A multi-point focused laser differential interferometer for characterizing freestream disturbances in hypersonic wind tunnels

Gillespie, Graeme; Ceruzzi, Andrew; Laurence, Stuart J.

doi:10.1007/s00348-022-03522-6

Cited by 14 publications

(21 citation statements)

References 46 publications

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“…The signals were then digitized by a 14-bit Picoscope 5444D and sampled at 25 MHz. The relationship between the output voltage, measured phase change and density gradient is outlined in Gillespie et al (2022).…”

Section: Focused Laser Differential Interferometermentioning

confidence: 99%

“…Low-wavenumber disturbances, however, may still be corrupted by sidewall boundary layers, while high wavenumbers are more representative of disturbances in the core flow region. Gillespie et al (2022) presents an analysis of this signal attenuation for a similar four-point FLDI in the Mach-6 configuration of the HyperTERP facility. An important parameter used when determining the influence of the sidewall boundary layers on the measured signal is the Gaussian beam radius, ω.…”

Section: Focused Laser Differential Interferometermentioning

confidence: 99%

“…To do so, the FLDI sensitivity transfer function developed by Ceruzzi and Cadou (2022) was applied to the four-point FLDI setup. Following the procedure outlined by Gillespie et al (2022), a cutoff wavenumber is conservatively estimated, whereby disturbances with larger wavenumbers can be attributed to the core flow. In addition to properties of the FLDI (λ 0 , ω 0 , ∆x 1 ), the calculation of the cutoff wavenumber is dependent on the sidewall boundary-layer thickness, half-width of the flow region (25.4 mm), and the ratio of frequency-averaged disturbance amplitudes of the sidewall boundary layers relative to the core flow.…”

Section: Focused Laser Differential Interferometermentioning

confidence: 99%

“…Using the procedure described by Gillespie et al (2022), the streamwise convection velocities were analyzed with a cross-correlation of the streamwise FLDI signal pairs 1-3 and 2-4, computed over consecutive 1 ms intervals throughout the 5 ms test time. For each injection condition, no significant differences in mean convection velocity was found, indicating that the injection process is not affecting the external flowfield.…”

Section: Fldi Convection Velocitymentioning

confidence: 99%

“…For each condition listed in Table 2, the FLDI voltage signals were converted to phase fluctuations as described in Gillespie et al (2022). The power spectral density (PSD) of the phase fluctuations was then calculated using Welch's method with Hanning windows of length 278 µs and 50% overlap, and the amplitude spectral density (ASD) was computed from the square root of the PSD.…”

Section: Fldi Fluctuationsmentioning

confidence: 99%

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Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Gillespie

Laurence

2023

Preprint

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The effects of vibrational nonequilibrium processes on turbulence-generated acoustic noise were investigated in a Mach-2.8 shock-tunnel facility. Gas mixtures with relevant absorption characteristics were first identified from measurements of attenuation coefficients using a heated acoustic chamber. In the shock-tunnel facility, CO2, N2, He, and He/CO2 mixtures were injected into the lower boundary layer of the flow through a porous plate. A four-point Focused Laser Differential Interferometer (FLDI) positioned above the turbulent boundary layer was used to obtain simultaneous freestream measurements of entropic fluctuations propagating along streamlines and acoustic disturbances along Mach lines. Correlated fluctuations of Mach-line and streamline FLDI signal pairs were analyzed with a cross power spectral density (CPSD). Compared to a boundary layer of pure air, the injection of 30%, 35%, and 40% He/CO2 mixtures resulted in reduced fluctuation powers correlated along a Mach line in the frequency range of 200-800 kHz. Minimal reductions in fluctuation power were found along a streamline, indicating that the vibrationally active gas is affecting acoustic disturbances and not entropic disturbances. A mathematical disturbance model was created to examine the sensitivity of the measured attenuation to acoustic disturbances propagating from the lower boundary layer only. Disturbances were modeled as Gaussian wave packets of finite width, propagating in the streamwise direction and along Mach lines from the four walls of the test section. Modeling the acoustic disturbances from the lower boundary layer with a 15-30% amplitude reduction resulted in amplitude spectral densities and CPSDs that agreed well with the FLDI measurements.

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Section: Focused Laser Differential Interferometermentioning

confidence: 99%

Section: Focused Laser Differential Interferometermentioning

confidence: 99%

Section: Focused Laser Differential Interferometermentioning

confidence: 99%

Section: Fldi Convection Velocitymentioning

confidence: 99%

Section: Fldi Fluctuationsmentioning

confidence: 99%

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Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Gillespie

Laurence

2023

Preprint

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Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Gillespie,

Laurence

2024

Exp Fluids

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Experimental investigation about the aerodynamic noise caused by hypersonic turbulence

Liu,

2024

Physics of Fluids

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In this study, experimental investigations pertaining to aerodynamic noise are conducted in a hypersonic quiet wind tunnel, which possesses the unique capability of operating in both quiet and conventional modes, achieved by controlling the bleed slot to regulate the boundary layer flow. The measurement of aerodynamic noise and analysis of coherent structures of hypersonic turbulence are accomplished employing pressure probes and the nano-tracer-based planar laser scattering technique. The characterization of aerodynamic noise within the freestream unveils that noise generated by turbulent structures on the nozzle wall is the primary factor affecting the turbulence intensity of the freestream flow. Regarding the acoustic radiation noise generated by the turbulence on the nozzle wall, a peak frequency ranging from 54 to 57 kHz is observed in its spectrum within a unit Reynolds number range of 0.3×107–1.1×107 m−1. Under different operation modes, the freestream pitot-pressure data feature the similar spectral slope of f−2.2 and f−12 before and after the aforementioned peak. Through wavelet analysis, scales of the coherent structure in the turbulent boundary layer are examined, revealing that the maximum energy streamwise scale of the coherent structure is approximately 2.47 mm under the unit Reynolds number of 0.7×107 m−1. The product of this scale with the characteristic frequency of 56 kHz obtained from fluctuating pressure measurements is close to the local sound speed of about 140 m/s.

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A multi-point focused laser differential interferometer for characterizing freestream disturbances in hypersonic wind tunnels

Cited by 14 publications

References 46 publications

Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Attenuation of the acoustic noise radiated by a compressible boundary layer through injection of a vibrationally active gas

Experimental investigation about the aerodynamic noise caused by hypersonic turbulence

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