Interaction of second-mode wave packets with an axisymmetric expansion corner

Butler, Cameron; Laurence, Stuart J.

doi:10.1007/s00348-021-03235-2

Cited by 15 publications

(12 citation statements)

References 22 publications

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“…The angle of these radiating features (which remains approximately constant) is suggestive of frozen Mach radiation, which would indicate that the generating disturbances are moving supersonically with respect to the external flow. To confirm this, in figure 31 we present disturbance propagation speeds computed based on the cross-correlation methodology described by Butler & Laurence (2021b). The cross-correlation was performed along a pseudo-streamline now constructed using the maximum intensity of the shear-layer disturbances, with the intensity time-series bandpass filtered from 40 kHz to 120 kHz.…”

Section: Separated-flow Casesmentioning

confidence: 87%

“…The total specific enthalpy was held approximately constant at MJ kg, corresponding to a temperature of K, with unit Reynolds numbers, , of , and achieved by varying the reservoir pressure (viscosity is calculated here using Sutherland's law). Reference reservoir (subscript 0) and corresponding free stream properties (subscript ) for each condition are detailed in table 1; the methodology used to calculate these conditions and an overview of the free stream characterization are given in Butler & Laurence (2021 b ). Typical reservoir pressure traces for all conditions are provided in figure 1.…”

Section: Experimental Methodologymentioning

confidence: 99%

“…A discussion of the major SPOD mode shapes for the +10 extension at the three conditions has been provided in Butler & Laurence (2021 b ). Here we give a brief overview, focusing on those shapes corresponding to frequencies that exhibit significant nonlinear interactions in § 6.…”

Section: Spectral Proper Orthogonal Decompositionmentioning

confidence: 99%

“…Finally, the present authors (Butler & Laurence 2021 b ) experimentally examined the transitional Mach-6 flow over a slender, 5 cone/flare configuration with a 10 angle increase, sufficient to generate a limited separation bubble at the conditions tested. Both second-mode disturbances and lower-frequency shear-layer instability waves along the boundary of the separated region were observed with an ultra-high-speed schlieren visualization technique and high-frequency pressure measurements.…”

Section: Introductionmentioning

confidence: 98%

“…This choice of angles encompasses a range of mean flow fields from fully attached through to substantially separated, while limiting the deflection to within a range that one might realistically expect to encounter on a practical hypersonic vehicle. The global diagnostic and analysis techniques introduced in our earlier work (Butler & Laurence 2021 a , b ) are employed to examine both the behaviour of incoming second-mode disturbances as they traverse the SWBLI and the instability mechanisms intrinsic to the SWBLI itself. In § 2 we describe the experimental facility, test article and diagnostics used.…”

Section: Introductionmentioning

confidence: 99%

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Transitional hypersonic flow over slender cone/flare geometries

Butler

Laurence

2022

J. Fluid Mech.

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Experiments are performed in a Mach-6 shock tunnel to examine the laminar-to-turbulent transition process associated with a sudden increase in surface angle on a slender body. A cone/flare geometry with a 5 $^\circ$ frustum and compression angles ranging from 5 $^\circ$ to 15 $^\circ$ allow a range of mean flow configurations, spanning an attached shock-wave/boundary-layer interaction to a fully separated one; the unit Reynolds number of the flow is also varied to modify the state of incoming second-mode boundary-layer disturbances. Ultra-high-speed schlieren visualizations provide a global picture of the flow development, supplemented by high-frequency surface pressure measurements. For the 5 $^\circ$ compression, the unsteady flow field is dominated by the second-mode waves, whose breakdown to turbulence is generally accelerated (compared with the straight-cone configuration) by encountering the angle change. As the compression angle is increased to induce separation, lower-frequency disturbances appear along the separated shear layer that exhibit much larger amplification rates than the incoming second-mode waves; the latter effectively freeze in amplitude downstream of the separation point before rapidly breaking down upon reattachment. The shear-layer disturbances become dominant at the largest compression angle tested. Radiation of disturbance energy to the external flow is consistently observed: this generally occurs along mean flow features (flare, separation or reattachment shocks) for the second-mode disturbances and spontaneously for the shear-layer waves. The combined application of spectral proper orthogonal decomposition and a global bispectral analysis allows the identification of important unsteady flow structures and the association of these with prominent nonlinear interactions in the various configurations.

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Section: Separated-flow Casesmentioning

confidence: 87%

Section: Experimental Methodologymentioning

confidence: 99%

Section: Spectral Proper Orthogonal Decompositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Transitional hypersonic flow over slender cone/flare geometries

Butler

Laurence

2022

J. Fluid Mech.

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Transitional shockwave/boundary layer interaction experiments in the R2Ch blowdown wind tunnel

et al. 2022

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Transitional Shockwave/Boundary Layer Interactions (SBLI) is studied experimentally. Experiments are conducted on a hollow-cylinder flare model in the R2Ch blowdown facility at a Mach number of 5 for three different Reynolds numbers in the transitional regime. Unsteady wall pressure measurements are conducted along with mean and unsteady heat flux measurements and high-speed Schlieren imaging. The images are then processed using Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) to extract relevant information. Two main phenomena are identified and documented: the oblique modes traveling in the shear layer above the recirculation region and the streaks appearing in the reattachment region. New results illustrating the multiple physical origins of the streaks, either linked with globally unstable modes and convectively unstable mechanisms, are discussed.

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