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http://hdl.handle.net/10985/22738
Dewetting Dynamics of Sheared Thin Polymer Films: An Experimental Study
DMOCHOWSKA, Anna; PEIXINHO, Jorge; SOLLOGOUB, Cyrille; MIQUELARD-GARNIER, Guillaume
An experimental investigation is reported on the effect of shear on the bursting of molten ultrathin polymer films embedded in an immiscible matrix. By use of an optical microscope coupled with a shearing hot stage, the dewetting dynamics, i.e., the growth of dewetting holes, is monitored over time at various shear rates. It is observed that their circularity is modified by shear and that for all temperatures and thicknesses studied the growth speed of the formed holes rapidly increases with increasing shear rate. A model balancing capillary forces and viscous dissipation while taking into account shear thinning is then proposed and captures the main features of the experimental data, such as the ellipsoid shape of the holes and the faster dynamics in the direction parallel to the shear. This research will help to understand the instabilities occurring during processing of layered polymeric structures, such as multilayer coextrusion.
Fri, 01 Apr 2022 00:00:00 GMThttp://hdl.handle.net/10985/227382022-04-01T00:00:00ZDMOCHOWSKA, AnnaPEIXINHO, JorgeSOLLOGOUB, CyrilleMIQUELARD-GARNIER, GuillaumeAn experimental investigation is reported on the effect of shear on the bursting of molten ultrathin polymer films embedded in an immiscible matrix. By use of an optical microscope coupled with a shearing hot stage, the dewetting dynamics, i.e., the growth of dewetting holes, is monitored over time at various shear rates. It is observed that their circularity is modified by shear and that for all temperatures and thicknesses studied the growth speed of the formed holes rapidly increases with increasing shear rate. A model balancing capillary forces and viscous dissipation while taking into account shear thinning is then proposed and captures the main features of the experimental data, such as the ellipsoid shape of the holes and the faster dynamics in the direction parallel to the shear. This research will help to understand the instabilities occurring during processing of layered polymeric structures, such as multilayer coextrusion.Drop dynamics of viscoelastic filaments
http://hdl.handle.net/10985/18383
Drop dynamics of viscoelastic filaments
PINGULKAR, Hrishikesh; PEIXINHO, Jorge; CRUMEYROLLE, Olivier
The stretching of viscoelastic polymer solutions close to breakup can create attached drops on a filament, whose properties and dynamics are little understood. The stretching of capillary bridges and the consecutive filament, until its breakup, can be quantified using diameter-space-time diagrams, which demonstrate hierarchy, as well as asymmetry of satellite drops around a big central drop. All drops experience migration, oscillation, and merging. In addition, the position of the minimum diameter on the filament is determined, along with the number of drops, their positions, the diameters of drops and the filament breakup time. The maximum number of drops on the filament can be predicted using the Deborah number. The diagrams also quantify the large Hencky strains in the filaments before pinch-off. The obtained minimum diameter is used to measure the extensional viscosity, which indicates the effect of polymer concentration and direction of filament thinning.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/183832020-01-01T00:00:00ZPINGULKAR, HrishikeshPEIXINHO, JorgeCRUMEYROLLE, OlivierThe stretching of viscoelastic polymer solutions close to breakup can create attached drops on a filament, whose properties and dynamics are little understood. The stretching of capillary bridges and the consecutive filament, until its breakup, can be quantified using diameter-space-time diagrams, which demonstrate hierarchy, as well as asymmetry of satellite drops around a big central drop. All drops experience migration, oscillation, and merging. In addition, the position of the minimum diameter on the filament is determined, along with the number of drops, their positions, the diameters of drops and the filament breakup time. The maximum number of drops on the filament can be predicted using the Deborah number. The diagrams also quantify the large Hencky strains in the filaments before pinch-off. The obtained minimum diameter is used to measure the extensional viscosity, which indicates the effect of polymer concentration and direction of filament thinning.Direct numerical simulations of laminar and transitional flows in diverging pipes
http://hdl.handle.net/10985/18599
Direct numerical simulations of laminar and transitional flows in diverging pipes
VITTAL SHENOY, Dhanush; SHADLOO, M. S.; PEIXINHO, Jorge; HADJADJ, Abdellah
