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 P39: Geophysical Fluid Dynamics Stratified Turbulence 
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Chair: Elizabeth Follett, Cardiff University Room: 6a 
Monday, November 25, 2019 5:16PM  5:29PM 
P39.00001: Analysis of Mixing in Rotating Stratified Turbulence Matthew Klema, Annick Pouquet, Duane Rosenberg, Karan Venayagamoorthy This research introduces a parametric framework for the evaluation of rotating stratified turbulence (RST). Four dominant flow regimes in RST are delineated using the turbulent Froude number, $Fr_t = \epsilon/Nk$, and the turbulent Rossby number, $Ro_t = \epsilon/ f k$ where $k$ is the turbulent kinetic energy, $\epsilon$ is the dissipation rate of $k$, $N$ is the buoyancy frequency and $f$ is the Coriolis frequency. These four regimes reflect the relative contributions of buoyancy and rotation to the characteristics of the flow. Thirteen direct numerical simulations (DNS) are used for evaluation of the framework and analyzing the effects of forced rotation on turbulent mixing. The intensity of turbulent mixing is analyzed using the buoyancy Reynolds, $Re_B=\epsilon/\nu N^2$, and the ratio of turbulent to molecular diffusivities, $\hat{\kappa}=\kappa_{\rho t}/\kappa$. Results from the simulations show that forced rotation does not impact the behavior of the turbulence or impact scaling relationships with the turbulent Froude number when compared to nonrotating stratified DNS data. Ratios of the buoyancy frequency $N$ and the Coriolis rotational frequency $f$ is also shown to not be a useful ratio for the classification of stratified flow. [Preview Abstract] 
Monday, November 25, 2019 5:29PM  5:42PM 
P39.00002: Upward and downward transfer of energy in rotating stratified flows Ernesto Horne, Mohammed Hussein Hamede, JeanMarc Chomaz, Paul Billant We investigate experimentally and numerically the evolution of forced turbulence in the strongly stratified regime and for rotation rates covering the regimes associated to a direct and an inverse energy cascade. The experiments are performed by means of a rotating table with a diameter of 2 m. The energy is injected by periodically creating columnar dipoles. Direct numerical simulations (DNS) complement the experiments in order to reach higher Reynolds numbers. The turbulence exhibits pancake structures with a large horizontal scale and a vertical thickness increasing with the rotation rate. For strong enough rotating rates, horizontal scales larger than the forcing scales appear in the experiments consistently with the observation of an inverse cascade in the DNS. We have found that the critical Rossby number below which the inverse cascade appears depends on the horizontal Froude number $F_h$. [Preview Abstract] 
Monday, November 25, 2019 5:42PM  5:55PM 
P39.00003: FreeFall Estimates for Rapidly Rotating Heat and Momentum Transport Jonathan Aurnou, Susanne Horn, Keith Julien Dimensional analysis is employed here to provide freefall scaling estimates for the convective heat and momentum transport in the limit of rapid rotation, and to relate these to scalings for nonrotating RayleighB\'enard convection (RBC) systems. Our analysis shows that the scalings for freefall dominated heat (Nusselt number, $Nu$) and momentum transfer (Reynolds number, $Re$) of rapidly rotating convection differ from their nonrotating RBC counterparts by a factor of $Ro_{ \! f \! \! f}^2$, where $Ro_{ \! f \! \! f} = \tau_\Omega/\tau_{ \! f \! \! f}$ is the freefall Rossby number defined as the ratio of the characteristic rotation time $\tau_\Omega$ and the buoyant freefall time $\tau_{ \! f \! \! f}$. Since $Ro_{ \! f \! \! f} \ll 1$ in the rapidly rotating limit, our predicted rapidly rotating, freefall transport rates remain far below the associated rates in nonrotating systems. [Preview Abstract] 
Monday, November 25, 2019 5:55PM  6:08PM 
P39.00004: Symmetry Breaking of Vortex Patterns in a Rotating Fluid Hamid Abderrahmane, Mira Kim, Giuseppe Di Labbio, Hoi Dick Ng, Georgios Vatistas The stirring flow driven by a rotating disk of a shallow water layer confined in a cylindrical bucket is revisited. The formation of a system of two and three satellite vortices, nested within slightly elliptical and triangular paraboloid free surface, orbiting around the center of the disk, is observed. At critical disk speeds transitions between these two systems of satellite vortices occur. These transitions were imaged and the velocity fields at the free surface of the shallow water were obtained via particle image velocimetry (PIV) measurement.~The nucleation or the inhalation of the satellite vortex during the two transitions is discussed in relation with the eigenmodes of the vortexpatterns.~ . [Preview Abstract] 
