Nonlinear transition mechanism on a blunt cone at Mach 6: oblique breakdown

Hartman, Andrew; Hader, Christoph; Fasel, Hermann F.

doi:10.1017/jfm.2021.109

Cited by 29 publications

(16 citation statements)

References 22 publications

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“…The transition investigation presented here follows the strategy employed in the earlier studies by Fasel and co-workers (see, [29,35]). The first step is to simulate the twodimensional laminar base flow over a blunted flat plate, including the leading edge, with a low-order scheme on a relatively coarse grid.…”

Section: Numerical Methodology and Boundary Conditionsmentioning

confidence: 99%

“…Other mechanisms, such as the interaction of boundary-and entropic-instabilities, subharmonic resonance of entropic-instabilities, may also lead to transition, but are not pursued in the current paper, since the focus is on the transition induced by oblique disturbances in the entropy-layer. This aids in clarifying the differences in the oblique breakdown mechanisms on blunt cones [29,30] with blunted plates. Nevertheless, the transition process depends on the freestream/tunnel disturbance spectrum, which needs to be modeled to gain a more complete picture of the dominant mechanisms.…”

Section: Linear Evolution Of Three-dimensional Wavepacketsmentioning

confidence: 97%

“…For the same experimental conditions, Paredes et al [24] also reported very-low growth of modal entropic-instabilities. Hartman et al [29] studied the evolution of linear wavepackets on the above cone configuration and reported oblique entropic-instabilities of very large growth-rates. The corresponding disturbance profile reported by Meersman et al [34] closely resembles that of the flat plate entropic-instabilities discussed earlier.…”

Section: A Steady Base Flow and Linear Stability Analysismentioning

confidence: 99%

“…Potential mechanisms for the receptivity of these non-modal waves was provided by Russo et al [27] by considering particle impingement and Goparaju et al [28] by the interaction of stochastic disturbances with the leading-edge. Further, Hartman et al [29] examined the response of wavepackets initiated in the entropy-layer and reported large growth of linear oblique disturbances closer to the leading edge, which were not captured by the conventional linear/parabolic stability theories.…”

Section: Introductionmentioning

confidence: 99%

“…Their analysis indicated that such disturbances can nonlinearly interact above the boundary-layer edge, and induce stationary streaks that penetrate the boundary-layer, leading to turbulence onset by streak breakdown. Furthermore, Hartman et al [29] noted the importance of including nonlinear effects to capture relevant transition phenomena observed in high-speed tunnel experiments, and considered the evolution of high-amplitude entropic-instabilities through controlled oblique breakdown mechanisms [31][32][33]. They identified the progression of transition through the dynamics of positive and negative temperature fluctuations, with the latter penetrating and contaminating the boundary-layer, leading to turbulence onset, while the former remaining largely unchanged.…”

Section: Introductionmentioning

confidence: 99%

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Role of entropic-instabilities in laminar-turbulent transition on a blunted flat plate

Goparaju¹,

Gaitonde²

2021

Preprint

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The effects of entropic-instabilities on the laminar-turbulent transition dynamics of a blunted flat plate at Mach 4 are numerically investigated through linear and nonlinear approaches. Linear wavepacket analysis reveals amplifying oblique first-modes as well as planar and oblique entropylayer disturbances. The receptivity of entropic-instabilities is found to be largest for actuation seeded in the entropy-layer; the corresponding linear evolution is characterized by an intensification in the wall-normal plane, coupled with streamwise tilting. Disturbances in the entropy-layer interact non-linearly with each other through the oblique breakdown mechanism, inducing streamwise streaks in the boundary-layer. These undergo further destabilization downstream leading to turbulence onset. Different mechanisms of interest are extracted with modal decomposition techniques best suited for each. Dynamic mode decomposition (DMD) reveals sinuous subharmonic oscillations induced by the entropic-disturbances as the dominant streak instability mechanism. On the other hand, spectral proper orthogonal decomposition (SPOD) elicits the slanted hook -shaped structures in the temperature perturbations, which are attributable to the Orr like-mechanism in the entropy-layer. Furthermore, cross-bispectral mode decomposition (CBMD) shows that the temperature perturbations amplify on the crests of the low-speed streaks in the entropy-layer and generates disturbances through triadic interactions. These newer disturbances further interact, resulting in the transfer of perturbation energy into the boundary-layer. This eventually leads to spanwise homogenization and near-wall streak generation, reflecting late nonlinear stages of transition. Towards the end of breakdown region, spectral broadening accompanied by the appearance of an inertial sub-range in the boundary-layer indicates the approach of the flow towards turbulence.

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Section: Numerical Methodology and Boundary Conditionsmentioning

confidence: 99%

Section: Linear Evolution Of Three-dimensional Wavepacketsmentioning

confidence: 97%