Results 1  10
of
25
Turbulent Wind Fields for Gaseous Phenomena
, 1993
"... The realistic depiction of smoke, steam, mist and water reacting to a turbulent field such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent fields, gaseous flow, and realistic illumination. We present a model for turbulent wind flow having a d ..."
Abstract

Cited by 106 (9 self)
 Add to MetaCart
The realistic depiction of smoke, steam, mist and water reacting to a turbulent field such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent fields, gaseous flow, and realistic illumination. We present a model for turbulent wind flow having a deterministic component to specify largescale behaviour, and a stochastic component to model turbulent smallscale behaviour. The smallscale component is generated using spacetime Fourier synthesis. Turbulent wind fields can be superposed interactively to create subtle behaviour. An advectiondiffusion model is used to animate particlebased gaseous phenomena embedded in a wind field, and we derive an efficient physicallybased illumination model for rendering the system. Because the number of particles can be quite large, we present a clustering algorithm for efficient animation and rendering. CR Categories and Subject Descriptors: I.3.7 [Com puter Graphics]: ThreeDimensional Graphics...
J.E.: Numerical simulations of the Lagrangian averaged NavierStokes (LANSα) equations for homogeneous isotropic turbulence
 Physics of Fluids
, 2001
"... The modeling capabilities of the Lagrangian Averaged NavierStokesα equations (LANSα) is investigated in statistically stationary threedimensional homogeneous and isotropic turbulence. The predictive abilities of the LANSα equations are analyzed by comparison with DNS data. Two different forcing ..."
Abstract

Cited by 28 (10 self)
 Add to MetaCart
The modeling capabilities of the Lagrangian Averaged NavierStokesα equations (LANSα) is investigated in statistically stationary threedimensional homogeneous and isotropic turbulence. The predictive abilities of the LANSα equations are analyzed by comparison with DNS data. Two different forcing techniques were implemented to model the energetics of the energy containing scales. The resolved flow is examined by comparison of the energy spectra of the LANSα and the DNS computations; furthermore, the correlation between the vorticity and the eigenvectors of the rate of the resolved strain tensor is studied. We find that the LANSα equations captures the gross features of the flow while the wave activity below a given scale α is filtered by the nonlinear dispersion. 1
SemiImplicit RungeKutta Schemes for NonAutonomous Differential Equations in Reactive Flow Computations
 Proceedings of the 27th AIAA Fluid Dynamics Conference. AIAA
, 1996
"... This paper is concerned with timestepping numerical methods for computing stiff semidiscrete systems of ordinary differential equations for transient hypersonic flows with thermochemical nonequilibrium. The stiffness of the equations is mainly caused by the viscous flux terms across the boundary ..."
Abstract

Cited by 7 (0 self)
 Add to MetaCart
This paper is concerned with timestepping numerical methods for computing stiff semidiscrete systems of ordinary differential equations for transient hypersonic flows with thermochemical nonequilibrium. The stiffness of the equations is mainly caused by the viscous flux terms across the boundary layers and by the source terms modeling finiterate thermochemical processes. Implicit methods are needed to treat the stiff terms while more efficient explicit methods can still be used for the nonstiff terms in the equations. For additively split autonomous differential equations in the form of u 0 = f(u) + g(u), three different semiimplicit RungeKutta methods have been derived and tested in previous papers, where f is treated by explicit RungeKutta methods and g is simultaneously treated by three implicit RungeKutta methods. The coefficients of up to thirdorder accuracy have been derived such that the methods are both highorder accurate and strongly Astable for the implicit terms...
Needs and Opportunities for UncertaintyBased Multidisciplinary Design Methods for Aerospace Vehicles
, 2002
"... this report: Govind Chanani, Wei Chen, Raymond Cosner, Evin Cramer, William Follett, Glenn Havskjold, HanPin Kan, George Karniadakis, Sallie KellerMcNulty, Jerry Lockenour, Mary Mahler, William Oberkampf, Raj Rajagopal, Munir Sindir, Alyson Wilson, and Rudy Yurkovich ..."
Abstract

Cited by 7 (0 self)
 Add to MetaCart
this report: Govind Chanani, Wei Chen, Raymond Cosner, Evin Cramer, William Follett, Glenn Havskjold, HanPin Kan, George Karniadakis, Sallie KellerMcNulty, Jerry Lockenour, Mary Mahler, William Oberkampf, Raj Rajagopal, Munir Sindir, Alyson Wilson, and Rudy Yurkovich
Alphamodeling strategy for LES of turbulent mixing
, 2002
"... The αmodeling strategy is followed to derive a new subgrid parameterization of the turbulent stress tensor in largeeddy simulation (LES). The LESα modeling yields an explicitly filtered subgrid parameterization which contains the filtered nonlinear gradient model as well as a model which represen ..."
Abstract

