Influence of channel aspect ratio on the onset of purely-elastic flow instabilities in three-dimensional planar cross-slots

Cruz, Filipe António Nogueira da; Poole, Robert J.; Afonso, A.M.; Pinho, F.T.; Oliveira, Paulo J.; Alves, M.A.

doi:10.1016/j.jnnfm.2015.11.008

Cited by 31 publications

(37 citation statements)

References 36 publications

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“…This includes designs such as cross-slots, T-junctions, and flow-focusing configurations. To date, the use of cross-slot geometries has found great success and has been widely used both in numerical (Poole et al 2007;Afonso et al 2010;Cruz et al 2016;Zografos et al 2018) and experimental (Arratia et al 2006;Dylla-Spears et al 2010;Gossett et al 2012b;Haward et al 2012a;Burshtein et al 2017;Abed et al 2017) studies related to Newtonian flows, viscoelastic flows, and singlemolecule/single-cell responses, due to the fact that they are able to generate strong extensional flows exploiting the presence of the stagnation point (SP). Moreover, improved counterparts have also been proposed employing optimisation techniques as potential platforms for achieving accurate rheological measurements (Alves 2008;Haward et al 2012b;Haward and McKinley 2013;Galindo-Rosales et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Optimised multi-stream microfluidic designs for controlled extensional deformation

Zografos

Haward

Oliveira

2019

Microfluid Nanofluid

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In this study, we optimise two types of multi-stream configurations (a T-junction and a flow-focusing design) to generate a homogeneous extensional flow within a well-defined region. The former is used to generate a stagnation point flow allowing molecules to accumulate significant strain, which has been found very useful for performing elongational studies. The latter relies on the presence of opposing lateral streams to shape a main stream and generate a strong region of extension in which the shearing effects of fluid-wall interactions are reduced near the region of interest. The optimisations are performed in two (2D) and three dimensions (3D) under creeping flow conditions for Newtonian fluid flow. It is demonstrated that in contrast with the classical-shaped geometries, the optimised designs are able to generate a well-defined region of homogeneous extension. The operational limits of the obtained 3D optimised configurations are investigated in terms of Weissenberg number for both constant viscosity and shear-thinning viscoelastic fluids. Additionally, for the 3D optimised flow-focusing device, the operational limits are investigated in terms of increasing Reynolds number and for a range of velocity ratios between the opposing lateral streams and the main stream. For all obtained 3D optimised multi-stream configurations, we perform the experimental validation considering a Newtonian fluid flow. Our results show good agreement with the numerical study, reproducing the desired kinematics for which the designs are optimised.

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Section: Introductionmentioning

confidence: 99%

Optimised multi-stream microfluidic designs for controlled extensional deformation

Zografos

Haward

Oliveira

2019

Microfluid Nanofluid

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“…At relatively low Re [ Fig. 14(a), Wi eff ¼ 0.02, Re ¼ 4.76), the first normal stress difference exhibits the anticipated behavior of an extension-dominated flow, where a thin strand of high stress is formed along the flow centerline emanating from the stagnation point [32,35,49,91]. This indicates that significant stretching and orientation occurs at the region close to the stagnation point, which has been demonstrated in previous experiments by the observation of "birefringent strands" [89].…”

Section: Detailed Analysis and Phase Diagramsmentioning

confidence: 99%

Inertioelastic Flow Instability at a Stagnation Point

et al. 2017

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A number of important industrial applications exploit the ability of small quantities of high molecular weight polymer to suppress instabilities that arise in the equivalent flow of Newtonian fluids, a particular example being turbulent drag reduction. However, it can be extremely difficult to probe exactly how the polymer acts to, e.g., modify the streamwise near-wall eddies in a fully turbulent flow. Using a novel crossslot flow configuration, we exploit a flow instability in order to create and study a single steady-state streamwise vortex. By quantitative experiment, we show how the addition of small quantities (parts per million) of a flexible polymer to a Newtonian solvent dramatically affects both the onset conditions for this instability and the subsequent growth of the axial vorticity. Complementary numerical simulations with a finitely extensible nonlinear elastic dumbbell model show that these modifications are due to the growth of polymeric stress within specific regions of the flow domain. Our data fill a significant gap in the literature between the previously reported purely inertial and purely elastic flow regimes and provide a link between the two by showing how the instability mode is transformed as the fluid elasticity is varied. Our results and novel methods are relevant to understanding the mechanisms underlying industrial uses of weakly elastic fluids and also to understanding inertioelastic instabilities in more confined flows through channels with intersections and stagnation points.

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“…They found that for smaller aspect ratios the symmetry breaking bifurcation required a larger Weissenberg number (W e ), and that for sufficiently small aspect ratios, the symmetry breaking bifurcation was superseded by a transient bifurcation. Cruz et al [15] performed computational investigations using a PTT fluid model. Cruz et al reported the same behavior as Sousa et al [14], finding that the unstable flow regimes are along the diagonals of the cross-slot.…”

Section: Introductionmentioning

confidence: 99%

Viscoelastic Hele-Shaw flow in a cross-slot geometry

Chaffin

Rees

2018

European Journal of Mechanics - B/Fluids

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a b s t r a c tIn this paper a cross-slot geometry for which the height of the channel is small compared to the other channel dimensions is considered. The normal components of the viscoelastic stresses are found analytically for a second order fluid up to numerical inversion. The validity of the theoretical analysis was corroborated by comparison with numerical simulations based on a stabilized Galerkin least squares finite element method using an Oldroyd B fluid. Close agreement was found between numerical predictions and analytical results for Weissenberg numbers up to 0.2. An explicit expression is formulated for viscoelastic parameters in terms of the variation and strength of the first normal stress difference around the stagnation point. The analysis is generalized for the case where the inlet channel width is different from the outlet channel width. For such configurations it was found that uniformity of the elongation rate was reduced.

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Influence of channel aspect ratio on the onset of purely-elastic flow instabilities in three-dimensional planar cross-slots

Cited by 31 publications

References 36 publications

Optimised multi-stream microfluidic designs for controlled extensional deformation

Optimised multi-stream microfluidic designs for controlled extensional deformation

Inertioelastic Flow Instability at a Stagnation Point

Viscoelastic Hele-Shaw flow in a cross-slot geometry

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