Hypersonic Boundary-Layer Transition Features from High-Speed Schlieren Images

Kennedy, Richard E.; Laurence, Stuart J.; Smith, Michael S.; Marineau, Eric C.

doi:10.2514/6.2017-1683

Cited by 15 publications

(4 citation statements)

References 8 publications

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“…Experiment S3 is chosen here to demonstrate the wavepacket development as it contains the most mature waves, although it is noted that the waves from experiment S2 evolve similarly, with a two-profile peak in the fundamental content observed for more mature waves. These observations are also qualitatively consistent with the findings of Kennedy et al (2017) for mature second-mode wavepackets developing in a Mach-14 free stream. No near-wall peak such as that observed…”

Section: Individual Wavepacket Developmentsupporting

confidence: 89%

Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6

et al. 2022

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Experiments are performed to investigate the effect of nose-tip bluntness on the instability mechanisms leading to boundary-layer transition on a $7^{\circ }$ half-angle cone in a Mach-6 free stream. The development of disturbances is characterized using a combination of high-speed calibrated schlieren images and pressure measurements, and the data are compared with results computed using the parabolized stability equations. The approximately 414 mm long cone model is equipped with an interchangeable nose tip ranging from sharp to 5.08 mm in radius. For nose tips with a radius $R_{N}<2.54\ {\rm mm}$ , second-mode instability waves are the dominant mechanism leading to transition. Time-averaged frequency spectra computed from the calibrated schlieren visualizations and pressure measurements are used to compute the second-mode most-amplified frequencies and integrated amplification rates ( $N$ factors). Good agreement is observed between the measurements and computations in the linear-growth regime for the sharp-nose configuration at each free-stream condition. Additionally, a bispectral analysis identifies quadratic phase locking of frequency content responsible for the growth of higher harmonics. For nose tips of $R_{N}\geqslant 2.54\ {\rm mm}$ , the schlieren visualization region is upstream of the entropy-layer swallowing length, and second-mode waves are no longer visible within the boundary layer; instead, elongated, steeply inclined features believed to be associated with non-modal instability mechanisms develop between the entropy-layer and boundary-layer edges. Simultaneously acquired surface pressure measurements reveal high-frequency pressure oscillations similar to second-mode instability waves associated with the trailing edge of these non-modal features.

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Section: Individual Wavepacket Developmentsupporting

confidence: 89%

Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6

et al. 2022

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“…The ratio of propagation speed to boundary-layer-edge velocity, U p /U e , is also shown for each condition, with U e calculated using the Taylor-Maccoll equation. The second-mode propagation speeds are equal to approximately 90% of the edge velocity, consistent with prior work on hypersonic boundary layers over slender cones [16,5].…”

Section: Propagation Speedssupporting

confidence: 85%

“…Although this reconstruction technique has already been described in Ref. [16], given its importance in the present analysis, we outline it again here. The first step in the reconstruction is the calculation of the average propagation speed of the second-mode wave-packets; further details of this procedure are provided in section 3.2.…”

Section: Time-resolved Pixel Intensity Signal Reconstructionmentioning

confidence: 99%

“…If analysis is directly applied to the schlieren videos, however, then the bandwidth is Nyquist-limited to frequencies below one half the frame rate, which will generally preclude resolving harmonic development. The temporal reconstruction technique of Kennedy et al [16] takes advantage of the uniform propagation speed of second-mode fundamental and harmonic disturbances [19] to significantly increase the effective sampling rate. Studies on hypersonic boundary layers over slender cones by Kennedy [14] utilized this technique for discrete locations along the maximum rms disturbance streamline.…”

Section: Introductionmentioning

confidence: 99%

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Global analysis of nonlinear second-mode development in a Mach-6 boundary layer from high-speed schlieren data

Sousa

Kennedy

King

et al. 2022

Preprint

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The second-mode instability on a 7◦ half-angle sharp cone at Mach 6 is analyzed using high-speed calibrated schlieren imagery at a frame rate near the expected fundamental frequency. Experiments were conducted in the NASA Langley 20-Inch Mach 6 facility at unit Reynolds numbers between 6.56×106 and 9.71×106 m−1. Time-resolved pixel intensity signals throughout the boundary layer are reconstructed using spatially available data in the schlieren images to recover an effective sampling rate of over 10 MHz; these are then converted to quantitative density gradients using a thin-lens-based calibration technique. A global analysis is performed on the schlieren data to investigate the nonlinear growth of the second-mode fundamental and harmonic content. Pointwise measures of the autobicoherence are used to identify specific triadic interactions and the locations of their highest levels of quadratic phase coupling. Significant resonance interactions between the second-mode fundamental and harmonic instabilities were found along with interactions between these and the mean flow. Bispectral mode decomposition is employed to educe the flow structures associated with these interactions. A similar analysis is performed for the power spectrum, with power spectral densities computed for each pixel’s time-series and spectral proper orthogonal decomposition employed to derive the modal structure and energy of the flow at specific frequencies. Comparisons between the bispectral quantities and second-mode power show that nonlinear interactions, particularly resonance interactions, are closely correlated with spatiotemporal modulation of disturbances during the nonlinear stage of transition.

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Global analysis of nonlinear second-mode development in a Mach-6 boundary layer from high-speed schlieren data

Sousa,

Kennedy,

King

et al. 2024

Exp Fluids

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Hypersonic Boundary-Layer Transition Features from High-Speed Schlieren Images

Cited by 15 publications

References 8 publications

Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6

Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6

Global analysis of nonlinear second-mode development in a Mach-6 boundary layer from high-speed schlieren data

Global analysis of nonlinear second-mode development in a Mach-6 boundary layer from high-speed schlieren data

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