A5005975375- Fluid Dynamics and Turbulent Flows
- Meteorological Phenomena and Simulations
- Wind and Air Flow Studies
- Particle Dynamics in Fluid Flows
- Combustion and flame dynamics
- Plant Water Relations and Carbon Dynamics
- Solar and Space Plasma Dynamics
- Gas Dynamics and Kinetic Theory
- Fluid Dynamics and Vibration Analysis
- Oceanographic and Atmospheric Processes
- Computational Fluid Dynamics and Aerodynamics
- Advanced Thermodynamics and Statistical Mechanics
- Complex Systems and Time Series Analysis
- Distributed and Parallel Computing Systems
- Atmospheric and Environmental Gas Dynamics
- Field-Flow Fractionation Techniques
- Advanced Data Storage Technologies
- Statistical Mechanics and Entropy
- Parallel Computing and Optimization Techniques
- Computer Graphics and Visualization Techniques
- Geomagnetism and Paleomagnetism Studies
- Aerodynamics and Acoustics in Jet Flows
- Computational Physics and Python Applications
- Mathematical Biology Tumor Growth
- Target Tracking and Data Fusion in Sensor Networks
Georgia Institute of Technology
2015-2025
Johns Hopkins University
2024
University of Rome Tor Vergata
2017
New York University
2017
Hong Kong University of Science and Technology
1996-2014
University of Hong Kong
1985-2014
Atlanta Technical College
2012
Rambus (United Kingdom)
2011
Tel Aviv University
2001
Delft University of Technology
2001
A comprehensive study is reported of the Lagrangian statistics velocity, acceleration, dissipation and related quantities, in isotropic turbulence. High-resolution direct numerical simulations are performed on 64 3 128 grids, resulting Taylor-scale Reynolds numbers R λ range 38-93. The low-wavenumber modes velocity field forced so that turbulence statistically stationary. Using an accurate scheme, order 4000 fluid particles tracked through computed flow field, hence time series gradients...
▪ Abstract A Lagrangian description of turbulence has unique physical advantages that are especially important in studies mixing and dispersion. We focus on fundamental aspects, using mainly data from direct numerical simulations capable great detail precision when specific accuracy requirements met. Differences between time evolution Eulerian frames illustrate the dominance advective transport. examine basic results Kolmogorov similarity, giving an estimate inertial-range universal constant...
Motivated by a recent survey of experimental data [K. R. Sreenivasan, Phys. Fluids 7, 2778 (1995)], we examine on the Kolmogorov spectrum constant in numerical simulations isotropic turbulence, using results both from previous studies and new direct over range Reynolds numbers (up to 240 Taylor scale) at grid resolutions up ${512}^{3}.$ It is noted that addition ${k}^{\ensuremath{-}5/3}$ scaling, identification true inertial requires spectral isotropy same wave-number range. The indicate...
Existing experimental and numerical data suggest that the turbulence energy dissipation enstrophy (i.e., square of vorticity) possess different scaling properties, while available theory suggests there should be no differences at sufficiently high Reynolds numbers. We have performed a series direct simulations with up to 20483 grid points where advanced computational power is used increase number (up 650 on Taylor scale) or resolve small scales better (down 1∕4 Kolmogorov scale). Our primary...
We present a collection of eight data sets from state-of-the-art experiments and numerical simulations on turbulent velocity statistics along particle trajectories obtained in different flows with Reynolds numbers the range Rλ∈[120∶740]. Lagrangian structure functions all are found to collapse onto each other wide time lags, pointing towards existence universal behavior, within statistical convergence, calling for unified theoretical description. Parisi-Frisch multifractal theory, suitably...
We have performed direct numerical simulations of homogeneous and isotropic turbulence in a periodic box with 8,192(3) grid points. These are the largest performed, to date, aimed at improving our understanding small-scale structure. present some basic statistical results focus on "extreme" events (whose magnitudes several tens thousands mean value). The structure these extreme is quite different from that moderately large (of order 10 times In particular, intense vorticity occurs primarily...
Abstract We use data from well-resolved direct numerical simulations at Taylor-scale Reynolds numbers 140 to 1000 study the statistics of energy dissipation rate and enstrophy density (i.e. square local vorticity). Despite substantial variability in each these variables, their extreme events not only scale a similar manner but also progressively tend occur spatially together as number increases. Though they possess non-Gaussian tails enormous amplitudes, ratios some characteristic properties...
As the US Department of Energy (DOE) computing facilities began deploying petascale systems in 2008, DOE was already setting its sights on exascale. In that year, DARPA published a report feasibility reaching The authors identified several key challenges pursuit exascale including power, memory, concurrency, and resiliency. That informed DOE's strategy for With deployment Oak Ridge National Laboratory's Frontier supercomputer, we have officially entered era. this paper, discuss Frontier's...
