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1

NASA Technical Reports Server (NTRS)

The principal objective is to extend the boundaries within which large eddy simulations (LES) and direct numerical simulations (DNS) can be applied in computational analyses of high speed reacting flows. A summary of work accomplished during the last six months is presented.

Givi, Peyman; Madnia, Cyrus K.; Steinberger, C. J.; Frankel, S. H.

1992-01-01

2

NASA Astrophysics Data System (ADS)

Conceptually simple and computationally most efficient polygonal computational grains with voids/inclusions are proposed for the direct numerical simulation of the micromechanics of piezoelectric composite/porous materials with non-symmetrical arrangement of voids/inclusions. These are named "Multi-Physics Computational Grains" (MPCGs) because each "mathematical grain" is geometrically similar to the irregular shapes of the physical grains of the material in the micro-scale. So each MPCG element represents a grain of the matrix of the composite and can include a pore or an inclusion. MPCG is based on assuming independent displacements and electric-potentials in each cell. The trial solutions in each MPCG do not need to satisfy the governing differential equations, however, they are still complete, and can efficiently model concentration of electric and mechanical fields. MPCG can be used to model any generally anisotropic material as well as nonlinear problems. The essential idea can also be easily applied to accurately solve other multi-physical problems, such as complex thermal-electro-magnetic-mechanical materials modeling. Several examples are presented to show the capabilities of the proposed MPCGs and their accuracy.

Bishay, Peter L.; Dong, Leiting; Atluri, Satya N.

2014-11-01

3

Numerical simulation of supersonic boundary layer transition

NASA Technical Reports Server (NTRS)

The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.

Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.

1994-01-01

4

Numerical simulation of turbulent jet primary breakup in Diesel engines

Numerical simulation of turbulent jet primary breakup in Diesel engines Peng Zeng1 Marcus Herrmann" IRMA Strasbourg, 23.Jan.2008 #12;Introduction DNS of Primary Breakup in Diesel Injection Phase Transition Modeling Turbulence Modeling Summary Outline 1 Introduction 2 DNS of Primary Breakup in Diesel

Helluy, Philippe

5

Predictive Inner-Outer Model for Turbulent Boundary Layers Applied to Hypersonic DNS Data

Predictive Inner-Outer Model for Turbulent Boundary Layers Applied to Hypersonic DNS Data Clara numerical simulation (DNS) data of supersonic and hypersonic turbulent boundaries with Mach 3 and Mach 7, and Martin12Â14 on DNS of hypersonic turbulent boundary layers demonstrates the existence of large scale

MartÃn, Pino

6

Direct Numerical Simulation of Turbulent Flows Using Spectral Methods

Direct Numerical Simulation of Turbulent Flows Using Spectral Methods K. Sengupta, and F. Mashayek University of Illinois at Chicago G. B. Jacobs, San Diego State University Direct numerical simulation (DNS categories: theory, physical experiments and numerical simulation. The explosive growth of computational

Jacobs, Gustaaf "Guus"

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Efficient Parallel Algorithm For Direct Numerical Simulation of Turbulent Flows

NASA Technical Reports Server (NTRS)

A distributed algorithm for a high-order-accurate finite-difference approach to the direct numerical simulation (DNS) of transition and turbulence in compressible flows is described. This work has two major objectives. The first objective is to demonstrate that parallel and distributed-memory machines can be successfully and efficiently used to solve computationally intensive and input/output intensive algorithms of the DNS class. The second objective is to show that the computational complexity involved in solving the tridiagonal systems inherent in the DNS algorithm can be reduced by algorithm innovations that obviate the need to use a parallelized tridiagonal solver.

Moitra, Stuti; Gatski, Thomas B.

1997-01-01

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Direct numerical simulation (DNS) has become a powerful tool in studying fundamental phenomena of laminar-turbulent transition of high-speed boundary layers. Previous DNS studies of supersonic and hypersonic boundary layer transition have been limited to perfect-gas flow over flat-plate boundary layers without shock waves. For hypersonic boundary layers over realistic blunt bodies, DNS studies of transition need to consider the effects

Xiaolin Zhong

1998-01-01

9

Direct numerical simulation of particle interaction with ejections in turbulent channel flows

Direct numerical simulations (DNS) of incompressible turbulent channel flows coupled with Lagrangian particle tracking are performed to study the characteristics of ejections that surround solid particles. The behavior of particles in dilute turbulent channel flows, without particle collisions and without feedback of particles on the carrier fluid, is studied using high Reynolds number DNS (Re=12,500). The results show that particles

I. Vinkovic; D. Doppler; J. Lelouvetel; M. Buffat

2011-01-01

10

Validation of a DNS code for wall-bounded turbulence including

in the reaction rates. In addition, the turbulent motion is enhanced by the exothermic reactions, while is dampedValidation of a DNS code for wall-bounded turbulence including finite-rate reactions and surface, and numerical methods for direct numerical simulation (DNS) of wall- bounded turbulence including finite-rate

MartÃn, Pino

11

numerical simulations of compressible turbulence Ellen M. Taylor, Minwei Wu, M. Pino MartiÂ´n * Department of stencil adaptation away from the linear optimal stencil. Direct numerical simulations (DNS) include a one. Keywords: Direct numerical simulation; Compressible turbulence; Shock capturing; Numerical dissipation; Non

MartÃn, Pino

12

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

The basic objective of this research is to extend the capabilities of Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows. In the efforts related to LES, we were primarily involved with assessing the performance of the various modern methods based on the Probability Density Function (PDF) methods for providing closures for treating the subgrid fluctuation correlations of scalar quantities in reacting turbulent flows. In the work on DNS, we concentrated on understanding some of the relevant physics of compressible reacting flows by means of statistical analysis of the data generated by DNS of such flows. In the research conducted in the second year of this program, our efforts focused on the modeling of homogeneous compressible turbulent flows by PDF methods, and on DNS of non-equilibrium reacting high speed mixing layers. Some preliminary work is also in progress on PDF modeling of shear flows, and also on LES of such flows.

Givi, P.; Madnia, C. K.; Steinberger, C. J.; Frankel, S. H.

1992-01-01

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Numerical Simulation of the Sound Radiated from a Turbulent Vortex Ring

Numerical Simulation of the Sound Radiated from a Turbulent Vortex Ring Hongyu Ran and Tim Colonius. Direct Numerical Simulations (DNS) of the fully compressible, three-dimensional Navier-Stokes equations of the dynamics of large-scale vortices in a turbulent jet. In particular, we use numerical simulations to study

Dabiri, John O.

14

Numerical simulations of dense clouds on steep slopes: Application to powdersnow avalanches

Numerical simulations of dense clouds on steep slopes: Application to powderÂsnow avalanches of Glaciology, vol. 38 Abstract In this paper twoÂdimensional Direct Numerical Simulations (DNS) of dense clouds in the laboratory. Direct numerical simulations give, in addition to the overall flow structure, local density

Saramito, Pierre

15

Numerical simulations of dense clouds on steep slopes: Application to powder-snow avalanches

Numerical simulations of dense clouds on steep slopes: Application to powder-snow avalanches of Glaciology, vol. 38 Abstract In this paper two-dimensional Direct Numerical Simulations (DNS) of dense clouds in the laboratory. Direct numerical simulations give, in addition to the overall flow structure, local density

Saramito, Pierre

16

PDF turbulence modeling and DNS

NASA Technical Reports Server (NTRS)

The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in probability density function (pdf). A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models. The effect of Coriolis forces on compressible homogeneous turbulence is studied using direct numerical simulation (DNS). The numerical method used in this study is an eight order compact difference scheme. Contrary to the conclusions reached by previous DNS studies on incompressible isotropic turbulence, the present results show that the Coriolis force increases the dissipation rate of turbulent kinetic energy, and that anisotropy develops as the Coriolis force increases. The Taylor-Proudman theory does apply since the derivatives in the direction of the rotation axis vanishes rapidly. A closer analysis reveals that the dissipation rate of the incompressible component of the turbulent kinetic energy indeed decreases with a higher rotation rate, consistent with incompressible flow simulations (Bardina), while the dissipation rate of the compressible part increases; the net gain is positive. Inertial waves are observed in the simulation results.

Hsu, A. T.

1992-01-01

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Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

This research is involved with the implementation of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program to extend the present capabilities of this method was initiated for the treatment of chemically reacting flows. In the DNS efforts, the focus is on detailed investigations of the effects of compressibility, heat release, and non-equilibrium kinetics modelings in high speed reacting flows. Emphasis was on the simulations of simple flows, namely homogeneous compressible flows, and temporally developing high speed mixing layers.

Givi, Peyman; Madnia, Cyrus K.; Steinberger, Craig J.

1990-01-01

18

Applications of direct numerical simulation of turbulence in second order closures

NASA Technical Reports Server (NTRS)

This paper discusses two methods of developing models for the rapid pressure-strain correlation term in the Reynolds stress transport equation using direct numerical simulation (DNS) data. One is a perturbation about isotropic turbulence, the other is a perturbation about two-component turbulence -- an extremely anisotropic turbulence. A model based on the latter method is proposed and is found to be very promising when compared with DNS data and other models.

Shih, Tsan-Hsing; Lumley, John L.

1995-01-01

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Direct Numerical Simulation of a Hypersonic Turbulent Boundary Layer on a Large Domain

Direct Numerical Simulation of a Hypersonic Turbulent Boundary Layer on a Large Domain Stephan Priebe , M. Pino MartÂ´in The direct numerical simulation (DNS) of a spatially-developing hypersonic There are few studies of hypersonic flows at Mach number greater than 5 and few involve the measurement of mean

MartÃn, Pino

20

discretization. In this work, a novel coupled direct numerical simulation DNS -LES a posteriori method is usedA posteriori analysis of numerical errors in subfilter scalar variance modeling for large eddy simulation C. M. Kaula and V. Raman Department of Aerospace Engineering and Engineering Mechanics

Raman, Venkat

21

Equations for direct numerical simulation of sound propagation in a moving atmosphere

Most previous analytical and numerical studies of sound propagation in a moving atmosphere have been based on wave equations for the sound pressure and on various parabolic approximations to the wave equations. However, these equations cannot be used as starting equations for recently proposed direct numerical simulation (DNS) of sound propagation outdoor since such starting equations should be first-order differential

Vladimir E. Ostashev; Lanbo Liu; D. Keith Wilson; Mark L. Moran; David F. Aldridge; David Marlin

2003-01-01

22

Using DNS to Understand Aerosol Dynamics

NASA Astrophysics Data System (ADS)

In recent years, direct numerical simulations (DNS) have been increasingly used to investigate aerosol processes in turbulent flows. Most of these studies are based on solving the fluid velocity on an Eulerian mesh and tracking the particles in a Lagrangian frame of reference, with appropriate interpolation to bring the two representations together. We have used simulations of this kind to study turbulent coagulation of particles with small, but finite inertia. Inertia causes particles to cluster outside regions of high rotation (Maxey 1987), causing the collision frequency to increase by as much as two orders of magnitude. An effect of this size has profound implications for a broad range of aerosol processes, from the growth of nucleated water droplets in a cloud to powder manufacturing processes. Earlier work has shown that the effect of clustering on collision is captured by the two-particle radial distribution function (RDF) evaluated at contact. We have used DNS to systematically explore the dependence of the RDF on the particle Stokes number (ratio of particle response time to the Kolmogorov time scale), size parameter (ratio of the particle diameter to the Kolmogorov length scale) and Reynolds number. We will summarize those findings. In the latter part of the talk, we will discuss recent experiments by H. Meng's group using holographic imaging to determine the three-dimensional position of suspended particles in a turbulence box. We will show comparisons between the DNS and the experimentally measured RDF.

Collins, Lance

2003-11-01

23

Direct Numerical Simulations of Multiphase Flows

NASA Astrophysics Data System (ADS)

Many natural and industrial processes, such as rain and gas exchange between the atmosphere and oceans, boiling heat transfer, atomization and chemical reactions in bubble columns, involve multiphase flows. Often the mixture can be described as a disperse flow where one phase consists of bubbles or drops. Direct numerical simulations (DNS) of disperse flow have recently been used to study the dynamics of multiphase flows with a large number of bubbles and drops, often showing that the collective motion results in relatively simple large-scale structure. Here we review simulations of bubbly flows in vertical channels where the flow direction, as well as the bubble deformability, has profound implications on the flow structure and the total flow rate. Results obtained so far are summarized and open questions identified. The resolution for DNS of multiphase flows is usually determined by a dominant scale, such as the average bubble or drop size, but in many cases much smaller scales are also present. These scales often consist of thin films, threads, or tiny drops appearing during coalescence or breakup, or are due to the presence of additional physical processes that operate on a very different time scale than the fluid flow. The presence of these small-scale features demand excessive resolution for conventional numerical approaches. However, at small flow scales the effects of surface tension are generally strong so the interface geometry is simple and viscous forces dominate the flow and keep it simple also. These are exactly the conditions under which analytical models can be used and we will discuss efforts to combine a semi-analytical description for the small-scale processes with a fully resolved simulation of the rest of the flow. We will, in particular, present an embedded analytical description to capture the mass transfer from bubbles in liquids where the diffusion of mass is much slower than the diffusion of momentum. This results in very thin mass-boundary layers that are difficult to resolve, but the new approach allows us to simulate the mass transfer from many freely evolving bubbles and examine the effect of the interactions of the bubbles with each other and the flow. We will conclude by attempting to summarize the current status of DNS of multiphase flows.

Tryggvason, Gretar

2013-03-01

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We present a purely-radiative hydrodynamic model of the kappa-mechanism that sustains radial oscillations in Cepheid variables. We determine the physical conditions favourable for the kappa-mechanism to occur by the means of a configurable hollow in the radiative conductivity profile. By starting from these most favourable conditions, we complete nonlinear direct numerical simulations (DNS) and compare them with the results given by a linear-stability analysis of radial modes. We find that well-defined instability strips are generated by changing the location and shape of the conductivity hollow. For a given position in the layer, the hollow amplitude and width stand out as the key parameters governing the appearance of unstable modes driven by the kappa-mechanism. The DNS confirm both the growth rates and structures of the linearly-unstable modes. The nonlinear saturation that arises is produced by intricate couplings between the excited fundamental mode and higher damped overtones. These couplings are measured by projecting the DNS fields onto an acoustic subspace built from regular and adjoint eigenvectors and a 2:1 resonance is found to be responsible for the saturation of the kappa-mechanism instability.

T. Gastine; B. Dintrans

2008-09-29

25

CoDNS: Improving DNS Performance and Reliability via Cooperative Lookups

The Domain Name System (DNS) is a ubiquitous part of everyday computing, translating human-friendly ma- chine names to numeric IP addresses. Most DNS re- search has focused on server-side infrastructure, with the assumption that the aggressive caching and redundancy on the client side are sufficient. However, through sys- tematic monitoring, we find that client-side DNS fail- ures are widespread and

Vivek S. Pai; Larry L. Peterson; Zhe Wang

2004-01-01

26

DNS Study of spatial discrete suction for Laminar Flow Control

By means of spatial direct numerical simulations (DNS) based on the complete Navier-Stokes equations the effect of three-dimensional\\u000a discrete suction on the spatial development of a laminar boundary-layer flow generic for the front part of a swept-back airliner\\u000a wing has been investigated. The baseflow is an accelerated Falkner-Skan-Cooke boundary layer, on a swept wedge with semi-opening\\u000a angle of 45 (Hartree

Ralf Messing; Markus Kloker

27

Direct Numerical Simulation of Tilted Rayleigh-Taylor Instability

NASA Astrophysics Data System (ADS)

The tilted Rayleigh-Taylor instability, where the initial interface is not perpendicular to the driving acceleration, is investigated using Direct Numerical Simulations (DNS). In this configuration, the inclination of the initial interface results in a large-scale overturning motion in addition to the buoyancy driven instability. The DNS results are compared to the rocket-rig experiments of Smeeton and Youngs (AWE Report No. 35/87) at several Atwood numbers (A=0.267, 0.48, and 0.90). Since the initial conditions in these experiments are largely unknown, an extensive range of initial conditions have been explored to match the mixing layer growth between DNS and experiments. The evolution of the mixing layer was found to be strongly influenced, for the duration of the experiments, by the initial spectrum shape and peak location, as well as the perturbation amplitude. A set of initial conditions matching the experimental growth rates has been determined. Results are also presented on the interaction between shear and buoyancy, including the parameters influencing the overturning and mixing.

Wei, Tie; Livescu, Daniel

2011-11-01

28

NASA Astrophysics Data System (ADS)

Context: We study the ?-mechanism that excites radial oscillations in Cepheid variables. Aims: We address the mode couplings that manage the nonlinear saturation of the instability in direct numerical simulations (DNS). Methods: We project the DNS fields onto an acoustic subspace built from the regular and adjoint eigenvectors that are solutions to the linear oscillation equations. Results: We determine the time evolution of both the amplitude and kinetic energy of each mode that propagates in the DNS. More than 98% of the total kinetic energy is contained in two modes that correspond to the linearly-unstable fundamental mode and the linearly-stable second overtone. Because the eigenperiod ratio is close to 1/2, we discover that the nonlinear saturation is due to a 2:1 resonance between these two modes. An interesting application of this result concerns the reproduction of Hertzsprung's progression observed in Bump Cepheids.

Gastine, T.; Dintrans, B.

2008-11-01

29

Double-diffusive interfaces in Lake Kivu reproduced by direct numerical simulations

NASA Astrophysics Data System (ADS)

diffusion transforms uniform background gradients of temperature and salinity into "staircases" of homogeneous mixed layers that are separated by high-gradient interfaces. Direct numerical simulations (DNS) and microstructure measurements are two independent methods of estimating double-diffusive fluxes. By performing DNS under similar conditions as found in our measurements in Lake Kivu, we are able to compare results from both methods for the first time. We find that (i) the DNS reproduces the measured interface thicknesses of in situ microstructure profiles, (ii) molecular heat fluxes through interfaces capture the total vertical heat fluxes for density ratios larger than three, and (iii) the commonly used heat flux parameterization underestimates the total fluxes by a factor of 1.3 to 2.2.

