Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session BP: Turbulence Simulations: DNS I |
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Chair: Kenneth Ball, Virginia Polytechnic Institute and State University Room: Hilton Chicago Stevens 1 |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BP.00001: Direct Numerical Simulation of Turbulent Mass Transfer around a Rotating Circular Cylinder Jong-Yeon Hwang, Kyung-Soo Yang, Klaus Bremhorst, Sungsu Lee Characteristics of turbulent mass transfer around a rotating circular cylinder are investigated by Direct Numerical Simulation for Schmidt numbers \textit{Sc}=1 and 1670. The concentration field is computed for three different cases of low Reynolds number, \textit{Re}=161, 348 and 623, based on the cylinder radius and friction velocity for \textit{Sc}=1670. Results confirm that the thickness of Nernst diffusion layer is very thin compared with that of viscous sub-layer in the case of high Sc mass transfer. Visualization of instantaneous concentration reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. Reynolds analogy identified at \textit{Sc}=1 causes a strong correlation between concentration fluctuation and streamwise velocity fluctuation but this is not the case at \textit{Sc}=1670. For \textit{Sc}=1670, small positive values of concentration fluctuations are frequently observed particularly outside of the Nernst diffusion layer but inside of the viscous sublayer, while negative values occur less often, but with large magnitude. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BP.00002: Intermittency and Direct Numerical Simulations Katepalli R. Sreenivasan, Joerg Schumacher, Victor Yakhot The conventional wisdom in direct numerical simulations (DNS) is that the turbulent velocity field can be regarded as fully resolved if the linear dimension of the discretization grid is the Kolmogorov scale. It then follows that the computational work in DNS increases with the large-scale Reynolds number Re as Re$^{3}$. The arguments leading to this conclusion, which will be reviewed briefly, ignore the effects of small-scale intermittency. It will be shown that the effect of this intermittency is to establish scales that are smaller than the Kolmogorov scale, and that a full resolution of the velocity field requires computational power of the order Re$^{4}$. This places more severe computational demands on DNS of turbulence. A few results from simulations performed with a grid resolution that is substantially finer than the Kolmogorov scale will be discussed. The changes that manifest in the tails of the probability density function and the multifractal spectrum will be discussed. The results demonstrate that extreme events of the dissipation field indeed require superfine resolution below the Kolmogorov scale. Similar issues relate to the passive scalar field as well, and the DNS performed with grid resolution that is finer than the Batchelor scale are discussed. The conclusions for the scalar field are qualitatively similar to those for the velocity field. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BP.00003: An Optimized WENO Smoothness Measurement for the Direct Numerical An Optimized Smoothness Measurement for the Direct Numerical Simulation of Compressible Turbulent Flow Minwei Wu, Ellen Taylor, M. Pino Martin The adaption mechanism and dissipation properties of a bandwidth-optimized weighted essentially non-oscillatory (WENO) scheme for the direct numerical simulation of compressible turbulence are discussed and an optimized WENO smoothness measurement is introduced. We find that the new smoothness measurement results in reduced numerical dissipation. In turn, accurate flow fields of isotropic turbulence can be obtained using coarser grids than those required with the original smoothness measurement. In addition, the modified smoothness measurement gives better results for shockwave and turbulent boundary layer interaction flows. [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BP.00004: Reynolds number dependnce of Lagrangian velocity, acceleration and dissipation statistics in large numerical simulations of isotropic turbulence P.K. Yeung, D.A. Donzis, E.A. Kurth, S.B. Pope Recent experiments and numerical simulations have shown that the Lagrangian fluid particle acceleration is highly intermittent, and that higher Reynolds numbers are required to resolve issues of Kolmogorov similarity in the Lagrangian versus Eulerian frame of reference. We have made progress in direct numerical simulations (DNS) at grid resolution $2048^3$ and Taylor-scale Reynolds number close to 700. The Lagrangian velocity structure function is found to approach Kolmogorov similarity, with the scaling constant ($C_0$) within 10-15\% of an estimated asymptotic value in the literature. Analyses of Eulerian data show that the acceleration has a strong dependence on local relative motion involving straining and rotational effects. At higher Reynolds numbers the autocorrelation of energy dissipation is approximately exponential, with an integral time scale of several Kolmogorov time scales. Velocity and acceleration autocorrelations conditioned on dissipation, enstrophy or pseudo-dissipation are all indicative of more rapid changes for particles moving in regions of large velocity gradients. DNS at $2048^3$ has helped