Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q30: General Fluid Dynamics 
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Chair: Samuel Paolucci, Notre Dame Room: 612 
Tuesday, November 26, 2019 7:45AM  7:58AM 
Q30.00001: Surface morphology and flow dynamics for fog harvesting Fan Kiat Chan, Aida Shahrokhian, Hunter King, Mattia Gazzola Harvesting fog as a source of fresh water is a practical solution for inhabitants of foggy coastal deserts, whether human, animal or plant. Namib desert beetles famously lean their textured bodies into the fogladen wind; their evolved strategy has been interpreted mostly in the context of surface wetting and its role in transporting of water as it is accumulated. However, little is known about how the interplay between flow dynamics and surface morphology affects droplet interception. From experiments with controlled flow and fog delivery and sensitive accumulation measurements as well as complementary numerical flow simulations, we find mechanisms for significant enhancement of collection efficiency on two scales: millimetric surface features which affect droplet trajectories; and microscopic features which aid evacuation of lubricating film before contact. [Preview Abstract] 
Tuesday, November 26, 2019 7:58AM  8:11AM 
Q30.00002: Simple Flows Using a Second Order Theory of Fluids Samuel Paolucci The NavierStokesFourier (NSF) equations have proved very valuable in modeling fluid flows over the last two centuries. However, there are cases in which large gradients in velocity and/or thermal fields occur where it has been shown that they do not provide accurate results. Second order equations were derived and shown to reproduce experimental results of the shock structure of gases over a large range of Mach numbers (Paolucci \& Paolucci JFM, {\bf 486}, 686710 (2018)). Computer experiments using the direct simulation Monte Carlo (DSMC) method have shown that at small Knudsen number the pressure and temperature profiles in the thermal stress problem as well as in the Couette and forcedriven compressible plane Poiseuille flows exhibit different qualitative behavior from the profiles obtained by NSF equations. We compare the DSMC measurements with the numerical solutions of equations resulting from the second order theory. We find that the second order equations recover many of the anomalous features (e.g., nonconstant pressure and nonzero parallel heat flux). Comparisons of the predictions coming from the second order theory are provided in order to critically assess its validity and usefulness. [Preview Abstract] 
Tuesday, November 26, 2019 8:11AM  8:24AM 
Q30.00003: Can we always neglect the bulk viscous pressure in variable density flows? Miltiadis Papalexandris In linearly isotropic (Newtonian) fluids, the bulk viscous pressure is proportional to the velocity divergence, with the bulk viscosity of the fluid being the proportionality coefficient. Stokes' hypothesis states that the bulk viscosity of a Newtonian fluid can be set equal to zero. Although not valid for many fluids, it is common practice to invoke this hypothesis in the study of lowMachnumber, variabledensity flows. In this talk, based on simple scaling arguments we provide a necessary condition for neglecting the bulk viscous pressure from the governing equations of lowMach number flows. More specifically, we show that the Reynolds number defined with respect to the bulk viscosity must be very large. We further show that even when this condition is not satisfied, the bulk viscous pressure does not need to be taken explicitly into account because it can be combined with the dynamic pressure. [Preview Abstract] 
Tuesday, November 26, 2019 8:24AM  8:37AM 
Q30.00004: New Memory Effects in Unsteady Forces on Slip Particles HsienHung Wei, A.R. Premlata For a slip particle moving unsteadily in a viscous fluid, the extent of slip is not fixed but constantly varies with time, depending on the slip length $\lambda $ relative to the boundary layer thickness $\delta $. For this dynamic slip situation, we show that that even the amount of slip is minuscule, it can significantly change the characteristics of the history force. Our analysis reveals that there exists a constant force plateau for $\delta $\textless $\lambda $, persisting until the slipstick transition point $\delta \sim \lambda $ after which the usual noslip Basset 1/$\delta $ decay dominates the force response. We also analyze the unsteady force response for a stickslip Janus particle, showing that a slightly smaller Basset force can reemerge in place of the slip force plateau in the small $\delta $ regime. This reentrant history force transition becomes even more evident for a slip particle having a small noslip patch. These unusual force responses may not only provide unique hydrodynamic fingerprints for characterizing heterogeneous particles, but also have potential uses in active manipulation and sorting of these particles. [Preview Abstract] 
Tuesday, November 26, 2019 8:37AM  8:50AM 
