On Nature of K-Breakdown of a Laminar Boundary Layer. New Experimental Data

Kachanov, Y. S.; Козлов, В. В.; Levchenko, V. Ya.; Ramazanov, M. P.

doi:10.1007/978-3-642-82462-3_7

Cited by 28 publications

(29 citation statements)

References 5 publications

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“…This picture was doubted by Kleiser (1982Kleiser ( , 1985, on the basis that the high-frequency components of the energy spectrum grew continuously from the secondary instability stage, long before the appearance of the high-shear layer. Kachanov et al (1985) claimed that the development of the spikes is an entirely deterministic event, and is not involved in the development of unpredictability (Kachanov calls this 'randomization ') in the flow. This viewpoint is entirely supported by the observation in $ 5 of this paper that the shear-layer roll-up occurs in exactly the same way in both halves of the channel, well before the two halves become decorrelated.…”

Section: Generality Of Findingsmentioning

confidence: 99%

“…The work of Nishioka et al (1980), claiming to confirm the presence of a tertiary instability, has been criticized by Kachanov et al (1985) and Borodulin & Kachanov (1989). Kachanov et al (1985) observed that the spike formation occurred strictly periodically and concluded that the formation of the spikes was a deterministic event, and therefore not a manifestation of a tertiary instability. Borodulin & Kachanov (1989) distinguished between the process of spike formation and the shearlayer instability.…”

Section: Introductionmentioning

confidence: 99%

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The late stages of transition to turbulence in channel flow

Sandham

Kleiser²

1992

J. Fluid Mech.

106

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The late stages of transition, from the Λ-vortex stage up to turbulence, are investigated by postprocessing data from a direct numerical simulation of the complete K-type transition process in plane channel flow at a Reynolds number of 5000 (based on channel half-width and laminar centreline velocity). The deterministic roll-up of the high-shear layer that forms around the Λ-vortices is examined in detail. The new vortices arising from this process are visualized by plotting three-dimensional surfaces of constant pressure. Five vortices are observed, with one of these developing into a strong hairpin-shaped vortex. Interactions between the different vortices, and between the two channel halves, are found to be important. In the very last stage of transition second-generation shear layers are observed to form and roll up into new vortices. It is postulated that at this stage a sustainable mechanism of wall-bounded turbulence exists in an elementary form. The features which are locally present include high wall shear, sublayer streaks, ejections and sweeps. Large-scale energetic vortices are found to be an important part of the mechanism by which the turbulence spreads to other spanwise positions. The generality of the findings are discussed with reference to data from simulations of H-type and mixed-type transition.

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Section: Generality Of Findingsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The late stages of transition to turbulence in channel flow

Sandham

Kleiser²

1992

J. Fluid Mech.

106

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“…Some of those works showed that the basic mechanisms for the nonlinear stages of transition are similar for harmonic and for modulated TS waves. For instance, it was found experimentally by Kachanov et al (1985Kachanov et al ( , 1989 and Bake, Fernholz & Kachanov (2000) (see also Borodulin et al 2002a) that vortical structures formed in the boundary layer (such as Λ-vortices, spikes, and ring-like vortices) are qualitatively similar in the cases of harmonic and modulated primary TS waves. It was also shown by Breuer et al (1997), Medeiros & Gaster (1999a,b), Zelman & Smorodsky (1988), Craik (2001) and Wu et al (2007) that at weakly nonlinear stages of transition the subharmonic-type (often detuned) resonances are as important for the packets of TS waves as for the harmonic ones.…”

mentioning

confidence: 93%

“…The modulation of the TS waves during the transition process was simulated in several experimental investigations by means of excitation of either localized wave packets (see Gaster 1979;Cohen 1994;Breuer et al 1997;Medeiros & Gaster 1999a,b;Borodulin, Gaponenko & Kachanov 2000) or by modulated periodic TS waves usually consisting of a superposition of two or more harmonic waves (see Saric & Reynolds 1980;Kachanov et al 1985Kachanov et al , 1989Corke 1990;Würz et al 2012b). The corresponding theoretical models were studied within the framework of the weakly nonlinear approach (see e.g.…”

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confidence: 99%

Weakly nonlinear stages of boundary-layer transition initiated by modulated Tollmien–Schlichting waves

et al. 2013

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Weakly nonlinear interactions involving amplitude-modulated Tollmien-Schlichting waves in an incompressible, two-dimensional aerofoil boundary layer are investigated experimentally. Selected resonant regimes are examined with emphasis on the regimes where more than one fundamental Tollmien-Schlichting (TS) wave is present in the flow. The experiments were performed on an NLF-type aerofoil section for glider applications. Disturbances with controlled frequency-spanwise-wavenumber spectra were excited in the boundary layer and studied by phase-locked hot-wire measurements. The results show that nonlinear mechanisms connected with the steepening of the primary TS wave modulation do not play any significant role in the transition scenarios studied. It is also shown that modulations of the twodimensional fundamental waves tend to generate additional modes at modulation frequency. These low-frequency disturbances are found to be produced by a nonresonant quadratic combination of spectral components of the primary, modulated TS wave. The investigations show that the efficiency of the process is higher for three-dimensional low-frequency modes in comparison with two-dimensional modes. Thus, the emergence of three-dimensionality for the low-frequency waves does not require any resonant interactions. In a subsequent nonlinear stage, the self-generated detuned subharmonics are found to be strongly amplified due to resonant interactions with the primary TS waves. The sequence of weakly nonlinear mechanisms found and investigated here seems to be the most likely route to the laminar-turbulent transition, at least for two-dimensional boundary layers of aerofoils with a long extent of laminar flow and in a 'natural' disturbance environment.

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“…6. Distributions of the velocity deviation from the mean at R = 650 for the flow as a whole (a) and its laminar (b) and turbulent (c) regions: 1-4 relate to η = 0.2, 1.6, 3, and 11; 5 denotes the normal distribution is typical of the velocity oscillograms measured in [20] in the nonlinear transition stage caused by Tollmien-Schlichting waves, though their maxima and minima were arranged in a regular order. Apparently, this type of fluctuation is a general property of the nonlinear development of vortex disturbances in wall flows.…”

Section: Calculated Resultsmentioning

confidence: 99%

Numerical modeling of laminar-turbulent transition in a boundary layer at a high freestream turbulence level

Ustinov¹

2006

Fluid Dyn

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Disturbances generated by external turbulence in the boundary layer on a flat plate set suddenly in motion are determined by numerically solving the Navier-Stokes equations. The results of direct numerical simulation of isotropic homogenous turbulence are taken as initial conditions. The solution obtained models laminar-turbulent transition in the flat-plate boundary layer at a high freestream turbulence level, time measured from the onset of the motion serving as the longitudinal coordinate. The solution makes it possible to estimate the effect of different factors, such as flow unsteadiness and nonlinearity and the characteristics of the freestream velocity fluctuation spectrum, on laminar-turbulent transition in the boundary layer.Here, U 0 (z, t) is the mean flow velocity which is equal to zero before the plate appears and corresponds to the laminar flow velocity profile in the channel after it appears, while 2L x and 2D are the longitudinal

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On Nature of K-Breakdown of a Laminar Boundary Layer. New Experimental Data

Cited by 28 publications

References 5 publications

The late stages of transition to turbulence in channel flow

The late stages of transition to turbulence in channel flow

Weakly nonlinear stages of boundary-layer transition initiated by modulated Tollmien–Schlichting waves

Numerical modeling of laminar-turbulent transition in a boundary layer at a high freestream turbulence level

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