Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session V53: Fluid Mechanics - General |
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Sponsoring Units: DFD Room: Hilton Baltimore Holiday Ballroom 4 |
Thursday, March 17, 2016 2:30PM - 2:42PM |
V53.00001: Equivalence of Non-Equilibrium Ensembles and Representation of Friction in Turbulent Flows: The Lorenz 96 Model Valerio Lucarini, Giovanni Gallavotti We construct different equivalent non-equilibrium ensembles in the Lorenz '96 model of atmospheric turbulence. The vector field can be decomposed into an energy-conserving, time-reversible part, plus a non-time reversible part, including forcing and dissipation. We construct a modified version of the model where viscosity varies with time, so that energy is conserved, and the dynamics is time-reversible. The statistical properties of the irreversible and reversible model are in excellent agreement, if in the latter the energy is kept constant at a value equal to the time-average realized with the irreversible model. The average contraction rate of the phase space of the time-reversible model agrees with that of the irreversible model, where it is constant by construction. We show that the phase space contraction rate obeys the fluctuation relation, and we interpret its finite time corrections. A local version of the fluctuation relation is explored and successfully checked. The equivalence between the two ensembles extends to the Lyapunov exponents.These results have relevance in motivating the importance of the chaotic hypothesis. in explaining that we have the freedom to model non-equilibrium systems using different but equivalent approaches. [Preview Abstract] |
Thursday, March 17, 2016 2:42PM - 2:54PM |
V53.00002: Optimum design of vortex generator elements using Kriging surrogate modelling and genetic algorithm Rithwik Neelakantan, Raman Balu, Abhinav Saji Vortex Generators (VG’s) are small angled plates located in a span wise fashion aft of the leading edge of an aircraft wing. They control airflow over the upper surface of the wing by creating vortices which energise the boundary layer. The parameters considered for the optimisation study of the VG’s are its height, orientation angle and location along the chord in a low subsonic flow over a NACA0012 airfoil. The objective function to be maximised is the L/D ratio of the airfoil. The design data are generated using the commercially available ANSYS FLUENT software and are modelled using a Kriging based interpolator. This surrogate model is used along with a Generic Algorithm software to arrive at the optimum shape of the VG’s. The results of this study will be confirmed with actual wind tunnel tests on scaled models. [Preview Abstract] |
Thursday, March 17, 2016 2:54PM - 3:06PM |
V53.00003: Predicting the Noise of High Power Fluid Targets Using Computational Fluid Dynamics Michael Moore, Silviu Covrig Dusa The 2.5 kW liquid hydrogen (LH2) target used in the $Q_{weak}$ parity violation experiment is the highest power LH2 target in the world and the first to be designed with Computational Fluid Dynamics (CFD) at Jefferson Lab. The $Q_{weak}$ experiment determined the weak charge of the proton by measuring the parity-violating elastic scattering asymmetry of longitudinally polarized electrons from unpolarized liquid hydrogen at small momentum transfer ($Q^2=0.025$ GeV$^2$). This target satisfied the design goals of $<1\%$ luminosity reduction and $<5\%$ contribution to the total asymmetry width (the $Q_{weak}$ target achieved $~2\%$ or 55ppm). State of the art time dependent CFD simulations are being developed to improve the predictions of target noise on the time scale of the electron beam helicity period. These predictions will be bench-marked with the $Q_{weak}$ target data. This work is an essential component in future designs of very high power low noise targets like MOLLER (5 kW, target noise asymmetry contribution $<25$ ppm ) and MESA (4.5 kW). [Preview Abstract] |
Thursday, March 17, 2016 3:06PM - 3:18PM |
V53.00004: Fluid Dynamical Consequences of Current and Stress-Energy Conservation Dillon Scofield, Pablo Huq The dynamical consequences of fluid current conservation combined with the conservation of fluid stress-energy are used to develop the geometrodynamical theory of fluid flow (GTF). In the derivation of the GTF, we highlight the fact the continuity equation, equivalently the conservation of current density, implies the existence of the fluid dynamical vortex field. The vortex field transports part of the stress-energy; the other part of the stress-energy is transported by the fluid inertia field. Two channels of energy dissipation are determined by the GTF. One is an analog of the Joule heating found in electrodynamics. This follows from the conservation of stress-energy. The other dissipation channel arises from mechanisms leading to complex-valued constitutive parameters described in the electrodynamical analogy as due to a lossy medium. The dynamical consequences of the continuity equation, combined with the conservation of total stress-energy, then lead to a causal, covariant, theory of fluid flow, consistent with thermodynamics for all physically possible flow rates. [Preview Abstract] |
Thursday, March 17, 2016 3:18PM - 3:30PM |