Sommer, Tobias; Carpenter, Jeffrey R.; Wüest, Alfred

2014-07-01

30

Entropy Splitting for High Order Numerical Simulation of Compressible Turbulence

NASA Technical Reports Server (NTRS)

A stable high order numerical scheme for direct numerical simulation (DNS) of shock-free compressible turbulence is presented. The method is applicable to general geometries. It contains no upwinding, artificial dissipation, or filtering. Instead the method relies on the stabilizing mechanisms of an appropriate conditioning of the governing equations and the use of compatible spatial difference operators for the interior points (interior scheme) as well as the boundary points (boundary scheme). An entropy splitting approach splits the inviscid flux derivatives into conservative and non-conservative portions. The spatial difference operators satisfy a summation by parts condition leading to a stable scheme (combined interior and boundary schemes) for the initial boundary value problem using a generalized energy estimate. A Laplacian formulation of the viscous and heat conduction terms on the right hand side of the Navier-Stokes equations is used to ensure that any tendency to odd-even decoupling associated with central schemes can be countered by the fluid viscosity. A special formulation of the continuity equation is used, based on similar arguments. The resulting methods are able to minimize spurious high frequency oscillation producing nonlinear instability associated with pure central schemes, especially for long time integration simulation such as DNS. For validation purposes, the methods are tested in a DNS of compressible turbulent plane channel flow at a friction Mach number of 0.1 where a very accurate turbulence data base exists. It is demonstrated that the methods are robust in terms of grid resolution, and in good agreement with incompressible channel data, as expected at this Mach number. Accurate turbulence statistics can be obtained with moderate grid sizes. Stability limits on the range of the splitting parameter are determined from numerical tests.

Sandham, N. D.; Yee, H. C.; Kwak, Dochan (Technical Monitor)

2000-01-01

31

Numerical Aerodynamic Simulation (NAS)

NASA Technical Reports Server (NTRS)

The history of the Numerical Aerodynamic Simulation Program, which is designed to provide a leading-edge capability to computational aerodynamicists, is traced back to its origin in 1975. Factors motivating its development and examples of solutions to successively refined forms of the governing equations are presented. The NAS Processing System Network and each of its eight subsystems are described in terms of function and initial performance goals. A proposed usage allocation policy is discussed and some initial problems being readied for solution on the NAS system are identified.

Peterson, V. L.; Ballhaus, W. F., Jr.; Bailey, F. R.

1983-01-01

32

DNS of partially premixed flame propagating in a turbulent rotating flow

The propagation of non-premixed and premixed flames in a turbulent rotating flow is studied. A synthetic Direct Numerical Simulation (DNS) model problem is proposed in which a turbulent columnar vortex interacts with an initially planar and stoichiometric premixed flame. Various cases are obtained by varying the characteristic circumferential velocity of the vortex and the incoming fuel and air distribution. Turbulent

Pascale Domingo; Luc Vervisch

2007-01-01

33

NASA Technical Reports Server (NTRS)

Transitional databases from Direct Numerical Simulation (DNS) of three-dimensional mixing layers for single-phase flows and two-phase flows with evaporation are analyzed and used to examine the typical hypothesis that the scalar dissipation Probability Distribution Function (PDF) may be modeled as a Gaussian. The databases encompass a single-component fuel and four multicomponent fuels, two initial Reynolds numbers (Re), two mass loadings for two-phase flows and two free-stream gas temperatures. Using the DNS calculated moments of the scalar-dissipation PDF, it is shown, consistent with existing experimental information on single-phase flows, that the Gaussian is a modest approximation of the DNS-extracted PDF, particularly poor in the range of the high scalar-dissipation values, which are significant for turbulent reaction rate modeling in non-premixed flows using flamelet models. With the same DNS calculated moments of the scalar-dissipation PDF and making a change of variables, a model of this PDF is proposed in the form of the (beta)-PDF which is shown to approximate much better the DNS-extracted PDF, particularly in the regime of the high scalar-dissipation values. Several types of statistical measures are calculated over the ensemble of the fourteen databases. For each statistical measure, the proposed (beta)-PDF model is shown to be much superior to the Gaussian in approximating the DNS-extracted PDF. Additionally, the agreement between the DNS-extracted PDF and the (beta)-PDF even improves when the comparison is performed for higher initial Re layers, whereas the comparison with the Gaussian is independent of the initial Re values. For two-phase flows, the comparison between the DNS-extracted PDF and the (beta)-PDF also improves with increasing free-stream gas temperature and mass loading. The higher fidelity approximation of the DNS-extracted PDF by the (beta)-PDF with increasing Re, gas temperature and mass loading bodes well for turbulent reaction rate modeling.

Selle, L. C.; Bellan, Josette

2006-01-01

34

Direct numerical simulation of turbulent reacting flows

The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.

Chen, J.H. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

35

Validation of Direct Numerical Simulations in 3D pore geometries and Large-Eddy Simulations

NASA Astrophysics Data System (ADS)

Numerical solutions of the Navier-Stokes Equations became more popular in recent decades with increasingly accessible and powerful computational resources. Simulations in reconstructed or artificial pore geometries are often performed to gain insight into microscopic fluid flow structures or are used for upscaling quantities of interest, like hydraulic conductivity. A physically adequate representation of pore scale flow fields requires analysis of large domains in combination with turbulence models. We solve incompressible Navier-Stokes Equations in a cubic lattice and cubic close packing of spheres placed in a square duct with Direct Numerical Simulations (DNS) and analyze the validity of the results. The influence of the number of spheres and mesh discretization is investigated for fluid flow up to Reynolds numbers of 5000 based on the spheres' diameter. The numerical simulations are performed with the OpenFOAM open-source CFD software. We statistically investigate spatial and temporal properties of the resulting fluid flow field and its kinetic energy spectra, and compare them to Large-Eddy Simulations (LES) performed for the same geometries. Differences between the DNS and LES are discussed together with upscaled hydraulic properties with respect to the number of spheres and the Reynolds number.

Naumov, Dmitri

2013-04-01

36

The present study addresses the capability of a large set of shock-capturing schemes to recover the basic interactions between acoustic, vorticity and entropy in a direct numerical simulation (DNS) framework. The basic dispersive and dissipative errors are first evaluated by considering the advection of a Taylor vortex in a uniform flow. Two transonic cases are also considered. The first one

C. Tenaud; E. Garnier; P. Sagaut

2000-01-01

37

Direct Numerical Simulation of a Weakly Stratified Turbulent Wake

NASA Technical Reports Server (NTRS)

Direct numerical simulation (DNS) is used to investigate a time-dependent turbulent wake evolving in a stably stratified background. A large initial Froude number is chosen to allow the wake to become fully turbulent and axisymmetric before stratification affects the spreading rate of the mean defect. The uncertainty introduced by the finite sample size associated with gathering statistics from a simulation of a time-dependent flow is reduced, compared to earlier simulations of this flow. The DNS reveals the buoyancy-induced changes to the turbulence structure, as well as to the mean-defect history and the terms in the mean-momentum and turbulence-kinetic-energy budgets, that characterize the various states of this flow - namely the three-dimensional (essentially unstratified), non-equilibrium (or 'wake-collapse') and quasi-two-dimensional (or 'two-component') regimes observed elsewhere for wakes embedded in both weakly and strongly stratified backgrounds. The wake-collapse regime is not accompanied by transfer (or 'reconversion') of the potential energy of the turbulence to the kinetic energy of the turbulence, implying that this is not an essential feature of stratified-wake dynamics. The dependence upon Reynolds number of the duration of the wake-collapse period is demonstrated, and the effect of the details of the initial/near-field conditions of the wake on its subsequent development is examined.

Redford, J. A.; Lund, T. S.; Coleman, Gary N.

2014-01-01

38

DNS of aerosol evolution in a turbulent jet

NASA Astrophysics Data System (ADS)

The effects of turbulence on the evolution of aerosols are not well understood. In this work, the interaction of aerosol dynamics and turbulence are studied in a canonical flow configuration by numerical means. The configuration consists of a hot nitrogen stream saturated with dibutyl phthalate (DBP) vapor mixing with cool air in a shear layer. A direct numerical simulation (DNS) for the momentum and scalar fields is coupled with the direct quadrature method of moments (DQMOM) for the condensing liquid phase. The effects of turbulent mixing on aerosol processes (nucleation, condensation, and coagulation) are quantified by analyzing the statistics of number density and droplet sizes.

Zhou, Kun; Attili, Antonio; Bisetti, Fabrizio

2011-11-01

39

Turbulence analysis of rough wall channel flows based on direct numerical simulation

Direct numerical simulation (DNS) of rough wall channel flows was performed for various surface roughnesses. The goal of the presented research is to investigate the effect of nucleating bubbles in subcooled boiling conditions on the turbulence. The nucleating bubbles are represented by hemispherical roughness elements at the wall. The stabilized finite element based code, PHASTA, is used to perform the simulations. Validation against theoretical, experimental and numerical data is performed for smooth channel flow and rectangular rod type of roughness. The presence of roughness elements affects the flow structure within the roughness sublayer, which is estimated to be 5 times the height of roughness elements. DNS observations are consistent with this result and demonstrate the flow homogeneity above 50 viscous units. The influence of roughness elements layout and density on the turbulence parameters is also demonstrated and analyzed. (authors)

Mishra, A. V.; Bolotnov, I. A. [Dept. of Nuclear Engineering, North Carolina State Univ., Campus Box 7909, Raleigh, NC 27695-7909 (United States)

2012-07-01

40

Resilience of helical fields to turbulent diffusion - II. Direct numerical simulations

NASA Astrophysics Data System (ADS)

Blackman and Subramanian (Paper I) found that sufficiently strong large-scale helical magnetic fields are resilient to turbulent diffusion, decaying on resistively slow rather than turbulently fast time-scales. This bolsters fossil field origins for magnetic fields in some astrophysical objects. Here, we study direct numerical simulations (DNS) of decaying large-scale helical magnetic fields in the presence of non-helical turbulence for two cases: (1) the initial helical field is large enough to decay resistively but transitions to fast decay; (2) the case of Paper I, wherein the transition energy for the initial helical field to decay fast directly is sought. Simulations and two-scale modelling (based on Paper 1) reveal the transition energy, Ec1 to be independent of the turbulent forcing scale, within a small range of RM. For case (2), the two-scale theory predicts a large-scale helical transition energy of Ec2 = (k1/kf)2Meq, where k1 and kf are the large-scale and small turbulent forcing scale, respectively, and Meq is the equipartition magnetic energy. The DNS agree qualitatively with this prediction but the RM, currently achievable, is too small to satisfy a condition 3/RM ? (k1/kf)2, necessary to robustly reveal the transition, Ec2. That two-scale theory and DNS agree wherever they can be compared suggests that Ec2 of Paper I should be identifiable at higher RM in DNS.

Bhat, Pallavi; Blackman, Eric G.; Subramanian, Kandaswamy

2014-03-01

41

Direct numerical simulation of compressible homogeneous turbulence using natural initial conditions

NASA Astrophysics Data System (ADS)

Reynolds averaged Navier Stokes (RANS) solvers have become the workhorse for simulating turbulent flows for most practical purposes. While the incompressible turbulence models used with RANS equations have improved considerably in their predictive capability, significant breakthrough has not been achieved for their compressible counterparts. With the advancement in computing power, high resolution direct numerical simulation (DNS) of low Reynolds number turbulent flows has become feasible. DNS of simple turbulent flows provides a detailed database which can be used for developing and testing turbulence models. In this work, we perform DNS of compressible homogeneous turbulence---decaying isotropic turbulence and homogeneous shear flow---for a range of initial turbulent Mach numbers, (Mt 0 = 0.05--0.4) using the more natural initial conditions. Simulations were performed on grids with 1283 and 2563 points. Compressibility effects on the evolution of turbulent kinetic energy were studied. We found negligible compressibility effects for decaying isotropic turbulence, while homogeneous shear flow demonstrated compressibility effects in the growth rate of turbulent kinetic energy. Compressibility corrections to turbulence models in the form of the ratio epsilond/epsilon s, have been tested with the results from the simulations. For decaying isotropic turbulence a M4t scaling was found to be better than M2t while for homogeneous shear flow it was the opposite. The small value of the ratio epsilond/epsilons in decaying isotropic turbulence makes the M4t scaling less relevant. Based on the DNS results of homogeneous shear flow, a new correction parameterized by the gradient Mach number, Mg, is proposed. The parameter Cmu, which is assumed constant for incompressible two equation eddy viscosity models, is computed explicitly from the DNS data. An Mg, dependence of the parameter, Cmu, is proposed.

Bhutoria, Vaibhav

42

Direct numerical simulations of supercritical fluid mixing layers applied to heptane{nitrogen

Direct numerical simulations (DNS) are conducted of a model hydrocarbon{nitrogen mixing layer under supercritical conditions. The temporally developing mixing layer conguration is studied using heptane and nitrogen supercritical fluid streams at a pressure of 60 atm as a model system related to practical hydrocarbon-fuel\\/air systems. An entirely self-consistent cubic Peng{Robinson equation of state is used to describe all thermodynamic mixture

JOSETTE B ELLAN

2001-01-01

43

In spite of the availability of DNSSEC, which protects against cache poisoning even by MitM attackers, many caching DNS resolvers still rely for their security against poisoning on merely validating that DNS responses contain some 'unpredictable' values, copied from the re- quest. These values include the 16 bit identifier field, and other fields, randomised and validated by different 'patches' to DNS. We investigate the prominent patches, and show how attackers can circumvent all of them, namely: - We show how attackers can circumvent source port randomisation, in the (common) case where the resolver connects to the Internet via different NAT devices. - We show how attackers can circumvent IP address randomisation, using some (standard-conforming) resolvers. - We show how attackers can circumvent query randomisation, including both randomisation by prepending a random nonce and case randomisation (0x20 encoding). We present countermeasures preventing our attacks; however, we believe that our attacks provide ...

Herzberg, Amir

2012-01-01

44

DepenDNS: Dependable Mechanism against DNS Cache Poisoning

NASA Astrophysics Data System (ADS)

DNS cache poisoning attacks have been proposed for a long time. In 2008, Kaminsky enhanced the attacks to be powerful based on nonce query method. By leveraging Kaminsky's attack, phishing becomes large-scale since victims are hard to detect attacks. Hence, DNS cache poisoning is a serious threat in the current DNS infrastructure. In this paper, we propose a countermeasure, DepenDNS, to prevent from cache poisoning attacks. DepenDNS queries multiple resolvers concurrently to verify an trustworthy answer while users perform payment transactions, e.g., auction, banking. Without modifying any resolver or authority server, DepenDNS is conveniently deployed on client side. In the end of paper, we conduct several experiments on DepenDNS to show its efficiency. We believe DepenDNS is a comprehensive solution against cache poisoning attacks.

Sun, Hung-Min; Chang, Wen-Hsuan; Chang, Shih-Ying; Lin, Yue-Hsun

45

Numerical Simulations in Cosmology I

The purpose of these lectures is to give a short introduction into a very vast field of numerical simulations for cosmological applications. I focus on major features of the simulations: the equations, main numerical techniques, effects of resolution, and methods of halo identification.

A. Klypin

1996-05-29

46

Direct Numerical Simulations of a Stratified Self-Propelled Wake

NASA Astrophysics Data System (ADS)

Direct Numerical Simulations (DNS) of a self-propelled wake subject to stratification are utilized to study the characteristics of the mean flow and turbulence fluctuations in the wake. Results include wake height, wake width, peak defect velocity, r.m.s. velocity fluctuations and turbulent fluxes, < uiuj> and

Brucker, Kyle; Sarkar, Sutanu

2007-11-01

47

DNS of the kappa-mechanism. I. Radial modes in the purely radiative case

Context: Hydrodynamical model of the kappa-mechanism in a purely radiative case. Aims: First, to determine the physical conditions propitious to kappa-mechanism in a layer with a configurable conductivity hollow and second, to perform the (nonlinear) direct numerical simulations (DNS) from the most favourable setups. Methods: A linear stability analysis applied to radial modes using a spectral solver and DNS thanks to a high-order finite difference code are compared. Results: Changing the hollow properties (location and shape) lead to well-defined instability strips. For a given position in the layer, the amplitude and width of the hollow appear to be the key parameters to get unstable modes driven by kappa-mechanism. The DNS achieved from these more auspicious configurations confirm the growth rates as well as structures of linearly unstable modes. The nonlinear saturation follows through intricate couplings between the excited fundamental mode and higher damped overtones.

T. Gastine; B. Dintrans

2007-11-08

48

The mechanism of large-scale dynamos in rigidly rotating stratified convection is explored by direct numerical simulations (DNS) in Cartesian geometry. A mean-field dynamo model is also constructed using turbulent velocity profiles consistently extracted from the corresponding DNS results. By quantitative comparison between the DNS and our mean-field model, it is demonstrated that the oscillatory $\\alpha^2$ dynamo wave, excited and sustained in the convection zone, is responsible for large-scale magnetic activities such as cyclic polarity reversal and spatiotemporal migration. The results provide strong evidence that a nonuniformity of the $\\alpha$-effect, which is a natural outcome of rotating stratified convection, can be an important prerequisite for large-scale stellar dynamos, even without the $\\Omega$-effect.

Masada, Youhei

2014-01-01

49

NASA Astrophysics Data System (ADS)

The mechanism of large-scale dynamos in rigidly rotating stratified convection is explored by direct numerical simulations (DNS) in Cartesian geometry. A mean-field dynamo model is also constructed using turbulent velocity profiles consistently extracted from the corresponding DNS results. By quantitative comparison between the DNS and our mean-field model, it is demonstrated that the oscillatory ?2 dynamo wave, excited and sustained in the convection zone, is responsible for large-scale magnetic activities such as cyclic polarity reversal and spatiotemporal migration. The results provide strong evidence that a nonuniformity of the ?-effect, which is a natural outcome of rotating stratified convection, can be an important prerequisite for large-scale stellar dynamos, even without the ?-effect.

Masada, Youhei; Sano, Takayoshi

2014-10-01

50

Numerical simulations in turbomachinery

The continued increase in the complexity of modern turbomachinery designs dictates greater reliance computer simulations to analyze their flow fields and hardware. Turbomachinery flows are complicated by three dimensional effects, viscous-inviscid interactions, complex shock structures in transonic machines, and the injected coolant flows in gas turbines. It is important to be able to capture the complex flow structures associated with

Hamed

1991-01-01

51

Numerical simulation of hydraulic fracturing

NUMERICAL SIMULATION OF HYDRAULIC FRACTURING A Thesis by JOSEPH BARNES WARNER Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 1987 Maj or Subj ect...: Petroleum Engineering NUMERICAL SIMULATION OF HYDRAULIC FRACTURING A Thesis by JOSEPH BARNES WARNER Approved as to style and content by: S. A. Holditch (Chairman of Committee) D. D. Van Fleet (member) J. E. Russell (m be ) W. D. Von onten ( ead...

