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

Önder, Asim; Liu, Philip L.‐F.

doi:10.1017/jfm.2020.1141

Cited by 1 publication

(3 citation statements)

References 38 publications

(75 reference statements)

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“…The main numerical set-ups in this section are finalised by referring to the combination of parameters in tables 1 and 2. A numerical configuration similar to that of Önder & Liu (2021) is adopted to take the advantage of the high efficiency of the quasi-3-D approach and N 3 p denote the different interpolation orders of the Legendre basis for the p-type refinement for three sub-domains, which are divided by the vertical coordinate at y s1 = 0.2 and y s2 = 2. The explicit or implicit mapping denotes the option of treatment regarding to the spurious pressure term induced by coordinate transformation.…”

Section: Dns Modelmentioning

confidence: 99%

Section: Dns For Random Wall Roughnessmentioning

confidence: 99%

“…For the DNS tests in § 5, the coordinate transformation technique is employed to map the stochastic wall roughness onto the smooth bottom boundary. Since it is an in-built module named as VCSMapping in Nektar++ and the detailed operations were elaborated in Önder & Liu (2021), we actually follow their practice to determine the mesh configuration and set up the numerical parameters as described in § 2.3. The numbers of -type elements are 10, 38 and 32 for these sub-domains from the bottom up, where the size of element increases exponentially with coefficients 1.08, 1.05 and 1.05, while 40 -elements are homogeneously distributed in the streamwise direction.…”

Section: Tablementioning

confidence: 99%

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Non-modal growth of finite-amplitude disturbances in oscillatory boundary layer

et al. 2022

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The essence of sub-critical transition of oscillatory boundary-layer flows is the non-modal growth of finite-amplitude disturbances. The current understanding of the mechanisms of the orderly and bypass transitions of oscillatory boundary-layer flows is limited. The present study adopts optimisation approaches to predict the maximum energy amplification of two- and three-dimensional perturbations in response to the optimal initial disturbance with or without external forcing. A series of direct numerical simulations are also performed to compare with the results obtained from the stability analyses. In particular, the optimal initial perturbation similar to a Tollmien–Schlichting (T–S) wave yields the largest transient growth under the combined effects of the Orr mechanism and inflectional point instability. With a considerable level of two-dimensional disturbance, the vortex tube nonlinearly develops from the T–S-like wave, and then either deforms into a $\varLambda$ -vortex in the near-wall region or rolls up to the free shear region. The further burst of turbulence can follow the first pathway as K-type transition or the second one as vortex tube breakdown due to the elliptical instability. Additionally, non-modal growth can initiate the inception of streaky structures by favourable three-dimensional initial perturbations and/or forcing. The secondary instabilities responsible for the streak breakdown are classified as the varicose (symmetric) and sinuous (anti-symmetric) modes. Under a sufficiently high level of three-dimensional disturbance, the bypass transition is predominantly characterised by the formation of the sinuous mode and turbulent spots, which leads to the suppression of inflection point instability.

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Section: Dns Modelmentioning

confidence: 99%

Section: Dns For Random Wall Roughnessmentioning

confidence: 99%