Occurrence of global instability in hypersonic compression corner flow

Hao, Jiaao; Wen, Chih-Yung; Olivier, H.

doi:10.1017/jfm.2021.372

Cited by 31 publications

(68 citation statements)

References 48 publications

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“…On the S-plane in figure 8(a), spanwise-periodic flow structures are seen inside the separation bubble between the wedge surface, H l = 0, and the outer envelope of the separation bubble, a H l ≈ 0.15L y , where the spanwise vorticity, ωy , is zero. The outer envelope of the bubble can also be seen to be corrugated sinusoidally, on account of the stationary growing LSB instability, the three-dimensional footprint of which leads to the well-known striations that originate inside the LSB (Ginoux 1958;Shvedchenko 2009;Dwivedi et al 2019;Hao et al 2021). This spanwise-periodic global instability is identified here for the first time in the context of kinetic theory simulations.…”

Section: Analysis Of the Three-dimensional Dsmc Signalmentioning

confidence: 56%

“…Amplification of the spanwise-periodic perturbations was documented beyond a certain value of the corner angle, scaled according to triple-deck theory (Neiland 1969;Stewartson & Williams 1969;Rizzetta, Burggraf & Jenson 1978a;Neiland et al 2008). More recently, global linear instability analyses have unequivocally demonstrated the existence and linear amplification of stationary three-dimensional self-excited perturbations originating inside LSBs formed on account of shock impingement on a laminar boundary layer (Robinet 2007;Nichols et al 2017) or that forming in the steady laminar nominally two-dimensional compression ramp flow (Dwivedi et al 2019;Cao et al 2021;Hao et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

2022

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Linear three-dimensional instability is studied in the shock layer and the laminar separation bubble (LSB) induced by shock-wave/boundary-layer interactions in a Mach 7 flow of nitrogen over a double wedge with a $30^{\circ }\text {--}55^{\circ }$ cross-sectional profile. At a free-stream unit Reynolds number $Re=5.2\times 10^{4}\,{\rm m}^{-1}$ this flow exhibits rarefaction effects and has shock thicknesses comparable to the thickness of the boundary layer at separation. Flow features have been fully resolved using a high-fidelity massively parallel implementation of the direct simulation Monte Carlo method that captures the flow evolution from the inception of three-dimensionality, through linear growth of instabilities, to the early stages of nonlinear saturation. It is shown that the LSB sustains self-excited, small-amplitude perturbations that originate past the primary separation line and lead to spanwise-periodic wall striations inside the bubble and downstream of the primary reattachment line, as known from earlier experiments, simulations and instability analyses. A spanwise-periodic instability, synchronised with that in the separation zone, is identified herein for the first time, which exists in the internal structure of the separation and detached shock layers, and manifests itself as spanwise-periodic cats-eyes patterns in the global mode amplitude functions. The growth rate and the spanwise-periodicity length of linear disturbances in the shock layers and the LSB are found to be identical. Linear amplification of the most unstable three-dimensional flow perturbations leads to synchronised low-frequency unsteadiness of the triple point, with a Strouhal number of $St\approx 0.028$ .

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Section: Analysis Of the Three-dimensional Dsmc Signalmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

2022

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“…It is known that a separated flow has the potential to support self-sustained global instability (Theofilis 2011). Therefore, a globally stable flow can turn to an unstable one by enhancing the interaction strength, as shown by Hildebrand et al (2018) and Hao et al (2021).…”

Section: Introductionmentioning

confidence: 99%

“…In a significantly separated flow (i.e. a very strong interaction), self-excited instability may occur (Theofilis 2011;Hildebrand et al 2018;Hao et al 2021). Global stability analysis (GSA) considers the linear stability of small-amplitude perturbations superposed on a steady base flow without assumptions on the spatial variation of the base flow and the directionality of perturbation waves.…”

Section: Introductionmentioning

confidence: 99%

“…The identified unstable mode was shown to originate from the streamwise deceleration of the recirculating flow in the separation bubble. Hao et al (2021) found that the occurrence of global instability is closely linked with the onset of secondary separation (Shvedchenko 2009) beneath the primary separation bubble. Cao et al (2021b) studied a hypersonic compression-ramp flow at Mach 7.7 using direct numerical simulation (DNS) and GSA and demonstrated the presence of streamwise heat-flux streaks in the absence of external disturbances.…”

Section: Introductionmentioning

confidence: 99%

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Transition to turbulence in hypersonic flow over a compression ramp due to intrinsic instability

et al. 2022

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In this work, a transition process in a hypersonic flow over a cold-wall compression ramp is studied using direct numerical simulation (DNS) and global stability analysis (GSA). The free-stream Mach number and the Reynolds number based on the flat-plate length are 7.7 and $8.6 \times 10^5$ , respectively. The shock-induced pressure rise causes the boundary layer to separate on the flat plate, forming a separation bubble around the corner. Without introducing any external disturbances, the DNS captures the transition to turbulence downstream of flow reattachment. The DNS results agree well with the experimental data as well as theoretical predictions. To uncover the intrinsic instability in the flow system, GSA is employed to investigate the three-dimensionality of the two-dimensional base flow. Several stationary and oscillatory unstable modes are revealed, which result in spanwise periodicity inside and downstream of the separation bubble. The GSA and DNS results indicate that the intrinsic instability of the flow system triggers the formation of streamwise counter-rotating vortices and boundary-layer streaks near reattachment. The downstream transition to turbulence starts from the breakdown of the streamwise vortices and streaks. Moreover, the second harmonic of the most unstable global mode and a broadband low-frequency unsteadiness occur in the saturated flow, which has a significant influence on the transition process. In summary, the present study demonstrates a transition process in a hypersonic compression-ramp flow as a result of the intrinsic instability of the flow system.

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Investigation of turbulent high-speed flow over the double wedge at varying aft-wedge deflections

Ray,

2025

European Journal of Mechanics - B/Fluids

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Occurrence of global instability in hypersonic compression corner flow

Abstract: Abstract

Cited by 31 publications

References 48 publications

On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

Transition to turbulence in hypersonic flow over a compression ramp due to intrinsic instability

Investigation of turbulent high-speed flow over the double wedge at varying aft-wedge deflections

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