Warner, Joseph Barnes

2012-06-07

52

Numerical simulation of Bootstrap Current

The neoclassical theory of Bootstrap Current in toroidal systems is calculated in magnetic flux coordinates and confirmed by numerical simulation. The effects of magnetic ripple, loop voltage, and magnetic and electrostatic perturbations on bootstrap current for the cases of zero and finite plasma pressure are studied. The numerical results are in reasonable agreement with analytical estimates.

Wu, Yanlin; White, R.B.

1993-05-01

53

Numerical simulations of galaxy formation

The current status of numerical simulations of galaxy formation is reviewed. After a short description of the main numerical simulation techniques, three sample applications illustrate how numerical simulations have provided deeper insight in the galaxy formation process and how they have illuminated success and failure of the hierarchical galaxy formation paradigm: N-body simulations demonstrate that the density profiles of dark matter halos that form in hierarchical clustering scenarios follow a characteristic law. A comparison with the kinematics of disk galaxies however unravels that these density profiles are too concentrated. Hydrodynamical simulation show that the highly irregular velocity field of merging subclumps at redshift $z\\approx 3$ can easily account for the observed asymmetry in the absorption profiles of low ionization species in damped \\Lya absorption systems. The built-up of galaxies due to mergers is however also cause for one of the major inconsistencies of hierarchical structure formati...

Steinmetz, M

1999-01-01

54

Estimating uncertainties in statistics computed from direct numerical simulation

NASA Astrophysics Data System (ADS)

Rigorous assessment of uncertainty is crucial to the utility of direct numerical simulation (DNS) results. Uncertainties in the computed statistics arise from two sources: finite statistical sampling and the discretization of the Navier-Stokes equations. Due to the presence of non-trivial sampling error, standard techniques for estimating discretization error (such as Richardson extrapolation) fail or are unreliable. This work provides a systematic and unified approach for estimating these errors. First, a sampling error estimator that accounts for correlation in the input data is developed. Then, this sampling error estimate is used as part of a Bayesian extension of Richardson extrapolation in order to characterize the discretization error. These methods are tested using the Lorenz equations and are shown to perform well. These techniques are then used to investigate the sampling and discretization errors in the DNS of a wall-bounded turbulent flow at Re? ? 180. Both small (Lx/? × Lz/? = 4? × 2?) and large (Lx/? × Lz/? = 12? × 4?) domain sizes are investigated. For each case, a sequence of meshes was generated by first designing a "nominal" mesh using standard heuristics for wall-bounded simulations. These nominal meshes were then coarsened to generate a sequence of grid resolutions appropriate for the Bayesian Richardson extrapolation method. In addition, the small box case is computationally inexpensive enough to allow simulation on a finer mesh, enabling the results of the extrapolation to be validated in a weak sense. For both cases, it is found that while the sampling uncertainty is large enough to make the order of accuracy difficult to determine, the estimated discretization errors are quite small. This indicates that the commonly used heuristics provide adequate resolution for this class of problems. However, it is also found that, for some quantities, the discretization error is not small relative to sampling error, indicating that the conventional wisdom that sampling error dominates discretization error for this class of simulations needs to be reevaluated.

Oliver, Todd A.; Malaya, Nicholas; Ulerich, Rhys; Moser, Robert D.

2014-03-01

55

NUMERICAL SIMULATION OF A STROKE : NUMERICAL PROBLEMS AND METHODOLOGY

NUMERICAL SIMULATION OF A STROKE : NUMERICAL PROBLEMS AND METHODOLOGY STÂ´EPHANE DESCOMBES dimensional more realistic simulations 16 7. Conclusion 16 References 16 1. Introduction The numerical simulation of a stroke is a challenging problem, with many sources of numerical difficulties: a complex

Boyer, Edmond

56

Numerical simulations of solar macrospicules

NASA Astrophysics Data System (ADS)

Context. We consider a localized pulse in the component of velocity, parallel to the ambient magnetic field lines, that is initially launched in the solar chromosphere. Aims: We aim to generalize our recent numerical model of spicule formation by implementing a VAL-C model of solar temperature. Methods: With the use of the code FLASH we solve two-dimensional ideal magnetohydrodynamic equations numerically to simulate the solar macrospicules. Results: Our numerical results reveal that the pulse located below the transition region triggers plasma perturbations, which exhibit many features of macrospicules. We also present an observational (SDO/AIA 304 Å) case study of the macrospicule that approximately mimics the numerical simulations. Conclusions: In the frame of the model we devised, the solar macrospicules can be triggered by velocity pulses launched from the chromosphere.

Murawski, K.; Srivastava, A. K.; Zaqarashvili, T. V.

2011-11-01

57

NASA Astrophysics Data System (ADS)

High resolution direct numerical simulations (DNS) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier-Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two, and three-dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring mesh performance in capturing the range of dynamics. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. Use of discontinuous discretisations and adaptive unstructured meshing technologies, which reduce the required element count by approximately two orders of magnitude, results in high resolution DNS models of turbidity currents at a fraction of the cost of traditional FE models. The benefits of this technique will enable simulation of turbidity currents in complex and large domains where DNS modelling was previously unachievable.

Parkinson, S. D.; Hill, J.; Piggott, M. D.; Allison, P. A.

2014-05-01

58

Numerical simulation of turbulent duct flows with constant power input

The numerical simulation of a flow through a duct requires an externally specified forcing that makes the fluid flow against viscous friction. To this aim, it is customary to enforce a constant value for either the flow rate (CFR) or the pressure gradient (CPG). When comparing a laminar duct flow before and after a geometrical modification that induces a change of the viscous drag, both approaches (CFR and CPG) lead to a change of the power input across the comparison. Similarly, when carrying out the (DNS and LES) numerical simulation of unsteady turbulent flows, the power input is not constant over time. Carrying out a simulation at constant power input (CPI) is thus a further physically sound option, that becomes particularly appealing in the context of flow control, where a comparison between control-on and control-off conditions has to be made. We describe how to carry out a CPI simulation, and start with defining a new power-related Reynolds number, whose velocity scale is the bulk flow that can be atta...

Hasegawa, Yosuke; Frohnapfel, Bettina

2014-01-01

59

A review of direct numerical simulations of astrophysical detonations and their implications

NASA Astrophysics Data System (ADS)

Multi-dimensional direct numerical simulations (DNS) of astrophysical detonations in degenerate matter have revealed that the nuclear burning is typically characterized by cellular structure caused by transverse instabilities in the detonation front. Type Ia supernova modelers often use onedimensional DNS of detonations as inputs or constraints for their whole star simulations.While these one-dimensional studies are useful tools, the true nature of the detonation is multi-dimensional. The multi-dimensional structure of the burning influences the speed, stability, and the composition of the detonation and its burning products, and therefore, could have an impact on the spectra of Type Ia supernovae. Considerable effort has been expended modeling Type Ia supernovae at densities above 1×107 g·cm-3 where the complexities of turbulent burning dominate the flame propagation. However, most full star models turn the nuclear burning schemes off when the density falls below 1×107 g·cm-3 and distributed burning begins. The deflagration to detonation transition (DDT) is believed to occur at just these densities and consequently they are the densities important for studying the properties of the subsequent detonation. This work will review the status of DNS studies of detonations and their possible implications for Type Ia supernova models. It will cover the development of Detonation theory from the first simple Chapman-Jouguet (CJ) detonation models to the current models based on the time-dependent, compressible, reactive flow Euler equations of fluid dynamics.

Parete-Koon, Suzanne T.; Smith, Christopher R.; Papatheodore, Thomas L.; Bronson Messer, O. E.

2013-04-01

60

A Review of Direct Numerical Simulations of Astrophysical Detonations and Their Implications

Multi-dimensional direct numerical simulations (DNS) of astrophysical detonations in degenerate matter have revealed that the nuclear burning is typically characterized by cellular structure caused by transverse instabilities in the detonation front. Type Ia supernova modelers often use one- dimensional DNS of detonations as inputs or constraints for their whole star simulations. While these one-dimensional studies are useful tools, the true nature of the detonation is multi-dimensional. The multi-dimensional structure of the burning influences the speed, stability, and the composition of the detonation and its burning products, and therefore, could have an impact on the spectra of Type Ia supernovae. Considerable effort has been expended modeling Type Ia supernovae at densities above 1 107 g cm 3 where the complexities of turbulent burning dominate the flame propagation. However, most full star models turn the nuclear burning schemes off when the density falls below 1 107 g cm 3 and distributed burning begins. The deflagration to detonation transition (DDT) is believed to occur at just these densities and consequently they are the densities important for studying the properties of the subsequent detonation. This work will review the status of DNS studies of detonations and their possible implications for Type Ia supernova models. It will cover the development of Detonation theory from the first simple Chapman-Jouguet (CJ) detonation models to the current models based on the time-dependent, compressible, reactive flow Euler equations of fluid dynamics.

Parete-Koon, Suzanne T [ORNL; Messer, Bronson [ORNL; Smith, Chris R [ORNL; Papatheodore, Thomas L [ORNL

2013-01-01

61

Turbulent flame-wall interaction: a DNS study

A turbulent flame-wall interaction (FWI) configuration is studied using three-dimensional direct numerical simulation (DNS) and detailed chemical kinetics. The simulations are used to investigate the effects of the wall turbulent boundary layer (i) on the structure of a hydrogen-air premixed flame, (ii) on its near-wall propagation characteristics and (iii) on the spatial and temporal patterns of the convective wall heat flux. Results show that the local flame thickness and propagation speed vary between the core flow and the boundary layer, resulting in a regime change from flamelet near the channel centreline to a thickened flame at the wall. This finding has strong implications for the modelling of turbulent combustion using Reynolds-averaged Navier-Stokes or large-eddy simulation techniques. Moreover, the DNS results suggest that the near-wall coherent turbulent structures play an important role on the convective wall heat transfer by pushing the hot reactive zone towards the cold solid surface. At the wall, exothermic radical recombination reactions become important, and are responsible for approximately 70% of the overall heat release rate at the wall. Spectral analysis of the convective wall heat flux provides an unambiguous picture of its spatial and temporal patterns, previously unobserved, that is directly related to the spatial and temporal characteristic scalings of the coherent near-wall turbulent structures.

Chen, Jackie [Sandia National Laboratories (SNL); Hawkes, Evatt R [Sandia National Laboratories (SNL); Sankaran, Ramanan [ORNL; Gruber, Andrea [SINTEF Energy Research

2010-01-01

62

The effects of mixture fraction value ? and the magnitude of its gradient |??| at the ignitor location on the localised forced ignition of turbulent mixing layers under decaying turbulence is studied\\u000a based on three-dimensional compressible Direct Numerical Simulations (DNS) with simplified chemistry. The localised ignition\\u000a is accounted for by a spatial Gaussian power distribution in the energy transport equation,

Nilanjan Chakraborty; E. Mastorakos

2008-01-01

63

Laboratory experiments and direct numerical simulations (DNS) of passive scalar contaminant dispersal in bounded shear flows have been carrried out. Both mass and heat transport have been experimentally studied. Statistical results for the temperature plume which develops from a line heat source at the wall are compared to the DNS results. The DNS results for this case and for the case of a uniform source with constant temperature boundaries are also compared to various model predictions.

Wallace, J.M.; Bernard, P.S.; Balint, J.L.; Ong, L.

1992-12-31

64

Laboratory experiments and direct numerical simulations (DNS) of passive scalar contaminant dispersal in bounded shear flows have been carrried out. Both mass and heat transport have been experimentally studied. Statistical results for the temperature plume which develops from a line heat source at the wall are compared to the DNS results. The DNS results for this case and for the case of a uniform source with constant temperature boundaries are also compared to various model predictions.

Wallace, J.M.; Bernard, P.S.; Balint, J.L.; Ong, L.

1992-01-01

65

Numerical Simulation of Deoilin Hydrocyclones

Abstract—In this research the separation efficiency of deoiling hydrocyclone is evaluated using three-dimensional simulation of multiphase flow based on Eulerian-Eulerian finite volume method. The mixture approach of Reynolds Stress Model is also employed to capture the features of turbulent multiphase swirling flow. The obtained separation efficiency of Colman's design is compared with available experimental data and showed that the separation curve of deoiling hydrocyclones can be predicted using numerical simulation. Keywords—Deoiling hydrocyclone, Eulerian-Eulerian Model,

unknown authors

66

Numerical Simulation of Black Holes

NASA Astrophysics Data System (ADS)

Einstein's equations of general relativity are prime candidates for numerical solution on supercomputers. There is some urgency in being able to carry out such simulations: Large-scale gravitational wave detectors are now coming on line, and the most important expected signals cannot be predicted except numerically. Problems involving black holes are perhaps the most interesting, yet also particularly challenging computationally. One difficulty is that inside a black hole there is a physical singularity that cannot be part of the computational domain. A second difficulty is the disparity in length scales between the size of the black hole and the wavelength of the gravitational radiation emitted. A third difficulty is that all existing methods of evolving black holes in three spatial dimensions are plagued by instabilities that prohibit long-term evolution. I will describe the ideas that are being introduced in numerical relativity to deal with these problems, and discuss the results of recent calculations of black hole collisions.

Teukolsky, Saul

2003-04-01

67

Autoignition of hydrogen and air using direct numerical simulation

NASA Astrophysics Data System (ADS)

Direct numerical simulation (DNS) is used to study to auto--ignition in laminar vortex rings and turbulent diffusion flames. A novel, all--Mach number algorithm developed by Doom et al (J. Comput. Phys. 2007) is used. The chemical mechanism is a nine species, nineteen reaction mechanism for H2 and Air from Mueller at el (Int. J. Chem. Kinet. 1999). The vortex ring simulations inject diluted H2 at ambient temperature into hot air, and study the effects of stroke ratio, air to fuel ratio and Lewis number. At smaller stroke ratios, ignition occurs in the wake of the vortex ring and propagates into the vortex core. At larger stroke ratios, ignition occurs along the edges of the trailing column before propagating towards the vortex core. The turbulent diffusion flame simulations are three--dimensional and consider the interaction of initially isotropic turbulence with an unstrained diffusion flame. The simulations examine the nature of distinct ignition kernels, the relative roles of chemical reactions, and the relation between the observed behavior and laminar flames and the perfectly stirred reactor problem. These results will be discussed.

Doom, Jeffrey; Mahesh, Krishnan

2008-11-01

68

On locating the obstruction in the upper airway via numerical simulation.

The fluid dynamical properties of the air flow in the upper airway (UA) are not fully understood at present due to the three-dimensional (3D) patient-specific complex geometry of the airway, flow transition from laminar to turbulent and flow-structure interaction during the breathing cycle. It is quite difficult at present to experimentally measure the instantaneous velocity and pressure at specific points in the human airway. On the other hand, direct numerical simulation (DNS) can predict all the flow properties and resolve all its relevant length- and time-scales. We developed a DNS solver with the state-of-the-art lattice Boltzmann method (LBM), and used it to investigate the flow in two patient-specific UAs reconstructed from CT scan data. Inspiration and expiration flows through these two airways are studied. The time-averaged first spatial derivative of pressure (pressure gradient), ?p/?z, is used to locate the region of the UA obstruction. But the time-averaged second spatial derivative, ?(2)p/?z(2), is used to pinpoint the exact location of the obstruction. The present results show that the DNS-LBM solver can be used to obtain accurate flow details in the UA and is a powerful tool to locate its obstruction. PMID:24389271

Wang, Yong; Elghobashi, S

2014-03-01

69

Numerical Propulsion System Simulation Architecture

NASA Technical Reports Server (NTRS)

The Numerical Propulsion System Simulation (NPSS) is a framework for performing analysis of complex systems. Because the NPSS was developed using the object-oriented paradigm, the resulting architecture is an extensible and flexible framework that is currently being used by a diverse set of participants in government, academia, and the aerospace industry. NPSS is being used by over 15 different institutions to support rockets, hypersonics, power and propulsion, fuel cells, ground based power, and aerospace. Full system-level simulations as well as subsystems may be modeled using NPSS. The NPSS architecture enables the coupling of analyses at various levels of detail, which is called numerical zooming. The middleware used to enable zooming and distributed simulations is the Common Object Request Broker Architecture (CORBA). The NPSS Developer's Kit offers tools for the developer to generate CORBA-based components and wrap codes. The Developer's Kit enables distributed multi-fidelity and multi-discipline simulations, preserves proprietary and legacy codes, and facilitates addition of customized codes. The platforms supported are PC, Linux, HP, Sun, and SGI.

Naiman, Cynthia G.

2004-01-01

70

Simulating Reionization in Numerical Cosmology

The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized. Here, we present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by a set of discrete point sources. A diffuse background radiation field is also computed self-consistently in our procedure. The method requires relatively few time steps and can be employed with simulations having high resolution. We describe the details of the algorithm and provide a description of how the method can be applied to the output from a pre-existing cosmological simulation to study the systematic reionization of a particular ionic species. As a first application, we compute the reionization of He II by quasars in the redshift range 3 to 6.

Aaron Sokasian; Tom Abel; Lars E. Hernquist

2001-05-10

71

LES, DNS and RANS for the analysis of high-speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

The purpose of this research is to continue our efforts in advancing the state of knowledge in large eddy simulation (LES), direct numerical simulation (DNS), and Reynolds averaged Navier Stokes (RANS) methods for the computational analysis of high-speed reacting turbulent flows. In the second phase of this work, covering the period 1 Aug. 1994 - 31 Jul. 1995, we have focused our efforts on two programs: (1) developments of explicit algebraic moment closures for statistical descriptions of compressible reacting flows and (2) development of Monte Carlo numerical methods for LES of chemically reacting flows.

Adumitroaie, V.; Colucci, P. J.; Taulbee, D. B.; Givi, P.

1995-01-01

72

Statistically Steady Turbulence in Soap Films: Direct Numerical Simulations with Ekman Friction

We present a detailed direct numerical simulation (DNS) designed to investigate the combined effects of walls and Ekman friction on turbulence in forced soap films. We concentrate on the forward-cascade regime and show how to extract the isotropic parts of velocity and vorticity structure functions and thence the ratios of multiscaling exponents. We find that velocity structure functions display simple scaling whereas their vorticity counterparts show multiscaling; and the probability distribution function of the Weiss parameter $\\Lambda$, which distinguishes between regions with centers and saddles, is in quantitative agreement with experiments.

