Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session D12: Turbulence Simulation II |
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Chair: Dale Pullin, California Institute of Technology Room: 315 |
Sunday, November 20, 2011 2:10PM - 2:23PM |
D12.00001: Scaling exponents of energy dissipation, enstrophy and scalar dissipation in high-resolution direct numerical simulations of turbulence K.P. Iyer, P.K. Yeung, K.R. Sreenivasan A central issue in the study of intermittency and refined similarity in turbulence is the behavior of higher-order moments of the locally-averaged energy dissipation rate ($\epsilon_r$) within a domain of linear size $r$, especially for $r$ in the inertial range. However, accurate determination of these quantities requires full-field knowledge of all components of velocity gradients which must be well-resolved in space, with the degree of difficulty increasing with the order of the moment. We examine a large DNS database in isotropic turbulence, with emphasis on well-resolved simulations up to $4096^3$ at Taylor-scale Reynolds number 650. Efficient algorithms have been developed to extract the statistics of $\epsilon_r$, and those of local averages of enstrophy and scalar dissipation rate, with averages taken both along a line of length $r$ and within a cube of linear size $r$. Scaling exponents appearing in relations of the form $\langle\epsilon_r^p\rangle \propto r^{-\zeta_p}$ have been assessed, although the inference of a clear scaling range depends on numerical resolution in addition to Reynolds and Schmidt numbers. Data from 1D and 3D averages differ systematically, but both are useful for comparison with intermittency models in the literature. [Preview Abstract] |
Sunday, November 20, 2011 2:23PM - 2:36PM |
D12.00002: Dynamics of non-local interactions in isotropic turbulence Agustin Maqui, Diego Donzis A large database of isotropic turbulence with $R_{\lambda}$ ranging from 38 to 1100 and resolutions up to $4096^3$ is used to study aspects of the dynamic response of the small scales to forcing at the largest scales. Time correlations of spectra and transfer show that changes in the large scales have an immediate effect on the smallest dissipative scales. Furthermore, these non-local interactions are strongly anti-correlated for wavenumbers beyond the so-called bottleneck. While the applied large-scale forcing is Gaussian, the probability density function of individual modes of the energy spectrum is skewed for all wavenumbers. On the other hand, transfer spectra shows departures from Gaussianity only at high wavenumbers. Short-term behavior is studied through the evolution of the ratio of spectral levels at different wavenumbers as forcing is abruptly introduced or discontinued. All results demonstrate the direct connection between distant scales. More importantly, the observed trends do not appear to decrease as the Reynolds numbers increases. Different models for the spectral transfer are shown to capture some of the observed behavior. Further consequences of the results will be discussed. [Preview Abstract] |
Sunday, November 20, 2011 2:36PM - 2:49PM |
D12.00003: Direct numerical simulation of top-down and bottom-up scalar diffusion in the convective Ekman layer Scott Waggy, Sedat Biringen The turbulent Ekman layer commonly serves as a model of the atmospheric boundary layer. In this work we study the unstably-stratified turbulent Ekman layer by means of a direct numerical simulation. Studies have demonstrated that entrainment processes at the top of the atmospheric boundary layer affect turbulence within the mixed-layer. In order to differentiate between bottom-up and top-down diffusion, surface fluxes are separated from entrainment effects by monitoring passive scalars with conditions indicative of these processes. For each case, the scalar variance is parameterized as a function of $z/z_{i}$, the distance from the wall normalized by the temperature inversion height. The ability of these idealized variance functions to represent scalar flux through the convective boundary layer, where both bottom-up and top-down diffusion occur, is assessed. [Preview Abstract] |
Sunday, November 20, 2011 2:49PM - 3:02PM |
D12.00004: Simulation of Homogeneous Turbulence Subjected to Plane Strain Chris Zusi, J. Blair Perot Direct numerical simulation is used at a resolution of 512$^{3}$ to investigate the behavior of turbulence subjected to plane strain. The initial isotropic turbulence is generated by the stirring action of many small randomly placed cubes, rather than imposed as an initial condition. Anisotropic turbulent structure is then generated by dimensionless plane strain rates Sk/$\epsilon$ ranging from 2.2 to 54. Twenty different simulations are used to investigate the influence of initial conditions, strain rate, Reynolds number, and dimensionless strain time on the strained turbulence structure and its subsequent anisotropic decay. [Preview Abstract] |
Sunday, November 20, 2011 3:02PM - 3:15PM |
