Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H9: Interfacial/Thin Film Instability IV |
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Chair: Jacopo Seiwert, Institut de Physique de Rennes Room: 25B |
Monday, November 19, 2012 10:30AM - 10:43AM |
H9.00001: Influence of Heat Transfer on Stability of Newtonian and Non-Newtonian Extending Films Zheming Zheng, Olus Boratav, Chunfeng Zhou We consider the stability of Newtonian and Non-Newtonian extending films under local or global heating or cooling conditions. We derive the thickness-averaged mass, momentum and energy equations (energy equation including both convective and radiative heat transfer) and analyze the stability using eigenvalue analysis. We show that the influence of heating and cooling on stability strongly depends on the magnitude of the Peclet number. Examples of stabilization or destabilization of heating or cooling are shown for very small and very large Peclet numbers. The impact of three non-Newtonian (viscoelastic) models (Maxwell, PTT and Giesekus) on stability results is also discussed. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H9.00002: Fluid pumping in thin films using thermal waves Alexander Alexeev, Wenbin Mao, Alexander Oron Open microfluidic devices are used in many applications, including bio-sensing, molecule manipulation, and microchip cooling. We use direct numerical simulations of the full continuity, Navier-Stokes, and energy equations along with the analysis based on the long-wave theory to examine the dynamics of thin films on substrates with periodic heating that propagates in form of thermal waves along the substrate. Using these two modeling techniques, we probe how the periodic thermal wave can be harnessed to induce and regulate directed fluid flows along the substrate. Furthermore, we study the stability of these solutions to identify the parameter range providing robust fluid pumping in open microfluidic systems. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H9.00003: Two-phase investigation of hydrothermal waves in saturated atmospheres Khellil Sefiane, Pedro Saenz, Prashant Valluri, George Karapetsas, Omar Matar A liquid layer subject to a sufficiently large thermal gradient along its interface is prone to depart from its equilibrium state and to develop into an oscillatory regime whose features may differ notably from the original state. In shallow liquid pools, the preferred instability mode is obliquely-travelling hydrothermal waves (HTWs). We investigate this Marangoni-driven flow by means of two-phase direct numerical simulations in 3D with the interface captured via the volume-of-fluid method. Validated against experiments (Riley et al. 1998) and linear theory (Smith \& Davis 1983), the results reveal the highly-intricate spatio-temporal evolution of the instabilities and the presence of interfacial waves tightly coupled with the HTWs. The instability's development and the interdependencies amongst HTWs, interface deformations and bulk flows (liquid and gas phases) are thoroughly investigated for the linear (early times) and non-linear (late times) stages. We also elucidate the heat-transfer mechanism across the interface which is significantly affected by the propagating disturbances. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H9.00004: Thermocapillarity driven Instabilities in thin liquid layers subject to long-wave analysis Aneet Narendranath, James Hermanson, Allan Struthers, Robert Kolkka, Jeffrey Allen An evolution equation describing the dynamics of an evaporating liquid film has previously been developed from the governing equations of fluid dynamics after the application of the lubrication approximation and the choice of a viscous time scale. The authors have solved the evaporating liquid film evolution equation with a validated numeric program. The role of domain size and thermocapillarity on the formation of secondary finger like structures is studied. The effect that gravity has on the formation of these finger patterns is evaluated. It is observed that the formation of secondary structures is strongly tied to a balance between destabilizing thermocapillarity and stabilizing surface tension. The secondary structures are amplified in a zero gravity environment. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H9.00005: Instability of a fluctuating membrane driven by an AC electric field Jacopo Seiwert, Petia Vlahovska We consider theoretically the stability of a biomimetic planar membrane stressed by a perpendicularly applied time-varying electric field. The membrane, which separates two fluids, is modeled as a leaky capacitor. We investigate the influence of membrane electrical properties, as well as those of the surrounding fluids, on membrane stability. Our linear stability analysis shows that unlike what happens with DC electric fields, a purely capacitive membrane can be destabilized in an AC electric field. The theory highlights that the instability originates from electric pressure exerted on the membrane. