Transient disturbance growth in a corrugated channel

Szumbarski, Jacek; Floryan, J. M.

doi:10.1017/s0022112006002023

Cited by 36 publications

(38 citation statements)

References 17 publications

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“…Klebanoff & Tidstrom 1972), in which roughness influences one or more of the three stages of the transition, namely the generation of linear instability waves (receptivity), the linear growth of such waves and the nonlinear breakdown (Nayfeh & Ashour 1994). However, since the 1980s, it has been shown by many researchers that, for 3D roughness elements, transient growth is an alternative possible explanation of some roughness-induced transition (Reshotko 1984(Reshotko , 2008Reshotko & Tumin 2004;Szumbarski & Floryan 2006).…”

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confidence: 99%

Turbulence in a transient channel flow with a wall of pyramid roughness

Seddighi

Pokrajac

et al. 2015

J. Fluid Mech.

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A direct numerical simulation investigation of a transient flow in a channel with a smooth top wall and a roughened bottom wall made of close-packed pyramids is presented. An initially stationary turbulent flow is accelerated rapidly to a new flow rate and the transient flow behaviour after the acceleration is studied. The equivalent roughness heights of the initial and final flows are k + s = 14.5 and 41.5, respectively. Immediately after the acceleration ends, the induced change behaves in a 'plug-flow' manner. Above the roughness crests, the additional velocity due to the perturbation flow is uniform; below the crest, it reduces approximately linearly to zero at the bottom of the roughness elements. The interaction of the perturbation flow with the rough wall is characterised by a series of events that resemble those observed in roughness-induced laminar-turbulent transitions. The process has two broad stages. In the first of these, large-scale vortices, comparable in extent to the roughness wavelength, develop around each roughness element and high-speed streaks form along the ridge lines of the elements. After a short time, each vortex splits into two, namely (i) a standing vortex in front of the element and (ii) a counter-rotating hairpin vortex behind it. The former is largely inactive, but the latter advects downstream with increasing strength, and later lifts away from the wall. These hairpin vortices wrap around strong low-speed streaks. The second stage of the overall process is the breakdown of the hairpin vortices into many smaller multi-scale vortices distributed randomly in space, leading eventually to a state of conventional turbulence. Shortly after the beginning of the first stage, the three components of the r.m.s of the velocity fluctuation all increase significantly in the near-wall region as a result of the vortical structures, and their spectra bear strong signatures of the surface topology. During the second stage, the overall turbulence energy in this region varies only slightly, but the spectrum evolves significantly, eventually approaching that of conventional turbulence. The direct effect of roughness on the flow is confined to a region up to approximately three element heights above the roughness crests. Turbulence in the core region does not begin to increase until after the transition near the wall is largely complete. The processes of transition over the smooth and rough walls of † Email addresses for correspondence: m.seddighi@ljmu.ac.uk, s.he@sheffield.ac.uk Turbulence in a transient channel flow with a rough wall 227 the channel are practically independent of each other. The flow over the smooth wall follows a laminar-turbulent transition and, as known from previous work, resembles a free-stream turbulence-induced boundary layer bypass transition.

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Turbulence in a transient channel flow with a wall of pyramid roughness

Seddighi

Pokrajac

et al. 2015

J. Fluid Mech.

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“…among others, Szumbarski and Floryan (2006), Luo et al (2008), Scholle et al (2008), Malevich et al (2008), Khanafer et al (2009), andElshafei et al (2010). One common theme among these studies is to look into the geometrical effects due to wall corrugations on the flow resistance or pressure drop in the channel.…”

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Darcy–Brinkman Flow Through a Corrugated Channel