isolate some previous observations as due to low-Reynolds-number effects. [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BP.00005: Acceleration, enstrophy and dissipation in isotropic turbulence Changhoon Lee, Jaedal Jeong, Kyongmin Yeo Recent studies showed that fluid particle acceleration in turbulence is quite an intermittent variable. Source of the intermittency was found to be closely related to the rotational motion of coherent vortical structures. However, local dissopation in part contributes to the intermittency of acceleration. In order to clearly understand the relation between acceleration, local dissipation and local enstrophy which represents rotational components of the velocity strain tensors, we use a decomposition of acceleration into $a^{\Omega} $ and $a^{\epsilon}$ which are contributions from the rotational motion of eddies and irrotational straining motion, respectively. Statistics of each components of acceleration and cross correlation between them are investigated by using direct numerical simulation of isotropic turbulence. The flow is forced by large-scale forcing, thus hardly influencing directly the small-scale motion. Classical Kolmogorov scaling relation for accelerations are also checked for each component. Detailed statistics will be presented in the meeting. [Preview Abstract] |
Sunday, November 20, 2005 12:01PM - 12:14PM |
BP.00006: Direct and Large Eddy Simulation of non-equilibrium wall-bounded turbulent flows Hee-Jun Park, Rayhaneh Akhavan The performance of several existing SGS models in non-equilibrium wall-bounded turbulent flows is investigated through comparisons of LES and DNS. The test problem is a shear-driven three-dimensional turbulent channel flow at base $Re_{\tau} \sim 210$ established by impulsive motion of one of the channel walls in the spanwise direction with a spanwise velocity equal to 3/4 of the bulk mean velocity in the channel. The DNS and LES are performed using pseudo-spectral methods with resolutions of 128${\times}$128${\times}$129 and 32${\times}$64${\times}$65, respectively. The SGS models tested include the nonlinear Interactions Approximation model (NIA) [Haliloglu and Akhavan (2004)], the Dynamic Smagorinsky model (DSM) [Germano et al. (1991)], and the Dynamic Mixed Model (DMM) [Zang et al. (1993)]. The results show that NIA gives the best overall agreement with DNS. Both DMM and DSM over-predict the decay of the mean streamwise wall shear stress on the moving wall, while NIA gives results in close agreements with DNS. Similarly, NIA gives the best agreement with DNS in the prediction of the mean velocity, the higher-order turbulence statistics, and the lag angle between the mean shear and the turbulent shear stress. These results suggest that non-equilibrium wall-bounded turbulent flows can be accurately computed by LES with NIA as the SGS model. [Preview Abstract] |
Sunday, November 20, 2005 12:14PM - 12:27PM |
BP.00007: On the Modification of Near-Wall Structures in Stably Stratified Turbulence Junwoo Lim, Kyongmin Yeo, Changhoon Lee We investigate the Eulerian and Lagrangian characteristics of turbulent channel flows under stable stratification with particular emphasis on the modification of the near-wall structures. From the direct numerical simulations in the range of $Re_\tau=180 \sim 400$ and $Ri = 0 \sim 200$, we find that the near-wall turbulent structures become more energetic and intermittent under stable stratification, while the basic shapes still remain the same. We observe some evidences, however, that the stratification effect may eventually modify the shapes of near-wall structures as well at higher Richardson number. On the other hand, in the center region, the buoyancy already suppresses large scale turbulence significantly as the Richardson number increases. Due to the presence of internal gravity waves near the center region, the particles released from the one half of the channel are shown to be hindered from migrating to the other side. Other high- order statistics will be presented in the meeting in more detail. [Preview Abstract] |
Sunday, November 20, 2005 12:27PM - 12:40PM |
BP.00008: Puff-like Structures Captured in DNS of the Turbulent Poiseuille Flow at Low Reynolds Numbers Takahiro Tsukahara, Kaoru Iwamoto, Hiroshi Kawamura, Daisuke Tochio Direct numerical simulation (DNS) of a fully developed turbulent channel flow for very low Reynods numbers has been executed with larger computational box-sizes than those of common DNS. The present Reynolds number is decreased down to $Re_\tau$=64, where $Re_\tau$ is based on the friction velocity and the channel half width $\delta$. For lower Reynolds numbers of $Re_\tau \le 80$ with the largest box of $51.2\delta \times 2\delta \times 22.5 \delta$, the periodic weak-turbulence regions are observed. This type of locally disordered flow is similar to a turbulent puff observed in a transitional pipe flow. The equilibrium puff-like structures observed in the channel flow incline against the streamwise direction. The propagation velocity of the puff-like structure is approximately equal to the bulk mean velocity. The significant effects of the captured puff-like structures exist upon the turbulence statistics, such as a mean velocity and turbulence intensities. [Preview Abstract] |
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