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 S18: Turbulent General 
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Chair: Robert Breidenthal, University of Washington Room: 400 
Tuesday, November 26, 2019 10:31AM  10:44AM 
S18.00001: Can we achieve statistically stationary Homogeneous Shear Turbulence? Chandru Dhandapani, Guillaume Blanquart Homogeneous shear turbulence (HST) is an idealized version of the shear turbulence observed in practical free shear flows, and can be simulated using simple computational domains. One of the numerically efficient configurations to simulate turbulent flows is to use triply periodic domains. However, owing to the mean streamwise velocity being nonhomogeneous, periodic boundary conditions cannot be used along one of the directions. Several studies included shear periodic boundary conditions in the crossstream direction. However, in these simulations, the turbulence statistics grew exponentially with time, whereas the turbulence observed in free shear flows is statistically stationary. The authors fixed this problem earlier by performing HST simulations with only shear production and neglected shear convection, thereby obtaining statistically stationary shear turbulence. The current study improves upon the previous simulations by including shear convection, by introducing an inflow/outflow in the crossstream direction. The turbulence statistics reach a statistically stationary state, and the Reynolds shear stress and the anisotropy values agree very well with the results from experiments and simulations of mixing layers, planar jets, and round jets. [Preview Abstract] 
Tuesday, November 26, 2019 10:44AM  10:57AM 
S18.00002: The effects of signaling speed and density on the compressible boundary layer Robert Breidenthal Density effects are known to be weak in the free shear layer, yet they are commonly assumed to be strong in the compressible boundary layer. This apparent inconsistency is addressed in a single model by assuming that the acoustic signaling speed rather than density variations always controls the physics, in both free shear and wall flows. The model assumes that turbulent transport by an eddy requires information to propagate across the diameter of that eddy during the period of one eddy rotation, the time interval of importance in the physics. The turbulent fluxes are dominated by these 'sonic' eddies, whose rotational Mach number is about one. In this view, acoustic signaling controls the velocity fluctuations, which in turn determines the density field through the Reynolds stress. The density field is a consequence of the effect of finite signaling speed. According to the model, the skin friction coefficient and the velocity fluctuations normalized by the edge velocity both vary inversely with edge Mach number. The predictions of the model are in accord with the direct numerical simulations of Duan et al. (2011). Mach number plays a dual role in supersonic flow, measuring both kinetic energy and relative wave speed. Turbulent transport is controlled by the latter. [Preview Abstract] 

S18.00003: ABSTRACT WITHDRAWN 
Tuesday, November 26, 2019 11:10AM  11:23AM 
S18.00004: Subcritical turbulent condensate in rapidly rotating RayleighB\'enard convection Edgar Knobloch, Benjamin Favier, C\'eline Guervilly The possibility of subcritical behavior in the geostrophic turbulence regime of rapidly rotating thermally driven convection is explored. In this regime a nonlocal inverse energy transfer may compete with the more traditional and local direct cascade. We show that, even for control parameters for which no inverse cascade has been previously observed, a subcritical transition towards a largescale vortex state can occur when the system is initialized with a vortex dipole of finite amplitude. This new example of bistability in a turbulent flow, which may not be specific to rotating convection, opens up new avenues for studying energy transfer in strongly anisotropic threedimensional flows. [Preview Abstract] 
Tuesday, November 26, 2019 11:23AM  11:36AM 
S18.00005: NonRayleighTaylor Variable Density Turbulence Daniel Israel The canonical test case for variable density turbulence is the unstable RayleighTaylor mixing layer, in which heavy fluid above mixes with light fluid below. Turbulent production is due to the baroclinic instability as the pressure and density gradients are aligned. For many flows of interest, however, other mechanisms can play a role. For example, in buoyant jets and plumes, the pressure and density gradients are not aligned, and there is also significant shear. Homogeneous turbulence can inform our understanding of the interplay of these different mechanisms. This presentation will survey different cases of homogeneous turbulence and how they inform modeling in different regimes. The cases considered will include both those for which experimental or DNS data exists, and some possibly novel cases for which data is needed. [Preview Abstract] 
Tuesday, November 26, 2019 11:36AM  11:49AM 
S18.00006: Effect of turbulence on wildfire propagation Stefano Leonardi, Martand Mayukh Garimella, Umberto Ciri Wildfires are natural hazards which pose existential threat to humanity and nature. To ensure minimal damage, predictive monitoring systems have been established and are being improved by research. In recent times, numerical fire prediction models have been developed by coupling numerical weather prediction (NWP) models with fire propagation models. However, to minimize computational time, the NWPs are run at a coarser resolution relative to the resolution of the fire models. This gap in resolution is counterproductive as details of small scale interactions, which can lead to extreme events such as crown fires, are neglected. To investigate this effect, large eddy simulations (LES) are performed to propagate a two dimensional fire front using the levelset method which is advanced in time by a thirdorder RungeKutta algorithm. The heat flux generated from the fire is fed back to LES as boundary condition and the effect of buoyancy on wind propagation is included to model a realistic fire weather interaction. From the simulation data, the effects of small scale turbulence structures and change in local atmospheric conditions on fire spread are analyzed. The LES simulation results are compared with the weather research and forecast (WRF) model simulation for wildland fire. [Preview Abstract] 
Tuesday, November 26, 2019 11:49AM  12:02PM 
S18.00007: On the Inertial Range Scaling in the High$R_{\lambda}$ Limit Christian Kuechler, Gregory P. Bewley, Eberhard Bodenschatz We investigate in a decaying laboratory flow the universal scaling laws Kolmogorov predicted in 1941 to emerge in the limit of infinite $R_{\lambda}$. In the past it has been found that this limit requires extreme $R_{\lambda}$, which are difficult to create in a wellcontrolled turbulent flow. The Variable Density Turbulence Tunnel (Bodenschatz et al., 2014) is the first wind tunnel capable of producing $R_{\lambda}>5000$ and fully resolved inertial scales. It combines the low kinematic viscosity of pressurized SF6 and a unique mosaiclike active grid with individually controllable tiles (Griffin et al., 2019). To resolve the smallest scales present in the flow, we use Nanoscale Thermal Anemometry Probes developed and generously provided by Princeton University (e.g. Bailey et al. (2009), Vallikivi et al. (2014)). We present results that the energy spectrum and structure functions differ from conventional scaling laws of isotropic turbulence when studying the logarithmic derivatives of these statistics. However, these local scaling exponents approach a universal form when $R_{\lambda} > 2000$. We show that those results are welldescribed by the generalized selfsimilar spectrum of decaying turbulence introduced by Yang et al. (2018). [Preview Abstract] 
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