Impact of a forward-facing step on the development of crossflow instability

Rius-Vidales, Alberto F.; Kotsonis, Marios

doi:10.1017/jfm.2021.497

Cited by 16 publications

(45 citation statements)

References 60 publications

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“…simulating only stationary step-flow features) showed that as the primary CF disturbance reaches the FFS, it does not directly impinge on the step edge but instead lifts off the surface and passes over it. This behaviour is in agreement with previous experimental observations by Eppink (2020 b ) and Rius-Vidales & Kotsonis (2021). In addition, the numerical results of Casacuberta et al.…”

Section: Introductionsupporting

confidence: 93%

“…Recent experiments by Rius-Vidales & Kotsonis (2021) at a higher initial amplitude also report the amplification of the stationary CF vortices at two distinct regions near the FFS. The results showed that the first amplification region is characterized by a pronounced spanwise motion of the CF vortices, potentially underlying an energy exchange mechanism due to misalignment between perturbation and base flow vectors.…”

Section: Introductionmentioning

confidence: 82%

“…The present work follows in a series of recent investigations (e.g. Rius-Vidales & Kotsonis 2020, 2021) towards understanding the effect of surface irregularities in swept wing transition. The geometries at hand are two-dimensional surface irregularities in the form of forward-facing steps (FFS) known to result in a milder destabilization of the subsonic boundary layer than its backwards-facing counterpart (Perraud & Seraudie 2000; Tufts et al.…”

Section: Introductionmentioning

confidence: 99%

“…A brief summary of the main research efforts towards a universal method for determining the critical FFS step height (i.e. transition advancement) in both TS and CFI dominated cases is presented in Rius-Vidales & Kotsonis (2021). Despite the wealth of information available for the study of FFS surface irregularities, only a handful focus on three-dimensional boundary layers dominated by CFI.…”

Section: Introductionmentioning

confidence: 99%

“…Duncan et al. 2014 b ; Eppink 2018, 2020 b ; Rius-Vidales & Kotsonis 2020, 2021; Groot & Eppink 2021) studies revealed numerous unresolved aspects essential to the understanding of the FFS–CFI interaction.…”

Section: Introductionmentioning

confidence: 99%

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Unsteady interaction of crossflow instability with a forward-facing step

Rius-Vidales

Kotsonis

2022

J. Fluid Mech.

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Experiments have been conducted on a swept wing model in a low-turbulence wind tunnel at chord Reynolds number of $2.17 \times 10^{6}$ to investigate the unsteady interaction of a forward-facing step (FFS) with incoming stationary crossflow (CF) vortices. The impact of varying the FFS height on the development and growth of primary and secondary CF disturbances and the ensuing laminar–turbulent transition is quantified through detailed hot-wire anemometry and infrared thermography measurements. The presence of the FFS results in either a critical (i.e. moderate transition advancement) or a supercritical behaviour (i.e. transition advancing abruptly to the FFS location). The arrival of the forced stationary CF vortices at the step is accompanied by their amplification. Unsteady analysis for the critical cases indicates temporal velocity fluctuations following closely the development of the baseline configuration (i.e. agreeing with the development of secondary instabilities). Consequently, laminar breakdown originates from the outer side of the upwelling region of the CF vortices. In contrast, for the supercritical FFS, the laminar breakdown unexpectedly originates from the inner side of the upwelling region. Evidence points to an unsteady mechanism possibly supported by locally enhanced spanwise-modulated shears and the recirculation region downstream of the FFS edge. This mechanism appears to govern the abrupt tripping of the flow in supercritical step cases. The findings in this work provide insight into the unsteady FFS–CF vortex interaction, which is pivotal to understanding the influence of an FFS on the laminar–turbulent boundary-layer transition in swept aerodynamic surfaces.

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Section: Introductionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Unsteady interaction of crossflow instability with a forward-facing step

Rius-Vidales

Kotsonis

2022

J. Fluid Mech.

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Laminar-Turbulent Transition in Swept-Wing Flows with a Supercritical Forward-Facing Step

Casacuberta,

Hickel,

Kotsonis

2023

ERCOFTAC Series

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Influence of deep gaps on laminar–turbulent transition in two-dimensional boundary layers at subsonic Mach numbers

Risius,

Costantini,

Klein

2023

Exp Fluids

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Systematic experimental investigations on the influence of deep gaps on the location of laminar–turbulent transition are reported. The tests were conducted in the Cryogenic Ludwieg–Tube Göttingen, a blow-down wind tunnel with good flow quality, at eight different unit Reynolds numbers ranging from $$Re_1 = {17.5\,\,\times 10^{6}\,\mathrm{{m}^{-1}}}$$ R e 1 = 17.5 × 10 6 m - 1 to $$ 80\,\times\,10^{6}\,\mathrm{m}^{-1}$$ 80 × 10 6 m - 1 , three Mach numbers, $$M= 0.35$$ M = 0.35 , 0.50 and 0.65, and various pressure gradients. A flat-plate configuration, the extended two-dimensional wind tunnel model PaLASTra was modified in order to allow the installation of gaps with nominal widths of $$30$$ 30 $$\upmu $$ μ m, $$100$$ 100 $$\upmu $$ μ m and $$200$$ 200 $$\upmu $$ μ m and a depth of $$d = {9\,\mathrm{mm}}$$ d = 9 mm . A maximum Reynolds number based on the gap width $$Re_{w} = Re_1 \cdot w \approx {16{,}000}$$ R e w = R e 1 · w ≈ 16 , 000 was reached. Transition Reynolds numbers ranging from $$Re_{tr}\approx $$ R e tr ≈ 1 × 106 to 11 × 106 were measured, as a function of gap width, pressure gradient and Mach and Reynolds number. This systematic investigation facilitates a linear approximation of $$Re_{tr}$$ R e tr dependent on the boundary layer shape factor $$H_{12}$$ H 12 for various flow conditions and gap widths. It was therefore possible to conduct an investigation of $$Re_{tr}$$ R e tr depending on $$Re_{1}$$ R e 1 and the relative change of the transition location depending on the gap width w. Incompressible linear stability analysis was used to calculate amplification rates of Tollmien–Schlichting waves and determine critical N-factors by correlation with measured transition locations. The change in the critical N-factor $$\varDelta N$$ Δ N by installation of the gap is investigated as a function of w and $$Re_w$$ R e w . It was found that a gap width of 30 $$\upmu $$ μ m reduces the critical N-factors in the range of $$\varDelta N \approx 0.5 \pm 0.25$$ Δ N ≈ 0.5 ± 0.25 , while gap widths of 100 $$\upmu $$ μ m and 200 $$\upmu $$ μ m reduce the critical N-factor in the range of $$\varDelta N \approx 1.5 \pm 1$$ Δ N ≈ 1.5 ± 1 . Interestingly, an increase in gap width from 100 to 200 $$\upmu $$ μ m was not found to induce smaller transition Reynolds numbers or reduced N-factors, which might be due to resonance effects.

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Impact of a forward-facing step on the development of crossflow instability

Abstract: Abstract

Cited by 16 publications

References 60 publications

Unsteady interaction of crossflow instability with a forward-facing step

Unsteady interaction of crossflow instability with a forward-facing step

Laminar-Turbulent Transition in Swept-Wing Flows with a Supercritical Forward-Facing Step

Influence of deep gaps on laminar–turbulent transition in two-dimensional boundary layers at subsonic Mach numbers

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