Wang

2010

Transp Porous Med

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A perturbation analysis is carried out to the second order to give effective equations for Darcy-Brinkman flow through a porous channel with slightly corrugated walls. The flow is either parallel or normal to the corrugations, and the corrugations of the two walls are either in phase or half-period out of phase. The present study is based on the assumptions that the corrugations are periodic sinusoidal waves of small amplitude, and the channel is filled with a sparse porous medium so that the flow can be described by the Darcy-Brinkman model, which approaches the Darcian or Stokes flow limits for small or large permeability of the medium. The Reynolds number is also assumed to be so low that the nonlinear inertia can be ignored. The effects of the corrugations on the flow are examined, quantitatively and qualitatively, as functions of the flow direction, the phase difference, and the wavelength of the corrugations, as well as the permeability of the channel. It is found that the corrugations will have greater effects when it is nearer the Stokes' flow limit than the Darcian flow limit, and when the wavelength is shorter. For the same wavelength and phase difference, cross flow is more affected than longitudinal flow by the corrugations. Opposite effects can result from 180 • out-of-phase corrugations, depending on the flow direction, the wavelength, as well as the permeability.

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“…The channel length is probably too short to allow for fully developed flow instabilities to occur spontaneously. However, it is assumed that initial spanwise flow disturbances generated by the strongly divergent flow inlet may become amplified by the wall waviness, if the theoretical prediction [10,11] …”

Section: Corrugated Wallmentioning

confidence: 99%

“…The design and optimisation of microfluidic devices is usually based on our knowledge gained for macro scale hydrodynamics. However, it can be expected that small channel hydrodynamics has to be reconsidered in different contexts: relative large surface area can be responsible for delayed (or accelerated) laminar-turbulent transition [1][2][3][4][5][6][7][8]; wall roughness becomes elevated relative to small channel size and may influence laminar-turbulent transition [9]; appropriate wall corrugation can be used to activate flow instability and effectively diminish critical Reynolds number [10]. In spite of the existence of numerous experimental and theoretical investigations, a number of principal problems related to laminar-turbulent transition in micro scales are not fully resolved.…”

Section: Introductionmentioning

confidence: 99%

“…The occurrence of laminar/turbulent transition can be strongly modified by wall roughness, which becomes an issue for small channels [9]. On the other hand it was predicted by Szumbarski [10,11] that controlled wall waviness may lead to flow destabilization already at Reynolds number close to 100. The outcome of our numerical and experimental study of this remarkable feature is reported in the second part of the present paper.…”

Section: Introductionmentioning

confidence: 99%

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Turbulence in Microchannels

Kowalewski¹,

Błoński²,

Pan³

SpringerReference

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ABSTRACT. Fluid mechanics in small channels, i.e. channels of micrometer size, is dominated by surface effects and often exhibits striking differences of flow characteristics when compared with macro scale. One of important microfluidic problems is flow destabilization and occurrence laminarturbulent transition. In this paper we describe our experimental and numerical attempts to understand growth of flow instabilities and development of turbulent structures in small channels. In the first configuration flow of water through 1mm long and 0.4mm high microchannel formed between two planes is investigated varying Reynolds number from 1000 to 6770. Fluorescent traces are used for flow visualization and microPIV acquisition of temporary velocity fields. The microPIV data are used to evaluate turbulent flow characteristics. Our experimental study shows that destabilization of flow in such a micro-channel does not necessarily occurs when it is usually expected. Nearly laminar flow structure is present within the channel even for the highest investigated flow Reynolds number. These findings are confirmed by numerical simulation performed using finite volume code. On the other hand it appears possible to achieve unstable flow pattern even for quite low Reynolds number flow regime by proper modification of the channel walls. In the second experimental and numerical study we demonstrate that appropriately chosen wall waviness of the micro-channel may lead to flow destabilization already at quite low flow Reynolds number (~100).

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Transient disturbance growth in a corrugated channel

Cited by 36 publications

References 17 publications

Turbulence in a transient channel flow with a wall of pyramid roughness

Turbulence in a transient channel flow with a wall of pyramid roughness

Darcy–Brinkman Flow Through a Corrugated Channel

Turbulence in Microchannels

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