Prasad Perlekar; Rahul Pandit

2008-11-09

73

Direct Numerical Simulation of Transition in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Direct numerical simulation (DNS) is performed to examine laminar to turbulent transition due to high-frequency secondary instability of stationary crossflow vortices in a subsonic swept-wing boundary layer for a realistic natural-laminar-flow airfoil configuration. The secondary instability is introduced via inflow forcing derived from a two-dimensional, partial-differential-equation based eigenvalue computation; and the mode selected for forcing corresponds to the most amplified secondary instability mode which, in this case, derives a majority of its growth from energy production mechanisms associated with the wall-normal shear of the stationary basic state. Both the growth of the secondary instability wave and the resulting onset of laminar-turbulent transition are captured within the DNS computations. The growth of the secondary instability wave in the DNS solution compares well with linear secondary instability theory when the amplitude is small; the linear growth is followed by a region of reduced growth resulting from nonlinear effects before an explosive onset of laminar breakdown to turbulence. The peak fluctuations are concentrated near the boundary layer edge during the initial stage of transition, but rapidly propagates towards the surface during the process of laminar breakdown. Both time-averaged statistics and flow visualization based on the DNS reveal a sawtooth transition pattern that is analogous to previously documented surface flow visualizations of transition due to stationary crossflow instability. The memory of the stationary crossflow vortex is found to persist through the transition zone and well beyond the location of the maximum skin friction.

Duan, Lian; Choudhari, Meelan M.; Li, Fei

2013-01-01

74

Direct Numerical Simulation of Soot Particle Dynamics using DQMOM

NASA Astrophysics Data System (ADS)

The understanding of soot particle dynamics in combustion systems is a key issue in the development of low emission engines. Of particular importance are the processes shaping the soot particle size distribution function (PSDF). However, it is not always necessary to represent exactly the full distribution but rather some of its moments. The Direct Quadrature Method of Moments (DQMOM) allows for a very accurate prediction of the moments of the soot PSDF without the cost of expensive methods like Direct Simulation Monte-Carlo (DSMC). This method has been validated for laminar premixed and diffusion flames with detailed chemistry and is now implemented in a semi-implicit low Mach number Navier-Stokes solver. A Direct Numerical Simulation (DNS) of an ethylene jet diffusion flame is performed to study the dynamics of soot particles in a turbulent environment. Soot particles are formed in very rich regions of the flames and are then transported to lean regions where they get oxidized. The time evolution of the soot PSDF will be analyzed and compared to similar distributions from laminar simulations.

Blanquart, Guillaume; Pitsch, Heinz; Fox, Rodney

2006-11-01

75

Numerical simulation of adjustable nozzles

NASA Astrophysics Data System (ADS)

This paper presents the optimal combination of the nozzle and needle valve in adjustable nozzles. With numerical simulation tool of FLUENT, water jet out of different nozzles with contraction angle 30°, 40°, 50°, 60°, 70°, 80°are simulated, and within nozzles there are different needle valves with contraction angle 20°, 30°, 40°, 50°, 60°, the simulation results are compared and analyzed. The needle valves locate at the same position in the nozzles in different combinations. After water jet flows out of the nozzle, along the direction of flow there are three flow stages: initial stage, transitional stage and basic stage. The sectional area of bundle of jet shrinks near the exit of the nozzle when fluid flows out of the nozzle. Ignoring the transitional stage, the shrinkage of the bundle of jet occurs in the initial stage. The severer the contraction of jet is, the bigger the maximum velocity of the jet is, the faster the axial velocity decays. When the contraction of the jet is slight, jet flow is stable, the attenuation of the axial velocity is slower. The flow field is investigated by two-dimensional numerical analysis. Different combinations are analyzed to find the performance variation in order to select the best combination. The study offers references for the selection of the nozzle shape and needle valve shape for adjustable nozzle. It has important significance in the design and manufacture of adjustable jet pump.

Zhang, S. B.; Zhu, J. M.

2013-12-01

76

Numerical Simulations in Particle Physics

Numerical simulations have become an important tool to understand and predict non-perturbative phenomena in particle physics. In this article we attempt to present a general overview over the field. First, the basic concepts of lattice gauge theories are described, including a discussion of currently used algorithms and the reconstruction of continuum physics from lattice results. We then proceed to present some results for QCD, both at low energies and at high temperatures, as well as for the electro-weak sector of the standard model.

F. Karsch; E. Laermann

1993-04-14

77

Numerical Simulations of Homogeneous Turbulence Using Lagrangian-Averaged Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

The Lagrangian-averaged Navier-Stokes (LANS) equations are numerically evaluated as a turbulence closure. They are derived from a novel Lagrangian averaging procedure on the space of all volume-preserving maps and can be viewed as a numerical algorithm which removes the energy content from the small scales (smaller than some a priori fixed spatial scale alpha) using a dispersive rather than dissipative mechanism, thus maintaining the crucial features of the large scale flow. We examine the modeling capabilities of the LANS equations for decaying homogeneous turbulence, ascertain their ability to track the energy spectrum of fully resolved direct numerical simulations (DNS), compare the relative energy decay rates, and compare LANS with well-accepted large eddy simulation (LES) models.

Mohseni, Kamran; Shkoller, Steve; Kosovic, Branko; Marsden, Jerrold E.; Carati, Daniele; Wray, Alan; Rogallo, Robert

2000-01-01

78

From Expert Words Directly to Numerical Simulations

From Expert Words Directly to Numerical Simulations: GroupÂTheoretic Approach to Computing to transform these expert words into numerical simulation (leadÂ ing to prediction) is to use the fuzzy control, therefore, desirable to get from the original words directly to numerical simulations, thus avoiding this de

Kreinovich, Vladik

79

Numerical simulation of prominence oscillations

We present numerical simulations, obtained with the Versatile Advection Code, of the oscillations of an inverse polarity prominence. The internal prominence equilibrium, the surrounding corona and the inert photosphere are well represented. Gravity and thermodynamics are not taken into account, but it is argued that these are not crucial. The oscillations can be understood in terms of a solid body moving through a plasma. The mass of this solid body is determined by the magnetic field topology, not by the prominence mass proper. The model also allows us to study the effect of the ambient coronal plasma on the motion of the prominence body. Horizontal oscillations are damped through the emission of slow waves while vertical oscillations are damped through the emission of fast waves.

N. A. J. Schutgens; G. Toth

1999-03-09

80

Relativistic Positioning Systems: Numerical Simulations

The motion of satellite constellations similar to GPS and Galileo is numerically simulated and, then, the region where bifurcation (double positioning) occurs is appropriately represented. In the cases of double positioning, the true location may be found using additional information (angles or times). The zone where the Jacobian, J, of the transformation from inertial to emission coordinates vanishes is also represented and interpreted. It is shown that the uncertainties in the satellite world lines produce positioning errors, which depend on the value of |J|. The smaller this quantity the greater the expected positioning errors. Among all the available 4-tuples of satellites, the most appropriate one -for a given location- should minimize positioning errors (large enough |J| values) avoiding bifurcation. Our study is particularly important to locate objects which are far away from Earth, e.g., satellites.

Neus Puchades; Diego Sáez

2014-04-03

81

Numerical simulations of magnetized jets

NASA Technical Reports Server (NTRS)

The present axisymmetric numerical simulations of light hypersonic jets allow unmagnetized jets and jets carrying a dynamically important magnetic field to be contrasted. After decelerating a weakly magnetized jet through a series of weak, oblique shocks, a Mach disk and a strong annular shock are encountered near the outer edges of the contact discontinuity separating the shocked fluid from the shocked ambient gas. Upon passing the annular shock, the gas quickly expands and enters a backflowing cocoon surrounding the jet. The overall speed of advance of the jet is reduced; matter near the jet axis which passes through the terminal Mach disk accumulates in a plug, and gas is discharged into the cocoon by the intermittent shedding of vortices. When magnetic stresses dominate, however, the jet is rapidly decelerated via a Mach disk and strong annular shock.

Lind, Kevin R.; Payne, David G.; Meier, David L.; Blandford, Roger D.

1989-01-01

82

The state-of-the-art for Direct Numerical Simulation (DNS) of boiling multiphase flows is reviewed, focussing on potential of available computational techniques, the level of current success for their applications to model several basic flow regimes (film, pool-nucleate and wall-nucleate boiling -- FB, PNB and WNB, respectively). Then, we discuss multiphysics and multiscale nature of practical boiling flows in LWR reactors, requiring high-fidelity treatment of interfacial dynamics, phase-change, hydrodynamics, compressibility, heat transfer, and non-equilibrium thermodynamics and chemistry of liquid/vapor and fluid/solid-wall interfaces. Finally, we outline the framework for the {\\sf Fervent} code, being developed at INL for DNS of reactor-relevant boiling multiphase flows, with the purpose of gaining insight into the physics of multiphase flow regimes, and generating a basis for effective-field modeling in terms of its formulation and closure laws.

Nourgaliev R.; Knoll D.; Mousseau V.; Berry R.

2007-04-01

83

NASA Technical Reports Server (NTRS)

Recently, several second order closure models have been proposed for closing the second moment equations, in which the velocity-pressure gradient (and scalar-pressure gradient) tensor and the dissipation rate tensor are two of the most important terms. In the literature, these correlation tensors are usually decomposed into a so called rapid term and a return-to-isotropy term. Models of these terms have been used in global flow calculations together with other modeled terms. However, their individual behavior in different flows have not been fully examined because they are un-measurable in the laboratory. Recently, the development of direct numerical simulation (DNS) of turbulence has given us the opportunity to do this kind of study. With the direct numerical simulation, we may use the solution to exactly calculate the values of these correlation terms and then directly compare them with the values from their modeled formulations (models). Here, we make direct comparisons of five representative rapid models and eight return-to-isotropy models using the DNS data of forty five homogeneous flows which were done by Rogers et al. (1986) and Lee et al. (1985). The purpose of these direct comparisons is to explore the performance of these models in different flows and identify the ones which give the best performance. The modeling procedure, model constraints, and the various evaluated models are described. The detailed results of the direct comparisons are discussed, and a few concluding remarks on turbulence models are given.

Shih, Tsan-Hsing; Lumley, John L.

1991-01-01

84

NASA Technical Reports Server (NTRS)

Analysis of Direct Numerical Simulations (DNS) transitional states of temporal, supercritical mixing layers for C7H16/N2 and O2/H2 shows that the evolution of all layers is characterized by the formation of high-density-gradient magnitude (HDGM) regions.

Okong'o, N. A.; Bellan, J.

2003-01-01

85

A direct numerical simulation study of higher order statistics in a turbulent round jet

NASA Astrophysics Data System (ADS)

Up until recently direct numerical simulation (DNS) studies involving round turbulent jets have focused on first and second order statistics and vortical behavior near the source of the jet. The third order statistics necessary to compute the turbulent kinetic energy and Reynolds stress transport equations have been examined using LES studies. However, further examination with DNS is important as, on the subgrid scale, LES uses models for Reynolds stress. In this study a DNS of a turbulent free jet with a Reynolds number equal to ReJ = 2000 is computed using a second order accurate, time splitting finite volume scheme. First, second, and third order statistics are compared with previous experimental and numerical studies. All terms of the turbulent kinetic energy balance are calculated directly. The results are compared to experimental studies such as those of Hussein et al. ["Velocity measurements in a high-Reynolds-number, momentum-conserving, axisymmetric, turbulent jet," J. Fluid Mech. 258, 31-75 (1994)], Panchapakesan and Lumley ["Turbulence measurements in axisymmetric jets of air and helium. Part 1. Air jet," J. Fluid Mech. 246, 197-233 (1993)], and others. The assumptions made by the various experimental studies in order to solve the dissipation and pressure diffusion terms are discussed and examined using the data from the current study. The Reynolds stress transport equations are also calculated and discussed. Vortical structures are visualized by the ?ci method and discussed along with entrainment of ambient fluid into the jet. The one dimensional energy spectra in the azimuthal direction are calculated directly and are also discussed.

Taub, G. N.; Lee, Hyungoo; Balachandar, S.; Sherif, S. A.

2013-11-01

86

Numerical Simulation of Protoplanetary Vortices

NASA Technical Reports Server (NTRS)

The fluid dynamics within a protoplanetary disk has been attracting the attention of many researchers for a few decades. Previous works include, to list only a few among many others, the well-known prescription of Shakura & Sunyaev, the convective and instability study of Stone & Balbus and Hawley et al., the Rossby wave approach of Lovelace et al., as well as a recent work by Klahr & Bodenheimer, which attempted to identify turbulent flow within the disk. The disk is commonly understood to be a thin gas disk rotating around a central star with differential rotation (the Keplerian velocity), and the central quest remains as how the flow behavior deviates (albeit by a small amount) from a strong balance established between gravitational and centrifugal forces, transfers mass and momentum inward, and eventually forms planetesimals and planets. In earlier works we have briefly described the possible physical processes involved in the disk; we have proposed the existence of long-lasting, coherent vortices as an efficient agent for mass and momentum transport. In particular, Barranco et al. provided a general mathematical framework that is suitable for the asymptotic regime of the disk; Barranco & Marcus (2000) addressed a proposed vortex-dust interaction mechanism which might lead to planetesimal formation; and Lin et al. (2002), as inspired by general geophysical vortex dynamics, proposed basic mechanisms by which vortices can transport mass and angular momentum. The current work follows up on our previous effort. We shall focus on the detailed numerical implementation of our problem. We have developed a parallel, pseudo-spectral code to simulate the full three-dimensional vortex dynamics in a stably-stratified, differentially rotating frame, which represents the environment of the disk. Our simulation is validated with full diagnostics and comparisons, and we present our results on a family of three-dimensional, coherent equilibrium vortices.

Lin, H.; Barranco, J. A.; Marcus, P. S.

2003-01-01

87

Numerical simulation of electrokinetically driven micro flows

Spectral element based numerical solvers are developed to simulate electrokinetically driven flows for micro-fluidic applications. Based on these numerical solvers, basic phenomena and devices for electrokinetic applications in micro and nano flows...

Hahm, Jungyoon

2005-11-01

88

Numerical simulation of Faraday waves

NASA Astrophysics Data System (ADS)

Faraday first described in 1831 the pattern of standing waves generated at the surface of a vertically oscillated fluid layer; the corresponding linear stability analysis was carried out in 1954 by Benjamin and Ursell for inviscid fluids and in 1994 by Kumar and Tuckerman for viscous fluids. Linear stability analysis, however, predicts only the critical wavenumber and oscillation amplitude, and not the variety of periodic lattice patterns manifested by Faraday waves which have long intrigued researchers. The experimental observation in 1992 of quasicrystalline patterns by Edwards and Fauve has inspired an abundance of experimental and theoretical research. However, this has not been accompanied by realistic numerical computations. Here, we report on fully three-dimensional and nonlinear Navier- Stokes simulations of Faraday waves using a front tracking method for the interface between two immiscible fluids. M. Faraday, Phil. Trans. R. Soc. Lond. 52, 319 (1831). T.B. Benjamin & F. Ursell, Proc. R. Soc. Lond. A 225, 505 (1954). K. Kumar & L.S. Tuckerman, J. Fluid Mech. 279, 49 (1994). W.S. Edwards & S. Fauve, J. Fluid Mech. 278, 123 (1994). S. Shin & D. Juric, J. Comput. Phys. 180, 427 (2002).

Perinet, Nicolas; Juric, Damir; Tuckerman, Laurette

2008-11-01

89

Numerical Simulations of the Slingatron

NASA Technical Reports Server (NTRS)

The slingatron mass accelerator is described for several track configurations (shapes), and numerical simulations of this accelerating mass traversing a given track configuration are presented. The sled is modeled as a point mass that interacts with the slingatron track using both a conventional and a new empirical velocity dependent friction law. The closed loop circular slingatron was found to produce high maximum sled velocities provided the gyration angular speed is always increasing. In contrast several spiral shaped slingatron tracks reveal that high maximum sled velocities are obtainable with the gyration speed held constant. In fact, a slingatron constructed out of semi-circles is shown capable of generating high velocity sleds in such a way that no initial sled injection is necessary. Choosing the proper initial gyration phase with an empirically determined friction model allows the mass sled to gain ever-increasing velocities when placed in a semi-circle slingatron. The sled bearing pressure and its total acceleration are examined and presented.

Cooper, Gene R.; Tidman, Derek A.; Bundy, Mark L.; Wilkerson, Stephen

2001-01-01

90

Resolution requirements for numerical simulations of transition

NASA Technical Reports Server (NTRS)

The resolution requirements for direct numerical simulations of transition to turbulence are investigated. A reliable resolution criterion is determined from the results of several detailed simulations of channel and boundary-layer transition.

Zang, Thomas A.; Krist, Steven E.; Hussaini, M. Yousuff

1989-01-01

91

Numerical Simulations of Granular Processes

NASA Astrophysics Data System (ADS)

Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a completely different gravitational environment than on the Earth. Understanding and modeling these motions can aid in the interpretation of imaged surface features that may exhibit signatures of constituent material properties. Also, upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the parallelized N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). Ongoing and recently completed projects include: impacts into granular materials using different projectile shapes [5]; possible tidal resurfacing of asteroid Apophis during its 2029 encounter [6]; the Brazil-nut effect in low gravity [7]; and avalanche modeling.Acknowledgements: DCR acknowledges NASA (grants NNX08AM39G, NNX10AQ01G, NNX12AG29G) and NSF (AST1009579). PM acknowledges the French agency CNES. SRS works on the NEOShield Project funded under the European Commission’s FP7 program agreement No. 282703. SM acknowledges support from the Center for Theory and Computation at U Maryland and the Dundee Fellowship at U Dundee. Most simulations were performed using the YORP cluster in the Dept. of Astronomy at U Maryland and on the Deepthought High-Performance Computing Cluster at U Maryland.References: [1] Richardson, D.C. et al. 2000, Icarus 143, 45; [2] Stadel, J. 2001, Ph.D. Thesis, U Washington; [3] Schwartz, S.R. et al. 2012, Gran. Matt. 14, 363. [4] Schwartz, S.R. et al. 2013, Icarus 226, 67; [5] Schwartz, S.R. et al. 2014, P&SS, 10.1016/j.pss.2014.07.013; [6] Yu, Y. et al. 2014, Icarus, 10.1016/j.icarus.2014.07.027; [7] Matsumura, S. et al. 2014, MNRAS, 10.1093/mnras/stu1388.

