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Journal ArticleDOI

On transition in a pipe. Part 1. The origin of puffs and slugs and the flow in a turbulent slug

Israel Wygnanski, +1 more
- 19 Jun 1973 - 
- Vol. 59, Iss: 2, pp 281-335
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TLDR
In this paper, hot-wire measurements were taken in a pipe at Reynolds numbers corresponding to the onset of turbulence, where the pipe was smooth and carefully aligned so that turbulent slugs appeared naturally at Re > 5 × 104.
Abstract
Conditionally sampled hot-wire measurements were taken in a pipe at Reynolds numbers corresponding to the onset of turbulence. The pipe was smooth and carefully aligned so that turbulent slugs appeared naturally at Re > 5 × 104. Transition could be initiated at lower Re by introducing disturbances into the inlet. For smooth or only slightly disturbed inlets, transition occurs as a result of instabilities in the boundary layer long before the flow becomes fully developed in the pipe. This type of transition gives rise to turbulent slugs which occupy the entire cross-section of the pipe, and they grow in length as they proceed downstream. The leading and trailing ‘fronts’ of a turbulent slug are clearly defined. A unique relation seems to exist between the velocity of the interface and the velocity of the fluid by which relaminarization of turbulent fluid is prevented. The length of slugs is of the same order of magnitude as the length of the pipe, although the lengths of individual slugs differ at the same flow conditions. The structure of the flow in the interior of a slug is identical to that in a fully developed turbulent pipe flow. Near the interfaces, where the mean motion changes from a laminar to a turbulent state, the velocity profiles develop inflexions. The total turbulent intensity near the interfaces is very high and it may reach 15% of the velocity at the centre of the pipe. A turbulent energy balance was made for the flow near the interfaces. All of the terms contributing to the energy balance must vanish identically somewhere on the interface if that portion of the interface does not entrain non-turbulent fluid. It appears that diffusion which also includes pressure transport is the most likely mechanism by which turbulent energy can be transferred to non-turbulent fluid. The dissipation term at the interface is negligible and increases with increasing turbulent energy towards the interior of the slug.Mixed laminar and turbulent flows were observed far downstream for \[ 2000 < Re < 2700 \] when a large disturbance was introduced into the inlet. The flow in the vicinity of the inlet, however, was turbulent at much lower Re. The turbulent regions which are convected downstream at a velocity which is slightly smaller than the average velocity in the pipe we shall henceforth call puffs. The leading front of a puff does not have a clearly defined interface and the trailing front is clearly defined only in the vicinity of the centre-line. The length and structure of the puff is independent of the character of the obstruction which created it, provided that the latter is big enough to produce turbulent flow at the inlet. The puff will be discussed in more detail later.

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Citations
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Journal ArticleDOI

Fully developed turbulent pipe flow: a comparison between direct numerical simulation and experiment

TL;DR: In this paper, the authors investigated the differences between fully developed turbulent flow in an axisymmetric pipe and a plane channel geometry, and compared the results obtained from a channel flow simulation.
Journal ArticleDOI

Front motion, metastability and subcritical bifurcations in hydrodynamics

TL;DR: In this paper, it is argued that the border separating in space two possible solutions of the flow equations (as turbulent and laminar in pipe flows or boundary layers) moves with a constant mean velocity, depending on the control parameter.
Journal ArticleDOI

The onset of turbulence in pipe flow

TL;DR: It is shown that in pipes, turbulence that is transient at low Reynolds numbers becomes sustained at a distinct critical point and is intrinsic to the nature of fluid turbulence.
Journal ArticleDOI

Turbulence transition in pipe flow

TL;DR: Pipe flow is a prominent example among the shear flows that undergo transition to turbulence without mediation by a linear instability of the laminar profile as discussed by the authors, which can consistently be explained on the assumption that the turbulent state corresponds to a chaotic saddle in state space.
Journal ArticleDOI

The mixing transition in turbulent flows

TL;DR: In this paper, the authors proposed a Taylor Reynolds number of ReT = u[prime prime or minute] [lambda]T/v [greater, similar] 100-140 for turbulent mixing.
References
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