Humps/Steps Influence on Stability Characteristics of Two-Dimensional Laminar Boundary Layer

Wörner, A.; Rist, Ulrich; Wagner, Siegfried

doi:10.2514/2.1960

Cited by 58 publications

(9 citation statements)

References 9 publications

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“…The result of our linear analysis reveal distinct behavior from the results for a sharp step (γ = 1) of height h/δ * = 0.235 ( ĥ = 8.24%) given by Wörner et al (2003) where they claim that a forward facing sharp step showed a stabilising effect without a local destablisation regime despite a separation bubble being reported in front of the step. Recently, through further numerical calculations, Edelmann & Rist (2015) observed that, for subsonic Mach numbers and large height scale (h/δ * = 0.94 or ĥ = 33%), two separation bubbles, in front and on top of the step, were observed and strong amplification of the disturbances was found in front of and behind the step.…”

Section: Numerical Strategycontrasting

confidence: 58%

“…They also found sub-and supersonic results showed significant differences in the generation mechanism of the separation bubbles. A different phenomenon was found for incompressible flows when investigated numerically, by using an immersed boundary technique (Wörner et al 2003). The authors observed that for a nondimensional frequency F = 49.34, the amplitude of the TS wave is reduced throughout the domain considered by the forward-facing step.…”

Section: Motivation Behind the Study Of Steps In Boundary Layersmentioning

confidence: 91%

“…The smooth step considered in this paper, shown in figure 1, is located in the unstable regime of the neutral stability curve close to the leading edge. This work mostly considers medium and high frequencies F ∈ {100, 140, 150, 160} TS waves but also the case of a low frequency forcing F = 49.34 is investigated for closer comparison with Wörner et al (2003). The low frequency forcing is particularly interesting because it offers, in the context of the neutral stability curve of the zero pressure gradient flat plate, a much larger unstable regime compatible with the so called critical amplification factor N = 8 (Edelmann & Rist 2015).…”

Section: Problem Definitionmentioning

confidence: 99%

“…The studies by Wörner et al (2003); Edelmann & Rist (2015) considered the effect of low frequency TS modes for a long range from the leading edge of the flat plate with Re δ * (i.e. Re δ * = 2200 1500).…”

Section: Does a Smooth Step Significantly Amplify The Low-frequency T...mentioning

confidence: 99%

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Influence of localised smooth steps on the instability of a boundary layer

Lombard

Sherwin

2017

J. Fluid Mech.

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We consider a smooth, spanwise-uniform forward-facing step defined by a Gauss error function of height 4 %-30 % and four times the width of the local boundary layer thickness δ 99 . The boundary layer flow over a smooth forward-facing stepped plate is studied with particular emphasis on stabilisation and destabilisation of the twodimensional Tollmien-Schlichting (TS) waves and subsequently on three-dimensional disturbances at transition. The interaction between TS waves at a range of frequencies and a base flow over a single or two forward-facing smooth steps is conducted by linear analysis. The results indicate that for a TS wave with a frequency F ∈ [140, 160] (F = ων/U 2 ∞ × 10 6 , where ω and U ∞ denote the perturbation angle frequency and free-stream velocity magnitude, respectively, and ν denotes kinematic viscosity), the amplitude of the TS wave is attenuated in the unstable regime of the neutral stability curve corresponding to a flat plate boundary layer. Furthermore, it is observed that two smooth forward-facing steps lead to a more acute reduction of the amplitude of the TS wave. When the height of a step is increased to more than 20 % of the local boundary layer thickness for a fixed width parameter, the TS wave is amplified, and thereby a destabilisation effect is introduced. Therefore, the stabilisation or destabilisation effect of a smooth step is typically dependent on its shape parameters. To validate the results of the linear stability analysis, where a TS wave is damped by the forward-facing smooth steps direct numerical simulation (DNS) is performed. The results of the DNS correlate favourably with the linear analysis and show that for the investigated frequency of the TS wave, the K-type transition process is altered whereas the onset of the H-type transition is delayed. The results of the DNS suggest that for the perturbation with the non-dimensional frequency parameter F = 150 and in the absence of other external perturbations, two forward-facing smooth steps of height 5 % and 12 % of the boundary layer thickness delayed the H-type transition scenario and completely suppressed for the K-type transition. By considering Gaussian white noise with both fixed and random phase shifts, it is demonstrated by DNS that transition is postponed in time and space by two forward-facing smooth steps.

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Section: Numerical Strategycontrasting

confidence: 58%

Section: Motivation Behind the Study Of Steps In Boundary Layersmentioning

confidence: 91%

Section: Problem Definitionmentioning

confidence: 99%

Section: Does a Smooth Step Significantly Amplify The Low-frequency T...mentioning

confidence: 99%

See 2 more Smart Citations

Influence of localised smooth steps on the instability of a boundary layer

Lombard

Sherwin

2017

J. Fluid Mech.

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“…However, the effect of a surface irregularity on the transition is poorly taken into account by these methods because of the assumptions made on the base flow. To overcome these limitations, Worner et al [17] and Edelmann and Rist [5] used Direct Numerical Simulations (DNS) to study the impact of humps and Forward-Facing Steps (FFS) respectively on the transition. More recently, Franco Sumariva et al [6] introduced the Adaptive Harmonic Linearized Navier-Stokes (AHLNS) method which they coupled with PSE upstream and downstream of the region with strong streamwise flow variations to study the effect of humps on the transition.…”

Section: Introductionmentioning

confidence: 99%

Neural Prediction Model for Transition Onset of a Boundary-Layer in Presence of 2D Surface Defects

Rouviere

Pascal

Méry

et al. 2022

AIAA SCITECH 2022 Forum

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Predicting the laminar to turbulent transition is an important aspect of computational fluid dynamics because of its impact on skin friction. Traditional methods of transition prediction do not make it possible to consider configurations where the boundary layer develops in presence of surface defects (bumps, steps, gaps, etc.). A neural network approach is used in this paper, based on an extensive database of boundary layer stability computations in presence of gap-like surface defects. These computations consists on linearized Navier-Stokes calculations and provide informations on the effect of surface irregularity geometry and aerodynamic conditions on the transition to turbulence. Physical and geometrical parameters characterizing the defect and the flow are provided to a neural network whose outputs inform about the effect of a given gap on the transition through the Δ𝑁 method.

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Predicting Laminar-Turbulent Transition Influenced by Surface-Induced Flow Distortions

Crouch

2021

IUTAM Laminar-Turbulent Transition

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Humps/Steps Influence on Stability Characteristics of Two-Dimensional Laminar Boundary Layer

Cited by 58 publications

References 9 publications

Influence of localised smooth steps on the instability of a boundary layer

Influence of localised smooth steps on the instability of a boundary layer

Neural Prediction Model for Transition Onset of a Boundary-Layer in Presence of 2D Surface Defects

Predicting Laminar-Turbulent Transition Influenced by Surface-Induced Flow Distortions

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