Richardson, Derek C.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Yu, Yang; Matsumura, Soko

2014-11-01

92

EDQNM and DNS — Comparitive calculations

EDQNM and DNS calculations of homogenous axisymmetric turbulence in the absence of a mean flow are compared. Special care is taken in making sure that exactly equivalent initial conditions are used in the two methods. Three calculations with different degrees of anisotropy have been carried out.

E. Lindborg; M. Hallbäck; A. D. Burden

1993-01-01

93

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

The primary objective of this research is to extend current capabilities of Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows. Our efforts in the first two years of this research have been concentrated on a priori investigations of single-point Probability Density Function (PDF) methods for providing subgrid closures in reacting turbulent flows. In the efforts initiated in the third year, our primary focus has been on performing actual LES by means of PDF methods. The approach is based on assumed PDF methods and we have performed extensive analysis of turbulent reacting flows by means of LES. This includes simulations of both three-dimensional (3D) isotropic compressible flows and two-dimensional reacting planar mixing layers. In addition to these LES analyses, some work is in progress to assess the extent of validity of our assumed PDF methods. This assessment is done by making detailed companions with recent laboratory data in predicting the rate of reactant conversion in parallel reacting shear flows. This report provides a summary of our achievements for the first six months of the third year of this program.

Givi, P.; Frankel, S. H.; Adumitroaie, V.; Sabini, G.; Madnia, C. K.

1993-01-01

94

Based on numerical simulation support scheme selection

Numerical simulation of the structure of underground rock engineering stress and strain, analysis of structural stability of the method has been widely recognized. Here used a computer simulation based design bolting method9ÿ Application of finite difference software as the core UDEC computer program can easily simulate mining, excavation, tunnel support during the large deformation problem, you can easily simulate bolting

Li Hui; Yuan Dongsheng; Xu Lu

2011-01-01

95

GPU accelerated flow solver for direct numerical simulation of turbulent flows

Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier–Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.

Salvadore, Francesco [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)] [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy); Bernardini, Matteo, E-mail: matteo.bernardini@uniroma1.it [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy)] [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy); Botti, Michela [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)] [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)

2013-02-15

96

DNS, Enstrophy Balance, and the Dissipation Equation in a Separated Turbulent Channel Flow

NASA Technical Reports Server (NTRS)

The turbulent flows through a plane channel and a channel with a constriction (2-D hill) are numerically simulated using DNS and RANS calculations. The Navier-Stokes equations in the DNS are solved using a higher order kinetic energy preserving central schemes and a fifth order accurate upwind biased WENO scheme for the space discretization. RANS calculations are performed using the NASA code CFL3D with the komega SST two-equation model and a full Reynolds stress model. Using DNS, the magnitudes of different terms that appear in the enstrophy equation are evaluated. The results show that the dissipation and the diffusion terms reach large values at the wall. All the vortex stretching terms have similar magnitudes within the buffer region. Beyond that the triple correlation among the vorticity and strain rate fluctuations becomes the important kinematic term in the enstrophy equation. This term is balanced by the viscous dissipation. In the separated flow, the triple correlation term and the viscous dissipation term peak locally and balance each other near the separated shear layer region. These findings concur with the analysis of Tennekes and Lumley, confirming that the energy transfer terms associated with the small-scale dissipation and the fluctuations of the vortex stretching essentially cancel each other, leaving an equation for the dissipation that is governed by the large-scale motion.

Balakumar, Ponnampalam; Rubinstein, Robert; Rumsey, Christopher L.

2013-01-01

97

A numerical study of flow-structure interactions with application to flow past a pair of cylinders

Flow-structure interaction is a generic problem for many engineering applications, such as flow--induced oscillations of marine risers and cables. In this thesis a Direct Numerical Simulation (DNS) approach based on ...

Papaioannou, Georgios (Georgios Vasilios), 1975-

2004-01-01

98

NASA Technical Reports Server (NTRS)

Direct numerical simulations (DNS) of Mach 6 turbulent boundary layer with nominal freestream Mach number of 6 and Reynolds number of Re(sub T) approximately 460 are conducted at two wall temperatures (Tw/Tr = 0.25, 0.76) to investigate the generated pressure fluctuations and their dependence on wall temperature. Simulations indicate that the influence of wall temperature on pressure fluctuations is largely limited to the near-wall region, with the characteristics of wall-pressure fluctuations showing a strong temperature dependence. Wall temperature has little influence on the propagation speed of the freestream pressure signal. The freestream radiation intensity compares well between wall-temperature cases when normalized by the local wall shear; the propagation speed of the freestream pressure signal and the orientation of the radiation wave front show little dependence on the wall temperature.

Duan, Lian; Choudhari, Meelan M.

2014-01-01

99

NUMERICAL SIMULATION OF LARYNGEAL FLOW

In this study, we have investigated laryngeal air flows by numerically solving the corresponding Navier-Stokes equations expressed in a two-dimensional cylindrical coordinate system. The glottal aperture, defined by the geometry of the vocal folds was allowed to change with the v...

100

Direct Numerical Simulations of High-Speed Turbulent Boundary Layers over Riblets

NASA Technical Reports Server (NTRS)

Direct numerical simulations (DNS) of spatially developing turbulent boundary layers over riblets with a broad range of riblet spacings are conducted to investigate the effects of riblets on skin friction at high speeds. Zero-pressure gradient boundary layers under two flow conditions (Mach 2:5 with T(sub w)/T(sub r) = 1 and Mach 7:2 with T(sub w)/T(sub r) = 0:5) are considered. The DNS results show that the drag-reduction curve (delta C(sub f)/C(sub f) vs l(sup +)(sub g )) at both supersonic speeds follows the trend of low-speed data and consists of a `viscous' regime for small riblet size, a `breakdown' regime with optimal drag reduction, and a `drag-increasing' regime for larger riblet sizes. At l l(sup +)(sub g) approx. 10 (corresponding to s+ approx 20 for the current triangular riblets), drag reduction of approximately 7% is achieved at both Mach numbers, and con rms the observations of the few existing experiments under supersonic conditions. The Mach- number dependence of the drag-reduction curve occurs for riblet sizes that are larger than the optimal size, with smaller slopes of (delta C(sub f)/C(sub f) for larger freestream Mach numbers. The Reynolds analogy holds with 2(C(sub h)=C(sub f) approximately equal to that of at plates for both drag-reducing and drag-increasing configurations.

Duan, Lian; Choudhari, Meelan, M.

2014-01-01

101

NASA Astrophysics Data System (ADS)

We present a comprehensive analysis of transport processes associated with electrohydrodynamic chaos in electrokinetic systems containing an ion-selective surface. The system considered is an aqueous symmetric binary electrolyte between an ion-selective surface and a stationary reservoir. Transport is driven by an external electric field. Using direct numerical simulations (DNS) of the coupled Poisson-Nernst-Planck and Navier-Stokes equations in 2D we show significant transitions in flow behavior from coherent vortex pairs to fully chaotic multi-layer vortex structures with a broadband energy spectrum. Additionally, we demonstrate that these vortices can eject both positive and negative free charge density into the bulk of the domain and completely disrupt the structure of the traditionally described extended space charge region. The resulting dynamical behavior poses a challenge for traditional asymptotic modeling that relies on the quasi-electroneutral bulk assumption. Furthermore, we quantify for the first time the relative importance of energy dissipation due to viscous effects in various transport regimes. Finally, we present a framework for the development of ensemble-averaged models (similar to Reynolds Averaged Navier-Stokes equations) and assess the importance of the unclosed terms based on our DNS data.

Druzgalski, C. L.; Andersen, M. B.; Mani, A.

2013-11-01

102

Combustion of fossil fuels is likely to continue for the near future due to the growing trends in energy consumption worldwide. The increase in efficiency and the reduction of pollutant emissions from combustion devices are pivotal to achieving meaningful levels of carbon abatement as part of the ongoing climate change efforts. Computational fluid dynamics featuring adequate combustion models will play an increasingly important role in the design of more efficient and cleaner industrial burners, internal combustion engines, and combustors for stationary power generation and aircraft propulsion. Today, turbulent combustion modelling is hindered severely by the lack of data that are accurate and sufficiently complete to assess and remedy model deficiencies effectively. In particular, the formation of pollutants is a complex, nonlinear and multi-scale process characterized by the interaction of molecular and turbulent mixing with a multitude of chemical reactions with disparate time scales. The use of direct numerical simulation (DNS) featuring a state of the art description of the underlying chemistry and physical processes has contributed greatly to combustion model development in recent years. In this paper, the analysis of the intricate evolution of soot formation in turbulent flames demonstrates how DNS databases are used to illuminate relevant physico-chemical mechanisms and to identify modelling needs. PMID:25024412

Bisetti, Fabrizio; Attili, Antonio; Pitsch, Heinz

2014-08-13

103

Coincidental match of numerical simulation and physics

NASA Astrophysics Data System (ADS)

Consequences of rapid pressure transients in pipelines range from increased fatigue to leakages and to complete ruptures of pipeline. Therefore, accurate predictions of rapid pressure transients in pipelines using numerical simulations are critical. State of the art modelling of pressure transient in general, and water hammer in particular include unsteady friction in addition to the steady frictional pressure drop, and numerical simulations rely on the method of characteristics. Comparison of rapid pressure transient calculations by the method of characteristics and a selected high resolution finite volume method highlights issues related to modelling of pressure waves and illustrates that matches between numerical simulations and physics are purely coincidental.

Pierre, B.; Gudmundsson, J. S.

2010-08-01

104

A Lagrangian VOF tensorial penalty method for the DNS of resolved particle-laden flows

NASA Astrophysics Data System (ADS)

The direct numerical simulation of particle flows is investigated by a Lagrangian VOF approach and penalty methods of second order convergence in space for incompressible flows interacting with resolved particles on a fixed structured grid. A specific Eulerian volume of fluid method is developed with a Lagrangian tracking of the phase function while the solid and divergence free constraints are ensured implicitly in the motion equations thanks to fictitious domains formulations, adaptive augmented Lagrangian approaches and viscous penalty methods. A specific strategy for handling particle collisions and lubrication effects is also presented. Various dilute particle laden flows are considered for validating the models and numerical methods. Convergence studies are proposed for estimating the time and space convergence orders of the global DNS approach. Finally, two dense particle laden flows are simulated, namely the flow across a fixed array of cylinders and the fluidization of 2133 particles in a vertical pipe. The numerical solutions are compared to existing theoretical and experimental results with success.

Vincent, Stéphane; Brändle de Motta, Jorge César; Sarthou, Arthur; Estivalezes, Jean-Luc; Simonin, Olivier; Climent, Eric

2014-01-01

105

Estimating Uncertainties in Statistics Computed from DNS

Rigorous assessment of uncertainty is crucial to the utility of DNS results. Uncertainties in the computed statistics arise from two sources: finite statistical sampling and the discretization of the Navier-Stokes equations. Due to the presence of non-trivial sampling error, standard techniques for estimating discretization error (such as Richardson extrapolation) fail or are unreliable. This work provides a systematic and unified approach for estimating these errors. First, a sampling error estimator that accounts for correlation in the input data is developed. Then, this sampling error estimate is used as part of a Bayesian extension of Richardson extrapolation in order to characterize the discretization error. These methods are tested using the Lorenz equations and are shown to perform well. These techniques are then used to investigate the sampling and discretization errors in the DNS of a wall-bounded turbulent flow. For both cases, it is found that while the sampling uncertainty is large enough to make the order of accuracy difficult to determine, the estimated discretization errors are quite small. This indicates that the commonly used heuristics provide ad- equate resolution for this class of problems. However, it is also found that, for some quantities, the discretization error is not small relative to sampling error, indicating that the conventional wisdom that sampling error dominates discretization error for this class of simulations needs to be reevaluated.

Todd A. Oliver; Nicholas Malaya; Rhys Ulerich; Robert D. Moser

2013-11-04

106

Numerical techniques of rigid body simulation

bodies. Complicated simulations require the development of sophisticated collision detection systems and numerical techniques. Previous work in the field has almost exclusively been restricted to geometries that are convex or a union of convex pieces...

Eberle, David Michael

2012-06-07

107

Numerical simulation of fresh SCC flow: applications

Numerical simulation of self-compacting concrete (SCC) flow shows great potential for developing into a powerful tool for\\u000a prediction of SCC form filling. Numerical simulation is also of interest for modelling small scale material phenomena. This\\u000a paper presents three different applications useful for modelling different phenomena on different scales: (i) particles, each\\u000a representing an aggregate in the concrete, (ii) fluid, modelling

Annika Gram; Johan Silfwerbrand

2011-01-01

108

Numerical tools for atomistic simulations.

The final report for a Laboratory Directed Research and Development project entitled 'Parallel Atomistic Computing for Failure Analysis of Micromachines' is presented. In this project, atomistic algorithms for parallel computers were developed to assist in quantification of microstructure-property relations related to weapon micro-components. With these and other serial computing tools, we are performing atomistic simulations of various sizes, geometries, materials, and boundary conditions. These tools provide the capability to handle the different size-scale effects required to predict failure. Nonlocal continuum models have been proposed to address this problem; however, they are phenomenological in nature and are difficult to validate for micro-scale components. Our goal is to separately quantify damage nucleation, growth, and coalescence mechanisms to provide a basis for macro-scale continuum models that will be used for micromachine design. Because micro-component experiments are difficult, a systematic computational study that employs Monte Carlo methods, molecular statics, and molecular dynamics (EAM and MEAM) simulations to compute continuum quantities will provide mechanism-property relations associated with the following parameters: specimen size, number of grains, crystal orientation, strain rates, temperature, defect nearest neighbor distance, void/crack size, chemical state, and stress state. This study will quantify sizescale effects from nanometers to microns in terms of damage progression and thus potentially allow for optimized micro-machine designs that are more reliable and have higher fidelity in terms of strength. In order to accomplish this task, several atomistic methods needed to be developed and evaluated to cover the range of defects, strain rates, temperatures, and sizes that a material may see in micro-machines. Therefore we are providing a complete set of tools for large scale atomistic simulations that include pre-processing of realistic material configurations, processing under different environments, and post-processing with appropriate continuum quantities. By running simulations with these tools, we are able to determine size scale effects that correlate microstructure and defect configurations with mechanical properties of materials.

Fang, H. (Mississippi State University); Gullett, Philip Michael; Slepoy, Alexander (Sandia National Laboratories, Albuquerque, NM); Horstemeyer, Mark F. (Mississippi State University); Baskes, Michael I. (Los Alamos National Laboratory, Los Alamos, NM); Wagner, Gregory John; Li, Mo (Materials Science and Engineering, Atlanta, GA)

2004-01-01

109

NASA Astrophysics Data System (ADS)

Multi-sensor, hot-wire probes of various configurations have been used for 25 years to simultaneously measure the velocity vector and the velocity gradient tensor in turbulent flows. This is the same period in which direct numerical simulations (DNS) were carried out to investigate these flows. Using the first DNS of a turbulent boundary layer, Moin and Spalart ["Contributions of numerical simulation data bases to the physics, modeling and measurement of turbulence," NASA Technical Memorandum 100022 (1987)] examined, virtually, the performance of a two-sensor X-array probe with the sensors idealized as points in the numerical grid. Subsequently, several investigators have used DNS for similar studies. In this paper we use a highly resolved minimal channel flow DNS, following Jiménez and Moin ["The minimal flow unit in near-wall turbulence," J. Fluid Mech. 225, 213 (1991)], to study the performance of an 11-sensor probe. Our previous studies of this type have indicated that, on balance, a probe of the design described here may provide the most accurate measurements of many of the statistics formed from the velocity vector and the velocity gradient tensor (rms and skewness values of the velocity and vorticity components as well as the Reynolds shear stress and the dissipation and production rates). The results of the present study show that, indeed, the sensor and array configurations of a probe of this design are considerably better than previous designs that have been used, and they are likely to give reasonably satisfactory results for such measurements with a real probe in a real bounded flow.

Vukoslav?evi?, Petar V.; Wallace, James M.

2013-11-01

110

Numerical simulations of flames and detonations

Time-dependent numerical simulations of multidimensional flames and detonations are discussed in this paper. The differences in the processes which must be modelled and the approaches adopted in simulating flames and detonations are highlighted. A two-dimensional flame model is described and then results of calculations are presented that show the effects of gravity on the structure and propagation of laminar, premixed

K. Kailasanath; E. Oran; J. Boris

111

Numerical Simulations of Drop Collisions

NASA Technical Reports Server (NTRS)

Three-dimensional simulations of the off-axis collisions of two drops are presented. The full Navier-Stokes equations are solved by a Front-Tracking/Finite-Difference method that allows a fully deformable fluid interface and the inclusion of surface tension. The drops are accelerated towards each other by a body force that is turned off before the drops collide. Depending on whether the interface between the drops is ruptured or not, the drops either bounce or coalesce. For drops that coalesce, the impact parameter, which measures how far the drops are off the symmetry line, determines the eventual outcome of the collision. For low impact parameters, the drops coalesce permanently, but for higher impact parameters, a grazing collision, where the drops coalesce and then stretch apart again is observed. The results are in agreement with experimental observations.

Nobari, M. R. H.; Tryggvason, G.

1994-01-01

112

Numerical Simulation of Nanostructure Growth

NASA Technical Reports Server (NTRS)

Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.

Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.

2004-01-01

113

Numerical simulations of strong incompressible magnetohydrodynamic turbulence

Magnetised plasma turbulence pervades the universe and is likely to play an important role in a variety of astrophysical settings. Magnetohydrodynamics (MHD) provides the simplest theoretical framework in which phenomenological models for the turbulent dynamics can be built. Numerical simulations of MHD turbulence are widely used to guide and test the theoretical predictions; however, simulating MHD turbulence and accurately measuring its scaling properties is far from straightforward. Computational power limits the calculations to moderate Reynolds numbers and often simplifying assumptions are made in order that a wider range of scales can be accessed. After describing the theoretical predictions and the numerical approaches that are often employed in studying strong incompressible MHD turbulence, we present the findings of a series of high-resolution direct numerical simulations. We discuss the effects that insufficiencies in the computational approach can have on the solution and its physical interpretation.

