Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E19: Free-Surface Flows: InstabilityFree Surface
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Chair: Lou Kondic, New Jersey Institute of Technology Room: 702 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E19.00001: Nonlinear Instabilities on an Axisymmetric Ferrofluid Jet Michael Cornish, Demetrios Papageorgiou The stability properties of an inviscid axisymmetric ferrofluid jet running over a current carrying rod are investigated. The rod generates an azimuthal magnetic field which can fully stabilize the Rayleigh-plateau instability for a sufficiently large magnetic field. However, long wave instability can occur when the magnetic field is below critical; this regime has not been studied nonlinearly unlike the above critical regime where the magnetic stabilization property has led to theoretical and experimental discoveries of solitary waves on the ferrofluid jet. We study the flow asymptotically near the critical value of the magnetic field. In the stable regime, we derive the Boussinesq equation. Our interest is in the unstable regime, where magnetic forces are slightly smaller than capillary forces. The Rayleigh-plateau instability is no longer suppressed and a weakly nonlinear long wave model is derived and studied analytically and computationally. The final part of the study follows the nonlinear evolution of the free surface for magnetic fields away from the critical level. A fully nonlinear long-wave theory will be used to derive reduced model equations to evaluate the nonlinear competition between capillary instability of the liquid jet and the stabilizing magnetic field. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E19.00002: The role of surface viscosities in the instability of liquid threads Alejandro Martinez-Calvo, Alejandro Sevilla We analyse the effect of surface viscosities on the capillary instability of a free liquid thread in inviscid surroundings coated with insoluble surfactant, extending the results of Timmermans \& Lister (2002). To that end, we use the Boussinesq-Scriven constitutive equation, deriving the correct expressions for the normal and tangential stress boundary conditions at a general axisymmetric interface in cylindrical coordinates. These stress conditions are applied to obtain a new dispersion relation for the liquid thread, which is solved to describe its temporal stability as a function of four governing parameters, namely the capillary Reynolds number, the elasticity parameter, and the shear and dilational Boussinesq numbers. It is shown that surface viscosities have a stabilising influence for all values of the Reynolds number and elasticity parameter, the effect being more pronounced at low Reynolds numbers. It is also worth mentioning that, given a certain ratio of surface viscosities, the wave number associated with the maximum growth rate of perturbations has a non-monotonous behaviour with respect to the surface shear viscosity. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E19.00003: On the influence of thermal effects on the dynamics of thin films and filaments Lou Kondic, Ivana Seric, Shahriar Afkhami We report our recent progress on formulating fully self-consistent simulations the dynamics of thin films and filaments exposed to an external heat source on thermally conductive substrate. The simulations are based on the Volume of Fluid, and include novel components such as inclusion of Marangoni , as well as of van der Waals forces. Furthermore, the simulations couple dynamics directly with the spatio-temporal evolution of temperature field boththe fluid and in the substrate. The particular physical setup considered involvesfilms and geometries exposed to laser heating on silicon/silicon dioxide , with the focus on understanding the influence of variation of material (surface tension and viscosity) with temperature. We will discussrole that Marangoni effect has on the development of film instability, and willconsider the influence of variation of normal interfacial stresses due toevolution of the fluid temperature. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E19.00004: On break-up of a growing liquid cylinder Rouslan Krechetnikov In this talk we will discuss stability of a liquid cylinder of a time-varying radius with the goal to understand the effects of time-dependence of the underlying base state on a Rayleigh-Plateau instability. All the key processes contributing to instability development are revealed with an analytical analysis of the exact incompressible inviscid potential flow formulation. In particular, without invoking the `frozen' base state assumption, the entire time interval of a perturbation evolution is explored highlighting physical mechanisms at each stage of development. We find that the stability picture proves to be different from break-up of a static liquid cylinder. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E19.00005: Effect of Rheological Properties on Liquid Curtain Coating. Alireza Mohammad Karim, Wieslaw Suszynski, William Griffith, Saswati Pujari, Marcio Carvalho, Lorraine Francis Curtain coating is one of the preferred methods for high-speed precision application of single-layer and multi-layer coatings in technology. However, uniform coatings are only obtained in a certain range of operating parameters, called \textit{coating window}. The two main physical mechanisms that limit successful curtain coating are liquid curtain breakup and air entrainment. The rheological properties of the liquid play an important role on these mechanisms, but the fundamental understanding of these relations is still not complete. The effect of rate-dependent shear and extensional viscosities on the stability of viscoelastic and shear thinning liquid curtains were explored by high-speed visualization. Aqueous solutions of polyethylene oxide (PEO) and polyethylene glycol (PEG) were used as viscoelastic liquids. Xanthan Gum in water and glycerol solutions with a range of compositions were used as shear thinning liquids. The critical condition was determined by examining flow rate below which curtain broke. In this work, we also analyze relative importance of rate-dependent shear and extensional viscosity on both curtain breakup and air entrainment. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E19.00006: Buoyancy-Marangoni convection in confined volatile binary fluids subject to a horizontal temperature gradient Tongran Qin, Roman Grigoriev We consider convection in a layer of binary fluid with free surface subject to a horizontal temperature gradient in the presence of noncondensable gases, which is driven by a combination of three different forces: buoyancy, thermocapillarity, and solutocapillarity. Unlike buoyancy, both thermo- and solutocapillary stresses depend sensitively on the local phase equilibrium at the liquid-gas interface. In particular, thermocapillarity associated with the interfacial temperature gradient is controlled by the vapors' concentration along the interface, and solutocapillarity associated with the interfacial concentration gradient is controlled by differential phase change of two components of the liquid, which is strongly influenced by the presence of noncondensables. Therefore, flows in both phases, phase change,and effect of noncondensables all have to be considered. Numerical simulations based on a comprehensive model taking these effects into account show qualitative agreement with recent experiments which identified a number of flow regimes at various compositions of both phases. In particular,we find that the composition of both the gas and liquid phase have a significant effect on the observed convection patterns; this dependence can be understood using a simple analytical model. [Preview Abstract] |
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