On the transient nature of localized pipe flow turbulence

Avila, Marc; Willis, Ashley P.; Hof, Björn

doi:10.1017/s0022112009993296

Cited by 92 publications

(157 citation statements)

References 32 publications

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“…While some inferred from the rapid increase of mean lifetimes that the lifetime diverges at Re cr , and thus turbulence sustains [4,5,11,17,23], others reported a bounded lifetime and concluded a transient nature for turbulence [12,13]. This dispute was finally settled by Avila et al [2] whose extensive numerical investigation proved a super-exponential scaling of mean lifetimes that indicates no threshold of divergence exists.…”

Section: Introductionmentioning

confidence: 99%

Turbulent Spot in Linearly Stable Taylor Couette Flow

Alidai

Greidanus

Delfos

et al. 2015

Flow Turbulence Combust

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The transition from the laminar to the turbulent regime in linearly stable shear flows, for example, pipe and plane Couette flows, occurs abruptly with no precursor. The evolution of turbulent spots has been studied to better understand the dynamics of this transition and the onset of turbulence. These studies have mostly focused on pipe flows for which a finite lifetime of spots was proven. The same conclusion was drawn in the only available study performed in a Taylor Couette setup. Here, the spot lifetime is measured in a different size TC setup. It is shown that the lifetime is indeed finite and also very sensitive to boundary conditions, but not much to perturbation mechanisms. A scaling approach is provided which suggests in addition to the Reynolds number, the aspect and radius ratios are influential parameters on the lifetime. It is found that the spot size varies during its lifetime and increases with the Reynolds number that confirms the rise in turbulence proliferation by approaching the transitional point.

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Section: Introductionmentioning

confidence: 99%

Turbulent Spot in Linearly Stable Taylor Couette Flow

Alidai

Greidanus

Delfos

et al. 2015

Flow Turbulence Combust

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“…The governing equations are integrated with a second-order semiimplicit time-stepping scheme (for details, see 23 ). The code has been verified and extensively used in many studies (for example, 24,25,26 ). In Supplementary Table 1, we list the Re numbers, pipe lengths and resolutions we considered in our simulations.…”

Section: Competing Interestsmentioning

confidence: 99%

“…The pipe length was doubled for Re = 4,000 and 5,000 to verify that the pipe lengths here in the table are sufficient. The resolutions are set to be able to sufficiently resolve the nearwall structures (see reference grid sizes shown in Table 1 of 24 ). Note that there is a difference of a factor of two in length scales between our normalization and theirs (double ours to compare with theirs).…”

Section: Competing Interestsmentioning

confidence: 99%

Destabilizing turbulence in pipe flow

et al. 2018

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Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities [1][2][3] , so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism 4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.Flows through pipes and hydraulic networks are generally turbulent and the friction losses encountered in these flows are responsible for approximately 10% of the global electric energy consumption. Here turbulence causes a severe drag increase and consequently much larger forces are needed to maintain desired flow rates. In pipes, both laminar and turbulent states are stable (the former is believed to be linearly stable for all Reynolds number (Re) values; the latter is stable if Re > 2, 040 (ref. 6 )), but with increasing speed the laminar state becomes more and more susceptible to small disturbances. Hence, in practice most flows are turbulent at sufficiently large Re. While the stability of laminar flow has been studied in great detail, little attention has been paid to the susceptibility of turbulence, the general assumption being that once turbulence is established it is stable.Many turbulence control strategies have been put forward to reduce the drag encountered in shear flows [7][8][9][10][11][12][13][14][15][16][17] . Recent strategies employ feedback mechanisms to actively counter selected velocity components or vortices. Such methods usually require knowledge of the full turbulent velocity field. In computer simulations 7,8 , it could be demonstrated that under these ideal conditions, flows at a low Re number can even be relaminarized. In experiments, the required detailed manipulation of the time-dependent velocity field is, however, currently impossible to achieve. Other studies employ passive (for example, riblets) or active (oscillations or excitation of travelling waves) methods to interfere with the near-wall turbulence creation. Typically here drag reduction of 10 to 40% has been reported, but often the control cost is substantially higher than the gain, or a net gain can be achieved only in a narrow Re number regime.Instead of attempting to control or counter certain components of the complex fluctuating flow fields, we will show in the following that by appropriately dist...

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“…This linear stability can also arise in special cases of classical turbulence, most notably in pipe flow through a pipe of circular cross section, where again finite lifetimes are observed (see, e.g., ref. 25). This type of finite lifetime had been observed in effect in much earlier experiments with vibrating structures, most notably by Schoepe and his colleagues (see, e.g., ref.…”

Section: −1mentioning

confidence: 99%

Quantum turbulence generated by oscillating structures

Vinen

Skrbek

2014

Proc. Natl. Acad. Sci. U.S.A.

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The paper summarizes important aspects of quantum turbulence that have been studied successfully with oscillating structures. It describes why some aspects are proving hard to interpret, and it outlines the need for new types of experiment and new developments in theoretical and computational work. superfluid helium | quantized vortex linesThis paper is concerned with the generation of quantum turbulence (1-3) in liquid helium by various forms of oscillating structure, such as a cylinder oscillating in a direction normal to its length. Many experiments on the generation of quantum turbulence by such structures have been reported, involving not only cylinders (or wires), but also spheres, tuning forks, and grids. Many of these experiments and their possible interpretation have already been reviewed (4). We are not aiming to produce another conventional review, and we shall not consider all that has been achieved. Instead, our aim is to focus on three particular aspects of this type of work: first, on experiments that have already contributed significantly to our understanding of issues that are, as we see them, of general and fundamental importance; second, on an exposure of the difficulties in interpreting many of the experiments in any real detail, in the way that has been achieved in analogous work on classical fluids; and third, on ways in which we might overcome these difficulties, which are both theoretical and experimental. We shall be concerned ultimately with both superfluid He. There are of course connections between quantum turbulence produced by oscillating structures and more general aspects of such turbulence. The role of remanent vorticity in the nucleation and stability of quantum turbulence is universally important, and, as we discuss in a later section, it is here that experiments with oscillating structures have been particularly instructive. At a more subtle level, there is the question of the extent to which quantum turbulence is similar to classical turbulence. The observation of a Kolmogorov energy spectrum on large length scales (larger than the vortex-line spacing) in homogeneous quantum turbulence is often quoted as evidence for this similarity. As we shall see, some aspects of the quantum turbulence produced by oscillating structures provide additional evidence. However, in contrast to homogeneous turbulence, quantum turbulence produced by an oscillating structure must be strongly influenced by the boundary conditions at a solid wall. As we discuss in a section devoted to the development of quantum turbulence, uncertainty about the boundary conditions relevant to quantum turbulence hinders interpretation of the experiments and calls for renewed experimental and theoretical study.Almost all of the experiments have involved measurements of the fluid dynamical force on the structure as a function of the amplitude of the oscillations. This force can be divided into a drag, which is in phase with the velocity and therefore dissipative, and a force that is in quadrature with the velocity and ...

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On the transient nature of localized pipe flow turbulence

Cited by 92 publications

References 32 publications

Turbulent Spot in Linearly Stable Taylor Couette Flow

Turbulent Spot in Linearly Stable Taylor Couette Flow

Destabilizing turbulence in pipe flow

Quantum turbulence generated by oscillating structures

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