Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A11: Rotating Flows I |
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Chair: Patrice Meunier, L'Institut de Recherche sur les Phenomenes Hors Equilibre Room: 3007 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A11.00001: DNS and PIV investigation of nonlinear instability in a precessing cylinder flow Hugh Blackburn, Thomas Albrecht, Richard Manasseh, Juan Lopez, Patrice Meunier Direct numerical simulation results for flow inside a spinning, precessing cylinder of fluid corresponding to a previous experimental study and its extensions are presented and analysed in relation to experimental results and weakly nonlinear theory based on triad interaction of inviscid Kelvin modes. Simulation outcomes agree well with the experimental results both qualitatively and quantitatively, and additional processing reveals more in-depth support for the weakly nonlinear theory than could be demonstrated in the experiments. Additionally, numerical results provide meridional and azimuthal mean flow data. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A11.00002: Precessional forcing of a mean geostrophic flow in a rotating cylinder Thomas Albrecht, Patrice Meunier, Hugh Blackburn, Juan Lopez, Richard Manasseh It has often been observed that inertial waves in rotating flows can interact nonlinearly to create a mean geostrophic motion due to a streaming effect. This mean geostrophic flow has a large effect in rotating flows since it changes the base flow and thereby detunes all the possible resonances. However, in a cylinder, inviscid Kelvin modes (KM) are known theoretically to create \emph{no} mean geostrophic motion by nonlinear coupling. It was thus assumed that the observed geostrophic flow relies on viscous effects in the Ekman boundary layers together with nonlinear interaction. We present here a simple flow configuration where both the KM and the geostrophic flow can be quantified in order to analyse this mechanism in detail. We have studied the case of a KM forced by precession. This allows to reach a very large amplitude of the KM at the resonance, even for small precession angles. PIV measurements are compared to numerical simulations. The profiles of mean azimuthal velocity are studied in the laminar and in the turbulent case. They seem to be correlated to the profiles of velocity of the forced KM. The amplitude of the geostrophic flow seems to agree with the viscous nonlinear theory which predicts that it scales as the square of the forced KM's amplitude. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A11.00003: Behind the Rotating Flattop: when vortex meets a deformable surface J.-C. Tsai, Y.-C. Sun, K.-H. Huang, C.-Y. Lai, C.-Y. Tao, J.-R. Huang We study experimentally a two-fluid system, driven by a rotating upper boundary, inside a stationary cylinder. For a range of aspect ratios, the interface displays various changes with driving rates, with the most striking being the formation of a plateau. Direct imaging and flow visualization allow us to identify the interplay between the morphology of our two-fluid interface and the vortex loops reported previously in literatures, in a way that we can rigorously define the transition by the switch of topology in the flow structure rather than just the shape of the free surface. Further extensions of the parameter space show a wealth of phenomena involving various instabilities on the interface that call for further understanding. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A11.00004: Vibrational Dynamics of Light Body in Rotating Cavity with Liquid Nikolai Kozlov, Stanislav Subbotin Dynamics of a light body of cylindrical or spherical shape in a rotating cavity (cylindrical or spherical) with liquid is studied. The system is set at rotation, the body occupies a steady position near the cavity axis under the action of centrifugal force. Action of an external periodic force excites inertial oscillations of the body and, as consequence, its differential rotation. The mechanism of the latter is the generation of an average mass force in a viscous boundary layer on the oscillating body surface [Fluid Dyn. 43, 9 (2008); 47, 683 (2012)]. In experiments, two types of external action are used. Rotation of a horizontal cavity in the gravity field leads to circular body oscillations with the frequency of rotation; as a result the body rotates slower than the cavity. External vibration, perpendicular to the rotation axis, leads to a resonant excitation of intensive body oscillations; as a result the body spins in the cavity rotation direction (outrunning rotation), or in the opposite (lagging rotation). The eigenfrequency of rotating system is mainly determined by the ratio of vibration and rotation frequencies $n=\Omega_v/\Omega_r$. Body motion intensity is determined by the dimensionless acceleration $\Gamma=g/R_s\Omega_r^2$ or $\Gamma_v=b_v\Omega_v^2/R_s\Omega_r^2$. