Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session MR: Rotating Flows |
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Chair: Frank Jacobitz, University of California, San Diego Room: 200F |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
MR.00001: Dynamics of a fluid inside a precessing cylinder Romain Lagrange, Patrice Meunier, Christophe Eloy, Fran\c{c}ois Nadal The instability of a fluid inside a precessing cylinder is studied theoretically and experimentally, motivated by aeronautical and geophysical applications. Precessional motion forces hydrodynamic waves called Kelvin modes whose structure and amplitude are predicted by a linear inviscid theory. When a forced Kelvin mode is resonant, its amplitude diverges (and saturates due to viscous effects), which makes the flow unstable for sufficiently high Reynolds numbers. A linear stability analysis based on a triadic resonance between a forced Kelvin mode and two free modes has been carried out. The precessing angle for which the flow becomes unstable is predicted and compared successfully to experimental measurements. A weakly nonlinear theory was developed and allowed to show that the bifurcation of the instability of precession is subcritical. It also showed that, depending on the Reynolds number, the unstable flow can be steady or intermittent. Finally, this weakly nonlinear theory allowed to predict, with a good agreement with experiments, the mean flow in the cylinder; even if it is turbulent. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
MR.00002: Rotating spin-up in three dimensions Jin-Qiang Zhong, Michael Patterson, John Wettlaufer Motivated by previous studies we revisit the well known transient spin up problem, with and without buoyancy forcing, using a new experimental technique. In so doing, we are able to examine the fluids behavior by extracting a series of two-dimensional velocity fields at multiple levels simultaneously thereby producing a three-dimensional view of the evolving flow. The results provide startling detail of the rich three dimensional structure of the flow, and reveal, amongst other things, depth dependent axisymmetric pattern formation and breakdown. Vertical slices of the velocity field reveal highly localized up and downwellings. Our quantitative probing produces continuous velocity fields amenable to direct comparison with simulations. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
MR.00003: Large scale flow instabilities in rotating flows L. Del Castello, H.J.H. Clercx, R.R. Trieling, A. Tsinober Background rotation affects the dynamics of fluid flows with a combination of linear and nonlinear effects, according to the relative importance of the Coriolis acceleration compared to the convective and forcing terms in the Navier-Stokes equation. We perform experiments on a turbulent flow ($Re_{\lambda}\sim150$) electromagnetically forced in a confined tank put on a rotating table, and we measure the flow using Particle Tracking Velocimetry. We focus here on the anisotropic effects of rotation at the large scales, and we define the Rossby number $Ro_f=\frac{U_f^2/L}{2\Omega U_f}$ based on the forced velocity scale $U_f$. With a mild rotation of $0.2~\mathrm{s^{-1}}$ ($Ro_f\sim1.8$), we observe an enhancement of horizontal and vertical velocity gradients of the large scale flow, but the overall forced flow pattern remains stable. When the rotation is increased to $2.0~\mathrm{s^{-1}}$ ($Ro_f\sim0.2$), we observe instead the dampening of the velocity gradients at large scales, while the forced flow pattern strongly fluctuates. With a strong rotation of $5.0~\mathrm{s^{-1}}$ ($Ro_f\sim0.07$), the stability of the forced mean flow structures is finally restored. [Preview Abstract] |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
MR.00004: Effect of the Sign of Ro on the Stability of Stewartson Layers Generated by a Rotating Disc Jozef H.A. Vlaskamp, Peter J. Thomas, Rainer Hollerbach The effect of the sign of rotation on the stability of the Stewartson layer formed by a rotating disc in a rotating fluid is investigated experimentally and numerically. A discrepancy exists between two earlier studies. Ref. [1] found the sign of Ro to have no influence, while Ref. [2] found a strong asymmetric behaviour. Numerical investigations in Ref. [3] suggested a difference in the boundaries along the disc as a possible cause of the discrepancy between the studies. In the current study experimental work is performed on the large scale facility at the University of Warwick (overall height 5.7m and 1.4 m diameter), with a single disc inside a movable end-wall. The size of the facility allows a much larger height to radius ratio than in previous experiments. A fully automated, traverse mounted 3D PIV system is used to allow data- acquisition over the length of the Taylor column without the need for recalibration. Further numerical work is conducted using the code described in Ref. [3]. REFERENCES: [1] W. G. Fr\"uh,. P.L. Read, J. Fluid Mech., vol. 383, p. 143, 1999. [2] R. Hide, R., C.W. Titman J. Fluid Mech., vol. 29, p. 39, 1967. [3] R. Hollerbach, J. Fluid Mech., vol. 492, p. 289, 2003. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
MR.00005: Anisotropy properties and geometrical scale-dependent statistics of sheared and rotating turbulence Frank Jacobitz, Kai Schneider, Wouter Bos, Marie Farge The anisotropy properties of homogeneous turbulence with mean shear and system rotation are studied using both conventional and wavelet-based anisotropy measures. The study is based on a series of nine direct numerical simulations in which the rotation ratio $f/S$ of Coriolis parameter to shear rate is varied. The presence of rotation stabilizes the flow, except for a narrow range of rotation ratios $0 < f/S < 1$. The main mechanism for the destabilization is an increased turbulence production due to increased anisotropy. This anisotropy at large and small scales is quantified by applying conventional measures, such as the Reynolds stress and the dissipation rate anisotropy tensors, respectively. Recently introduced directional wavelet based measures are also applied and compared with the classical ones. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
MR.00006: Small-scale Statistics of Turbulence induced by Vortices Kelken Chang, Gregory P. Bewley, Eberhard Bodenschatz We report measurements of the small-scale statistics of a moderate Reynolds number (up to a Taylor microscale Reynolds number of 500) turbulent flow induced by large-scale vortices. We study the flow using Lagrangian particle tracking technique, in which the three-dimensional motion of neutrally bouyant oil particles in air is followed optically using multiple high speed cameras. We compare the results with experimental measurements obtained in a nearly homogeneous and isotropic turbulent flow at comparable Reynolds number. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
MR.00007: ABSTRACT WITHDRAWN |
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