Transitional flow structures in heated hypersonic boundary layers

Zhu, Yiding; Zhu, Wenkai; Gu, Dejian; Lee, Cunbiao; Smith, Charles R.

doi:10.1063/5.0091192

Cited by 7 publications

(1 citation statement)

References 80 publications

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“…However, further support for the corresponding experiments or full three-dimensional (3-D) DNS was not provided. Zhu et al (2022) also experimentally demonstrated that a nearly adiabatic wall or heated wall enabled the first mode to be comparable to or overtake the second mode in frequency spectra. Under other wind-tunnel conditions, solid experimental evidence of interactions between the second mode and the low-frequency component was presented by Kimmel & Kendall (1991), Bountin et al (2008), Munoz, Heitmann & Radespiel (2014) and Craig et al (2019).…”

Section: Introductionmentioning

confidence: 94%

Interaction and breakdown induced by multiple optimal disturbances in hypersonic boundary layer

Guo,

Hao,

Wen

2023

J. Fluid Mech.

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The present paper finds that the coexistence of multiple primary instability waves may cause a non-trivial nonlinear interaction and breakdown process, which has not been reported before. In the considered Mach 6 flat-plate boundary layer, a global resolvent analysis reports three optimal disturbances (local maxima): a high-frequency planar wave, a low-frequency oblique wave and a stationary streak. For the dominant planar and oblique waves, a parabolised stability equation analysis identifies the initial non-modal transient growth and downstream modal growth. Initiated by these two optimal disturbances jointly, the complete linear and nonlinear instability processes until breakdown to turbulence are shown with direct numerical simulation. Owing to the transient growth, the oblique wave may be more significant than the planar wave in the breakdown. The oblique wave and scales of nonlinear interactions are pronounced in the outer layer, whose significance may not be comprehensively characterised by the wall pressure measurement. Fourier modes characterising the oblique-wave oblique breakdown, the planar-wave fundamental resonance, the planar-wave subharmonic resonance and the combination resonance related to a detuned mode are observed successively. The detuned mode seems to dominate the near-wall dynamics in the late nonlinear stage, characterised by $\varLambda$ -like structures. Meanwhile, the existence of this detuned mode is independent of the initial amplitude ratio and the absolute amplitude of the oblique and planar waves. Weakly nonlinear stability analyses demonstrate that the detuned mode is mainly a consequence of the secondary instability under the combination of planar and oblique primary waves. Wave vector plots reveal the resonant state of multiple triads. Energy budget and amplitude-correction analyses provide a clear physical image of energy transfer.

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Section: Introductionmentioning

confidence: 94%

Interaction and breakdown induced by multiple optimal disturbances in hypersonic boundary layer

Guo,

Hao,

Wen

2023

J. Fluid Mech.

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Improvement of transition prediction model in hypersonic boundary layer based on field inversion and machine learning framework

et al. 2023

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The classical four-equation γ-Re transition model has presented excellent accuracy in low-speed boundary layer transition prediction. However, once the incoming flow reaches hypersonic speed, the original model is no longer applicable due to the compressibility problem and the appearance of multiple instability modes. Recently, there has been widespread interest in data-driven modeling for quantifying uncertainty or improving model prediction accuracy. In this paper, a data-driven framework based on field inversion and machine learning is performed to extend the prediction capability of the original γ-Re transition model for the hypersonic boundary layer transition.First, the iterative regularized ensemble Kalman filter method is applied to obtain the spatial distribution of the perturbation correction term β for the switching function Fonset1, and the effectiveness of this method is initially verified in the hypersonic flat plate case. Then, the random forest algorithm is adopted to construct a mapping from the average flow features to β. The generalizability of the well-trained learning model is fully validated in the blunt cone cases with different unit Reynolds numbers, free-stream flow temperature, and bluntness. The simulation results indicate that the performance of the original γ-Re transition model in the hypersonic boundary layer transition prediction is significantly improved, and the boundary layer transition onset location and the length of transition zone can be correctly obtained. In addition, the machine learning model investigates the importance of the input features and confirms that the effective length scale plays a significant role in the numerical simulation of the hypersonic boundary layer transition.

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Active transition control by synthetic jets in a hypersonic boundary layer

Zhuang

Wan

et al. 2023

Physics of Fluids

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We investigate by direct numerical simulation the active control of laminar-turbulent transition in a hypersonic flat-plate boundary layer at a freestream Mach number of 5.86. The control mechanism is a synthetic jet. Based upon the linear stability theory of Mack, in hypersonic flow the important path to transition involves a high-frequency, second-mode fundamental resonance. Through systematic investigation, we reveal that the forcing the boundary layer with a synthetic jet at appropriate combinations of amplitude and frequency suppresses the second mode and delays transition. To gain physical insights into the major control mechanism, we employ the momentum potential theory (MPT) to analyse the flows with and without control. Essentially, the underlying control mechanism relies on an intriguing effect of the synthetic jet via generating the outwards radiated wave structures}, which are identified to split the upstream acoustic and vortical components. The splitting treatment presents the second-mode energy to drop sharply after the flow passes through the synthetic jet slot. The MPT source-term analysis reveals that the significantly suppressed near-wall source terms are responsible for suppressing the second mode downstream. Compared with the vortical and thermal source terms, the acoustic source term is found to be suppressed most. The kinetic budget analysis further reveals that the splitting treatment is related to the non-parallel effect and the nonlinear interaction.

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Transitional flow structures in heated hypersonic boundary layers

Cited by 7 publications

References 80 publications

Interaction and breakdown induced by multiple optimal disturbances in hypersonic boundary layer

Interaction and breakdown induced by multiple optimal disturbances in hypersonic boundary layer

Improvement of transition prediction model in hypersonic boundary layer based on field inversion and machine learning framework

Active transition control by synthetic jets in a hypersonic boundary layer

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