Mason, J.; Cattaneo, F. [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States); Perez, J. C. [Space Science Center and Department of Physics, University of New Hampshire, Durham, New Hampshire 03824 (United States); Boldyrev, S. [Department of Physics, University of Wisconsin at Madison, 1150 University Ave, Madison, Wisconsin 53706 (United States)

2012-05-15

114

Quantifying and Improving DNS Availability Casey Deccio

of availability. We begin our analysis by providing relevant background on the DNS. We sum- marize protocol details surrounding name resolution, protocol and implementation vulnerabilities, and security extensions and maintenance of DNS. -iii- #12;To my wife, Talia, and children, Zion, Hyrum, and Ezra. -iv- #12;Contents List

California at Davis, University of

115

Reliability of Complex Nonlinear Numerical Simulations

NASA Technical Reports Server (NTRS)

This work describes some of the procedure to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.

Yee, H. C.

2004-01-01

116

NASA Technical Reports Server (NTRS)

Turbulent non-premixed stoichiometric methane-air flames modeled with reduced kinetics have been studied using the direct numerical simulation approach. The simulations include realistic chemical kinetics, and the molecular transport is modeled with constant Lewis numbers for individual species. The effect of turbulence on the internal flame structure and extinction characteristics of methane-air flames is evaluated. Consistent with earlier DNS with simple one-step chemistry, the flame is wrinkled and in some regions extinguished by the turbulence, while the turbulence is weakened in the vicinity of the flame due to a combination of dilatation and an increase in kinematic viscosity. Unlike previous results, reignition is observed in the present simulations. Lewis number effects are important in determining the local stoichiometry of the flame. The results presented in this work are preliminary but demonstrate the feasibility of incorporating reduced kinetics for the oxidation of methane with direct numerical simulations of homogeneous turbulence to evaluate the limitations of various levels of reduction in the kinetics and to address the formation of thermal and prompt NO(x).

Card, J. M.; Chen, J. H.; Day, M.; Mahalingam, S.

1994-01-01

117

Numerical Simulations of Lateral Stress Profiles

A series of numerical simulations have been conducted to provide insight into the observed lateral stress profiles in shocked silicon carbide reported in [1]. Utilizing a coupled eulerian-lagrangian simulation approach, the thin epoxy layer has been included in the model. When utilizing the Johnson-Holmquist ceramic model with the constants published in [2], the two-step structure of the lateral stress measurement

Bryan Cheeseman; Dattatraya Dandekar

2009-01-01

118

Numerical Simulation Of Silicon-Ribbon Growth

NASA Technical Reports Server (NTRS)

Mathematical model includes nonlinear effects. In development simulates growth of silicon ribbon from melt. Takes account of entire temperature and stress history of ribbon. Numerical simulations performed with new model helps in search for temperature distribution, pulling speed, and other conditions favoring growth of wide, flat, relatively defect-free silicon ribbons for solar photovoltaic cells at economically attractive, high production rates. Also applicable to materials other than silicon.

Woda, Ben K.; Kuo, Chin-Po; Utku, Senol; Ray, Sujit Kumar

1987-01-01

119

Direct numerical simulations of tonal noise generated by laminar flow past airfoils

NASA Astrophysics Data System (ADS)

A numerical investigation is presented of noise generated by flow past symmetric NACA airfoils with different thickness and at various angles of attack at M=0.4 and a Reynolds number based on chord of Re=50,000. Direct numerical simulations (DNS) are employed to directly compute both the near-field hydrodynamics and the far-field sound. The DNS data are then used to investigate whether the approach of determining tonal noise radiation based on the surface pressure difference, as done in the classical trailing-edge theory of Amiet, yields satisfactory results for finite thickness airfoils subject to mean loading effects. In addition, the accuracy of Amiet's surface pressure jump function is evaluated. Overall, the modified theory of Amiet appears to be suitable for finite thickness airfoils up to moderate incidence. However, when increasing the airfoil thickness to 12% chord, which corresponds to a trailing-edge angle of 16.8?, an unexpected phase change between the incident and scattered pressure is found at the frequency of the forced instability waves. This phase change is attributed to the flow oscillating around the trailing edge at a separate wake frequency. For the largest incidence investigated, Amiet's response function does not predict the total surface pressure difference as accurately as for zero or small incidence at the vortex shedding frequency, resulting in a poor prediction of the directivity and amplitude of the acoustic pressure. Moreover, predicting the airfoil self-noise based on the surface pressure difference appears not to be generally applicable at higher angles of attack because the radiated sound is only partly due to classical trailing-edge noise mechanisms. In these cases, it appears as if volume sources in the flow cannot be neglected.

Sandberg, R. D.; Jones, L. E.; Sandham, N. D.; Joseph, P. F.

2009-03-01

120

Scattering of Electromagnetic Waves, Numerical Simulations

NASA Astrophysics Data System (ADS)

A timely and authoritative guide to the state of the art of wave scattering Scattering of Electromagnetic Waves offers in three volumes a complete and up-to-date treatment of wave scattering by random discrete scatterers and rough surfaces. Written by leading scientists who have made important contributions to wave scattering over three decades, this new work explains the principles, methods, and applications of this rapidly expanding, interdisciplinary field. It covers both introductory and advanced material and provides students and researchers in remote sensing as well as imaging, optics, and electromagnetic theory with a one-stop reference to a wealth of current research results. Plus, Scattering of Electromagnetic Waves contains detailed discussions of both analytical and numerical methods, including cutting-edge techniques for the recovery of earth/land parametric information. The three volumes are entitled respectively Theories and Applications, Numerical Simulation, and Advanced Topics. In the second volume, Numerical Simulations, Leung Tsang (University of Washington) Jin Au Kong (MIT), Kung-Hau Ding (Air Force Research Lab), and Chi On Ao (MIT) cover: Layered media simulations Rough surface and volume scattering simulations Dense media models and simulations Electromagnetic scattering by discrete scatterers and a buried object Scattering by vertical cylinders above a surface Electromagnetic waves scattering by vegetation Computational methods and programs used for performing various simulations

Tsang, Leung; Kong, Jin Au; Ding, Kung-Hau; Ao, Chi On

2001-05-01

121

Numerical Simulations of Heated Supersonic Rectangular Jets

The heated supersonic flow from rectangular jets with paddles in the flow field have been simulated numerically to study the effects of heating on the flow field and near-field noise. The flapping motion across the narrow dimension of the jet, which is the dominant feature of the unheated jet, is also found to be present in heated jets with temperature

R. L. Kolbe; K. Kailasanath; J. P. Boris

1996-01-01

122

Numerical simulations on ion acoustic double layers

A numerical study of ion-acoustic double layer in the upper atmosphere has been performed for both periodic and nonperiodic systems by means of one-dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated

T. Sato; H. Okuda

1981-01-01

123

Local Defect Correction in Numerical Simulation

Local Defect Correction in Numerical Simulation of Surface Remelting Martijn Anthonissen Technische with moving heat sources. To account for the local high activity due to the heat source, we introduce local uniform grids and couple the solutions on the global coarse and local fine grids using local defect

Eindhoven, Technische Universiteit

124

Improved numerical simulation of Euler equations

Numerical simulation of nonlinear partial differential equations has been viewed as a process by which a discrete solution is sought which satisfies the conservation laws on the discrete level, without requiring that higher order properties of the differential equation are conserved by the discrete system. For example when the two dimensional incompressible Euler equations in conservation form are solved, the

David Brucker

1991-01-01

125

Simple Numerical Simulation of Strain Measurement

NASA Technical Reports Server (NTRS)

By adopting the basic principle of the reflection (and transmission) of a plane polarized electromagnetic wave incident normal to a stack of films of alternating refractive index, a simple numerical code was written to simulate the maximum reflectivity (transmittivity) of a fiber optic Bragg grating corresponding to various non-uniform strain conditions including photo-elastic effect in certain cases.

Tai, H.

2002-01-01

126

Numerical methods for semiconductor device simulation

NASA Astrophysics Data System (ADS)

This paper describes the numerical techniques used to solve the coupled system of nonlinear partial differential equations which model semiconductor devices. These methods have been encoded into our device simulation package which has successfully simulated complex devices in two and three space dimensions. The discussion focuses on nonlinear operator iteration, discretization and scaling procedures, and the efficient solution of the resulting nonlinear and linear algebraic equations. The companion paper (Fichtner, et al., 1983) discusses physical aspects of the model equations and presents results from several actual device simulations.

Bank, R. E.; Rose, D. J.; Fichtner, W.

1983-09-01

127

Numerical Simulation of a Convective Turbulence Encounter

NASA Technical Reports Server (NTRS)

A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.

Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.

2002-01-01

128

Numerical Simulation of Water Transport into Porous Membranes

Numerical Simulation of Water Transport into Porous Membranes Diplomarbeit vorgelegt von Thomas in a numerical simulation of the process. After a simulation of the forward process has been achieved the numerical simulation of the forward process, i.e., the simulation of the osmotic water flow

MÃ¼nster, WestfÃ¤lische Wilhelms-UniversitÃ¤t

129

Numerical Simulations of Lateral Stress Profiles

NASA Astrophysics Data System (ADS)

A series of numerical simulations have been conducted to provide insight into the observed lateral stress profiles in shocked silicon carbide reported in [1]. Utilizing a coupled eulerian-lagrangian simulation approach, the thin epoxy layer has been included in the model. When utilizing the Johnson-Holmquist ceramic model with the constants published in [2], the two-step structure of the lateral stress measurement has been successfully reproduced. The influence of the epoxy layer on the development of the stress profile will be discussed. Additional simulations of specimens having buffer plates will be performed to simulate the lateral stress profile. [4pt] [1] Millett, J.C.F., Bourne, N.K. and Dandekar, D.P. 2005. ``Delayed failure in shock-loaded silicon carbide,'' J. Appl. Phys. 97, 113513. [0pt] [2] Holmquist, T.J. and Johnson, G.R., 2002. ``Response of silicon carbide to high velocity impact,'' J. Appl. Phys. 91, 5858-5866..

Cheeseman, Bryan; Dandekar, Dattatraya

2009-06-01

130

Numerical Simulation of a Tornado Generating Supercell

NASA Technical Reports Server (NTRS)

The development of tornadoes from a tornado generating supercell is investigated with a large eddy simulation weather model. Numerical simulations are initialized with a sounding representing the environment of a tornado producing supercell that affected North Carolina and Virginia during the Spring of 2011. The structure of the simulated storm was very similar to that of a classic supercell, and compared favorably to the storm that affected the vicinity of Raleigh, North Carolina. The presence of mid-level moisture was found to be important in determining whether a supercell would generate tornadoes. The simulations generated multiple tornadoes, including cyclonic-anticyclonic pairs. The structure and the evolution of these tornadoes are examined during their lifecycle.

Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.

2012-01-01

131

NASA Astrophysics Data System (ADS)

Transition prediction in two-dimensional laminar boundary layers developing on airfoil sections at subsonic speeds and very low turbulence levels is still a challenge. The commonly used semi-empirical prediction tools are mainly based on linear stability theory and do not account for nonlinear effects present unavoidably starting with certain stages of transition. One reason is the lack of systematic investigations of the weakly nonlinear stages of transition, especially of the strongest interactions of the instability modes predominant in non-self-similar boundary layers. The present paper is devoted to the detailed experimental, numerical, and theoretical study of weakly nonlinear subharmonic resonances of Tollmien-Schlichting waves in an airfoil boundary layer, representing main candidates for the strongest mechanism of these initial nonlinear stages. The experimental approach is based on phase-locked hot-wire measurements under controlled disturbance conditions using a new disturbance source being capable to produce well-defined, complex wave compositions in a wide range of streamwise and spanwise wave numbers. The tests were performed in a low-turbulence wind tunnel at a chord Reynolds number of Re = 0.7 × 106. Direct numerical simulations (DNS) were utilized to provide a detailed comparison for the test cases. The results of weakly nonlinear theory (WNT) enabled a profound understanding of the underlying physical mechanisms observed in the experiments and DNS. The data obtained in experiment, DNS and WNT agree basically and provide a high degree of reliability of the results. Interactions occurring between components of various initial frequency-wavenumber spectra of instability waves are investigated by systematic variation of parameters. It is shown that frequency-detuned and spanwise-wavenumber-detuned subharmonic-type resonant interactions have an extremely large spectral width. Similar to results obtained for self-similar base flows it is found that the amplification factors in the frequency-detuned resonances can be even higher than in tuned cases, in spite of the strong base-flow non-self-similarity. An explanation of this unusual phenomenon is found based on the theoretical analysis and comparison of experimental, theoretical, and DNS data.

Würz, W.; Sartorius, D.; Kloker, M.; Borodulin, V. I.; Kachanov, Y. S.; Smorodsky, B. V.

2012-09-01

132

Cost-effective numerical simulation of SEU

A highly modified version of the PISCES 2D simulator has been developed which allows simultaneous solution of the charge collection and circuit problems and the optional use of cylindrical coordinates. The new code has been designed for use in industry and employs robust numerical methods. The program runs on a VAX-11-780 and a typical simulation takes about 4 hours of CPU time. Fortran source code will be distributed at low cost. Test runs have been conducted on an advanced submicron IC process and excellent agreement with cyclotron test data was obtained.

Rollins, J.G.; Tsubota, T.K.; Kolasinski, W.A.; Haddad, N.F.; Rockett, L.; Cerrila, M.; Hennley, W.B.

1988-12-01

133

Numerical simulations of catastrophic disruption: Recent results

NASA Technical Reports Server (NTRS)

Numerical simulations have been used to study high velocity two-body impacts. In this paper, a two-dimensional Largrangian finite difference hydro-code and a three-dimensional smooth particle hydro-code (SPH) are described and initial results reported. These codes can be, and have been, used to make specific predictions about particular objects in our solar system. But more significantly, they allow us to explore a broad range of collisional events. Certain parameters (size, time) can be studied only over a very restricted range within the laboratory; other parameters (initial spin, low gravity, exotic structure or composition) are difficult to study at all experimentally. The outcomes of numerical simulations lead to a more general and accurate understanding of impacts in their many forms.

Benz, W.; Asphaug, E.; Ryan, E. V.

1994-01-01

134

Numerical simulation of microneedles' insertion into skin.

Microneedles have recently received much attention as a novel way for transdermal drug delivery. In this paper, a numerical simulation of the insertion process of the microneedle into human skin is reported using the finite element method. A multilayer skin model consisting of the stratum corneum, dermis and underlying hypodermis has been developed. The effective stress failure criterion has been coupled with the element deletion technique to predict the complete insertion process. The numerical results show a good agreement with the reported experimental data for the deformation and failure of the skin and the insertion force. The influences of the mechanical properties of the skin and the microneedle geometry (e.g. tip area, wall angle and wall thickness) on the insertion force are discussed. The numerical results are helpful for the optimum design of the microneedles for the transdermal drug delivery system. PMID:21480017

Kong, X Q; Zhou, P; Wu, C W

2011-09-01

135

A direct numerical simulation study of vorticity transformation in weakly turbulent premixed flames

NASA Astrophysics Data System (ADS)

Database obtained earlier in 3D Direct Numerical Simulations (DNS) of statistically stationary, 1D, planar turbulent flames characterized by three different density ratios ? is processed in order to investigate vorticity transformation in premixed combustion under conditions of moderately weak turbulence (rms turbulent velocity and laminar flame speed are roughly equal to one another). In cases H and M characterized by ? = 7.53 and 5.0, respectively, anisotropic generation of vorticity within the flame brush is reported. In order to study physical mechanisms that control this phenomenon, various terms in vorticity and enstrophy balance equations are analyzed, with both mean terms and terms conditioned on a particular value c of the combustion progress variable being addressed. Results indicate an important role played by baroclinic torque and dilatation in transformation of average vorticity and enstrophy within both flamelets and flame brush. Besides these widely recognized physical mechanisms, two other effects are documented. First, viscous stresses redistribute enstrophy within flamelets, but play a minor role in the balance of the mean enstrophy overline{? } within turbulent flame brush. Second, negative correlation overline{mathbf {u}^' } \\cdot nabla ? ^' }} between fluctuations in velocity u and enstrophy gradient contributes substantially to an increase in the mean overline{? } within turbulent flame brush. This negative correlation is mainly controlled by the positive correlation between fluctuations in the enstrophy and dilatation and, therefore, dilatation fluctuations substantially reduce the damping effect of the mean dilatation on the vorticity and enstrophy fields. In case L characterized by ? = 2.5, these effects are weakly pronounced and overline{? } is reduced mainly due to viscosity. Under conditions of the present DNS, vortex stretching plays a minor role in the balance of vorticity and enstrophy within turbulent flame brush in all three cases.

Lipatnikov, A. N.; Nishiki, S.; Hasegawa, T.

2014-10-01

136

Numerical simulations on ion acoustic double layers

A comprehensive numerical study of ion acoustic double layers has been performed for both periodic as well as for nonperiodic systems by means of one-dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection potential and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated potential buildup across the system increases with the system length.

Sato, T.; Okuda, H.

1980-07-01

137

Numerical simulations for the DRESDYN precession dynamo

The next generation dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) will consist of a precessing cylindrical container filled with liquid sodium. We perform numerical simulations of kinematic dynamo action applying a velocity field that is obtained from hydrodynamic models of a precession driven flow. So far, the resulting magnetic field growth-rates remain below the dynamo threshold for magnetic Reynolds numbers up to Rm=2000.

Giesecke, A; Gerbeth, G; Gundrum, T; Stefani, F

2014-01-01

138

A numerical simulation of pulsed reacting jets

Numerical simulations of unsteady combusting jets are performed using a dual-time, fully coupled, implicit procedure that enables time step sizes to be based on the particle velocity. Results are presented for a range of I'roude numbers that span the momentum dominated to buoyancy-dominated regimes. At high Froude number conditions, heat release is shown to be stabilizing while at low Froude

Ashvin Hosangadi; Charles L. Merkle; Stephen R. Turns

139

Numerical simulation of swept-wing flows

NASA Technical Reports Server (NTRS)

The transition process characteristics of flows over swept wings were computationally modelled. The crossflow instability and crossflow/T-S wave interaction are analyzed through the numerical solution of the full three dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. The leading-edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.

Reed, Helen L.

