Experiments in a boundary layer subjected to free stream turbulence. Part 1. Boundary layer structure and receptivity

Westin, K. J. A.; Бойко, А. В.; Klingmann, Barbro G. B.; Козлов, В. В.; Alfredsson, P. Henrik

doi:10.1017/s0022112094003083

Cited by 317 publications

(301 citation statements)

References 11 publications

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“…Matsubara & Alfredsson's data demonstrated that the spanwise scale of the disturbances approaches the boundary layer thickness downstream after an initial adjustment, and that the energy of the streamwise velocity fluctuation grows linearly with downstream distance, which is consistent with observations in previous studies, e.g. Westin et al (1994). The proportionality constants, however, vary from one experiment to another.…”

Section: Bypass Transitionsupporting

confidence: 87%

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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Section: Bypass Transitionsupporting

confidence: 87%

Transition of transient channel flow after a change in Reynolds number

Seddighi

2015

J. Fluid Mech.

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“…Ricco [42] (hereafter referred to as R9), by adopting LWG99's asymptotic approach, showed that a balance between the free-stream pressure fluctuations and the streamwise velocity fluctuations is relevant for the formation of the streak fluctuations in the outer part of the boundary layer. A realistic streak profile along the whole wall-normal extent of the boundary layer was obtained by R9 and good agreement with the experimental data by Westin et al [56] was shown. Ricco & Dilib [43] employed R9's approach to show that the peak of the streak amplitude in the boundary-layer core may be completely suppressed if intense wall transpiration is applied and Ricco and co-authors [47,46,45] have studied the Klebanoff modes in compressible boundary layers.…”

Section: Theoretical Framework For the Laminar Streakssupporting

confidence: 81%

“…The objective of the analysis is to find the initial velocity profile near the leading edge that maximizes a specified cost function, which may represent the energy of the perturbation within the entire viscous layer or at a specified downstream distance. When the peak disturbance is normalized, the wallnormal profile agrees well with the Taylor-Stewartson mode and with the experimental rms profiles of the streamwise velocity in the boundary-layer core [56,33], although no comparison on the downstream evolution has been carried out.…”

Section: − the Taylor-stewartson Theorysupporting

confidence: 58%

“…The objective is to compare the profiles obtained through our boundary-region solutions with the measured wall-normal profiles of the streamwise velocity at a specified frequency and with the DNS profiles. R9 compared his numerical results with the data by Westin et al [56], but further comparison is needed to confirm the validity of the theoretical approach.…”

Section: • Assessment Of the Theorymentioning

confidence: 93%

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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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“…Hultgren & Gustavsson 1981;Westin et al 1994;Jacobs & Durbin 2001). Their elongated appearance is explained by the rapid distortion theory (Phillips 1969), and their spanwise scale can be predicted using transient growth analysis (Butler & Farrell 1992).…”

Section: Introductionmentioning

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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Experiments in a boundary layer subjected to free stream turbulence. Part 1. Boundary layer structure and receptivity

Cited by 317 publications

References 11 publications

Transition of transient channel flow after a change in Reynolds number

Transition of transient channel flow after a change in Reynolds number

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

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

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