Topic
Boundary layer
About: Boundary layer is a research topic. Over the lifetime, 64972 publications have been published within this topic receiving 1448944 citations.
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TL;DR: In this article, the behavior of laminar and turbulent boundary layers on a moving continuous cylindrical surface is investigated by the integral method, based on assumed velocity profiles that satisfy the appropriate boundary conditions.
Abstract: The behavior of laminar and turbulent boundary layers on a moving continuous cylindrical surface is investigated by the integral method, based on assumed velocity profiles that satisfy the appropriate boundary conditions. Equations for the characteristic boundary-layer parameters are presented for both the laminar and turbulent boundary layers, and comparison is made with the boundary-layer behavior over a cylindrical surface of finite length. The analysis for the laminar boundary layer with a logarithmic velocity profile leads to satisfactory results. The turbulent boundary-layer behavior on continuous cylindrical surfaces, and cylindrical surfaces of finite length, can best be investigated experimentally.
1,676 citations
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TL;DR: In this paper, the structure of energy-containing turbulence in the outer region of a zero-pressure-gradient boundary layer has been studied using particle image velocimetry (PIV) to measure the instantaneous velocity fields in a streamwise-wall-normal plane.
Abstract: The structure of energy-containing turbulence in the outer region of a zero-pressure-
gradient boundary layer has been studied using particle image velocimetry (PIV) to measure the instantaneous velocity fields in a streamwise-wall-normal plane. Experiments performed at three Reynolds numbers in the range 930 0) that occur on a locus inclined at 30–60° to the wall.In the outer layer, hairpin vortices occur in streamwise-aligned packets that propagate with small velocity dispersion. Packets that begin in or slightly above the buffer layer are very similar to the packets created by the autogeneration mechanism (Zhou, Adrian & Balachandar 1996). Individual packets grow upwards in the streamwise direction at a mean angle of approximately 12°, and the hairpins in packets are typically spaced several hundred viscous lengthscales apart in the streamwise direction. Within the interior of the envelope the spatial coherence between the velocity fields induced by the individual vortices leads to strongly retarded streamwise momentum, explaining the zones of uniform momentum observed by Meinhart & Adrian (1995). The packets are an important type of organized structure in the wall layer in which relatively small structural units in the form of three-dimensional vortical structures are arranged coherently, i.e. with correlated spatial relationships, to form much longer structures. The formation of packets explains the occurrence of multiple VITA events in turbulent ‘bursts’, and the creation of Townsend's (1958) large-scale inactive motions. These packets share many features of the hairpin models proposed by Smith (1984) and co-workers for the near-wall layer, and by Bandyopadhyay (1980), but they are shown to occur in a hierarchy of scales across most of the boundary layer.In the logarithmic layer, the coherent vortex packets that originate close to the wall frequently occur within larger, faster moving zones of uniform momentum, which may extend up to the middle of the boundary layer. These larger zones are the induced interior flow of older packets of coherent hairpin vortices that originate upstream and over-run the younger, more recently generated packets. The occurence of small hairpin packets in the environment of larger hairpin packets is a prominent feature of the logarithmic layer. With increasing Reynolds number, the number of hairpins in a packet increases.
1,627 citations
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TL;DR: In this paper, the authors proposed to represent the mean-velocity profile by a linear combination of two universal functions, namely the law of the wall and the wake, and compared the results with experimental data.
Abstract: After an extensive survey of mean-velocity profile measurements
in various two-dimensional incompressible turbulent boundary-layer
flows, it is proposed to represent the profile by a linear
combination of two universal functions. One is the well-known
law of the wall. The other, called the law of the wake, is
characterized by the profile at a point of separation or reattachment.
These functions are considered to be established empirically, by
a study of the mean-velocity profile, without reference to any
hypothetical mechanism of turbulence. Using the resulting
complete analytic representation for the mean-velocity field,
the shearing-stress field for several flows is computed from the
boundary-layer equations and compared with experimental data.
The development of a turbulent boundary layer is ultimately
interpreted in terms of an equivalent wake profile, which supposedly
represents the large-eddy structure and is a consequence of the
constraint provided by inertia. This equivalent wake profile is
modified by the presence of a wall, at which a further constraint is
provided by viscosity. The wall constraint, although it penetrates
the entire boundary layer, is manifested chiefly in the sublayer flow
and in the logarithmic profile near the wall.
Finally, it is suggested that yawed or three-dimensional flows
may be usefully represented by the same two universal functions,
considered as vector rather than scalar quantities. If the wall
component is defined to be in the direction of the surface shearing
stress, then the wake component, at least in the few cases studied,
is found to be very nearly parallel to the gradient of the pressure.
1,574 citations
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TL;DR: In this article, a similarity solution is presented which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb and thermophoresis number Nt.
1,565 citations
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TL;DR: In this article, an experimental work on the convective heat transfer of nanofluids, made of γ-Al2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime was conducted.
1,545 citations