A study on boundary-layer transition induced by free-stream turbulence

Mandal, AC; Venkatakrishnan, L.; Dey, J.

doi:10.1017/s0022112010002600

Cited by 64 publications

(52 citation statements)

References 61 publications

(156 reference statements)

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“…The same trend was observed in experiments of bypass transition (e.g. Mandal et al 2010). The deviation of U 0 from Blasius increases with the amplitude of the base streaks.…”

Section: Theoretical Formulationsupporting

confidence: 83%

“…This level was increased to 90% for the higher-frequency base flow, F = 60. Inflectional wall-normal velocity profiles were also reported by Mandal et al (2010), based on a PIV study of bypass transition. They argued that the inflectional profiles were important for varicose instabilities, such as the present inner mode.…”

Section: The Inner Modementioning

confidence: 85%

“…However, a discrepancy remains between the critical streak amplitude based on stability theory and experimental observations. While the former predicts a threshold amplitude of 26%, Arnal & Juillen (1978) showed that modest streak intensities with u rms ∼ 5-7% were sufficient for transition ;Mandal, Venkatakrishnan & DEY (2010) report u rms = 9% before transition.…”

Section: The Instability Due To Klebanoff Streaks In Bypass Transitionmentioning

confidence: 99%

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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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“…The same trend was observed in experiments of bypass transition (e.g. Mandal et al 2010). The deviation of U 0 from Blasius increases with the amplitude of the base streaks.…”

Section: Theoretical Formulationsupporting

confidence: 83%

Section: The Inner Modementioning

confidence: 85%

Section: The Instability Due To Klebanoff Streaks In Bypass Transitionmentioning

confidence: 99%

See 1 more Smart Citation

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

2011

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“…Brandt & Henningson 2002;Zaki & Durbin 2005;Schlatter et al 2008;Mandal, Venkatakrishnan & Dey 2010;Nolan, Walsh & Mceligot 2010;Nolan & Walsh 2012). Additionally, Andersson et al (2001), Vaughan & Zaki (2011) and Hack & Zaki (2014) have performed secondary instability analysis of streaks.…”

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 rms, skewness S, and third moment T are calculated from the full velocity signal, and from the positive and negative streaks separately (95% percentile of the full signal is considered, as in [29]). Figure 3 shows the statistics of the full signal of the streamwise velocity and of the positive and negative streaks.…”

Section: Time-averaged Statistics Of Streaksmentioning

confidence: 99%