Purpose: Fluid flows in pipes whose cross-sectional area are increasing in the stream-wise direction are prone to separation of the recirculation region. This paper aims to investigate such fluid flow in expansion pipe systems using direct numerical simulations. The flow in circular diverging pipes with different diverging half angles, namely, 45, 26, 14, 7.2 and 4.7 degrees, are considered. The flow is fed by a fully developed laminar parabolic velocity profile at its inlet and is connected to a long straight circular pipe at its downstream to characterise recirculation zone and skin friction coefficient in the laminar regime. The flow is considered linearly stable for Reynolds numbers sufficiently below natural transition. A perturbation is added to the inlet fully developed laminar velocity profile to test the flow response to finite amplitude disturbances and to characterise sub-critical transition. Design/methodology/approach: Direct numerical simulations of the Navier–Stokes equations have been solved using a spectral element method. Findings: It is found that the onset of disordered motion and the dynamics of the localised turbulence patch are controlled by the Reynolds number, the perturbation amplitude and the half angle of the pipe. Originality/value: The authors clarify different stages of flow behaviour under the finite amplitude perturbations and shed more light to flow physics such as existence of Kelvin–Helmholtz instabilities as well as mechanism of turbulent puff shedding in diverging pipe flows.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/185992019-01-01T00:00:00ZVITTAL SHENOY, DhanushSHADLOO, M. S.PEIXINHO, JorgeHADJADJ, AbdellahPurpose: Fluid flows in pipes whose cross-sectional area are increasing in the stream-wise direction are prone to separation of the recirculation region. This paper aims to investigate such fluid flow in expansion pipe systems using direct numerical simulations. The flow in circular diverging pipes with different diverging half angles, namely, 45, 26, 14, 7.2 and 4.7 degrees, are considered. The flow is fed by a fully developed laminar parabolic velocity profile at its inlet and is connected to a long straight circular pipe at its downstream to characterise recirculation zone and skin friction coefficient in the laminar regime. The flow is considered linearly stable for Reynolds numbers sufficiently below natural transition. A perturbation is added to the inlet fully developed laminar velocity profile to test the flow response to finite amplitude disturbances and to characterise sub-critical transition. Design/methodology/approach: Direct numerical simulations of the Navier–Stokes equations have been solved using a spectral element method. Findings: It is found that the onset of disordered motion and the dynamics of the localised turbulence patch are controlled by the Reynolds number, the perturbation amplitude and the half angle of the pipe. Originality/value: The authors clarify different stages of flow behaviour under the finite amplitude perturbations and shed more light to flow physics such as existence of Kelvin–Helmholtz instabilities as well as mechanism of turbulent puff shedding in diverging pipe flows.Dewetting of a thin polymer film under shear
http://hdl.handle.net/10985/21218
Dewetting of a thin polymer film under shear
KADRI, Kheireddin; PEIXINHO, Jorge; SALEZ, Thomas; MIQUELARD-GARNIER, Guillaume; SOLLOGOUB, Cyrille
The objective of this work is to give new insight into the stability of thin polymer films under shear, in order to pave the way to a better control of the nanolayer coextrusion process. To do so, a finite-difference numerical scheme for the resolution of the thin film equation was set up taking into account capillary and van der Waals (vdW) forces. This method was validated by comparing the dynamics obtained from an initial harmonic perturbation to established theoretical predictions. With the addition of shear, three regimes have then been evidenced as a function of the shear rate. In the case of low shear rates the rupture is delayed when compared to the no-shear problem, while at higher shear rates it is even suppressed: the perturbed interface goes back to its unperturbed state over time. In between these two limiting regimes, a transient one in which shear and vdW forces balance each other, leading to a non-monotonic temporal evolution of the perturbed interface, has been identified. While a linear analysis is sufficient to describe the rupture time in the absence of shear, the nonlinearities appear to be essential otherwise.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/212182021-01-01T00:00:00ZKADRI, KheireddinPEIXINHO, JorgeSALEZ, ThomasMIQUELARD-GARNIER, GuillaumeSOLLOGOUB, CyrilleThe objective of this work is to give new insight into the stability of thin polymer films under shear, in order to pave the way to a better control of the nanolayer coextrusion process. To do so, a finite-difference numerical scheme for the resolution of the thin film equation was set up taking into account capillary and van der Waals (vdW) forces. This method was validated by comparing the dynamics obtained from an initial harmonic perturbation to established theoretical predictions. With the addition of shear, three regimes have then been evidenced as a function of the shear rate. In the case of low shear rates the rupture is delayed when compared to the no-shear problem, while at higher shear rates it is even suppressed: the perturbed interface goes back to its unperturbed state over time. In between these two limiting regimes, a transient one in which shear and vdW forces balance each other, leading to a non-monotonic temporal evolution of the perturbed interface, has been identified. While a linear analysis is sufficient to describe the rupture time in the absence of shear, the nonlinearities appear to be essential otherwise.Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder
http://hdl.handle.net/10985/21219
Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder
AGEORGES, Valentin; PEIXINHO, Jorge; PERRET, Gaële; LARTIGUE, Ghislain; MOUREAU, Vincent
