Effect of free-stream turbulence and other 
vortical disturbances on a laminar boundary layer

Leib, S. J.; Wundrow, David W.; Goldstein, M. E.

doi:10.1017/s0022112098003504

Cited by 164 publications

(267 citation statements)

References 28 publications

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“…The four most relevant theoretical frameworks describing the Klebanoff modes have been thoroughly discussed and parallels and complimentary aspects of the theories have been pointed out. This discussion has supported our choice to use the Goldstein theory [26].…”

Section: Resultsmentioning

confidence: 89%

“…A complete understanding of the bypass transition has not been attained, despite research efforts based on experiments [33,11,16,17,37,39], numerical simulations [20,24,38], and theoretical analysis [26] (hereafter referred to LWG99) [28,60,44,13]. The boundary layer has been revealed to act as a filter for the full-spectrum free-stream vortical disturbances, thereby allowing low frequency disturbances to penetrate into the boundary-layer core and to amplify significantly, whilst preventing high-frequency fluctuations from growing downstream.…”

Section: The Laminar Streaks and Bypass Transitionmentioning

confidence: 99%

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Growth of boundary-layer streaks due to free-stream turbulence

Riccó

Walsh

Brighenti

et al. 2016

International Journal of Heat and Fluid Flow

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Section: Resultsmentioning

confidence: 89%

Section: The Laminar Streaks and Bypass Transitionmentioning

confidence: 99%

Growth of boundary-layer streaks due to free-stream turbulence

Riccó

Walsh

Brighenti

et al. 2016

International Journal of Heat and Fluid Flow

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“…This was also achieved independently by Luchini (2000). Leib, Wundrow & Goldstein (1999)'s theoretical study was based on the solution of the boundary-region equation, which allowed them to more closely consider the interactions between the boundary layer and the free-stream disturbances. Their results showed that continuous free-stream forcing could play an important role in producing the large Klebanoff-mode growth rates observed in experiments, and that this growth exhibited a strong sensitivity to low-frequency anisotropy of the FST.…”

Section: Bypass Transitionmentioning

confidence: 99%

Transition of transient channel flow after a change in Reynolds number

Seddighi

2015

J. Fluid Mech.

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It has previously been shown that the transient flow in a channel following a step increase of Reynolds number from 2800 to 7400 (based on channel half-height and bulk velocity) is effectively a laminar-turbulent bypass transition even though the initial flow is turbulent (He & Seddighi, J. Fluid Mech., vol. 715, 2013, pp. 60-102). In this paper, it is shown that the transient flow structures exhibit strong contrasting characteristics in large and small flow perturbation scenarios. When the increase of Reynolds number is large, the flow is characterized by strong elongated streaks during the initial period, followed by the occurrence and spreading of isolated turbulent spots, as shown before. By contrast, the flow appears to evolve progressively and the turbulence regeneration process remains largely unchanged during the flow transient when the Reynolds number ratio is low, and streaks do not appear to play a significant role. Despite the major apparent differences in flow structures, the transient flow under all conditions considered is unambiguously characterized by laminar-turbulent transition, which exhibits itself clearly in various flow statistics. During the pre-transition period, the time-developing boundary layers in all the cases show a strong similarity to each other and follow closely the Stokes solution for a transient laminar boundary layer. The streamwise fluctuating velocity also shows good similarity in the various cases, irrespective of the appearance of elongated streaks or not, and the maximum energy growth exhibits a linear rate similar to that in a spatially developing boundary layer. The onset of transition is clearly definable in all cases using the minimum friction factor, and the critical time thus defined is strongly correlated with the free-stream turbulence in a power-law form.

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“…The spanwise size of the streaks is of the order of the boundary-layer thickness and, as a result, both wall-normal and cross-flow ellipticity must be taken into account in predicting their evolution. In order to account for these effects, the boundary region equations can be used (Goldstein & Leib 1993;Leib, Wundrow & Goldstein 1999). However, the linear formulation is not sufficient because the streaks reach a high amplitude.…”

Section: Theoretical Formulationmentioning

confidence: 99%

“…The domain used in the DNS is marked by the dashed line. III in Leib et al (1999). Since our flow is computed using DNS, both non-parallel and nonlinear effects are fully captured, and the streak profiles downstream include higher harmonics of the inlet ω and k z .…”

Section: Theoretical Formulationmentioning

confidence: 99%

Stability of zero-pressure-gradient boundary layer distorted by unsteady Klebanoff streaks

2011

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The secondary instability of a zero-pressure-gradient boundary layer, distorted by unsteady Klebanoff streaks, is investigated. The base profiles for the analysis are computed using direct numerical simulation (DNS) of the boundary-layer response to forcing by individual free-stream modes, which are low frequency and dominated by streamwise vorticity. Therefore, the base profiles take into account the nonlinear development of the streaks and mean flow distortion, upstream of the location chosen for the stability analyses. The two most unstable modes were classified as an inner and an outer instability, with reference to the position of their respective critical layers inside the boundary layer. Their growth rates were reported for a range of frequencies and amplitudes of the base streaks. The inner mode has a connection to the TollmienSchlichting (T-S) wave in the limit of vanishing streak amplitude. It is stabilized by the mean flow distortion, but its growth rate is enhanced with increasing amplitude and frequency of the base streaks. The outer mode only exists in the presence of finite amplitude streaks. The analysis of the outer instability extends the results of Andersson et al. (J. Fluid Mech. vol. 428, 2001, p. 29) to unsteady base streaks. It is shown that base-flow unsteadiness promotes instability and, as a result, leads to a lower critical streak amplitude. The results of linear theory are complemented by DNS of the evolution of the inner and outer instabilities in a zero-pressure-gradient boundary layer. Both instabilities lead to breakdown to turbulence and, in the case of the inner mode, transition proceeds via the formation of wave packets with similar structure and wave speeds to those reported by Nagarajan, Lele & Ferziger (J. Fluid Mech., vol. 572, 2007, p. 471).

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Effect of free-stream turbulence and other vortical disturbances on a laminar boundary layer

Cited by 164 publications

References 28 publications

Growth of boundary-layer streaks due to free-stream turbulence

Growth of boundary-layer streaks due to free-stream turbulence

Transition of transient channel flow after a change in Reynolds number

Stability of zero-pressure-gradient boundary layer distorted by unsteady Klebanoff streaks

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