Roughness-Induced Bypass Transition, Revisited

Denissen, Nicholas; White, Edward B.

doi:10.2514/1.35304

Cited by 23 publications

(17 citation statements)

References 5 publications

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“…Time-mean streamwise-velocity contours match experimental results by, e.g. Denissen & White (2008). A subcritical roughness configuration revealed the existence of a system of two horseshoe vortices.…”

Section: Introductionsupporting

confidence: 57%

“…A series of experiments aimed at the understanding of roughness-induced transient growth was conducted by, e.g. White & Ergin (2003), Ergin & White (2005, Denissen & White (2008); the major findings are compiled in White (2005). White & Ergin (2003) observed that the energy associated with transiently amplified disturbances scales with Re 2 kk for roughness elements.…”

Section: Introductionmentioning

confidence: 98%

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Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

Kurz

Kloker

2016

J. Fluid Mech.

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The effects of a spanwise row of finite-size cylindrical roughness elements in a laminar, compressible, three-dimensional boundary layer on a wing profile are investigated by direct numerical simulations (DNS). Large elements are capable of immediately tripping turbulent flow by either a strong, purely convective or an absolute/global instability in the near wake. First we focus on an understanding of the steady near-field past a finite-size roughness element in the swept-wing flow, comparing it to a respective case in unswept flow. Then, the mechanisms leading to immediate turbulence tripping are elaborated by gradually increasing the roughness height and varying the disturbance background level. The quasi-critical roughness Reynolds number above which turbulence sets in rapidly is found to be Re kk,qcrit ≈ 560 and global instability is found only for values well above 600 using nonlinear DNS; therefore the values do not differ significantly from two-dimensional boundary layers if the full velocity vector at the roughness height is taken to build Re kk . A detailed simulation study of elements in the critical range indicates a changeover from a purely convective to a global instability near the critical height. Finally, we perform a three-dimensional global stability analysis of the flow field to gain insight into the early stages of the temporal disturbance growth in the quasi-critical and over-critical cases, starting from a steady state enforced by damping of unsteady disturbances.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 98%

Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

Kurz

Kloker

2016

J. Fluid Mech.

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“…The value of Re h has an important effect on the streak amplitude, length scales and perturbation growth rate (Choudhari & Fischer 2005;Ergin & White 2006;Denissen & White 2008). The former factors can modulate the route towards transition.…”

Section: Introductionmentioning

confidence: 99%

On Reynolds number dependence of micro-ramp-induced transition

Schrijer

Scarano

2018

J. Fluid Mech.

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The variation of transitional flow features past a micro-ramp is investigated when the Reynolds number is decreased approaching the critical regime. Experiments are conducted in the incompressible flow spanning from supercritical to subcritical roughness-height-based Reynolds number (Re h = 1170, 730, 460 and 320) with tomographic particle image velocimetry. The effect of Re h on three-dimensional flow behaviour is analysed in a domain encompassing 73 ramp heights in the streamwise direction. Above the critical Re h , the primary vortex pair and induced central low-speed region in the mean flow field are active over longer range when decreasing Re h . In the instantaneous flow, at Re h < 1000, the hairpin vortices induced by Kelvin-Helmholtz (K-H) instability progress gradually from close to the micro-ramp into the region where the overall shear layer is destabilized, indicating the correlation between the K-H instability and the onset of transition. The breakdown of K-H vortices as observed at Re h = 1170, does not occur at lower Re h . Decreasing Re h , the secondary vortex structures make their first appearance significantly downstream, postponing the formation of sideward disturbances, which destabilize the local shear layer by ejection events. Two major types of eigenmodes with symmetric and asymmetric spatial distribution of velocity fluctuations in the near wake are clearly identified by proper orthogonal decomposition. The symmetric and asymmetric modes correspond to the presence of vortex shedding and a sinuous wiggling motion respectively. It is found that Re h is the key factor determining the importance of the symmetric mode. At Re h = 1170, the disturbance energy of the symmetric mode decays before the onset of transition, suggesting that it is relatively insignificant in the process. However, decreasing Re h to 730 and 460, the symmetric mode produces continuous growth of high level disturbance energy, leading to transition.

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“…As already explained, due to the lift-up effect (Landahl 1990), these streamwise aligned vortices can trigger strong transient growth of the boundary layer streaks (Joslin & Grosch 1995), strong enough to yield their breakdown and subsequent transition to turbulence. The receptivity of the boundary layer flow to an array of three-dimensional cylindrical roughness elements and the associated transient growth of the velocity streaks have been thoroughly investigated by various authors as Fischer & Choudhari (2004), Ergin & White (2006), Fransson et al (2004Fransson et al ( , 2005, as well as Denissen & White (2008, 2009. Their major finding is that the streamwise transient growth of the induced streaks roughly scales with the square of the roughness Reynolds number, Re h = U Bl (x k , h)h/ν (U Bl being the value of the Blasius velocity profile evaluated at the roughness element's position x k and height h).…”

Section: Introductionmentioning

confidence: 99%

Investigation of the roughness-induced transition: global stability analyses and direct numerical simulations

et al. 2014

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. Investigation of the roughness-induced transition: global stability analyses and direct numerical simulations. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2014, 760, pp.175-211. 10.1017/jfm.2014.589. hal-01086744 Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The linear global instability and resulting transition to turbulence induced by an isolated cylindrical roughness element of height h and diameter d immersed within an incompressible boundary layer flow along a flat plate is investigated using the joint application of direct numerical simulations and fully three-dimensional global stability analyses. For the range of parameters investigated, base flow computations show that the roughness element induces a wake composed of a central low-speed region surrounded by a threedimensional shear layer and a pair of low-and high-speed streaks on each of its sides. Results from the global stability analyses highlight the unstable nature of the central low-speed region and its crucial importance in the laminar-turbulent transition process. It is able to sustain two different global instabilities: a sinuous and a varicose one. Each of these globally unstable modes are related to a different physical mechanism. While the varicose mode finds its root in the instability of the whole three-dimensional shear layer surrounding the central low-speed region, the sinuous instability turns out to be similar to the von Kármán instability in the two-dimensional cylinder wake and finds its root in the lateral shear layers of the separated zone. The aspect ratio of the roughness element plays a key role on the selection of the dominant instability. Indeed, whereas the flow over thin cylindrical roughness elements transitions due to a sinuous instability of the near-wake, for larger roughness element the varicose instability of the central low-speed region turns out to be the dominant one. Direct numerical simulations of the flow past an aspect ratio η = 1 (with η = d/h) roughness element sustaining only the sinuous instability have revealed that the bifurcation occurring in this particular case is supercritical. Finally, comparison of the transition thresholds predicted by global linear stability analyses with the von Doenhoff-Braslow transition diagram provides qualitatively good agreements.

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Roughness-Induced Bypass Transition, Revisited

Cited by 23 publications

References 5 publications

Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

On Reynolds number dependence of micro-ramp-induced transition

Investigation of the roughness-induced transition: global stability analyses and direct numerical simulations

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