Optimal disturbances in suction boundary layers

Byström, Martin G.; Levin, Ori; Henningson, Dan S.

doi:10.1016/j.euromechflu.2006.07.003

Cited by 12 publications

(11 citation statements)

References 25 publications

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“…Fransson and Alfredsson 17 and Yoshioka, Fransson, and Alfredsson 18 carried out windtunnel experiments on streaks evolving in the asymptotic suction boundary layer ͑ASBL͒ and showed that the perturbations were significantly suppressed. Laminar boundary layers with mean flow suction ͑mostly ASBL͒ disturbed by laminar streaks have been studied numerically by Levin, Davidsson, and Henningson 19 via direct numerical simulations, by Davidsson and Gustavsson 20 by the linearized Navier-Stokes equations, and by Fransson and Corbett, 21 Zuccher, Luchini, and Bottaro, 22 and by Bystrom et al 23 through optimal growth theory.…”

Section: Introductionmentioning

confidence: 98%

“…The main difference with previous works resides in the fact that herein the laminar streaks are generated by the continuous, external forcing action of the free-stream vortical disturbances, as highlighted by experimental evidence. 7 On the contrary, other studies have adopted iterative methods 19,[21][22][23] or localized initial conditions 20 to generate the streaks and have neglected freestream vortical fluctuations, which are responsible for the formation and evolution of the laminar streaks. Furthermore, studies based on optimal theory treat the streaks as steady, whereas the effect of the frequency of the free-stream perturbations is considered here.…”

Section: Introductionmentioning

confidence: 99%

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The influence of wall suction and blowing on boundary-layer laminar streaks generated by free-stream vortical disturbances

Riccó

Dilib

2010

Physics of Fluids

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The effect of mean flow wall transpiration on boundary-layer fluctuations generated by free-stream disturbances of the convected gust type is investigated numerically. The theoretical frameworks of Leib et al. ͓J. Fluid Mech. 380, 169 ͑1999͔͒ and Ricco ͓J. Fluid Mech. 638, 267 ͑2009͔͒, based on the linearized unsteady boundary-region equations, are adopted. It is found that wall suction has a more significant attenuating effect on the low-frequency laminar streaks, while high-frequency disturbances are brought closer to the wall, but unaffected in magnitude. A simple asymptotic result, confirmed by the numerical calculations, shows that the characteristic peak of the laminar streaks in the core of the boundary layer may be suppressed completely by suction if this is sufficiently intense. Thought experiments of the modification induced by suction on existing wind-tunnel root-mean-square data are carried out. The findings are compared with other laboratory data with wall suction, and the reasons for discrepancy are outlined.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

The influence of wall suction and blowing on boundary-layer laminar streaks generated by free-stream vortical disturbances

Riccó

Dilib

2010

Physics of Fluids

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“…This indicates that the strong effect of damping obtained by suction on the asymptotic growth of TS waves is not achieved in the case of the algebraic growth. Bystrom et al 22 computed LOPs for the semi-suction boundary layer in order to take into account the presence of a small region free of suction close to the leading edge of the flat plate. Using such a model, they could improve the agreement of the numerical results with experimental data, demonstrating that the optimal energy growth is indeed obtained in the upstream region without suction.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear optimals in the asymptotic suction boundary layer: Transition thresholds and symmetry breaking

2015

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The effect of a constant homogeneous wall suction on the nonlinear transient growth of localized finite amplitude perturbations in a boundary-layer flow is investigated. Using a variational technique, nonlinear optimal disturbances are computed for the asymptotic suction boundary layer (ASBL) flow, defined as those finite amplitude disturbances yielding the largest energy growth at a given target time T. It is found that homogeneous wall suction remarkably reduces the optimal energy gain in the nonlinear case. Furthermore, mirror-symmetry breaking of the shape of the optimal perturbation appears when decreasing the Reynolds number from 10 000 to 5000, whereas spanwise mirror-symmetry was a robust feature of the nonlinear optimal perturbations found in the Blasius boundary-layer flow. Direct numerical simulations show that the different evolutions of the symmetric and of the non-symmetric initial perturbations are linked to different mechanisms of transport and tilting of the vortices by the mean flow. By bisecting the initial energy of the nonlinear optimal perturbations, minimal energy thresholds for subcritical transition to turbulence have been obtained. These energy thresholds are found to be 1-4 orders of magnitude smaller than those provided in the literature for other transition scenarios. For low to moderate Reynolds numbers, the energy thresholds are found to scale with Re −2 , suggesting a new scaling law for transition in the ASBL. C 2015 AIP Publishing LLC. [http://dx.

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“…13 Wind-tunnel experiments have shown that wall suction can attenuate the growth of streaks. 12,42 The effect of wall suction on the laminar streaks has also been studied through direct numerical simulations, 22 optimal growth theory, 6,11,43 and by Ricco and Dilib, who used LWG's mathematical framework. 30 For aircraft flight, the use of wall suction as a mechanism for controlling the disturbance growth has also been widely investigated.…”

Section: Introductionmentioning

confidence: 99%

Compressible laminar streaks with wall suction

2013

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The response of a compressible laminar boundary layer subject to free-stream vortical disturbances and steady mean-flow wall suction is studied. The theoretical frameworks of Leib et al. [J. Fluid Mech. 380, 169–203 (1999)10.1017/S0022112098003504] and Ricco and Wu [J. Fluid Mech. 587, 97–138 (2007)10.1017/S0022112007007070], based on the linearized unsteady boundary-region equations, are adopted to study the influence of suction on the kinematic and thermal streaks arising through the interaction between the free-stream vortical perturbations and the boundary layer. In the asymptotic limit of small spanwise wavelength compared with the boundary layer thickness, i.e., when the disturbance flow is conveniently described by the steady compressible boundary region equations, the effect of suction is mild on the velocity fluctuations and negligible on the temperature fluctuations. When the spanwise wavelength is comparable with the boundary layer thickness, small suction values intensify the supersonic streaks, while higher transpiration levels always stabilize the disturbances at all Mach numbers. At larger spanwise wavelengths, very small amplitudes of wall transpiration have a dramatic stabilizing effect on all boundary layer fluctuations, which can take the form of transiently growing thermal streaks, large amplitude streamwise oscillations, or oblique exponentially growing Tollmien-Schlichting waves, depending on the Mach number and the wavelengths. The range of wavenumbers for which the exponential growth occurs becomes narrower and the location of instability is significantly shifted downstream by mild suction, indicating that wall transpiration can be a suitable vehicle for delaying transition when the laminar breakdown is promoted by these unstable disturbances. The typical streamwise wavelength of these disturbances is instead not influenced by suction, and asymptotic triple deck theory predicts the strong changes in growth rate and the very mild modifications in streamwise wavenumber in the limit of larger downstream distance and small spanwise wavenumber.

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Optimal disturbances in suction boundary layers

Cited by 12 publications

References 25 publications

The influence of wall suction and blowing on boundary-layer laminar streaks generated by free-stream vortical disturbances

The influence of wall suction and blowing on boundary-layer laminar streaks generated by free-stream vortical disturbances

Nonlinear optimals in the asymptotic suction boundary layer: Transition thresholds and symmetry breaking

Compressible laminar streaks with wall suction

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