Visualization of Hypersonic Boundary-Layer Transition on a Slender Cone (Invited)

Laurence, Stuart J.; Wagner, Alexander; Ozawa, Hiroshi; Hannemann, Klaus

doi:10.2514/6.2014-3110

Cited by 16 publications

(5 citation statements)

References 42 publications

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“…A schlieren-based technique for the investigation of disturbances has been reported (Laurence et al 2012;Laurence, Wagner & Hannemann 2014a;Laurence et al 2014b). In those reports, high-resolution and time-resolved images of the second-mode instability structure, along with valuable spectral and cross-correlation data are presented.…”

Section: Measurement Of Second-mode Instabilitymentioning

confidence: 99%

Observations of hypervelocity boundary-layer instability

2015

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A novel optical method is used to measure the high-frequency (up to 3 MHz) density fluctuations that precede transition to turbulence within a laminar boundary layer in a hypervelocity flow. This optical method, focused laser differential interferometry, enables measurements of short-wavelength, high-frequency disturbances that are impossible with conventional instrumentation such as pressure transducers or hot wires. In this work, the T5 reflected-shock tunnel is used to generate flows in air, nitrogen and carbon dioxide with speeds between 3.5 and 5 km s ), density fluctuations are observed to grow in amplitude and transition from a single narrow band of frequencies consistent with the Mack or second mode of boundary-layer instability to bursts of large-amplitude and spectrally broad disturbances that appear to be precursors of turbulent spots. Disturbances that are sufficiently small in initial amplitude have a wavepacket-like signature and are observed to grow in amplitude between the upstream and downstream measurement locations. A cross-correlation analysis indicates propagation of wavepackets at speeds close to the edge velocity. The free stream flow created by the shock tunnel and the resulting boundary layer on the cone are computed, accounting for chemical and vibrational non-equilibrium processes. Using this base flow, local linear and parabolized stability (PSE) analyses are carried out and compared with the experimental results. Reasonable agreement is found between measured and predicted most unstable frequencies, with the greatest differences being approximately 15 %. The scaling of the observed frequency with the inverse of boundary-layer thickness and directly with the flow velocity are consistent with the characteristics of Mack's second mode, as well as results of previous researchers on hypersonic boundary layers.

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Section: Measurement Of Second-mode Instabilitymentioning

confidence: 99%

Observations of hypervelocity boundary-layer instability

2015

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“…In that work, the camera is used to gate the light at 500 ns. In [5,6], exposure times on the order of 10 ns are reported with the use of a commercially available laser capable of providing relatively short pulse trains.…”

Section: Introductionmentioning

confidence: 99%

Pulsed Laser Diode for Use as a Light Source for Short-Exposure, High-Frame-Rate Flow Visualization

Parziale

Schmidt

Damazo

et al. 2015

53rd AIAA Aerospace Sciences Meeting

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A pulsed laser diode (PLD) is demonstrated as a practical light source for high-speed digital schlieren and shearing-interferometric cinematogrpahy. Frame rates of greater than 300k fps with exposure times on the order of 10 ns have been achieved with an inexpensive and user-friendly setup. The light source has primarily been used in our laboratory to study nonsteady phenomena in high-speed gas flows. Examples are presented to illustrate the usefulness of the PLD as a light source with characteristics of a narrow band of wavelength, short exposure time, high frame-rate, and long pulse train duration.

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“…In the past, researchers have used shock tunnels and reflected-shock tunnels to study BLT [7][8][9][10][11][12][13]. More recently, in the HEG reflected-shock tunnel, Laurence et al [14][15][16] report a schlieren-based technique for the investigation of disturbances in hypervelocity boundary layers. In those reports, high-resolution and time-resolved images of the second-mode instability of a hypervelocity boundary layer on a slender cone data are presented.…”

Section: Introductionmentioning

confidence: 99%