We study fluctuations of the local energy cascade rate Φ_{ℓ} in turbulent flows at scales (ℓ) inertial range. According to Kolmogorov refined similarity hypothesis (KRSH), relevant statistical properties should depend on ε_{ℓ}, viscous dissipation locally averaged over a sphere size ℓ, rather than global average dissipation. However, validity KRSH applied has not yet been tested from data. Conditional averages such as ⟨Φ_{ℓ}|ε_{ℓ}⟩ well higher-order moments are measured direct numerical...
The scaling properties of one- and two-point statistics the acceleration, pressure, pressure gradient are studied in incompressible isotropic turbulence by direct numerical simulation. Ensemble-averaged Taylor-scale Reynolds numbers (Rλ) up to about 230 on grids from 323 5123. From Rλ 40 onwards acceleration variance normalized Kolmogorov variables is found increase as Rλ1/2. This nonuniversal behavior traced dominant irrotational contributions (whereas much weaker solenoidal viscous part...
We study by direct numerical simulations the effects of Schmidt number (Sc) on passive scalars mixed forced isotropic and homogeneous turbulence. The scalar field is maintained statistically stationary a uniform mean gradient. consider scaling spectra, structure functions, local isotropy intermittency. For moderately diffusive with Sc=1/8 1, Taylor-scale Reynolds flow either 140 or 240. A modest inertial-convective range obtained in spectrum, one-dimensional Obukhov–Corrsin constant about...
A brief report is given of a new 20483 direct numerical simulation the mixing passive scalars with uniform mean gradients in forced, stationary isotropic turbulence. The Taylor-scale Reynolds number close to 700 and Schmidt numbers 1 1∕8 are considered. data provide most convincing evidence date for inertial-convective scaling. Significant departures from small-scale isotropy sustained conventional measures. Subject some stringent resolution requirements, suggest that commonly observed...
Direct numerical simulations of turbulence are used to examine the straining on material surfaces, and behavior thin diffusive layers. The results related questions arising in study turbulent premixed diffusion flames flamelet regime. constant-density, homogeneous, isotropic turbulence, with artificial forcing velocity field maintain statistical stationarity. Taylor-scale Reynolds numbers (Rλ) up 93 achieved. It is found that total rate-of-strain a tangent plane surface positive (i.e.,...
The nonlinear interscale couplings in a turbulent flow are studied through direct numerical simulations of the response isotropic turbulence to and anisotropic forcing applied at large scales. Specifically, is energy-containing wave-number range for about two eddy turnover times fully developed Taylor-scale Reynolds number 32 on an 1283 grid. When forced isotropically, initially remains all wave numbers. However, array counter-rotating rectilinear vortices induces high levels anisotropy...
We examine available data from experiment and recent numerical simulations to explore the supposition that scalar dissipation rate in turbulence becomes independent of fluid viscosity when is small diffusivity small. The are interpreted context semi-empirical spectral theory Obukhov Corrsin Schmidt number, .
A study combining spectral filtering and numerical simulations at enhanced spatial and/or temporal resolution is used to clarify the proper scaling of dissipation enstrophy in forced incompressible isotropic turbulence.
From a database of direct numerical simulations homogeneous and isotropic turbulence, generated in periodic boxes various sizes, we extract the spherically symmetric part moments velocity increments first verify following (somewhat contested) results: $4/5$-ths law holds an intermediate range scales that second order exponent over same is {\it{anomalous}}, departing from self-similar value $2/3$ approaching constant $0.72$ at high Reynolds numbers. We compare with some typical theories...
Fully turbulent flows are characterized by intermittent formation of very localized and intense velocity gradients. These gradients can be orders magnitude larger than their typical value lead to many unique properties turbulence. Using direct numerical simulations the Navier-Stokes equations with unprecedented small-scale resolution, we characterize such extreme events over a significant range turbulence intensities, parameterized Taylor-scale Reynolds number ($R_\lambda$). Remarkably, find...
A study of the Lagrangian statistical properties velocity and passive scalar fields using direct numerical simulations is presented, for case stationary isotropic turbulence with uniform mean gradients. Data at higher grid resolutions (up to 512 3 Taylor-scale Reynolds number 234) allow an update previous results lower number, including intermittency dimensionality effects on vorticity time scales. The emphasis series which are new literature important stochastic mixing models. variance...
The physical mechanisms underlying the dynamics of dissipation passive scalar fluctuations with a uniform mean gradient in stationary isotropic turbulence are studied using data from direct numerical simulations (DNS), at grid resolutions up to 512 3 . ensemble-averaged Taylor-scale Reynolds number is about 240 and Schmidt ⅛ 1. Special attention given statistics conditioned upon energy rate because their important role Lagrangian spectral relaxation (LSR) model turbulent mixing. In general,...