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 F23: General Fluid Dynamics: Rotating Flow and Multiphysics PhenomenaGeneral

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Chair: Weili Luo, University of Central Florida Room: 710 
Monday, November 20, 2017 8:00AM  8:13AM 
F23.00001: Rotating channel flows over rough and smooth surfaces Ugo Piomelli, Wen Wu, Junlin Yuan In wallbounded flows rotating about the spanwise axis, if the signs of the rotation and mean vorticity vectors are the same, the flow tends to be destabilized; if they are opposite it may become more stable. In a channel, in which the vorticity has opposite signs near the two walls, one side is unstable and the other one stable. To investigate how roughness can change these dynamics, we performed DNS of channel flows with two rotation rates ($Ro_b=2\Omega\delta/U_{b}=0.42$ and 1.0), over both smooth and rough surfaces. The roughness is modelled using an immersedboundary method. At the high Rotation number, in the smooth case the Reynolds stresses vanish on the stable side, and the flow approaches 2D turbulence in the $xz$ plane. When the wall is rough, the increased momentum transfer due to the roughness results in significant $\langle u'v'\rangle$ and much more isotropic turbulent fluctuations. On the unstable side both rotation and roughness tend to destabilize the flow. Even at mild rotation rates Townsend's similarity hypothesis does not apply on the stable side, and only approximately on the unstable one. The role of production and redistribution due to rotation in the turbulent kinetic energy budget will be discussed. [Preview Abstract] 
Monday, November 20, 2017 8:13AM  8:26AM 
F23.00002: Rotating Polygon Instability on the free surface of rotating liquid nitrogen in Leidenfrost state Tomas Bohr, Jacob Bach, Alexis Duchesne, Martijn v. d. Ouderaa When liquid nitrogen is poured into a warm pot, film boiling will create a Leidenfrost effect insulating the liquid from the pot by a thin airlayer strongly reducing the friction. Stirring the fluid layer in a cylindrical pot will thus create a longlived vortex whose free surface can deform into polygons as described in Toph{\o}j \textit{et al}., Phys. Rev. Lett. \textbf{110}, 194502 (2013). We have investigated the relation of these instabilities to the stationary rotating polygons described in Vatistas, J. Fluid Mech. \textbf{217}, 241 (1990) and Jansson \textit{et al.}, Phys. Rev. Lett. \textbf{96}, 174502 (2006) as well as to the theory by Toph{\o}j et al. We further discuss the possible relation to the hexagonal north polar vortex of Saturn (D. A. Godfrey, Icarus, \textbf{76}. 335 (1988)). Compared to earlier experiments, the nitrogen flows appear strongly turbulent with violent bursts generating droplets. It is remarkable that they can still maintain welldefined polygonal structures that appear to be rotating like a solid body. We quantify the shape changes by the spectral dynamics of the contact line in the bottom of the pot. [Preview Abstract] 
Monday, November 20, 2017 8:26AM  8:39AM 
F23.00003: Stability Of Oscillatory RotatingDisk Boundary Layers Scott Morgan, Christopher Davies The rotating disk boundary layer has long been considered as an archetypal model for studying the stability of threedimensional boundarylayer flows. It is one of the few truly threedimensional configurations for which there is an exact similarity solution of the NavierStokes equations. Due to a crossflow inflexion point instability, the investigation of strategies for controlling the behaviour of disturbances that develop in the rotating disk flow may prove to be helpful for the identification and assessment of aerodynamical technologies that have the potential to maintain laminar flow over swept wings. We will consider the changes in the stability behaviour which arise when the baseflow is altered by imposing a periodic modulation in the rotation rate of the disk surface. Following similar work by Thomas et. al. [Proc. R. Soc. A (2011) 467, 26432662], preliminary results indicate that this modification can lead to significant stabilising effects. Current work encompasses linearised DNS, complemented by a local in time analysis made possible by imposing an artificial frozen flow approximation. This is deployed together with a more exact global treatment based upon Floquet theory, which avoids the need for any simplification of the temporal dependency of the baseflow. [Preview Abstract] 
Monday, November 20, 2017 8:39AM  8:52AM 
F23.00004: Librational forcing of a rapidly rotating fluidfilled cube Ke Wu, Juan M Lopez, Bruno W Welfert The dynamics of the fluid flow in a rapidly rotating cube excited via libration are explored numerically by solving the full 3D incompressible NavierStokes equations via a Chebyshev pseudospectral (collocation) code. The code is first validated against experimental results available in the literature, with rotational Reynolds number of order $10^4$ and relative libration amplitudes of order $0.02$. In particular, we confirm resonance at certain libration frequencies corresponding to intrinsic (Kelvin) modes of the cube. These Kelvin modes are obtained by solving the Euler equations linearized about the solidbody rotation state. We also verify the existence of waves beams emerging from both the top and bottom edges of the cube and propagating obliquely upward and downward when the ratio of libration frequency to background rotation frequency is less than 2. We then explore the weakly nonlinear nealy inviscid regime by increasing the rotational Reynolds number up to $10^7$ and reducing the relative libration amplitude to $10^{7}$. [Preview Abstract] 
Monday, November 20, 2017 8:52AM  9:05AM 