1991-01-01

140

Numerical simulation of free surface flows

Numerical simulation of free surface flows is of great interest for industrial applications. Here, numerical model is presented for the simulation of complex fluid flows with free surfaces. The unknowns are the velocity and pressure fields in the liquid region, together with a function defining the volume fraction of liquid. Although the mathematical formulation of the model is similar to the volume of fluid (VOF) method, the numerical schemes used to solve the problem are different. A splitting method is used for the time discretization. At each time step, two advection problems and a generalized Stokes problem are to be solved. Two different grids are used for the space discretization. The two advection problems are solved on a fixed, structured grid made out of small rectangular cells, using a forward characteristic method. The generalized Stokes problem is solved using a finite element method on a fixed, unstructured mesh. Numerical results are presented for several test cases: the filing of a S-shaped channel, the filling of a disk with core, the broken dam in a confined domain.

Maronnier, V.; Picasso, M.; Rappaz, J.

1999-11-01

141

Numerical simulation air pollution in urban areas

A three-dimensional, grid-based numerical air pollution model for the estimation and prediction of air pollutant concentrations in an urban area is developed. Based on the species continuity equation, the modeling system incorporates the combined influences of advective transport, turbulent diffusion, chemical transformation, source emissions and surface removal processes. The model is applied to study the behavior of SO{sub 2} and sulfate concentration distributions in an urban area using the St. Louis Regional Air Pollution Study (RAPS) data. Statistical techniques for the evaluation of the numerical model performance include paired analysis and resampling analysis. The comparisons of the numerical model with the new version of Pollution Episodic Model (PEM-2) and the RAM, a Gaussian model, are also performed using RAPS data base. A comparison between predicted and observed concentrations indicates that the numerical model can satisfactorily simulate the dynamics of the pollutant concentrations in the urban area. The results indicate that besides the uncertainty in the emission rate, the proper characterization of the emissions-as a point source or as an area source-is also critical to the accurate simulation of the concentration field in the urban areas.

Ku, J.Y.

1984-01-01

142

2000 Numerical Propulsion System Simulation Review

NASA Technical Reports Server (NTRS)

The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia, and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective. high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. Major accomplishments include the first formal release of the NPSS object-oriented architecture (NPSS Version 1) and the demonstration of a one order of magnitude reduction in computing cost-to-performance ratio using a cluster of personal computers. The paper also describes the future NPSS milestones, which include the simulation of space transportation propulsion systems in response to increased emphasis on safe, low cost access to space within NASA'S Aerospace Technology Enterprise. In addition, the paper contains a summary of the feedback received from industry partners on the fiscal year 1999 effort and the actions taken over the past year to respond to that feedback. NPSS was supported in fiscal year 2000 by the High Performance Computing and Communications Program.

Lytle, John; Follen, Greg; Naiman, Cynthia; Veres, Joseph; Owen, Karl; Lopez, Isaac

2001-01-01

143

Numerical Simulation Air Pollution in Urban Areas.

NASA Astrophysics Data System (ADS)

A three-dimensional, grid-based numerical air pollution model for the estimation and prediction of air pollutant concentrations in an urban area is developed. Based on the species continuity equation, the modeling system incorporates the combined influences of advective transport, turbulent diffusion, chemical transformation, source emissions and surface removal processes. Recent developments in plume rise and plume penetration processes, non-divergent wind field analysis procedures and numerical solution techniques are described and incorporated in the model. The model is applied to study the behavior of SO(,2) and sulfate concentration distributions in an urban area using the St. Louis Regional Air Pollution Study (RAPS) data. Statistical techniques for the evaluation of the numerical model performance include paired analysis and resampling analysis. The comparisons of the numerical model with the new version of Pollution Episodic Model (PEM-2) and the RAM, a Gaussian model, are also performed using RAPS data base. A comparison between predicted and observed concentrations indicates that the numerical model can satisfactorily simulate the dynamics of the pollutant concentrations in the urban area. The numerical model performs much better in the summer days than in the winter days. A tendency to underpredict the SO(,2) concentrations at the receptors located in the rural areas is observed. Much improvement over the PEM -2 model is the numerical model's consistent performance and accurate prediction for various meteorological conditions which include light winds and sudden changes of wind directions. The numerical model, as revealed by the resampling analysis, performed quite well considering the confidence intervals associated with the uncertainty or variability in the observed concentrations. Finally, the findings of the study regarding the behavior of point and area sources in an urban area provide insight into the complex interrelationships between the point and area source emissions and the various meteorological conditions in determining the surface concentration distribution. The results indicate that besides the uncertainty in the emission rate, the proper characterization of the emissions--as a point source or as an area source--is also critical to the accurate simulation of the concentration field in the urban areas.

Ku, Jia-Yeong

144

UNCORRECTED 2 A toolkit for numerical simulation of PDEs I

UNCORRECTED PROOF 2 A toolkit for numerical simulation of PDEÃ?s I: 3 fundamentals of generic finite-volume simulation 4 Carl Ollivier-Gooch 5 Advanced Numerical Simulation Laboratory, Department of Mechanical of the advanced numerical 21 simulation library framework. 22 Ã? 2002 Published by Elsevier Science B.V. 23 IDT: 18

Ollivier-Gooch, Carl

145

Numerical Simulation of Flowing Blood Cells

NASA Astrophysics Data System (ADS)

The cellular detail of blood is an essential factor in its flow, especially in vessels or devices with size comparable to that of its suspended cells. This article motivates and reviews numerical simulation techniques that provide a realistic description of cell-scale blood flow by explicitly representing its coupled fluid and solid mechanics. Red blood cells are the principal focus because of their importance and because of their remarkable deformability, which presents particular simulation challenges. Such simulations must couple discretizations of the large-deformation elasticity of the cells with the viscous flow mechanics of the suspension. The Reynolds numbers are low, so the effectively linear fluid mechanics is amenable to a wide range of simulation methods, although the constitutive models and geometric factors of the coupled system introduce challenging nonlinearity. Particular emphasis is given to the relative merits of several fundamentally different simulation methods. The detailed description provided by such simulations is invaluable for advancing our scientific understanding of blood flow, and their ultimate impact will be in the design of biomedical tools and interventions.

Freund, Jonathan B.

2014-01-01

146

Numerical recipes for mold filling simulation

Has the ability to simulate the filling of a mold progressed to a point where an appropriate numerical recipe achieves the desired results? If results are defined to be topological robustness, computational efficiency, quantitative accuracy, and predictability, all within a computational domain that faithfully represents complex three-dimensional foundry molds, then the answer unfortunately remains no. Significant interfacial flow algorithm developments have occurred over the last decade, however, that could bring this answer closer to maybe. These developments have been both evolutionary and revolutionary, will continue to transpire for the near future. Might they become useful numerical recipes for mold filling simulations? Quite possibly. Recent progress in algorithms for interface kinematics and dynamics, linear solution methods, computer science issues such as parallelization and object-oriented programming, high resolution Navier-Stokes (NS) solution methods, and unstructured mesh techniques, must all be pursued as possible paths toward higher fidelity mold filling simulations. A detailed exposition of these algorithmic developments is beyond the scope of this paper, hence the authors choose to focus here exclusively on algorithms for interface kinematics. These interface tracking algorithms are designed to model the movement of interfaces relative to a reference frame such as a fixed mesh. Current interface tracking algorithm choices are numerous, so is any one best suited for mold filling simulation? Although a clear winner is not (yet) apparent, pros and cons are given in the following brief, critical review. Highlighted are those outstanding interface tracking algorithm issues the authors feel can hamper the reliable modeling of today`s foundry mold filling processes.

Kothe, D.; Juric, D.; Lam, K.; Lally, B.

1998-07-01

147

NASA Astrophysics Data System (ADS)

Using direct numerical simulation (DNS) data base for wall turbulence, we performed critical assessment of representative dissipation-rate equations (i.e., epsilon of average-epsilon equations) for k-epsilon turbulence models and proposed a new dissipation-rate equation. The DNS data of mean velocity and turbulent kinetic energy are used as the known exact quantities for solving the epsilon or average-epsilon equation. Thus, the obtained values of epsilon are the true solutions with no contaminants. The assessment indicates that, except for one recent model, the performance in predicting the exact epsilon profiles is poor, irrespective of the model type. The proposed model constructed on the basis of the proposal of Nagano and Hishida (1987) provides a good performance, though the model formulation is very simple.

Nagano, Yasutaka; Youssef, Mahmound S.; Shimada, Masaya

1993-06-01

148

Direct numerical simulations of capillary wave turbulence

This work presents Direct Numerical Simulations of capillary wave turbulence solving the full 3D Navier Stokes equations of a two-phase flow. When the interface is locally forced at large scales, a statistical stationary state appears after few forcing periods. Smaller wave scales are generated by nonlinear interactions, and the wave height spectrum is found to obey a power law in both wave number and frequency in good agreement with weak turbulence theory. By estimating the mean energy flux from the dissipated power, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with the exact theoretical value. The time scale separation between linear, nonlinear interaction and dissipative times is also observed. These numerical results confirm the validity of weak turbulence approach to quantify out-of equilibrium wave statistics.

Luc Deike; Daniel Fuster; Michaël Berhanu; Eric Falcon

2014-06-03

149

Direct numerical simulations of capillary wave turbulence.

This work presents direct numerical simulations of capillary wave turbulence solving the full three-dimensional Navier-Stokes equations of a two-phase flow. When the interface is locally forced at large scales, a statistical stationary state appears after few forcing periods. Smaller wave scales are generated by nonlinear interactions, and the wave height spectrum is found to obey a power law in both wave number and frequency, in good agreement with weak turbulence theory. By estimation of the mean energy flux from the dissipated power, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with the exact theoretical value. The time scale separation between linear, nonlinear interaction, and dissipative times is also observed. These numerical results confirm the validity of the weak turbulence approach to quantify out-of equilibrium wave statistics. PMID:24972211

Deike, Luc; Fuster, Daniel; Berhanu, Michael; Falcon, Eric

2014-06-13

150

Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry

This SciDAC project enabled a multidisciplinary research consortium to develop a high fidelity direct numerical simulation (DNS) software package for the simulation of turbulent reactive flows. Within this collaboration, the authors, based at CMU's Pittsburgh Supercomputing Center (PSC), focused on extensive new developments in Sandia National Laboratories' "S3D" software to address more realistic combustion features and geometries while exploiting Terascale computational possibilities. This work significantly advances the state-of-the-art of DNS of turbulent reacting flows.

Raghurama Reddy; Roberto Gomez; Junwoo Lim; Yang Wang; Sergiu Sanielevici

2004-10-15

151

Numerical simulation of swept-wing flows

NASA Technical Reports Server (NTRS)

Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.

Reed, Helen L.

1991-01-01

152

Numerical Simulations Unravel the Cosmic Web

The universe is permeated by a network of filaments, sheets, and knots collectively forming a "cosmic web.'' The discovery of the cosmic web, especially through its signature of absorption of light from distant sources by neutral hydrogen in the intergalactic medium, exemplifies the interplay between theory and experiment that drives science, and is one of the great examples in which numerical simulations have played a key and decisive role. We recount the milestones in our understanding of cosmic structure, summarize its impact on astronomy, cosmology, and physics, and look ahead by outlining the challenges faced as we prepare to probe the cosmic web at new wavelengths.

C. -A. Faucher-Giguere; A. Lidz; L. Hernquist

2008-03-03

153

Direct numerical simulation of turbulent mixing.

The results of three-dimensional numerical simulations of turbulent flows obtained by various authors are reviewed. The paper considers the turbulent mixing (TM) process caused by the development of the main types of instabilities: those due to gravitation (with either a fixed or an alternating-sign acceleration), shift and shock waves. The problem of a buoyant jet is described as an example of the mixed-type problem. Comparison is made with experimental data on the TM zone width, profiles of density, velocity and turbulent energy and degree of homogeneity. PMID:24146009

Statsenko, V P; Yanilkin, Yu V; Zhmaylo, V A

2013-11-28

154

Numerical simulations unravel the cosmic web.

The universe is permeated by a network of filaments, sheets, and knots collectively forming a "cosmic web." The discovery of the cosmic web, especially through its signature of absorption of light from distant sources by neutral hydrogen in the intervening intergalactic medium, exemplifies the interplay between theory and experiment that drives science and is one of the great examples in which numerical simulations have played a key and decisive role. We recount the milestones in our understanding of cosmic structure; summarize its impact on astronomy, cosmology, and physics; and look ahead by outlining the challenges faced as we prepare to probe the cosmic web at new wavelengths. PMID:18174431

Faucher-Giguère, Claude-André; Lidz, Adam; Hernquist, Lars

2008-01-01

155

Nonisothermal flows of viscoelastic fluids Thermodynamics, analysis and numerical simulation

Nonisothermal flows of viscoelastic fluids Thermodynamics, analysis and numerical simulation #12;Nonisothermal flows of viscoelastic fluids Thermodynamics, analysis and numerical simulation De niet bijgedragen. CIP-DATA KONINKLIJKE BIBLIOTHEEK, DEN HAAG Wapperom, Peter Nonisothermal flows of viscoelastic

Wapperom, Peter

156

Characterizing electron temperature gradient turbulence via numerical simulation

Characterizing electron temperature gradient turbulence via numerical simulation W. M. Nevins, California 94551 Received 8 June 2006; accepted 6 November 2006; published online 20 December 2006 Numerical simulations of electron temperature gradient ETG turbulence are presented that characterize the ETG

Hammett, Greg

157

Numerical simulation for a centrifugal heart pump

NASA Astrophysics Data System (ADS)

The primary focus of this work is to investigate unsteady flow simulations for an incompressible fluid. Computational codes are developed and applied for the purpose of analyzing the flow in a centrifugal heart pump, the Innovative Ventricular Assist System (IVAS) pump, which was developed by the Cleveland Clinic Foundation as a part of the National Institute of Health's artificial heart program. In order to simulate the complex flow in the IVAS pump, three capabilities must be incorporated into the simulation codes. The first capability is that the code must be able to simulate the flow through an IVAS pump for Reynolds numbers 30,000~80,000 with numerical stability. The Reynolds numbers in this range are considered to be high in incompressible flow and to have difficulty in simulating a flow with numerical stability. The second capability is that the codes must solve 2-1/2 dimensional Navier-Stokes equations. The 2-1/2 dimensional Navier- Stokes equations are written in such a way that the effect of the variable thickness is included in two- dimensions. The 2-1/2 dimensional analysis enables the simulation of the flow, including the various thickness effects, at nearly the computational speed of two- dimensional analysis. The third capability is that the code must simulate the flow for the entire centrifugal pump, which includes an inlet, rotating blades, a volute, and a diffuser. To perform this intensive calculation, parallel computing is used because of its high computing speed and its ability to accommodate the large computational domain by task partitioning. An intensive parametric study using a single-processor computer is performed with a view to identifying certain problematic aspects of the design methodology. According to the present analysis, the effects of a Reynolds number based on the blade radius and its velocity are not significant for typical pump operation conditions. The flow characteristics, however, change with the Reynolds numbers when they are low. In general, the pressure rise across the pump impeller increases as the radius of the blade arc increases and as the number of blades increases. The findings of this study qualitatively agree with the Euler turbine equation with respect to the effects of the leading edge (inflow) angle and the trailing edge (outflow) angle.

Yano, Keiji

158

NUMERICAL SIMULATION OF SURFACE WATER WAVES ON THE SPHERE

NUMERICAL SIMULATION OF SURFACE WATER WAVES ON THE SPHERE Panayotis Panayotaros Department for the numerical simulation of small amplitude water waves in spherical geometry. The method is based on a free simulation we consider such equations, and our numerical implementation preserves the Hamiltonian structure

159

Numerical Simulation for Asset-Liability Management in Life Insurance

Numerical Simulation for Asset-Liability Management in Life Insurance T. Gerstner1 , M. Griebel1, such as quasi-Monte Carlo and sparse grid methods for the numerical simulation of such models. Their efficiency of regulatory authorities or by a stochastic modelling and simulation. In the latter case, numerical methods

Bartels, Soeren

160

Numerical simulation of the whispering gallery modes in prolate spheroids

Numerical simulation of the whispering gallery modes in prolate spheroids P. Amodioa , T. Levitinab University of Technology, Austria Abstract In this paper, we discuss the progress in the numerical simulation coordinates. However, the numerical simulation of `whispering gallery' phenomena is not straightforward

WeinmÃ¼ller, Ewa B.

161

Numerical simulation of wind effects: a probabilistic perspective Ahsan Kareem

Numerical simulation of wind effects: a probabilistic perspective Ahsan Kareem NatHaz Modeling Laboratory, University of Notre Dame, Notre Dame, IN 46556 ABSTRACT: Numerical simulations of wind loads, offshore structures, or tall buildings. Besides numerical analysis, digitally simulated data is also needed

Kareem, Ahsan

162

Wavelets in numerical simulation: one year study report

Wavelets in numerical simulation: one year study report P. Kagan pkagan@win.tue.nl H.G. ter Morsche reports on one year study concerned with practical applications of wavelets in numerical simulation wavelet based techniques can become core technology in numerical simulations. 1 #12; Contents 1 Objectives

Eindhoven, Technische Universiteit

163

Numerical Simulation in Applied Geophysics. From the Mesoscale to the

Numerical Simulation in Applied Geophysics. From the Mesoscale to the Macroscale Juan E. Santos Numerical Simulation in Applied Geophysics. From the Mesoscale to the Macroscale Â p. #12;Introduction. I process. Numerical Simulation in Applied Geophysics. From the Mesoscale to the Macroscale Â p. #12

Santos, Juan

164

RESEARCH Open Access Efficient procedures for the numerical simulation

RESEARCH Open Access Efficient procedures for the numerical simulation of mid-size RNA kinetics for simulating the kinetic folding of RNAs by numerically solving the chemical master equation have been the Gillespie algorithm, that will allow numerical simulations of mid-size (~ 60Â150 nt) RNA kinetics in some

Barash, Danny

165

Wavelets in numerical simulation: one year study report

Wavelets in numerical simulation: one year study report P. Kagan pkagan@win.tue.nl H.G. ter Morsche reports on one year study concerned with practical applications of wavelets in numerical simulation wavelet based techniques can become core technology in numerical simulations. 1 #12;Contents 1 Objectives

Eindhoven, Technische Universiteit

166

Direct Numerical Simulation of Solid Deformation During Dendritic Solidification

Direct Numerical Simulation of Solid Deformation During Dendritic Solidification M. YAMAGUCHI1, a polycrystalline phase-field model is combined with a material point method stress analysis to numerically simulate in castings. In the current study, a numerical method is developed for simulating the deformation

Beckermann, Christoph

167

The simulation of particulate flows for industrial applications often requires the use of two-fluid models, where the solid particles are considered as a separate continuous phase. One of the underlining uncertainties in the use of the two-fluid models in multiphase computations comes from the boundary condition of the solid phase. Typically, the gas or liquid fluid boundary condition at a solid wall is the so called no-slip condition, which has been widely accepted to be valid for single-phase fluid dynamics provided that the Knudsen number is low. However, the boundary condition for the solid phase is not well understood. The no-slip condition at a solid boundary is not a valid assumption for the solid phase. Instead, several researchers advocate a slip condition as a more appropriate boundary condition. However, the question on the selection of an exact slip length or a slip velocity coefficient is still unanswered. Experimental or numerical simulation data are needed in order to determinate the slip boundary condition that is applicable to a two-fluid model. The goal of this project is to improve the performance and accuracy of the boundary conditions used in two-fluid models such as the MFIX code, which is frequently used in multiphase flow simulations. The specific objectives of the project are to use first principles embedded in a validated Direct Numerical Simulation particulate flow numerical program, which uses the Immersed Boundary method (DNS-IB) and the Direct Forcing scheme in order to establish, modify and validate needed energy and momentum boundary conditions for the MFIX code. To achieve these objectives, we have developed a highly efficient DNS code and conducted numerical simulations to investigate the particle-wall and particle-particle interactions in particulate flows. Most of our research findings have been reported in major conferences and archived journals, which are listed in Section 7 of this report. In this report, we will present a brief description of these results.

