI instrument form two closely spaced ( ≤ 200 µ m ), orthogonally polarized, parallel laser lines at the instrument’s focus. On the receiver side of the instrument, the interference of the beams on a 16-element photodiode array results in a single line of measurements. The further addition of a Nomarski prism creates two separate measurement lines, and the addition of a second photodiode array to the instrument enables simultaneous measurements of density fluctuations along the two lines separated by several millimeters. These two lines of measurement can be conveniently oriented at any azimuthal angle relative to the instrument’s optical axis on the measurement plane, coinciding with the instrument’s focus. Two experiments were performed to demonstrate the capabilities of the instrument. In the first experiment, a laser-induced breakdown spark generated a traveling spherical shock wave, and measurements of the resulting density disturbance and wave velocity were obtained. These results were compared to high-speed schlieren images of the shock wave acquired at 400 kHz. In the second experiment, the multi-point FLDI instrument was used to measure density disturbances in the boundary layer of a flat plate in a Mach 6 freestream flow. The measurements were made along two lines, both approximately 6 mm in length, extending from the surface of the plate through the boundary layer. High-speed schlieren images were acquired at 100 kHz during separate wind tunnel runs at matching unit Reynolds numbers to visualize the unsteady boundary layer flow and compare to the FLDI measurements.

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Expansion Tube Freestream Disturbance Measurements using a Focused Laser Differential Interferometer

Cited by 16 publications

References 6 publications

Focused laser differential interferometer response to shock waves

Focused laser differential interferometer response to shock waves

Measurements and analysis of hypersonic tripped boundary layer turbulence

Multi-point line focused laser differential interferometer for high-speed flow fluctuation measurements

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