We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 <Re< 200,000 and 0.2<Fr<2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/212192021-01-01T00:00:00ZAGEORGES, ValentinPEIXINHO, JorgePERRET, GaëleLARTIGUE, GhislainMOUREAU, VincentWe present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 <Re< 200,000 and 0.2<Fr<2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments.Liquid Transfer for Viscoelastic Solutions
http://hdl.handle.net/10985/21075
Liquid Transfer for Viscoelastic Solutions
PINGULKAR, Hrishikesh; PEIXINHO, Jorge; CRUMEYROLLE, Olivier
Viscoelastic liquid transfer from one surface to another is a process that finds applications in many technologies, primarily in printing. Here, cylindrical-shaped capillary bridges pinned between two parallel disks are considered. Specifically, the effects of polymer mass fraction, solution viscosity, disk diameter, initial aspect ratio, final aspect ratio, stretching velocity, and filling fraction (alike contact angle) are experimentally investigated in uniaxial extensional flow. Both Newtonian and viscoelastic polymer solutions are prepared using polyethylene glycol and polyethylene oxide, with a wide variety of mass fractions. The results show that the increase in polymer mass fraction and solvent viscosity reduces the liquid transfer to the top surface. Moreover, the increase in the initial and final stretching heights of the capillary bridge also decreases the liquid transfer for both Newtonian and viscoelastic solutions. Finally, the shape of the capillary bridge is varied by changing the liquid volume. Now, Newtonian and viscoelastic solutions exhibit opposite behaviors for the liquid transfer. These findings are discussed in terms of interfacial shape instability and gravitational drainage.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/210752021-01-01T00:00:00ZPINGULKAR, HrishikeshPEIXINHO, JorgeCRUMEYROLLE, OlivierViscoelastic liquid transfer from one surface to another is a process that finds applications in many technologies, primarily in printing. Here, cylindrical-shaped capillary bridges pinned between two parallel disks are considered. Specifically, the effects of polymer mass fraction, solution viscosity, disk diameter, initial aspect ratio, final aspect ratio, stretching velocity, and filling fraction (alike contact angle) are experimentally investigated in uniaxial extensional flow. Both Newtonian and viscoelastic polymer solutions are prepared using polyethylene glycol and polyethylene oxide, with a wide variety of mass fractions. The results show that the increase in polymer mass fraction and solvent viscosity reduces the liquid transfer to the top surface. Moreover, the increase in the initial and final stretching heights of the capillary bridge also decreases the liquid transfer for both Newtonian and viscoelastic solutions. Finally, the shape of the capillary bridge is varied by changing the liquid volume. Now, Newtonian and viscoelastic solutions exhibit opposite behaviors for the liquid transfer. These findings are discussed in terms of interfacial shape instability and gravitational drainage.Flow and air-entrainment around partially submerged vertical cylinders
http://hdl.handle.net/10985/17944
Flow and air-entrainment around partially submerged vertical cylinders
AGEORGES, Valentin; PEIXINHO, Jorge; PÉRRET, Gaële
In this study, a partially submerged vertical cylinder is moved at constant velocity through water, which is initially at rest. During the motion, the wake behind the cylinder induces free-surface deformation. Eleven cylinders, with diameters from D=1.4 to 16 cm, were tested under two different conditions: (i) constant immersed height h and (ii) constant h/D. The range of translation velocities and diameters are in the regime of turbulent wake with experiments carried out for 4500<Re<240000 and 0.2<Fr<2.4, where Re and Fr are the Reynolds and Froude numbers based on D. The focus here is on drag-force measurements and relatively strong free-surface deformation up to air-entrainment. Specifically, two modes of air-entraiment have been uncovered: (i) in the cavity along the cylinder wall and (ii) in the wake of the cylinder. A scaling for the critical velocity for air-entrainment in the cavity has been observed in agreement with a simple model. Furthermore, for Fr>1.2, the drag force varies linearly with Fr.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/179442019-01-01T00:00:00ZAGEORGES, ValentinPEIXINHO, JorgePÉRRET, GaëleIn this study, a partially submerged vertical cylinder is moved at constant velocity through water, which is initially at rest. During the motion, the wake behind the cylinder induces free-surface deformation. Eleven cylinders, with diameters from D=1.4 to 16 cm, were tested under two different conditions: (i) constant immersed height h and (ii) constant h/D. The range of translation velocities and diameters are in the regime of turbulent wake with experiments carried out for 4500<Re<240000 and 0.2<Fr<2.4, where Re and Fr are the Reynolds and Froude numbers based on D. The focus here is on drag-force measurements and relatively strong free-surface deformation up to air-entrainment. Specifically, two modes of air-entraiment have been uncovered: (i) in the cavity along the cylinder wall and (ii) in the wake of the cylinder. A scaling for the critical velocity for air-entrainment in the cavity has been observed in agreement with a simple model. Furthermore, for Fr>1.2, the drag force varies linearly with Fr.