F23.00005: Introducing an experimental splitcylinder to study flows with geophysical interest: First steps and first results Jesus O. RodriguezGarcia, Javier Burguete A new experimental setup has been developed in order to study rotating flows. Our research is derived from the experiments carried out in our group relating to this kind of flows, and the setup is inspired by the simulations performed by Lopez \& GutierrezCastillo [JFM 800, 666687, 2016] using a splitcylinder flow. In their work they study the different bifurcations taking place into the flow, among others, finding inertial waves in different configurations of the movement of the splitcylinder. Our setup consists in a splitcylinder in which each half can move in corotation or in counterrotation. Moreover, we can set the rotation velocity of each half independently in order to study these different configurations of the flow. The aspect ratio defined as $\Gamma=H/R$ can be modified, where $H$ is the internal length of the cylinder and $R$ is its radius. With this setup, we study the flow developed inside the splitcylinder depending on the Reynolds number like the different symmetrybreaking that should appear according to Lopez \& GutierrezCastillo. To obtain the experimental data we use both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) techniques. The firsts results got are in the corotation case rotating one half faster than the other. [Preview Abstract] 
Monday, November 20, 2017 9:05AM  9:18AM 
F23.00006: Gyroscopic analogy of a rotating stratified flow confined in a tilted spheroid and its implication to stability of a heavy symmetrical top Yasuhide Fukumoto, Yuki Miyachi We address the suppression of the gravitational instability of rotating stratified flows in a confined geometry in two ways, continuous and discontinuous stratification. A rotating flow of a stratified fluid confined in an ellipsoid, subject to gravity force, whose velocity and density fields are linear in coordinates, bears an analogy with a mechanical system of finite degrees of freedom, that is, a heavy rigid body. An insight is gained into the mechanism of system rotation for the ability of a lighter fluid of sustaining, on top of it, a heavier fluid when the angular velocity is greater than a critical value. The sleeping top corresponds to such a state. First we show that a rotating stratified flow confined in a tilted spheroid is equivalent to a heavy symmetrical top with the symmetric axis tilted from the top axis. This tilting effect of the symmetric axis on the linear stability of the sleeping top and its bifurcation is investigated in some detail. Second, we explore the incompressible twolayer RTI of a discontinuously stratified fluid confined in the lowerhalf of an upright spheroid rotating about the axis of symmetry oriented parallel to the vertical direction. The gyroscopic analogy accounts for decrease of the critical rotation rate with oblateness. [Preview Abstract] 
Monday, November 20, 2017 9:18AM  9:31AM 
F23.00007: GasInduced Rectified Motion of a Solid Object in a LiquidFilled Housing during Vibration: Analysis and Experiments J.R. Torczynski, T.J. O'Hern, J.R. Clausen, T.P. Koehler The motion of a solid object (a piston) that fits closely within a housing filled with viscous liquid is studied. If a small amount of gas is introduced and the system is subjected to axial vibration, then the piston exhibits rectified motion when the drag on the piston depends on its position within the housing. An idealized system, in which the piston is suspended freely between two springs and the gas is replaced with two compressible bellows, is analyzed theoretically and studied experimentally. For a given vibration amplitude or frequency, the piston either remains near its original position (``up'') or moves to a different position (``down''), where its spring suspension is compressed. Analytical and experimental regime maps of the amplitudes and frequencies at which the piston is up or down are in good agreement. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DENA0003525. [Preview Abstract] 
(Author Not Attending)

F23.00008: Flow and mass transfer around a coreshell reservoir Badr Kaoui I have developed an alternative numerical approach to study mass transfer from a stationary coreshell reservoir under channel flow conditions. I use the lattice Boltzmann method to compute both the solvent fluid flow and the diffusion and advection of the solute. I have investigated the impact of the flow by reporting mass transfer quantities such as the instantaneous solute concentration and the local Sherwood number at the surface of the reservoir. The flow is found to enhance the release of the encapsulated material, but it prevents the released material from reaching the channel walls [B. Kaoui, Phys. Rev. E 95, 063310 (2017)] [Preview Abstract] 
Monday, November 20, 2017 9:44AM  9:57AM 
F23.00009: ABSTRACT WITHDRAWN 
Monday, November 20, 2017 9:57AM  10:10AM 
F23.00010: Abstract Withdrawn ~A new type of heat engine has been proposed in 2005 that defies fundamental thermodynamic law: A specifically designed magnetic body force can reverse heat flow from high temperature to low temperature [1]. This mechanism can drive heat to higher temperature, rendering the possibility to reuse the ``waste heat''. As the result, the efficiency is much higher than that of the Carnot Engine. In a recent paper [2] a realization of this proposed mechanism is reported: by using a specific configuration of temperature and magnetic field gradients, we observed that magnetic body force suppresses the gravitothermal convective heat when the gradients of temperature and field are antiparallel to each other. This driving force stops the heat flow of approaching to thermal equilibrium in the system, causing the temperature difference across the sample to increase with applied fields. In this work, I will discuss the driving mechanism for this phenomenon and its application in the proposed engine. This remarkable result suggests that the 2$^{\mathrm{nd}}$ law of thermodynamics maybe conditioned and needs to be reexamined. References: [1]Weili Luo, US Patent: WO 2007002127 A3 [2] Jun Huang, Weili Luo, and Tianshu Liu, ``Observation of localized, antiequilibration flow in a quasi onedimensional magnetic fluid in horizontal field and temperature gradients.'' (\underline {http://arxiv.org/abs/1611.00385}) 
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