Intermittency in Transitional Shear Flows

Duguet, Yohann

doi:10.3390/e23030280

Cited by 1 publication

(2 citation statements)

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“…The most common phenomenon of intermittency occurs in two cases: (a) at the boundary of a turbulent boundary layer and an external laminar flow; (b) in the case of time-variable laminar-turbulent motion, for example, during flow in a channel [15,18,20]. In jet flows, the intermittency phenomenon is usually considered on the interface boundary where the turbulent jet flow alternates with the laminar part of the ejected surrounding gas [30,31].…”

Section: Inert Jetsmentioning

confidence: 99%

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Turbulent Superstructures in Inert Jets and Diffusion Jet Flames

Леманов

Lukashov

Sharov

2021

Fluids

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An experimental study of spatially localized very large-scale motion superstructures, propagating in a jet of carbon dioxide at low Reynolds numbers, was carried out. A hot-wire anemometer and a high-speed 2D PIV with a frequency of 7 kHz were used as measuring instruments. Such a puff-type superstructure in a jet with a longitudinal dimension of up to 20–30 nozzle diameters are initially formed in the jet source—a long tube in a laminar-turbulent transition mode (without artificial disturbances). It is shown that this regime with intermittency in time, when part of the time flow is laminar and the other part of time is turbulent, exists both at the exit from the nozzle and in the near field of the jet. Thus, the structural stability of such turbulent superstructures in the near field of the jet was found. Despite the large longitudinal scale, these formations have a transverse dimension of the order of several nozzle diameters. These structures have a complex internal topology, that is, superstructures are a conglomeration of vortices of different sizes from macroscale to microscale. Using the example of diffusion combustion of methane in air, it is demonstrated that in reacting jets, the existence of such large localized perturbations is a powerful physical mechanism for a global change in the flame topology. At the same time, the presence of a cascade of vortices of different sizes in the puff composition can lead to fractal deformation of the flame front.

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Section: Inert Jetsmentioning

confidence: 99%

“…Currently, much attention is being paid to very large-scale motion superstructures [14,15]. Such large formations are observed both in forced convections in pipes and channels and in free convection flows [14].…”

Section: Introductionmentioning

confidence: 99%