D12.00005: Studying Lagrangian dynamics of turbulence using on-demand fluid particle tracking in the JHU turbulence database Huidan Yu, Kalin Kanov, Eric Perlman, Randal Burns, Alexander Szalay, Gregory Eyink, Charles Meneveau The JHU public turbulence database (http://turbulence.pha.jhu.edu) provides access to large datasets generated from DNS of turbulence, at present the output of a $1024^3$ pseudo-spectral DNS of forced isotropic turbulence ($Re_\lambda$=443) with 1024 time-steps. The resulting 27 TB dataset can be accessed remotely through an interface based on the Web-services model allowing remote users to issue subroutine-like calls on their host computers. Here we describe the newly developed getPosition function: Given an initial position, integration time-step, as well as an initial and end time, the getPosition function tracks arrays of fluid particles inside the database and returns particle locations at the end of the trajectory integration time. GetPosition is applied to study Lagrangian velocity structure functions as well as tensor-based Lagrangian time correlation functions. The roles of pressure Hessian and viscous terms in the evolution of the strain-rate and rotation tensors are also explored. [Preview Abstract] |
Sunday, November 20, 2011 3:15PM - 3:28PM |
D12.00006: On the Lagrangian Power Spectrum of Turbulence Energy in Isotropic Turbulence Francesco Lucci, Victor L'vov, Antonino Ferrante, Said Elghobashi We present, for the first time, a derivation of the transport equation of the Lagrangian frequency power spectrum, ${ E_{L}(t,\omega)}$, of turbulence energy in isotropic turbulence starting from the autocorrelation of the Lagrangian velocity. The new equation is: ${\partial E_L (t,\omega)} \big / {\partial t} = $ $ {\mathcal T}_L (t,\omega) -$ $ \varepsilon_L (t,\omega) +$ $ \Psi_L (t,\omega) $, where $ {\mathcal T}_{L} (t,\omega)$ is the transfer rate of ${ E_{L}(t,\omega)}$ across the frequency spectrum, $\varepsilon_{L} (t,\omega)$ is the viscous dissipation rate of ${ E_{L}(t,\omega)}$, and $ \Psi_L (t,\omega)$ is the external forcing rate. Our DNS shows that $\varepsilon_{L} (\omega)$ is maximum at low frequencies and vanishes at high frequencies. We also performed an analytical study which confirms the DNS result and shows that $\varepsilon_{L}(\omega) \sim (\omega_{\eta} - \omega)$, i.e. there is non-locality for {$\varepsilon_{L}(\omega)$} in the $\omega$ domain, whereas $E_{L}(\omega) \sim (1/\omega^2 - 1/\omega_{\eta}^2)$, i.e. the locality is valid for $E_{L}(\omega)$, where $\omega_{\eta}$ is the Kolmogorov scale frequency. [Preview Abstract] |
Sunday, November 20, 2011 3:28PM - 3:41PM |
D12.00007: Dynamics of the intense vorticity structures near the turbulent/nonturbulent interface in jets Carlos da Silva, Ricardo Reis Direct numerical simulations (DNS) of turbulent planar jets are used to analyse the dynamics of the intense vorticity structures (IVS) near the turbulent/nonturbulent (T/NT) interface in jets. Deep inside the jet shear layer the characteristics of the IVS are similar to the IVS found in many other flows: the mean radius, tangential velocity, and circulation Reynolds number are $R/\eta \approx 4.6$, $u_0/u' \approx 0.8$, and $Re_{\Gamma}/Re_{\lambda}^{1/2} \approx 28$, where $u_0$, and $Re_{\lambda}$ are the root-mean-square of the velocity fluctuations and the Reynolds number based on the Taylor micro-scale, respectively. Statistics conditioned on the distance from the T/NT interface are used to analyse the effect of the T/NT interface on the dynamics of the IVS and show that the mean radius $R$, tangential velocity $u_0$ and circulation $\Gamma$ of the IVS increases as the T/NT interface is approached, while the vorticity norm $|\omega|$ stays approximately constant. Unlike the IVS deep inside the shear layer, there is a small predominance of vortex diffusion over stretching for the IVS near the T/NT interface implying that the core of these structures is not stable {\it i.e.} it will tend to grow in time. [Preview Abstract] |
Sunday, November 20, 2011 3:41PM - 3:54PM |
D12.00008: Effects of polymer additives on bulk turbulent energy transfer Alexandre de Chaumont Quitry, Douglas H. Kelley, Nicholas T. Ouellette We study the effect of long-chain polymer additives on fully developed bulk turbulence in an experimental von Karman swirling flow. Counterrotating impellers inject turbulent kinetic energy inertially in a cylindrical tank 0.6m wide, whose central region is studied using particle tracking. This experiment emphasizes bulk effects over drag reduction, which allows us to quantitatively compare energy dissipation in dilute polymer solutions with that of pure water. This work is supported by the National Science Foundation. [Preview Abstract] |
Sunday, November 20, 2011 3:54PM - 4:07PM |
D12.00009: Dynamics on the laminar-turbulent boundary and the origin of the maximum drag reduction asymptote in polymer solutions Michael Graham, Li Xi Dynamical trajectories on the boundary in state space between laminar and turbulent plane channel flow -- edge states -- are computed for Newtonian and viscoelastic fluids. Viscoelasticity has a negligible effect on the properties of these solutions, despite the fact that their mean velocity profiles correspond closely to what is observed in experiments with drag-reducing polymer solutions in the maximum drag reduction regime. These results confirm the existence of weak turbulence states that cannot be suppressed by polymer additives, explaining the fact that there is an upper limit for polymer-induced drag reduction. The universality of this limit with regard to polymer properties arises from the fact that the edge states are too weakly three-dimensional to lead to persistent stretching of polymer chains. [Preview Abstract] |
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