Investigation of the steady engulfment regime in a three-dimensional T-mixer

Fani, Andrea; Camarri, Simone; Salvetti, Maria Vittoria

doi:10.1063/1.4809591

Cited by 88 publications

(109 citation statements)

References 19 publications

(27 reference statements)

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“…For the case with square inlet cross-sections (i.e., with Ä i = 1), the length of the mixing channel, L o , was varied between 12.5D and 45D, in order to assess the effect of this geometrical parameters on the onset of the different flow regimes. Note that L o = 12.5D was used in previous investigations (Galletti et al, 2012;Fani et al, 2013), while L o = 25D was used in a recent work (Fani et al, 2014). Following the results of this sensitivity analysis, L o = 25D was adopted for the other two considered T-mixer configurations, i.e.…”

Section: T-mixer Geometrymentioning

confidence: 99%

“…Here, the fluid elements at the confluence of the two inlet flows reach the opposite side of the mixing channel, thus largely increasing the degree of mixing. Many studies in the literature focused on the engulfment regime, because of the significant mixing efficiency achieved in this regime (see, e.g., Lindken et al, 2006;Soleymani et al, 2008;Ooms et al, 2009;Galletti et al, 2012;Fani et al, 2013;Poole et al, 2013). Finally, a few investigations have indicated that by further increasing Re, the flow becomes first unsteady and periodic in time and eventually chaotic (Dreher et al, 2009;Kockmann and Roberge, 2011;Fani et al, 2014).…”

Section: Introductionmentioning

confidence: 97%

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Flow regimes in T-shaped micro-mixers

Andreussi

Galletti

Mauri

et al. 2015

Computers & Chemical Engineering

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The different flow regimes occurring in T-mixers are investigated by means of direct numerical simulations. Three different values of the aspect ratio of the inlet channels, ki, that is their width to height ratio, are considered, namely ki= 0.75, 1 and 2. For the configurations with ki= 0.75 and 1, the same behavior as previously described in the literature, is found. In particular, as the Reynolds number is increased, the flow evolves from vortical to engulfment steady regimes, then to unsteady asymmetric and symmetric periodic regimes, until, finally, it becomes chaotic. All the critical values of the Reynolds number, at which the transitions between the different regimes occur, are found to be very similar for ki= 0.75 and 1, while some differences are highlighted in the vorticity dynamics and characteristic frequencies of the unsteady regimes. The observed scenario is completely different for ki= 2. Indeed, in this case, the flow evolves directly from the vortical regime to an unsteady symmetric behavior, with a vorticity dynamics that is significantly different from those observed for the other aspect ratios

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Section: T-mixer Geometrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Flow regimes in T-shaped micro-mixers

Andreussi

Galletti

Mauri

et al. 2015

Computers & Chemical Engineering

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“…At higher Re, the flow regains its symmetric state and the rate of mixing decreases. Recently, Fani et al (2013) studied the engulfment regime in a three-dimensional T-mixer with a quadratic cross-section by direct numerical simulation and a global stability analysis. The mechanism of engulfment was found to be the tilting of the vortical structures at the beginning of the exit channel.…”

Section: Introductionmentioning

confidence: 99%

The planar X-junction flow: stability analysis and control

et al. 2014

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The bifurcations and control of the flow in a planar X-junction are studied via linear stability analysis and direct numerical simulations. This study reveals the instability mechanisms in a symmetric channel junction and shows how these can be stabilized or destabilized by boundary modification. We observe two bifurcations as the Reynolds number increases. They both scale with the inlet speed of the two side channels and are almost independent of the inlet speed of the main channel. Equivalently, both bifurcations appear when the recirculation zone(s) reach a critical length. A two-dimensional stationary global mode becomes unstable first, changing the flow from a steady symmetric state to a steady asymmetric state via a pitchfork bifurcation. The core of this instability, whether defined by the structural sensitivity or the disturbance energy production, is at the edges of the recirculation bubbles, which are located symmetrically along the walls of the downstream channel. The energy analysis shows that the first bifurcation is due to a lift-up mechanism. We develop an adjustable control strategy for the first bifurcation with distributed suction/blowing at the walls. The linearly optimal wall-normal velocity distribution is computed through a sensitivity analysis and is shown to delay the first bifurcation from Re = 82.5 to Re = 150. This stabilizing effect arises because blowing at the walls weakens the streamwise velocity gradient around the recirculation zone and hinders the lift-up.At the second bifurcation, a three-dimensional stationary global mode with a span-wise wavenumber of order unity becomes unstable around the asymmetric steady state. Nonlinear three-dimensional simulations at the second bifurcation display transition to a nonlinear cycle involving growth of a three-dimensional steady structure, time-periodic secondary instability, and nonlinear breakdown restoring a two-dimensional flow. Finally, we show that the sensitivity to wall suction at the second bifurcation is as large as it is at the first bifurcation, providing a possible mechanism for destabilization.

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“…The study of changing the hydrodynamic mode of the mixer operation also does not reveal a significant reserve for reducing the energy costs of the process [18]. The use of a microchannel in a mixer is expedient in the opinion technology audit and Production reserVes -№ 3/3(35), 2017 ISSN 2226-3780 of the authors only if the influence on the central part of the jet providing pulsations [19].…”

Section: Research Of Existing Solutions Of the Problemmentioning

confidence: 99%