Stability of the laminar boundary layer flow encountering a row of roughness elements: Biglobal stability approach and DNS

Piot, Estelle; Casalis, Grégoire; Rist, Ulrich

doi:10.1016/j.euromechflu.2008.01.007

Cited by 29 publications

(48 citation statements)

References 32 publications

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“…Similarly to what has been observed for cylindrical roughness elements, they found that, behind each bump, a pair of counter-rotating vortices is generated, creating relatively high-and low-speed streaks in the wake downstream of the bump. An investigation of the local stability of streamwise streaks developing past a smooth, large, isolated roughness element has been carried out by Piot et al (2008). Assuming that the flow past the smooth roughness element evolves slowly in the streamwise direction, they have studied its local stability properties at each streamwise location just behind the roughness element, assessing the stabilizing effect of such a pre-streaky flow on the growth of TS waves.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, for the sharp-edged rectangular roughness element they considered, the varicose perturbations exhibit larger temporal and spatial growth rates than their sinuous counterparts. Though they provide valuable insights into the linear dynamics of the flow, stability analyses as performed by Piot et al (2008) (for bumps), de (for rectangular roughness elements), and Denissen & White (2013) (for cylinders), rely on the strong assumption of a nearly parallel flow. However, the flow past three-dimensional roughness elements exhibits some reversed flow regions where such parallel assumption can not hold.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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“…It is now commonly believed that the discrepancy in the spanwise positions of low-speed streaks rises from the competition between the wake of the roughness and the counter-rotating vortices at both sides of the roughness (Fransson et al 2004;Piot et al 2008). Since the strength of vortex largely depends on the height of the roughness (Fransson et al 2004), when roughness is relatively high compared to d, the counterrotating vortices will be more stronger, hence the down-wash effect induced by those vortices is strong enough to overcome the velocity deficit created by the wake of the roughness, and transforming the lowspeed streaks into high-speed streaks.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to the roughness, Tani and Komoda (1962) and Kachanov and Tararykin (1987) used small wings outside the boundary layer and periodical suction/blowing on the wall to generate streamwise vortices, respectively. Piot et al (2008) investigated the stability of laminar boundary layer behind small roughness by direct numerical simulation (DNS). The shape of the roughness was defined by h(x, z) = h 0 cos 3 (pr/d) where h 0 = 0.5d 1 and d = 16.84d 1 .…”

Section: Introductionmentioning

confidence: 99%

Effects of roughness elements on bypass transition induced by a circular cylinder wake

Wang

Zhang

Pan

2010

J Vis

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The bypass transition of flat-plate boundary layer induced by a circular cylinder wake under the influence of roughness elements is experimentally investigated. The hydrogen-bubble visualization results show that the boundary layer separation occurs upstream of the roughness, and the separated shear layer is incised by roughness to different extent, resulting in different kinds of secondary vortices formed immediately downstream of the roughness. During the evolution of the secondary vortex, two types of instabilities are observed, which are denoted as large-and small-scale instabilities, respectively, according to different spatial scale of the hairpin vortices formed afterward. A merging process of hairpin vortices is also observed when the secondary vortices undergo the small-scale instability, and a potential new transition control strategy based on the present observation is proposed.

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“…The sweptplate configuration excludes the flow field around the leading edge. In contrast, the DNS studies of swept-cylinder flow by Collis & Lele (1999) (parabolic cylinder) and Piot et al (2008) and Piot & Casalis (2009) (circular cylinder) also took the leading-edge receptivity into account.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of boundary-layer receptivity on a swept wing

Tempelmann

Schrader

Hanifi

et al. 2011

6th AIAA Theoretical Fluid Mechanics Conference

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Direct numerical simulations (DNS) of the flow over a wing with 45• sweep and −4• angle-of-attack are presented. This flow configuration was investigated in a series of wind-tunnel experiments at the Arizona State University (ASU). On the upper wing side, the flow develops a substantial crossflow and is therefore ideally suited for a study of the receptivity mechanisms of crossflow vortices. Here, we examine the boundary-layer receptivity to surface roughness and to single vortical free-stream modes. The roughness is modeled by a shallow circular disk and is identical with one single element of the spanwise roughness array considered in the ASU experiments. The boundary layer develops a steady crossflow mode downstream of the roughness. The spatial evolution of the modal amplitude obtained by the DNS is in excellent agreement with a solution to the nonlinear parabolized stability equations (NPSE) while being lower than that measured in the experiments. The reasons for this discrepancy are yet to be determined. Possible explanations are the idealization of the roughness array by spanwise periodic boundary conditions in our simulations, or the presence of traveling crossflow waves due to background free-stream turbulence in the experiments. We demonstrate that the boundary-layer receptivity to roughness can be successfully predicted by a nonlocal, adjoint-based receptivity model. Stationary crossflow vortices can also be triggered by zero-frequency free-stream vortical modes. We consider two types of mode, carrying streamwise and chordwise vorticity. Both modes give rise to nonmodal disturbances near the leading edge, which soon evolve into a steady crossflow mode. The boundary layer is found to be somewhat more receptive to the streamwisevorticity mode than to the chordwise vorticity.

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Stability of the laminar boundary layer flow encountering a row of roughness elements: Biglobal stability approach and DNS

Cited by 29 publications

References 32 publications

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

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

Effects of roughness elements on bypass transition induced by a circular cylinder wake

Numerical study of boundary-layer receptivity on a swept wing

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