Receptivity of secondary instability modes in streaky boundary layers

Zhang, Anyong; Dong, Ming; Zhang, Yongming

doi:10.1063/1.5046136

Cited by 10 publications

(1 citation statement)

References 42 publications

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“…When x 1 /L = 5 [Fig. 3(c)], slight asymmetry can be observed, indicating that the small-scale perturbations are amplified because of the secondary instability, which is similar as the bypass transition in boundary-layer flows [31]. This instability finally yields turbulent flow structures, as shown in Figs.…”

Section: B Dns Resultsmentioning

confidence: 86%

Existence of positive skewness of velocity gradient in early transition

et al. 2021

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The present study uses direct numerical simulations to calculate two different transitional flows from laminar flow to turbulence, that is, the two-scale wake flow and the two-dimensional Reyleigh-Taylor unstable flow, respectively. Both results show that the skewness of the longitudinal velocity gradient, S k , can become positive in the early transition stage, which is beyond our expectation since the turbulent equilibrium state always implies negative values of S k . These phenomena are explained analytically by considering only two dominant Fourier modes with harmonic relations. It is illustrated that the sign of S k is not only affected by the amplitudes of the perturbation velocities, but also related to their phases. We expect that the present results will be helpful for understanding the formation of turbulent equilibrium state and for constructing a new measurable criterion of the transition onset.

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Section: B Dns Resultsmentioning

confidence: 86%

Existence of positive skewness of velocity gradient in early transition

et al. 2021

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Linear optimal control of transient growth in turbulent channel flows

Yang

Huang

2019

Acta Mech. Sin.

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Influence of spanwise wall vibration on non-modal perturbations subject to freestream vortical disturbances in hypersonic boundary layers

Song,

Dong,

Zhao

et al. 2024

J. Fluid Mech.

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In this paper, we study the effect of lateral wall vibrations on the excitation and evolution of non-modal perturbations in hypersonic boundary layers subject to low-frequency freestream vortical disturbances (FSVDs). A novel, high-efficiency numerical approach, combining the harmonic weakly nonlinear Navier–Stokes and nonlinear parabolised stability equation approaches, is developed, which is sufficient to accommodate both the rapid distortion of the perturbation in the leading-edge vicinity and the nonlinear development of finite-amplitude high-order harmonics in the downstream region. The boundary-layer response to low-frequency FSVDs shows a longitudinal streaky structure, for which the temperature perturbation shows much greater magnitude than the streamwise velocity perturbation. The lateral vibration induces a Stokes layer solution for the spanwise velocity perturbation, which interacts with the FSVD-induced perturbations and leads to a suppression of the non-modal perturbation and an enhancement of the downstream modal perturbation. The new perturbations excited by the FSVD–vibration interaction strengthen as the vibration intensifies, and they could become comparable with the FSVD-induced perturbations in downstream locations at a high vibration intensity, indicating a remarkable modification of the streaky structure and its instability property. Secondary instability (SI) analyses based on the streaky base flow indicate that the vibration could enhance or suppress the SI modes, depending on their initial phases over the vibration period. Overall, the average effect is that the low-frequency and high-frequency SI modes are stabilised and destabilised by the vibration, respectively. Since the high-frequency SI modes undergo higher amplifications, the subsequent bypass transition is likely to be promoted by relatively strong vibrations.

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Receptivity of secondary instability modes in streaky boundary layers

Cited by 10 publications

References 42 publications

Existence of positive skewness of velocity gradient in early transition

Existence of positive skewness of velocity gradient in early transition

Linear optimal control of transient growth in turbulent channel flows

Influence of spanwise wall vibration on non-modal perturbations subject to freestream vortical disturbances in hypersonic boundary layers

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