Q30.00005: Exact NavierStokes solutions linear in one coordinate Jonathan Mestel If a 3D flow is independent of one coordinate it naturally reduces to a 2D flow. Similar simplification can occur if a flow varies ${\it linearly}$ with a coordinate. For example, the advectiondiffusion equation ${\bf u}\cdot\nabla c=\kappa\nabla^2c$ has solutions of the form $c=xf(y,z)$ when the velocity has the form ${\bf u}=(xu(y,z),v(y,z),w(y,z))$ with $\nabla\cdot{\bf u}=0$. The resulting system is essentially twodimensional, but retains some 3D aspects. This talk employs similar reductions in axisymmetry to derive several previously unknown solutions to the full NavierStokes equtions. As they extend to infinity, in some cases these similarity solutions exist without additional forcing. A family of 3D boundary layer flows is also derived, demonstrating for example that the FalknerSkan solutions are nonunique in 3D. Finally, it is shown that these flows can coexist with other fields of advectiondiffusion type. In particular, it is shown that these flows can act as dynamos, spontaneously generating magnetic fields with a related spatial structure. [Preview Abstract] 
Tuesday, November 26, 2019 8:50AM  9:03AM 
Q30.00006: Sedimentation of Triple Twisted M\"{o}bius Objects Nicolas Moreno, David VasquesCortes, Michael Grunwald, Johannes Schoenke, Eliot Fried Screwlike objects like helix and M\"{o}bius strips exhibit both rotation and translation as they move in a fluid due to external forces such as gravity. It is expected that the orientation of the twist in the structure determines the direction of the rotational motion. Here, we conduct both computational and experimental studies on the sedimentation of rigid M\"{o}bius bands with a threehalf twist. We vary the aspect ratio of the bands and analyze their trajectories. We use two different schemes to construct the bands corresponding ruled developable surfaces and ruled binormalscroll surfaces. For developable bands, we observe that the spinning direction is consistently determined by the orientation of the band, independent of its aspect ratio. Remarkably, for binormalscroll bands, the direction of spin depends not only on the twist orientation but also on aspect ratio. Experimentally, we track the sedimentation of 3Dprinted polystyrene bands in water. Computationally, we use the particlebase method dissipative particle dynamics. The hydrodynamic properties of these objects offer exciting applications for mixing and separation in microfluidics and may also serve as prototypes for passive swimmers. [Preview Abstract] 

Q30.00007: ABSTRACT WITHDRAWN 
Tuesday, November 26, 2019 9:16AM  9:29AM 
Q30.00008: Lubricated Rolling Over A Pool Hatef Rahmani, Sheldon Green, Boris Stoeber, Neil Balmforth Film splitting flows are important in many industrial processes, such as the coating of railroad tracks with liquid friction modifiers (LFM). Here, an LFM pool deposited on the track is overridden by an advancing wheel; a liquid film coats both the wheel and rail surfaces, splitting at a meniscus behind the wheel. Lubrication theory is used to predict the meniscus position, wetted length and pressure on the wheel, as a function of the pool depth and wheel load. For 2D flows without side leakage, two solutions exist: below a critical load, steady planing arises in which the minimum gap and wetted length are adjusted to match the incoming and outgoing fluid fluxes. Above that load, flooding occurs with a steady minimum gap, but the incoming flux exceeds that underneath, and fluid is ploughed before the wheel. In 3D, only planing is possible, with leakage to the sides eliminating flooding states. Laserinduced fluorescence and highspeed imaging measure coated film thicknesses in experiments that are within 19\% of model predictions. [Preview Abstract] 
Tuesday, November 26, 2019 9:29AM  9:42AM 
Q30.00009: Understanding the behavior of large scale structures in highly Scalable Spectral element simulations of Internal Combustion Engines in the framework of large eddy simulation Tanmoy Chatterjee, Saumil Patel, Muhsin Ameen In this talk, we investigate the large scale structures generated in various flow regimes (intake, compression, expansion, and~exhaust strokes) of a motored, TCCIII internal combustion (IC) engine. The study is performed with a highly scalable spectral element code Nek5000. The moving boundary problem corresponding to the valves and piston motion are incorporated through a spectrally accurate arbitrary LagrangianEulerian methodology. To avoid severe mesh distortions, we use a novel methodology of interpolating simulation data to a redesigned mesh insitu, thereby keeping the shape topology of the meshes in control during the simulations. We also use a novel oversetgrid methodology to mesh the spark plug region separately in order to reduce remeshing of the spark region and maintain stability in our simulations. Such high fidelity studies are not only crucial for understanding the multiscale engineflow dynamics and cyclic variability of the flow features, but also serves as an efficient guideline for developing more advanced models, like species reaction, and spray injection corresponding to realistic IC engines. [Preview Abstract] 
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