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H9.00006: Electrostatically induced long-wave dynamics in moderately conducting annular flows Alex Wray, Demetrios Papageorgiou, Omar Matar Annular flows on both the inner and outer walls of cylinders have a significant number of practical applications; these range from printing to fluid stabilisation, to the augmentation of heat and mass transfer. It is important to understand the spatiotemporal dynamics of the interface in order to facilitate the possible control of the flow and efficiency of underlying processes. We investigate the evolution and stability of a viscous fluid layer wetting the surface of a cylinder and surrounded by a gas. The inner cylinder is an electrode kept at constant voltage. A second concentric electrode, whose potential is allowed to vary as a function of both space and time, encloses the system. This induces electrostatic forces at the interface in competition with surface tension and viscous stresses. Asymptotic methods are use to derive a long-wave system of evolution equations, valid for moderate conductivities. The resulting system is investigated both analytically and numerically via a systematic parametric study. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H9.00007: Control of complex dynamics in highly conducting thin annular films Demetrios Papageorgiou, Alex Wray, Omar Matar Thin, highly conducting annular films represent a canonical scenario giving rise to both mathematical interest and practical physical relevance. A precise and complete understanding of the dynamics of such a flow is vital for its effective manipulation. We look at the case of a thin, highly conductive film on the outer surface of a conductive cylinder, with a potential difference set up between the coating cylinder and second, concentric cylinder. The disparity of electrical material properties in the two regions induces additional electric stresses at the interface. Asymptotic methods are used to derive a thin film type equation governing this situation. These lead to an additional term in the gravitationally modified Hammond equation, with a modified mobility coefficient, which can either augment disturbances, or drive them to cessation. We discuss the intricate effect that this has on both the linear and nonlinear regimes in one dimension. We also discuss briefly the full two-dimensional dynamics via transient numerical simulations. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H9.00008: Phase separation patterns in irradiated thin liquid films due to optical interference effects Fumihiro Saeki, Shigehisa Fukui, Hiroshige Matsuoka The pattern formation in irradiated thin liquid films on solid substrates is investigated within the framework of the long-wave approximation. The focus is placed on a transparent film/absorbable substrate system irradiated by a monochromatic wave with laterally uniform intensity distribution. The evolution of the film surface profile is described by an equation of Cahn-Hilliard type, and the free energy density that is a function of the film thickness has local minima due to optical interference between waves reflected from the gas-liquid and liquid-solid interfaces. Therefore, a small perturbation develops into a phase separation pattern if the unperturbed uniform state is unstable. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H9.00009: The Nanoworld Beyond B\'{e}nard Instability: Comparison Between Theory and Experiment Kevin Fiedler, Sandra Troian The spontaneous growth of fluid elongations in a viscous nanofilm whose free surface is held in close proximity to a cooler substrate has been attributed to three different mechanisms. Linear stability analyses in the long wavelength approximation indicate that such formations arise either from fluctuations in the electrostatic attraction between the fluid interface and the opposing substrate, the acoustic phonon pressure acting on the film, or thermocapillary stresses along the free surface. The latter mechanism represents the long wavelength limit of the B\'{e}nard-Marangoni problem in the absence of a critical number. Model validation requires direct comparison between experiment and linear stability theory, which necessitates that the film structuring process be analyzed at very early times. Previous measurements in our group of the fastest growing wavelength exceeded theoretical predictions of the thermocapillary model by a factor of 2 to 3. More detailed studies of the formation process highlight the importance of obtaining measurements at very early times. Recent data obtained by varying the substrate separation distance, initial film thickness and overall temperature difference indicate much improved agreement with the thermocapillary model. [Preview Abstract] |
Monday, November 19, 2012 12:27PM - 12:40PM |
H9.00010: Thermocapillary motion of a droplet on an inclined plate George Karapetsas, Kirti Sahu, Omar Matar We examine the dynamics of a droplet spreading on an inclined solid surface in the presence of constant wall thermal gradients. We use lubrication theory in combination with the Karman-Polhausen integral method to simplify the governing equations for the droplet motion and energy conservation leading to coupled evolution equations for the drop thickness and average temperature. An important feature of the spreading model developed here is the behaviour of the drop at the contact line; this is modeled using a constitutive relation, which is dependent on the local temperature of the wall. We use a finite-element formulation to obtain numerical solutions of the evolution equations and carry out a full parametric study. We investigate the various types of behaviour encountered due to the interplay of Marangoni stresses, gravity and the dynamics of the contact line. [Preview Abstract] |
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