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A11.00005: Flows in rotating cavity excited by oscillating solid core Stanislav Subbotin, Victor Kozlov, Nikolai Kozlov The flow excited by oscillations of free core in a rotating about horizontal axis cavity filled with liquid is experimentally investigated. The core is lighter than the liquid and is located near the rotation axis under the action of centrifugal force. The action of the gravity force field on the rotating system leads to the tidal oscillations of the core. As a result of the pulsating motion in the Stokes boundary layer the average mass force arises, spinning the core relative to the cavity. The phenomenon of the differential rotation was called a ``vibrational hydrodynamic top'' [Dokl. Phys. {\textbf 52}, 458 (2007)]. The core differential rotation leads to the formation of the flow in the form of a Taylor column. At slow differential rotation the column has the shape of a circular cylinder. Different types of instability manifest themselves: firstly -- the excitation of 2D vortex system inside the column; secondly -- the excitation of 2D azimuthal waves on the column boundary [Dokl. Phys. {\textbf 59}, 40 (2014)]. The nonlinear interaction of different instability modes resulting in synchronization of phase velocities and wave numbers is found. The stability of the structures of different type is determined by Reynolds number. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A11.00006: Experimental investigation of the rotating flow in a low speed axial compressor Lichao Jia, Yiding Zhu, Huijing Yuan, Cunbiao Lee This paper presents detailed experimental data on the flow and turbulence within the boundary layer of an axial compressor rotor blade. The velocity distribution of the entrance of the rotor has also been detected, which will be useful to determine the boundary condition in simulation. The experiments are performed in a low speed wind tunnel at different flow fluxes. During the experiments, high-resolution 2D Particle Image Velocimetry (PIV) measurements are conducted at different axial and radial positions. Phase-locking, boundary detection and virtual particle images methods are used to improve the performance of the PIV. Both the mean and instantaneous internal flow fields of the axial compressor are presented here. The experiments enrich the understanding of the rotating flow phenomenon in the low speed axial compressor. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A11.00007: From Newton's bucket to rotating polygons: experiments on surface instabilities in swirling flows Tomas Bohr, Bjarne Bach, Malene Vested, Anders Andersen, Erik Linnartz We present an experimental study of ``polygons'' forming on the free surface of a swirling turbulent water flow in a partially filled cylindrical container, where the rotation of the bottom plate and the cylinder wall is controlled independently. Thus we can move from a rigidly rotating ``Newton's bucket" flow to one where bottom and cylinder walls are rotating oppositely and the surface is turbulent but flat on average. Between those two extremes, we find polygonal states in two distinct bands. Further, we find a ``monogon,'' a figure with one corner, roughly an eccentric circle rotating in the same sense as the cylinder. We show that the system has a surprising multi-stability and excitability, and that small details can change the stability of polygon states. We investigate accurately the rotation of the plate compared to that of the polygon. Although the the frequency ratios can be close to rational, we do not find phase locking. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A11.00008: Three States of Counter--Rotating Turbulent Taylor--Couette Flow Sedat Tokgoz, Gerrit E. Elsinga, Rene Delfos, Jerry Westerweel In this study we experimentally investigate the change of torque at constant shear $Re$, and its relation to the coherent flow structures in turbulent Taylor-Couette (TC) flow. Torque measurements at counterrotating turbulent regimes show a change depending on the rotation number. In order to understand the mechanism behind this change we used tomographic PIV and measured the instantaneous 3D flow structures in turbulent TC flow. The instantaneous flow fields are decomposed into large (ILS) and smaller-scale (ISS) motions to study their contributions separately. Three distinctive flow states were found at counterrotating turbulent flow, associated with clear changes in the ILS and ISS structure. Close to only inner cylinder rotation, where well-organised Taylor-vortex-like flow structures are observed, the mean flow is responsible for the torque values. Close to exact-counter rotation, inclined ILS vortices induce velocities in the azimuthal and radial directions, contributing significantly to the torque. Close to only outer cylinder rotation the ILS vortices start to align themselves in the axial direction, resembling co-rotating Taylor column-like structures, which reduces the measured torque. The change of the orientation of the ILS vortices is also confirmed quantitatively. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A11.00009: Measurements of small radius ratio turbulent Taylor-Couette flow Roeland van der Veen, Sander Huisman, Sebastian Merbold, Chao Sun, Uwe Harlander, Christoph Egbers, Detlef Lohse In Taylor-Couette flows, the radius ratio ($\eta = r_i/r_o$) is one of the key parameters of the system. For small $\eta$, the asymmetry of the inner and outer boundary layer becomes more important, affecting the general flow structure and boundary layer characteristics. Using high-resolution particle image velocimetry we measure flow profiles, local transport, and statistical properties of the flow for a radius ratio of 0.5 and a Reynolds number of up to $4\cdot10^4$. By measuring flow profiles at varying heights, roll structures are characterized for two different rotation ratios of the inner and outer cylinder. In addition, we systematically vary the rotation ratio and the Reynolds number. These results exemplify how curvature affects flow in strongly turbulent Taylor-Couette Flow. [Preview Abstract] |
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