Monday, November 25, 2019 6:08PM  6:21PM 
P39.00005: Transient Convective SpinUp Dynamics S. Ravichandran, John S. Wettlaufer We study numerically the formation and breakdown of transient axisymmetric rings of up and downwelling fluid in impulsively started rotating Rayleigh Benard convection. First observed in laboratory experiments with constant negative heat flux at the top boundary [13], these rings form during spinup for a range of Taylor and Rossby (or flux Rossby) numbers, eventually breaking down into a grid of cyclonic vortices with descending flow surrounded by slowly ascending flow. The formation and longevity of the rings depends on the Prandtl number $Pr$, with no sustained rings forming for $Pr 

P39.00006: ABSTRACT WITHDRAWN 
Monday, November 25, 2019 6:34PM  6:47PM 
P39.00007: Instability driven relaxation of an anticyclone Eunok Yim, Paul Billant, Francois Gallaire We study the nonlinear evolution of the centrifugal instability appearing in a columnar anticyclone using a semilinear approach to model the transient unsteady flow evolution in a selfconsistent manner. For anticyclones in a homogeneous viscous flow, the fastest growing instability is without oscillation in time but with a finite axial wavenumber. Hence, the selfconsistent model is developed around the spatially averaged time dependent meanflow and the fluctuation, which reduces the problem from 2D nonlinear to 1D semilinear. The two linear meanflow and fluctuation equations are coupled via the Reynolds stress of the fluctuations. At a given rotation ratio between the vortex angular velocity and the background rotation, only the most linearly unstable mode is considered for Reynolds numbers $Re=800$ and $2000$ defined with the maximum angular velocity and the radius of the vortex. For both values of $Re$, the model predicts well the nonlinear evolution of the meanflow and the fluctuation amplitude. Higher harmonics are nonnegligible only at the highest value of $Re$. The results show that the angular momentum of the meanflow is homogenized to a stable state via the action of the Reynolds stresses of the fluctuation. [Preview Abstract] 
Monday, November 25, 2019 6:47PM  7:00PM 
P39.00008: resonant excitation of modes and triadic resonance in a precessing cube ke wu, Bruno Welfert, Juan Lopez The flow response of a rotating fluidfilled cube under precessional forcing is investigated numerically. The simulations are conducted over a wide range of forcing frequencies at various background rotation rates and a fixed precession angle of one degree. The periodic response is comprised of two main components: resonant excitation of the inviscid inertial eigenmodes of the cube, and inertial wave beams. The resonantly excited modes preserve the same spatiotemporal symmetries as the precessional forcing. Moreover, a symmetrybreaking response is also observed, which is due to triadic resonance, and the modes involved are identified. [Preview Abstract] 
Monday, November 25, 2019 7:00PM  7:13PM 
P39.00009: Aspects of Energetics of Stratified Turbulent Wakes Nidia Cristina Reyes Gil, Kristopher Rowe, Peter Diamessis, Greg Thomsen The study of the turbulent wake generated by a bluff body moving through a stably stratified fluid has important applications in physical oceanography and marine engineering. Significant progress has been made towards understanding the structure and dynamics of the turbulent wake core, as well as the internal gravity wave (IGW) radiation emitted by the wake. Analysis of terms in the wake kinetic energy (KE) budget has demonstrated that viscous dissipation is a stronger sink than IGW radiation before $Nt=10$, while the latter dominates during the midtolate nonequilibrium (NEQ) regime. Nevertheless, these processes do not close the wake KE budget: the largest gap occurring early in the NEQ regime. For a series of implicit large eddy simulations  spanning bodybased initial Reynolds number $Re=5\times10^3$, $10^5$ and $4\times10^5$, and Froude number $Fr=4$, $16$ and $64$  we calculate the complete KE budget of a stratified turbulent wake. The relative importance of viscous dissipation, IGW radiation, buoyancy flux, and nonlinear transport as sinks for wake KE is analyzed for different stages of the wake life cycle. Subsequently, numerical dissipation will be quantified and its impact compared to the physical processes in the KE budget. [Preview Abstract] 
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