Characterizing surface-gap effects on boundary-layer transition dominated by Tollmien–Schlichting instability

Crouch, J. D.; Kosorygin, V. S.; Sutanto, Mary I.; Miller, Gregory R.

doi:10.1017/flo.2022.1

Cited by 7 publications

(6 citation statements)

References 17 publications

(35 reference statements)

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“…In the present experimental campaign, both classic gaps and gaps with uneven sides, referred to as steps-and-gaps or S&G, were tested and compared to the Olive and Blanchard criteria for critical gaps. Although determining whether or not classic gaps were critical could not be ascertained due to some limitations in the wing model, the ∆N values based on the subcritical gaps showed relatively good agreement with the ∆N model for gaps proposed by Crouch et al (2022).…”

Section: Gaps and Steps-and-gapsmentioning

confidence: 92%

“…The influence of subcritical defects is then analysed. This proposed by Crouch et al (2022) and the BFS ∆N model from Crouch et al (2006).…”

Section: Gaps and Steps-and-gapsmentioning

confidence: 99%

“…Results from these studies are used to define either empirical criteria based on the defect dimensions and the local boundary-layer thickness at the defect location (Nenni and Gluyas (1966), Béguet et al (2016)), or models (Crouch et al (2006), Perraud et al (2014), Crouch et al (2022)).…”

Section: Introductionmentioning

confidence: 99%

“…N xT,S D corresponds to the N factor value at the transition position of the configuration with a surface defect. This method was successfully used on various types of surface defects (FFS, BFS and gaps) in works such as byEdelmann and Rist (2015) orCrouch et al (2006) andCrouch et al (2022). More details on the ∆N model can be found inMethel et al (2022).…”

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confidence: 99%

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Laminar-turbulent transition experiment on the effect of surface imperfections on an NLF airfoil in transonic flow

Methel

Méry

Vermeersch

et al. 2023

Preprint

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In the present study, the effect of various twodimensional surface defects (forward-facing steps and ramps, backward-facing steps and ramps, gaps and steps-and-gaps) on boundary-layer transition was experimentally investigated in the transonic regime. A laminar profile was specifically designed and manufactured by ONERA so as to allow for a maximum of defects to be tested simultaneously, and to include resin pockets to accurately monitor laminar-turbulent transition using infra-red thermography. Transition was also characterised using the ∆N model based on linear stability calculations. Relatively good agreement with existing ∆N models for forward and backward facing steps as well as gaps was found, indicating that these models, which were mostly developed for incompressible flows, can still be used as a conservative estimate for compressible flows. More practical defects referred as step-and-gap were also considered.

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Section: Gaps and Steps-and-gapsmentioning

confidence: 92%

“…The influence of subcritical defects is then analysed. This proposed by Crouch et al (2022) and the BFS ∆N model from Crouch et al (2006).…”

Section: Gaps and Steps-and-gapsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Laminar-turbulent transition experiment on the effect of surface imperfections on an NLF airfoil in transonic flow

Methel

Méry

Vermeersch

et al. 2023

Preprint

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“…Many studies have looked for empirical correlations linking the type of defect and its geometrical characteristics to the shift. Wind tunnel experiments were conducted by Crouch, Kosorygin, Sutanto, and Miller (2022) on gaps and by Wang and Gaster (2005) on BFSs. These studies showed that the corresponded to for the gaps and for the BFSs, where and denote the step height and step width, respectively, made dimensionless with the boundary layer displacement thickness for a Blasius boundary layer at the defect location .…”

Section: Introductionmentioning

confidence: 99%

Neural prediction model for transition onset of a boundary layer in presence of two-dimensional surface defects

Rouviere

Pascal

Méry

et al. 2023

Flow

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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 transition prediction methods such as local stability theory or the parabolized stability equation method do not allow for the consideration of strongly non-parallel boundary layer flows, as in the presence of surface defects (bumps, steps, gaps, etc.). A neural network approach, based on an extensive database of two-dimensional incompressible boundary layer stability studies in the presence of gap-like surface defects, is used. These studies consist of linearized Navier–Stokes calculations and provide information on the effect of surface irregularity geometry and aerodynamic conditions on the transition to turbulence. The physical and geometrical parameters characterizing the defect and the flow are then provided to a neural network whose outputs inform about the effect of a given gap on the transition through the ${\rm \Delta} N$ method (where N represents the amplification of the boundary layer instabilities).

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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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Characterizing surface-gap effects on boundary-layer transition dominated by Tollmien–Schlichting instability

Cited by 7 publications

References 17 publications

Laminar-turbulent transition experiment on the effect of surface imperfections on an NLF airfoil in transonic flow

Laminar-turbulent transition experiment on the effect of surface imperfections on an NLF airfoil in transonic flow

Neural prediction model for transition onset of a boundary layer in presence of two-dimensional surface defects

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

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