Cited by 6 (4 self)
 Add to MetaCart
The αmodeling strategy is followed to derive a new subgrid parameterization of the turbulent stress tensor in largeeddy simulation (LES). The LESα modeling yields an explicitly filtered subgrid parameterization which contains the filtered nonlinear gradient model as well as a model which represents ‘Lerayregularization’. The LESα model is compared with similarity and eddyviscosity models that also use the dynamic procedure. Numerical simulations of a turbulent mixing layer are performed using both a second order, and a fourth order accurate finite volume discretization. The Leray model emerges as the most accurate, robust and computationally efficient among the three LESα subgrid parameterizations for the turbulent mixing layer. The evolution of the resolved kinetic energy is analyzed and the various subgridmodel contributions to it are identified. By comparing LESα at different subgrid resolutions, an impression of finite volume discretization error dynamics is obtained.
On the Prediction of GasSolid Flows with TwoWay Coupling using Large Eddy Simulation
, 2000
"... The purpose of this paper is to examine the feasibility of large eddy simulation (LES) for predicting gassolid flows in which the carrier flow turbulence is modified by momentum exchange with particles. Several a priori tests of subgridscale (SGS) turbulence models are conducted utilising results ..."
Abstract

Cited by 5 (3 self)
 Add to MetaCart
The purpose of this paper is to examine the feasibility of large eddy simulation (LES) for predicting gassolid flows in which the carrier flow turbulence is modified by momentum exchange with particles. Several a priori tests of subgridscale (SGS) turbulence models are conducted utilising results from direct numerical simulation (DNS) of a forced homogeneous isotropic turbulent flow with the back effect of the particles modelled using the pointforce approximation. Properties of the subgridscale field are computed by applying Gaussian filters to the DNS database. Similar to the behavior observed in singlephase flows, a priori test results show that, while the local energy flux is inaccurately estimated, the overall SGS dissipation is reasonably predicted using the conventional Smagorinsky model and underestimated using the Bardina scalesimilarity model. Very good agreement between model predictions and DNS results are measured using closures whose coefficients are computed using ...
Prediction and the Quantification of Uncertainty
, 1998
"... Prediction is based on the comparison of results from the statistical analysis of observational data and from the scientific modeling of the system being observed. Effective prediction imposes new as well as familiar requirements on observation and scientific modeling, as will be reviewed here. W ..."
Abstract

Cited by 2 (0 self)
 Add to MetaCart
Prediction is based on the comparison of results from the statistical analysis of observational data and from the scientific modeling of the system being observed. Effective prediction imposes new as well as familiar requirements on observation and scientific modeling, as will be reviewed here. We emphasize issues specific to prediction in the context of technology. Recent results of the authors, colleagues, and others which address these requirements will be presented. PACS: 47.55.Kf, 47.55.Mh, 02.50.r, 02.50.Wp, 02.70.Lq Supported by the Applied Mathematics Subprogram of the U.S. Department of Energy DEFG0290ER25084, the Department of Energy Office of Inertial Fusion, the Army Research Office, grant DAAL0392G0185 and the National Science Foundation, grant DMS9500568. y Supported by the U.S. Department of Energy. 1 Information on Corresponding Author Professor James Glimm Department of Applied Mathematics and Statistics SUNY at Stony Brook Stony Brook NY 11794360...
Towards Lagrangian Large Vortex Simulation
 ESAIM Proc
, 1996
"... Construction of a Lagrangian largeeddysimulation scheme is performed based on filtering the vorticity transport equation and using simple eddydiffusivity models to account for subgridscale "Helmholtz" stresses. The resulting governing equations are simulated using a threedimensional particle meth ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
Construction of a Lagrangian largeeddysimulation scheme is performed based on filtering the vorticity transport equation and using simple eddydiffusivity models to account for subgridscale "Helmholtz" stresses. The resulting governing equations are simulated using a threedimensional particle method which discretizes the vorticity field into Lagrangian vortex elements of finite overlapping cores. Vortex elements are transported along particle trajectories, while their vorticities evolve according to stretching and tilting by the resolved scales, molecular diffusion, and subgridscale stresses. The behavior of the model is discussed in light of limited threedimensional computations of transitional vortex rings. It is shown that the model can capture the largescale features of the flow without requiring an excessively large number of elements. 1 Introduction Largeeddysimulation (LES) generally aims at overcoming the scale disparity of turbulent flow by constructing models which de...
Physics and modeling of small scale turbulence for Large Eddy Simulation
"... An important open question for Large Eddy Simulation (LES) of turbulent flow is whether the subgridscales (smaller than \Delta) and the associated stresses can be described by universal models. This question is examined in terms of the subgrid dissipation rate, which represents the rate at which la ..."
Abstract
 Add to MetaCart
An important open question for Large Eddy Simulation (LES) of turbulent flow is whether the subgridscales (smaller than \Delta) and the associated stresses can be described by universal models. This question is examined in terms of the subgrid dissipation rate, which represents the rate at which largescale turbulent kinetic energy or scalar fluctuations are transferred to, or from, the unresolved scales. This variable is of central importance in LES. In order to ascertain the dependence of SGS dissipation upon large scales and the degree of universality of subgrid models, various high Reynolds number flows are studied. Hotwire data (yielding, so far, 1D surrogates only) in the turbulent plane wake (at ReD = 8 \Delta 10 4 ) shows that the phaseaveraged surrogate SGS dissipation rate is very much affected by the presence of coherent (K'arm'an) vortices which occur at scales much larger than the filter scale, and that the effect persists down to very small scales. Strong effects of...