Laminar superlayer in a turbulent boundary layer

Semin, N. V.; Golub, V. V.; Elsinga, Gerrit E.; Westerweel, J.

doi:10.1134/s1063785011120285

Cited by 13 publications

(11 citation statements)

References 12 publications

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“…Chen & Blackwelder (1978) used temperature as a passive contaminant to show that steep variation in velocities in the outer part are associated with temperature fronts that essentially are 'backs' of the turbulent bulges. More recently, Semin et al (2011) used tomographic PIV data to document the conditionally averaged profiles of streamwise momentum and spanwise vorticity similar to those in figure 5. Their results do not quantitatively agree with our experiments, and this is attributed to the low Reynolds number in their study (Re τ = 600).…”

Section: Dynamics At the Interfacementioning

confidence: 97%

“…After the initial dismay at not finding a velocity jump across the interface in the 1970s (in boundary-layer flows by Kovasznay, Kibens & Blackwelder 1970), more recently it has been observed that, indeed, there does exist a velocity jump at the TNTI of boundary layers (Semin et al 2011) and in wakes and jets, though over a small but finite region (Bisset, Hunt & Rogers 2002;Westerweel et al 2005). Regarding the second hypothesis of spreading by turbulent diffusion, it is uncertain whether it is fully correct.…”

Section: Introductionmentioning

confidence: 94%

“…With the exception of the present study and that of Semin et al (2011) the understanding of TNTI characteristics in boundary layers is still largely based on the classical studies in the 1960s and 1970s. As our emphasis in this paper is on the turbulent boundary layer, only the relevant previous work is introduced to the reader.…”

Section: Introductionmentioning

confidence: 94%

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The turbulent/non-turbulent interface and entrainment in a boundary layer

et al. 2014

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The turbulent/non-turbulent interface in a zero-pressure-gradient turbulent boundary layer at high Reynolds number (Re τ = 14 500) is examined using particle image velocimetry. An experimental set-up is utilized that employs multiple high-resolution cameras to capture a large field of view that extends 2δ × 1.1δ in the streamwise/wallnormal plane with an unprecedented dynamic range. The interface is detected using a criteria of local turbulent kinetic energy and proves to be an effective method for boundary layers. The presence of a turbulent/non-turbulent superlayer is corroborated by the presence of a jump for the conditionally averaged streamwise velocity across the interface. The steep change in velocity is accompanied by a discontinuity in vorticity and a sharp rise in the Reynolds shear stress. The conditional statistics at the interface are in quantitative agreement with the superlayer equations outlined by Reynolds (J. Fluid Mech., vol. 54, 1972, pp. 481-488). Further analysis introduces the mass flux as a physically relevant parameter that provides a direct quantitative insight into the entrainment. Consistency of this approach is first established via the equality of mean entrainment calculations obtained using three different methods, namely, conditional, instantaneous and mean equations of motion. By means of 'mass-flux spectra' it is shown that the boundary-layer entrainment is characterized by two distinctive length scales which appear to be associated with a two-stage entrainment process and have a substantial scale separation.

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Section: Dynamics At the Interfacementioning

confidence: 97%

Section: Introductionmentioning

confidence: 94%

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The turbulent/non-turbulent interface and entrainment in a boundary layer

et al. 2014

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“…Across TNT interfaces, a peak in vorticity corresponding to a jump in streamwise velocity can be observed as shown in recent experimental studies of turbulent boundary layers using particle image velocimetry (PIV) (e.g. Semin et al 2011;Chauhan et al 2014). However, it should be noted that there are some cases where no vorticity peaks are observed (da ).…”

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confidence: 89%

The quiescent core of turbulent channel flow

et al. 2014

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The identification of uniform momentum zones in wall-turbulence, introduced by Adrian, Meinhart & Tomkins (J. Fluid Mech., vol. 422, 2000, pp. 1-54) has been applied to turbulent channel flow, revealing a large 'core' region having high and uniform velocity magnitude. Examination of the core reveals that it is a region of relatively weak turbulence levels. For channel flow in the range Re τ = 1000-4000, it was found that the 'core' is identifiable by regions bounded by the continuous isocontour lines of the streamwise velocity at 0.95U CL (95 % of the centreline velocity). A detailed investigation into the properties of the core has revealed it has a large-scale oscillation which is predominantly anti-symmetric with respect to the channel centreline as it moves through the channel, and there is a distinct jump in turbulence statistics as the core boundary is crossed. It is concluded that the edge of the core demarcates a shear layer of relatively intense vorticity such that the interior of the core contains weakly varying, very low-level turbulence (relative to the flow closer to the wall). Although channel flows are generally referred to as 'fully turbulent', these findings suggest there exists a relatively large and 'quiescent' core region with a boundary qualitatively similar to the turbulent/non-turbulent interface of boundary layers, jets and wakes.

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“…The thickness of the above interfaces with surrounding non-turbulent fluid has been reported to extend from the Kolmogorov scale to the Taylor microscale also in a free-shear flow or boundary layer (Rotta, 1962) (Pope, 2000) (Bisset, et al, 2002) (Westerweel, et al, 2005)(da Silva and Taveira, 2010) (Holzner andLüthi, 2011)(da Silva, et al, 2011) (Semin, et al, 2011). In this turbulent patch, the order of the Kolmogorov scale was estimated as approximately 0.1 mm.…”

mentioning

confidence: 99%

Laminar-turbulent transition of an inlet boundary layer in a circular pipe induced by periodic injection (Turbulence within isolated turbulent patches and its growth mechanism)

Ichimiya

Matsudaira

Fujimura

2014

JFST

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The laminar-turbulent transition of a boundary layer induced by a jet injection in the inlet region of a circular pipe was experimentally investigated. The jet was periodically injected radially from a small hole in the inlet region into the pipe flow. Axial velocity was measured by a hot-wire anemometer. The turbulence induced by the jet within the boundary layer developed into turbulent patches which grew in the axial, circumferential and radial directions downstream. Turbulent fluctuations within the patch were maximum a little inside the leading edge in the axial direction and slightly inside the circumferential interface in the circumferential direction. Non-turbulent fluid was entrained into the patch through the leading and trailing edges. This was the main reason for the axial growth of the patch downstream. If the entrainment is suppressed, the axial growth is inhibited. The axial distance between the leading edge and maximum fluctuation position varied little downstream. On the other hand, the distance between the maximum fluctuation position and the trailing edge increased downstream due to the increase in the entrainment of non-turbulent fluid across the trailing edge. Keywords

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Laminar superlayer in a turbulent boundary layer

Cited by 13 publications

References 12 publications

The turbulent/non-turbulent interface and entrainment in a boundary layer

The turbulent/non-turbulent interface and entrainment in a boundary layer

The quiescent core of turbulent channel flow

Laminar-turbulent transition of an inlet boundary layer in a circular pipe induced by periodic injection (Turbulence within isolated turbulent patches and its growth mechanism)

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