Stabilization of Subcritical Bypass Transition in the Leading-Edge Boundary Layer by Suction

John, Michael O.; Obrist, Dominik; Kleiser, Leonhard

doi:10.1615/tsfp8.1760

Cited by 1 publication

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“…151-152). Details on the stabilizing influence of wall suction are documented in John et al (2014b). (Arnal et al 1997) and the dashed curve show experimental results for the transition Reynolds number Re tr (κ).…”

Section: Comparison Of Dns Results To Experiments and Simulations Fro...mentioning

confidence: 99%

“…The streamwise baseflow velocity component w B (x, y) increases by approximately 0.1W ∞ near the wall where the amplified modes have significant amplitude, leading to increased phase speeds c r of all modes. Furthermore, the growth rates c i of most of the discrete modes decrease with increasing suction (John et al 2014b), analogously to the linear primary stability of the SHBL (Hall et al 1984). The open circles illustrate the parameter combinations {Re, γ } for which stability equations (3.3) were solved.…”

Section: Stabilization By Suctionmentioning

confidence: 87%

“…The implementation of the disturbances and the boundary conditions follow Obrist et al (2012) and John et al (2014b). The computational domain has inflow planes at z = 0 and y = L y and one (optionally permeable) wall at y = 0.…”

Section: Numerical Simulation Methodsmentioning

confidence: 99%

“…Motivated by this discrepancy between linear stability results and experimental findings, Obrist, Henniger & Kleiser (2012) and John, Obrist & Kleiser (2014b) carried out DNS of the SHBL flow with an additional damped, primary disturbance of finite amplitude. These authors reported a bypass transition mechanism at subcritical Reynolds numbers, which can explain the occurrence of turbulence in experiments.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Secondary Instability and Subcritical Transition in the Leading-Edge Boundary Layer

John¹,

Obrist²,

Kleiser³

2017

Direct and Large-Eddy Simulation X

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The leading-edge boundary layer (LEBL) in the front part of swept airplane wings is prone to three-dimensional subcritical instability, which may lead to bypass transition. The resulting increase of airplane drag and fuel consumption implies a negative environmental impact. In the present paper, we present a temporal biglobal secondary stability analysis (SSA) and direct numerical simulations (DNS) of this flow to investigate a subcritical transition mechanism. The LEBL is modelled by the swept Hiemenz boundary layer (SHBL), with and without wall suction. We introduce a pair of steady, counter-rotating, streamwise vortices next to the attachment line as a generic primary disturbance. This generates a high-speed streak, which evolves slowly in the streamwise direction. The SSA predicts that this flow is unstable to secondary, time-dependent perturbations. We report the upper branch of the secondary neutral curve and describe numerous eigenmodes located inside the shear layers surrounding the primary high-speed streak and the vortices. We find secondary flow instability at Reynolds numbers as low as Re ≈ 175, i.e. far below the linear critical Reynolds number Re crit ≈ 583 of the SHBL. This secondary modal instability is confirmed by our three-dimensional DNS. Furthermore, these simulations show that the modes may grow until nonlinear processes lead to breakdown to turbulent flow for Reynolds numbers above Re tr ≈ 250. The three-dimensional mode shapes, growth rates, and the frequency dependence of the secondary eigenmodes found by SSA and the DNS results are in close agreement with each other. The transition Reynolds number Re tr ≈ 250 at zero suction and its increase with wall suction closely coincide with experimental and numerical results from the literature. We conclude that the secondary instability and the transition scenario presented in this paper may serve as a possible explanation for the well-known subcritical transition observed in the leading-edge boundary layer.

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Section: Comparison Of Dns Results To Experiments and Simulations Fro...mentioning

confidence: 99%

Section: Stabilization By Suctionmentioning

confidence: 87%