The bypass transition mechanism of the Stokes boundary layer in the intermittently turbulent regime

Xiong, Chengwang; Qi, Xiang; Gao, An-Kang; Xu, Hanlin; Ren, Chengjiao; Cheng, Liang

doi:10.1017/jfm.2020.313

Cited by 8 publications

(24 citation statements)

References 53 publications

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“…The mixed representation allows significant cost reduction and was employed in previous DNS works on bottom boundary layers (Önder & Yuan 2019; Önder & Liu 2020; Xiong et al. 2020). We employ a bi-dimensional modified Legendre basis (Karniadakis & Sherwin 2005) in the streamwise-wall normal () plane, and Fourier expansions are defined in the spanwise () direction.…”

Section: Methodsmentioning

confidence: 99%

“…This mapping transforms the physical domain with undulated bottom to a rectangular box, which is suitable for a mixed discretization, where a bi-dimensional spectral-element discretization (Karniadakis & Sherwin 2005) can be combined with Fourier expansions (Karniadakis 1990). The mixed representation allows significant cost reduction and was employed in previous DNS works on bottom boundary layers (Önder & Yuan 2019;Önder & Liu 2020;Xiong et al 2020). We employ a bi-dimensional modified Legendre basis (Karniadakis & Sherwin 2005) in the streamwise-wall normal (x-z) plane, and Fourier expansions are defined in the spanwise (ȳ) direction.…”

Section: Numerical Detailsmentioning

confidence: 99%

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Receptivity and transition in a solitary wave boundary layer over random bottom topography

Önder

Liu

2021

J. Fluid Mech.

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Section: Methodsmentioning

confidence: 99%

Section: Numerical Detailsmentioning

confidence: 99%

Receptivity and transition in a solitary wave boundary layer over random bottom topography

Önder

Liu

2021

J. Fluid Mech.

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“…When the wall-normal vibration resonates with the unsteady inflow perturbations, the shear sheltering effect (Hunt & Durbin 1999) is interfered and the transient growth of the resonant perturbation is enhanced. For a streamwise oscillating wall, Xiong et al (2020) found that the roughness-induced perturbations evolve into velocity streaks via the inflection point instability of the Stokes layer.…”

Section: Vibration-induced Dynamicsmentioning

confidence: 99%

Transition induced by wall-normal vibration in flow around a flat plate with roughness

et al. 2022

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The effects of wall-normal vibration on bypass transition in a boundary-layer flow over a flat plate with roughness elements in the form of circular cylinders are investigated using direct numerical simulations (DNS), linear Floquet analyses and dynamic mode decompositions (DMD). The vibration of the plate strengthens the streamwise vorticity, consequently enhancing the velocity streaks and reducing the critical Reynolds number for transition. A map is constructed to identify the coupling effect of the vibration amplitude and Reynolds number on transition. Among all investigated combinations of height and diameter of roughness, the critical Reynolds numbers at different vibration amplitude $A$ can be unified by a scaling function of $(1-10A)$ . Two instability modes are identified in the vibration-induced transition process: a wake mode immediately downstream of the roughness, related to the inviscid Kelvin–Helmholtz instability of the wall-normal shear in the wake; and a streak mode, in response to the spanwise shear of the streaky flow, occurring further downstream. The first one results in the generation of central hairpin vortices which then feed the second one. Further development of the streak instability leads to two arrays of hairpin vortices. Results from linear Floquet analyses and DMD further confirm the two modes of instability observed in DNS. A quantitative study suggests that the amplification of vibration-induced disturbance by the base shear dominates the production of streamwise vorticity and subsequently the hairpin vortices.

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“…OBL flow structures have been examined in the past both experimentally (Sarpkaya 1993;Carstensen et al 2010) and numerically (Verzicco & Vittori 1996;Costamagna et al 2003;Mazzuoli et al 2011;Ozdemir et al 2014;Xiong et al 2020). Analyses have been also extended to rough bed OBL flows by others (Carstensen, Sumer & Fredsøe 2012;Ghodke & Apte 2016;Mujal-Colilles et al 2016;Mazzuoli & Vittori 2019).…”

Section: Flow Structuresmentioning

confidence: 99%

Mean flow structure and velocity–bed shear stress maxima phase difference in smooth wall, transitionally turbulent oscillatory boundary layers: direct numerical simulations

2021

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Direct numerical simulations of oscillatory boundary-layer flows in the transitional regime were performed to explain discrepancies in the literature regarding the phase difference ${\rm \Delta} \phi$ between the bed-shear stress and free-stream velocity maxima. Recent experimental observations in smooth bed oscillatory boundary-layer (OBL) flows, showed a significant change in the widely used ${\rm \Delta} \phi$ diagram (Mier et al., J. Fluid Mech., vol. 922, 2021, A29). However, the limitations of the point-wise measurement technique did not allow us to associate this finding with the turbulent kinetic energy budget and to detect the approach to a ‘near-equilibrium’ condition, defined in a narrow sense herein. Direct numerical simulation results suggest that a phase lag occurs as the result of a delayed and incomplete transition of OBL flows to a stage that mimics the fully turbulent regime. Data from the literature were also used to support the presence of the phase lag and propose a new ${\rm \Delta} \phi$ diagram. Simulations performed for ${\textit {Re}}_{\delta }=671$ confirmed the sensitivity in the development of self-sustained turbulence on the background disturbances ( $\textit{Re}_{\delta}=U_{o}\delta/\nu$ , where $\delta=[2\nu/\omega]^{1/2}$ is the Stokes' length, $U_{o}$ is the maximum free stream velocity of the oscillation, $\nu$ is the kinematic viscosity and $\omega=2{\rm \pi}/T$ is the angular velocity based on the period of the oscillation T). Variations of the mean velocity slope and intersect values for oscillatory flows are also explained in terms of the proximity to near-equilibrium conditions. Relaminarization and transition effects can significantly delay the development of OBL flows, resulting in an incomplete transition. The shape and defect factors are examined as diagnostic parameters for conditions that allow the formation of a logarithmic profile with the universal von Kármán constant and intersect. These findings are of relevance for environmental fluid mechanics and coastal morphodynamics/engineering applications.

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The bypass transition mechanism of the Stokes boundary layer in the intermittently turbulent regime

Cited by 8 publications

References 53 publications

Receptivity and transition in a solitary wave boundary layer over random bottom topography

Receptivity and transition in a solitary wave boundary layer over random bottom topography

Transition induced by wall-normal vibration in flow around a flat plate with roughness

Mean flow structure and velocity–bed shear stress maxima phase difference in smooth wall, transitionally turbulent oscillatory boundary layers: direct numerical simulations

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