V53.00005: The Geometry and Dynamics of a Propagating Front in a Chaotic Flow Field Mark Paul There are many important problems regarding transport in complex fluid flows with implications in science, nature, and technology. Examples include the combustion of pre-mixed gases in a turbulent flow, the complex patterns of reagents in a chemical system, the spread of a forest fire, and the outbreak of an epidemic. This talk explores the transport and dynamics of a reacting species in a chaotic fluid flow field. Large-scale parallel numerical simulations are used to explore the dynamics of propagating fronts in complex three-dimensional time-dependent fluid flows for the precise conditions of the laboratory. It is shown that a chaotic flow field enhances the front propagation when compared with a purely cellular flow field. This enhancement is quantified by computing measures of the spreading rate of the products and by quantifying the complexity of the three-dimensional front geometry for a range of chaotic flow conditions. [Preview Abstract] |
Thursday, March 17, 2016 3:30PM - 3:42PM |
V53.00006: Surface Acoustic Wave Transport and Mixing in Fluids in an Enclosed Nanoslit Morteza Miansarigavzan, James Friend Non-laminar fluid flow was generated in a nanoslit using 20~MHz surface acoustic waves. A novel acoustic nanofluidic device was fabricated by a unique room-temperature, high-strength bonding method combining a 128-$YX$ lithium niobate (LN) substrate with a second LN substrate containing a 1-cm long, 50--300-nm thick, 400~$\mu$m-wide planar nanoslit. The nanoslit was verified to be extremely smooth (roughness $<5$~nm) and possess a uniformly rectangular shape. Despite an exceptionally low ($\sim{10^{-5}}$) hydrodynamic Reynolds number within the nanoslit, acoustic streaming induced by the SAW is found to drive filling of the \emph{hydrophilic} nanoslit greatly in excess of the typical Washburn capillary filling rate, a unique ability to completely \emph{drain} the hydrophilic nanoslit of fluid, induce rapid mixing of fluid within, and drive nanoparticle and early evidence of molecular separation from the fluid at the nanoslit exit as the fluid passes through. The unique physical phenomena may prove to be useful across a broad range of applications where it facilitates the use of nanofluidics in chemistry and medicine. It illuminates an extraordinary ability to use sound at ever smaller scales to manipulate fluids and particles within in unexpected ways. [Preview Abstract] |
Thursday, March 17, 2016 3:42PM - 3:54PM |
V53.00007: Electroosmotic Entry Flow with Joule Heating Effects. Rama Prabhakaran, Akshay Kale, Xiangchun Xuan Electrokinetic flow, which transports liquids by electroosmosis and samples by electrophoresis, is the transport method of choice in microfluidic chips over traditional pressure-driven flows. Studies on electrokinetic flows have so far been almost entirely limited to inside microchannels. Very little work has been done on the electroosmotic fluid entry from a reservoir to a microchannel, which is the origin of all fluid and sample motions in microchips. We demonstrate in this talk that strong vortices of opposite circulating directions can be generated in electroosmotic entry flows. We also develop a two-dimensional depth-averaged numerical model of the entire microchip to predict and understand the fluid temperature and flow fields at the reservoir-microchannel junction. [Preview Abstract] |
Thursday, March 17, 2016 3:54PM - 4:06PM |
V53.00008: Accounting for anomalous energy-dissipation in guided flows Pablo Huq, Dillon Scofield The Navier-Stokes theory significantly underestimates energy-dissipation in time-dependent flows through flow guides such ones with helical geometry. We show the geometrodynamical theory of fluids (GTF) accounts for this anomalous energy-dissipation by predicting the excitation of transverse modes of flow leading to such dissipation. According to the GTF, the transverse modes are composed of vorticity and swirl fields which together constitute a vortex field F which is a function of the swirl and vorticity fields. Analysis shows the energy-dissipation depends on the wave energy, the dot product of the swirl and the vorticity, as well as their cross product. These lead to heating of the fluid at a rate proportional to the work the current does against the swirl field. For the constitutive parameters of the theory we find the values for water to be lamda = 0.01/(cm/s), and kappa = 1 [unitless]. A lower bound for the effective value of the speed of the first transverse modes is found to be 90 cm/sec. We determine that a dimensionless vortex number, Rv, usefully delineates the excitation of the transverse mode flow regime. [Preview Abstract] |
Thursday, March 17, 2016 4:06PM - 4:18PM |
V53.00009: Effect of Curvature Parameter on Non-Darcy Mixed Convective Flow in a Vertical Annulus: A LTNE Approach Moumita Bhowmik, Premananda Bera The influence of curvature parameter on fully developed mixed convective flow in a vertical annulus filled with porous medium under local thermal non-equilibrium (LTNE) state has been addressed here. Since the curvature parameter$(C)$ describes the size of the enclosure, therefore the main emphasize is given to understand its impact on other controlling parameters. Based on computational results, $C$ has a significant impact on both heat transfer rate as well as flow profiles for stably stratified flow. It has a tendency to reduce the magnitude of the maximum velocity. It is also observed that depending on other parameters, increment in $C$ may have tendency to make the velocity profile free from back flow. The heat transfer rate is obtained maximum at a small value of $C$ which is independent of media permeability and converges asymptotically on increasing$C$. At the end, the linear stability analysis based on normal mode technique has been used to verify the results obtained from basic flow study. Overall, from both basic flow as well as linear stability results, it is found that increment in $C$ makes the flow profile smooth which means $C$ has tendency to stabilize the flow. [Preview Abstract] |
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