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

Crouch, J. D.

doi:10.1007/978-3-030-67902-6_2

Cited by 2 publications

(2 citation statements)

References 35 publications

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“…In the variable N-factor approach, the threshold value N is defined as a function of key parameters that can alter the linear amplitude of the instability through either receptivity or enhanced amplification (Crouch, 2021). This is equivalent to a linear-amplitude method that correlates the transition onset to the amplitude A reaching some threshold value A T .…”

Section: Linear Stability Analysismentioning

confidence: 99%

“…This is equivalent to a linear-amplitude method that correlates the transition onset to the amplitude A reaching some threshold value A T . Rather than tracking an increase in the physical amplitude relative to A T , the variable N-factor approach tracks a reduction in the critical value N relative to a reference condition with N 0 , N = N 0 − ΔN (Crouch, 2021). The amplification factors m or n are calculated the same as for the standard e N method, with only the critical value N changing as a function of receptivity or growth modifiers.…”

Section: Linear Stability Analysismentioning

confidence: 99%

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

Crouch

Kosorygin

Sutanto

et al. 2022

Flow

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Effects of gaps (rectangular surface cavities) on boundary-layer transition are investigated using a combination of linear stability theory and experiments, for boundary layers where the smooth-surface transition results from Tollmien–Schlichting (TS) instability. Results are presented for a wide range of gap characteristics, with the associated transition locations ranging from the smooth-surface location all the way forward to the gap location. The transition movement is well described by a variable $N$ -factor, which links the gap characteristics to the level of instability amplification $e^N$ leading to transition. The gap effects on TS-wave transition are characterized by two limiting behaviours. For shallow gaps $d/w < 0.017$ , the reduction in $N$ -factor is a function of the gap depth $d$ and is independent of the gap width $w$ . For deep gaps $d/w > 0.028$ , the reduction in $N$ -factor is a function of the gap width and is independent of the gap depth. When both the gap width and depth are sufficiently large relative to the displacement thickness $\delta ^*$ , the TS-wave transition is bypassed, resulting in transition at the gap location. These behaviours are mapped out in terms of ( $w/ \delta ^*$ , $d/ \delta ^*$ ), providing a predictive model for gap effects on transition.

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Section: Linear Stability Analysismentioning

confidence: 99%

Section: Linear Stability Analysismentioning

confidence: 99%

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

Crouch

Kosorygin

Sutanto

et al. 2022

Flow

Self Cite

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

Cited by 2 publications

References 35 publications

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

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

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

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