Growth and breakdown of streaky structures in boundary layer transition induced by free stream turbulence

Matsubara, Masaharu; Bakchinov, Andrey; Fransson, Jens H. M.; Alfredsson, P. Henrik

doi:10.1007/978-3-662-03997-7_55

Cited by 10 publications

(11 citation statements)

References 5 publications

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“…The completion of the transition is at lower Re x for L = 7.5δ * 0 , thus confirming the trend observed in the experimental study of Jonáš, Mazur & Uruba (2000). The transition location in the present simulations is only slightly upstream of that observed in the experiments by Matsubara et al (2000) and Roach & Brierley (1990) (test case T3A) with a lower free-stream turbulence level of 3%. However, the difference is not so surprising: in the experiments the turbulence affects the boundary layer from the leading edge, while in the simulations it is induced a certain distance downstream.…”

Section: Effect Of the Integral Length Scale On The Boundary-layer Trsupporting

confidence: 91%

“…Andersson et al (1999) proposed also a transition prediction criterion which assumes that the Reynolds number at transition onset is inversely proportional to the square of the free-stream turbulence intensity. Although such a criterion is only based on the fact that the linear growth of optimal perturbations is proportional to the square root of the local Reynolds number and it does not consider any of the nonlinear processes occurring at the late stages of the breakdown, it is able to satisfactorily correlate data from several studies (see also Matsubara et al 2000). Wundrow & Goldstein (2001) and Goldstein & Wundrow (1998) used asymptotic expansions to study the effect of free-stream streamwise vorticity on a laminar boundary layer.…”

Section: Previous Experimental and Numerical Workmentioning

confidence: 99%

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Transition in boundary layers subject to free-stream turbulence

2004

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The effect of high levels of free-stream turbulence on the transition in a Blasius boundary layer is studied by means of direct numerical simulations, where a synthetic turbulent inflow is obtained as superposition of modes of the continuous spectrum of the Orr-Sommerfeld and Squire operators. In the present bypass scenario the flow in the boundary layer develops streamwise elongated regions of high and low streamwise velocity and it is suggested that the breakdown into turbulent spots is related to local instabilities of the strong shear layers associated with these streaks. Flow structures typical of the spot precursors are presented and these show important similarities with the flow structures observed in previous studies on the secondary instability and breakdown of steady symmetric streaks.Numerical experiments are performed by varying the energy spectrum of the incoming perturbation. It is shown that the transition location moves to lower Reynolds numbers by increasing the integral length scale of the free-stream turbulence. The receptivity to free-stream turbulence is also analysed and it is found that two distinct physical mechanisms are active depending on the energy content of the external disturbance. If low-frequency modes diffuse into the boundary layer, presumably at the leading edge, the streaks are induced by streamwise vorticity through the linear lift-up effect. If, conversely, the free-stream perturbations are mainly located above the boundary layer a nonlinear process is needed to create streamwise vortices inside the shear layer. The relevance of the two mechanisms is discussed.

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Section: Effect Of the Integral Length Scale On The Boundary-layer Trsupporting

confidence: 91%

Section: Previous Experimental and Numerical Workmentioning

confidence: 99%

Transition in boundary layers subject to free-stream turbulence

2004

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“…Assuming that transition occurs when the level of streamwise velocity fluctuations reaches a given threshold, roughly at the amplitudes at which the streaks become unstable, the transition location Re T can be related to the turbulence intensity by Re T Tu 2 = const. The model was validated against experimental results by Matsubara et al, 25 showing good correlation between transition location and the level of the free-stream turbulence only based on results of nonmodal growth.…”

Section: A Streak Formationmentioning

confidence: 99%

On streak breakdown in bypass transition

et al. 2008

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Recent theoretical, numerical, and experimental investigations performed at the Department of Mechanics, KTH Stockholm, and the Department of Mechanical Engineering, Eindhoven University of Technology, are reviewed, and new material is presented to clarify the role of the boundary-layer streaks and their instability with respect to turbulent breakdown in bypass transition in a boundary layer subject to free-stream turbulence. The importance of the streak secondary-instability process for the generation of turbulent spots is clearly shown. The secondary instability manifests itself as a growing wave packet located on the low-speed streak, increasing in amplitude as it is dispersing in the streamwise direction. In particular, qualitative and quantitative data pertaining to temporal sinuous secondary instability of a steady streak, impulse responses both on a parallel and a spatially developing streak, a model problem of bypass transition, and full simulations and experiments of bypass transition itself are collected and compared. In all the flow cases considered, similar characteristics in terms of not only growth rates, group velocity, and wavelengths but also three-dimensional visualizations of the streak breakdown have been found. The wavelength of the instability is about an order of magnitude larger than the local boundary-layer displacement thickness ␦ ‫ء‬ , the group velocity about 0.8 of the free-stream velocity U ϱ , and the growth rate on the order of a few percent of U ϱ / ␦ ‫ء‬ . The characteristic structures at the breakdown are quasistreamwise vortices, located on the flanks of the low-speed region arranged in a staggered pattern.

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“…Additionally, the amplitude growth is given there for the most locally powerful modes with dimensional wave numbers ␤ decreasing downstream, rather than for the modes with constant ␤ as in the present work that seems physically more reasonable. 21,35,36 The spanwise wave numbers of the most powerful and growing modes at Fϭ26.9•10 Ϫ6 in the range 60Ͻx Ͻ135 mm are given in Table I. Dimensional and normalized to local displacement thickness values are presented.…”

Section: B Growth Of Disturbance Amplitudementioning

confidence: 99%

Spectral analysis of localized disturbances in boundary layer at subcritical Reynolds numbers

2003

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A flat plate boundary layer disturbance in the form of a streak is excited by a vortex of limited spanwise extent generated upstream of the plate leading edge. Frequency-wave spectral analysis of the streamwise velocity component of the streak is performed. The most part of energy in the spectrum is contained in low-frequency waves with the angles of their wave vector inclination to streamwise direction more than 85°. Spanwise wave numbers, peculiarities of amplitude growth, as well as streamwise velocity profiles of the most powerful spectral components of the streak are in a good agreement with known theoretical data on linear transient growth. However, behavior of the total energy of the streak is not corresponding to that of theoretical ''optimal'' transient structures. We suspect that, to make the theoretical results concerning the streak energy valid, details of the receptivity process must be taken into consideration. As the frequency grows, dispersion characteristics and decrements of the spectral components approach results of stability theory for Tollmien-Schlichting waves.

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Growth and breakdown of streaky structures in boundary layer transition induced by free stream turbulence

Cited by 10 publications

References 5 publications

Transition in boundary layers subject to free-stream turbulence

Transition in boundary layers subject to free-stream turbulence

On streak breakdown in bypass transition

Spectral analysis of localized disturbances in boundary layer at subcritical Reynolds numbers

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