Zhi-Gang Feng

2012-05-31

168

Direct Numerical Simulation of dense particle-laden turbulent flows using immersed boundaries

NASA Astrophysics Data System (ADS)

Dense particle-laden turbulent flows play an important role in many engineering applications, ranging from pharmaceutical coating and chemical synthesis to fluidized bed reactors. Because of the complexity of the physics involved in these flows, current computational models for gas-particle processes, such as drag and heat transfer, rely on empirical correlations and have been shown to lack accuracy. In this work, direct numerical simulations (DNS) of dense particle-laden flows are conducted, using immersed boundaries (IB) to resolve the flow around each particle. First, the accuracy of the proposed approach is tested on a range of 2D and 3D flows at various Reynolds numbers, and resolution requirements are discussed. Then, various particle arrangements and number densities are simulated, the impact on particle wake interaction is assessed, and existing drag models are evaluated in the case of fixed particles. In addition, the impact of the particles on turbulence dissipation is investigated. Finally, a strategy for handling moving and colliding particles is discussed.

Wang, Fan; Desjardins, Olivier

2009-11-01

169

Communications in Nonlinear Science and Numerical Simulations Title: Wakes and vortex streets behind a localized force: numerical simulations Article Type: Research Paper Section/Category: Keywords a body force acting inside a small circular area are investigated using direct numerical simulations

Afanassiev, Iakov

170

NASA Technical Reports Server (NTRS)

Spatially evolving instabilities in a boundary layer on a flat plate are computed by direct numerical simulation (DNS) of the incompressible Navier-Stokes equations. In a truncated physical domain, a nonstaggered mesh is used for the grid. A Chebyshev-collocation method is used normal to the wall; finite difference and compact difference methods are used in the streamwise direction; and a Fourier series is used in the spanwise direction. For time stepping, implicit Crank-Nicolson and explicit Runge-Kutta schemes are used to the time-splitting method. The influence-matrix technique is used to solve the pressure equation. At the outflow boundary, the buffer-domain technique is used to prevent convective wave reflection or upstream propagation of information from the boundary. Results of the DNS are compared with those from both linear stability theory (LST) and parabolized stability equation (PSE) theory. Computed disturbance amplitudes and phases are in very good agreement with those of LST (for small inflow disturbance amplitudes). A measure of the sensitivity of the inflow condition is demonstrated with both LST and PSE theory used to approximate inflows. Although the DNS numerics are very different than those of PSE theory, the results are in good agreement. A small discrepancy in the results that does occur is likely a result of the variation in PSE boundary condition treatment in the far field. Finally, a small-amplitude wave triad is forced at the inflow, and simulation results are compared with those of LST. Again, very good agreement is found between DNS and LST results for the 3-D simulations, the implication being that the disturbance amplitudes are sufficiently small that nonlinear interactions are negligible.

Joslin, Ronald D.; Streett, Craig L.; Chang, Chau-Lyan

1992-01-01

171

Numerical Propulsion System Simulation: An Overview

NASA Technical Reports Server (NTRS)

The cost of implementing new technology in aerospace propulsion systems is becoming prohibitively expensive and time consuming. One of the main contributors to the high cost and lengthy time is the need to perform many large-scale hardware tests and the inability to integrate all appropriate subsystems early in the design process. The NASA Glenn Research Center is developing the technologies required to enable simulations of full aerospace propulsion systems in sufficient detail to resolve critical design issues early in the design process before hardware is built. This concept, called the Numerical Propulsion System Simulation (NPSS), is focused on the integration of multiple disciplines such as aerodynamics, structures and heat transfer with computing and communication technologies to capture complex physical processes in a timely and cost-effective manner. The vision for NPSS, as illustrated, is to be a "numerical test cell" that enables full engine simulation overnight on cost-effective computing platforms. There are several key elements within NPSS that are required to achieve this capability: 1) clear data interfaces through the development and/or use of data exchange standards, 2) modular and flexible program construction through the use of object-oriented programming, 3) integrated multiple fidelity analysis (zooming) techniques that capture the appropriate physics at the appropriate fidelity for the engine systems, 4) multidisciplinary coupling techniques and finally 5) high performance parallel and distributed computing. The current state of development in these five area focuses on air breathing gas turbine engines and is reported in this paper. However, many of the technologies are generic and can be readily applied to rocket based systems and combined cycles currently being considered for low-cost access-to-space applications. Recent accomplishments include: (1) the development of an industry-standard engine cycle analysis program and plug 'n play architecture, called NPSS Version 1, (2) A full engine simulation that combines a 3D low-pressure subsystem with a 0D high pressure core simulation. This demonstrates the ability to integrate analyses at different levels of detail and to aerodynamically couple components, the fan/booster and low-pressure turbine, through a 3D computational fluid dynamics simulation. (3) Simulation of all of the turbomachinery in a modern turbofan engine on parallel computing platform for rapid and cost-effective execution. This capability can also be used to generate full compressor map, requiring both design and off-design simulation. (4) Three levels of coupling characterize the multidisciplinary analysis under NPSS: loosely coupled, process coupled and tightly coupled. The loosely coupled and process coupled approaches require a common geometry definition to link CAD to analysis tools. The tightly coupled approach is currently validating the use of arbitrary Lagrangian/Eulerian formulation for rotating turbomachinery. The validation includes both centrifugal and axial compression systems. The results of the validation will be reported in the paper. (5) The demonstration of significant computing cost/performance reduction for turbine engine applications using PC clusters. The NPSS Project is supported under the NASA High Performance Computing and Communications Program.

Lytle, John K.

2000-01-01

172

Jurgen Geiser Numerical Simulations of Sublimation

A S Â¡ Â¢ Â¡ Â£ Â¤Â¥ Â£ Â¦ Â¤ Â¤Â§Â¨ Â¤Â¥ Â¢Â¥Â© Â¥Â¡ Â£ Â¢ Â¡ Â¨ Â¦ Â¤ Â¢ Â¤ Â¦ Â¨ Â¥ Â¦ Â¤Â¥ Â¢ Â¤ Â¢ Â¨ ! Â£ Â¤ Â© Â¨ " Â¤#Â¡ Â£ $ Â© Â¨ % Â¡ Â£ Â¢ Â¨ Â¡ & ' & JÂ¨urgen Geiser Numerical Simulations of Sublimation Growth for SiC single Crystal : Anisotropy of Sublimation Growth for SiC single Crystal: Anisotropy Materials, Radiation and Transient Heat Transfer. Â· Task apparatus SiC growth by physical vapor transport (PVT) SiC-seed-crystal , Gas : 2000 Â 3000 K , SiC

Geiser, Juergen

173

History of the numerical aerodynamic simulation program

NASA Technical Reports Server (NTRS)

The Numerical Aerodynamic Simulation (NAS) program has reached a milestone with the completion of the initial operating configuration of the NAS Processing System Network. This achievement is the first major milestone in the continuing effort to provide a state-of-the-art supercomputer facility for the national aerospace community and to serve as a pathfinder for the development and use of future supercomputer systems. The underlying factors that motivated the initiation of the program are first identified and then discussed. These include the emergence and evolution of computational aerodynamics as a powerful new capability in aerodynamics research and development, the computer power required for advances in the discipline, the complementary nature of computation and wind tunnel testing, and the need for the government to play a pathfinding role in the development and use of large-scale scientific computing systems. Finally, the history of the NAS program is traced from its inception in 1975 to the present time.

Peterson, Victor L.; Ballhaus, William F., Jr.

1987-01-01

174

Computing abstraction hierarchies by numerical simulation

We present a novel method for building ABSTRIPS-style abstraction hierarchies in planning. The aim of this method is to minimize the amount of backtracking between abstraction levels. Previous approaches have determined the criticality of operator preconditions by reasoning about plans directly. Here, we adopt a simpler and faster approach where we use numerical simulation of the planning process. We demonstrate the theoretical advantages of our approach by identifying some simple properties lacking in previous approaches but possessed by our method. We demonstrate the empirical advantages of our approach by a set of four benchmark experiments using the ABTWEAK system. We compare the quality of the abstraction hierarchies generated with those built by the ALPINE and HIGHPOINT algorithms.

Bundy, A.; Giunchiglia, F.; Sebastiani, R.; Walsh, T.

1996-12-31

175

Numerical Simulations of Type Ia Supernova Explosions

We present a systematic study of the diversity of three-dimensional deflagration simulations of Type Ia supernova explosions arising from variations of the initial parameters. By altering the carbon mass fraction, the central density, and the metallicity of the progenitor white dwarf star, we set up a grid of numerical explosion models. While changing the central density has the largest impact on the explosion energy, the largest variation in the 56Ni production is found by changing the metallicity of the models. Varying the carbon mass fraction hardly affects the 56Ni synthesized although it alters the energetics of the explosion. Possible consequences for the shape of light curves of Type Ia supernovae are discussed.

F. K. Roepke; W. Hillebrandt; M. Gieseler; M. Reinecke; C. Travaglio

2006-09-15

176

Direct Numerical Simulation of Automobile Cavity Tones

NASA Technical Reports Server (NTRS)

The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.

Kurbatskii, Konstantin; Tam, Christopher K. W.

2000-01-01

177

Numerical simulation of detonation failure in nitromethane

Detonation failure in the homogeneous liquid explosive nitromethane has been observed experimentally in a wide variety of confining geometries. However, numerical simulation of these failure situations with a wave propagation code has been essentially non-existent due to the large differences between the critical diameter and the length of the reaction zone - characteristic dimensions which differ by about two orders of magnitude. This inability to spatially resolve both the reaction zone and geometries of significant size has led us to propose a new numerical technique, based on the stability criterion for rate-type material models, in which only temporal resolution of the reaction zone is required. Using an improved model for nitromethane, we have carried out a series of two-dimensional calculations which illustrate the utility of the present approach in predicting a wide range of experimental observations. Of particular computational significance is the removal of the difficulty requiring spatial resolution of the reaction zone, so that problems of practical size can be analyzed with existing computer capabilities.

Kipp, M.E.; Nunziato, J.W.

1981-01-01

178

Collisionless microinstabilities in stellarators. II. Numerical simulations

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations.

Proll, J. H. E.; Xanthopoulos, P.; Helander, P. [Max-Planck-Institut für Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Wendelsteinstraße 1, 17491 Greifswald, Germany and Max-Planck/Princeton Research Center for Plasma Physics, 17491 Greifswald (Germany)] [Max-Planck-Institut für Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Wendelsteinstraße 1, 17491 Greifswald, Germany and Max-Planck/Princeton Research Center for Plasma Physics, 17491 Greifswald (Germany)

2013-12-15

179

Numerical simulation of the Polywell device

Recent ideas concerning inertial-electrostatic confinement (IEC) of fusion plasmas coupled with recent experimental results have motivated looking at the problem of confinement of these plasmas in both the gridded (pure electrostatic) and magnetically assisted (via confinement of high beta plasmas in a magnetic cusp) configuration. Questions exist as to the nature of the potential well structure and the confinement properties of high beta plasmas in magnetic cusp configurations. This work focuses on the magnetically assisted concept known as the Polywell{trademark}. Results are reported on the numerical simulation of IEC plasmas aimed at answering some of these questions. In particular the authors focus on two aspects of the Polywell, namely the structure of the magnetic cusp field in the Polywell configuration and the nature of the confinement of a high beta plasma in a magnetic cusp field. The existence of line cusps in the Polywell is still in dispute. A computer code for modeling the magnetic field structure and mod-B surface has been written and results are presented for the Polywell. Another source of controversy is the nature of the confinement of a high beta plasma in a magnetic cusp, and in particular in the polywell. Results from 2-D Particle In Cell (PIC) simulations aimed at answering some of these questions are presented.

Simmons, K.H.; Santarius, J.F. [Univ. of Wisconsin, Madison, WI (United States). Fusion Technology Inst.

1995-12-31

180

Reconnection Diffusion, Star Formation, and Numerical Simulations

NASA Astrophysics Data System (ADS)

We consider fast magnetic reconnection that takes place within turbulent magnetic flux and show that the process results in diffusion of magnetic fields and matter, which we term reconnection diffusion. The process of reconnection diffusion is based on the model of 3D reconnection of weakly turbulent magnetic fields and is applicable to both fully ionized and partially ionized gas. The rate of reconnection diffusion does not depend on the level of ionization and therefore the usually employed ambipolar diffusion idea gets irrelevant for magnetic field transport in turbulent fluids. We claim that the reconnection diffusion process is a manifestation of the violation of flux conservation in highly conducting turbulent fluids. We discuss the consequences of reconnection diffusion for star formation and stress. We show that reconnection diffusion on large scales is independent of small scale magnetic field dynamics of magnetic fields. We conclude that numerical simulations correctly represents the diffusion of actual astrophysical magnetic fields in flows with substantially larger Lundquist numbers if these simulated regions regions are turbulent.

Lazarian, A.

2013-04-01

181

Numerical Simulation of the Perrin - like Experiments

A simple model of random Brownian walk of a spherical mesoscopic particle in viscous liquids is proposed. The model can be both solved analytically and simulated numerically. The analytic solution gives the known Eistein-Smoluchowski diffusion law $ = Dt$ where the diffusion constant $D$ is expressed by the mass and geometry of a particle, the viscosity of a liquid and the average effective time between consecutive collisions of the tracked particle with liquid molecules. The latter allows to make a simulation of the Perrin experiment and verify in detailed study the influence of the statistics on the expected theoretical results. To avoid the problem of small statistics causing departures from the diffusion law we introduce in the second part of the paper the idea of so called Artificially Increased Statistics (AIS) and prove that within this method of experimental data analysis one can confirm the diffusion law and get a good prediction for the diffusion constant even if trajectories of just few particles immersed in a liquid are considered.

Zygmunt Mazur; Dariusz Grech

2006-12-19

182

NASA Astrophysics Data System (ADS)

Parameterization of turbulent momentum and heat fluxes in a turbulent, stably stratified boundary layer flow over water surface is important for numerical climate modeling and weather prediction. In this work, the detailed structure and statistical characteristics of a turbulent, stably stratified atmospheric boundary layer flow over water surface is studied by direct numerical simulation (DNS). The most difficult case for modeling is that of flows at high Reynolds numbers and sufficiently steep surface waves, when strongly non-linear effects (e.g. sheltering, boundary layer separation, vortex formation etc.) are encountered. Of special interest is the influence of the wind flow stratification on the properties of boundary-layer turbulence and the turbulent momentum and heat fluxes. In DNS a two-dimensional water wave with different wave age parameters (c/u*, where u* is the friction velocity and c is the wave celerity), wave slope ka varying from 0 to 0.2 and bulk Reynolds number Re (from 15000 to 80000) and different Richardson numbers are considered. The shape of the water wave is prescribed and does not evolve under the action of the wind. The full, 3D Navier-Stokes equations under the Boussinesq approximation are solved in curvilinear coordinates in a frame of reference moving the phase velocity of the wave. The shear driving the flow is created by an upper plane boundary moving horizontally with a bulk velocity in the x-direction. Periodic boundary conditions are considered in the horizontal (x) and lateral (y) directions, and no-slip boundary condition is considered in the vertical z-direction. The grid of 360 x 240 x 360 nodes in the x, y, and z directions is used. The Adams-Bashforth method is employed to advance the integration in time and the equation for the pressure is solved iteratively. Ensemble-averaged velocity and pressure fields are evaluated by averaging over time and the spanwise coordinate. Profiles of the mean velocity and turbulent stresses are obtained by averaging over wavelength. The DNS results show that the properties of the boundary layer flow are significantly affected by stratification. If the Richardson number Ri is sufficiently small, the flow remains turbulent and qualitatively similar to the non-stratified case. On the other hand, at high Ri turbulent fluctuations and momentum and heat fluxes decay to zero at low wave slope but remain finite at sufficiently large ka (>0.15). Parameterization of turbulent and heat production, diffusion and dissipation is also performed by a closure procedure and compared with the results of DNS. The criteria in terms of the product of the Kolmogorov time scale and local buoyancy frequency or/and the ratio of the Kolmogorov vs. Ozmidov lengh scales is proposed to characterize the different flow regimes observed in DNS. This work was supported by RFBR (project Nos. 10-05-91177, 14-05-00367) and by the grant from the Government of the Russian Federation under contract No. 11.G34.31.0048.

Druzhinin, Oleg; Troitskaya, Yuliya; Zilitinkevich, Sergej

2014-05-01

183

A numerical simulation of the Catalina Eddy

A shallow cyclonic eddy termed the Catalina Eddy has occasionally been observed during summer in the bight of southern California. The Catalina Eddy occurs within {approximately}100 km from the coastal mountains with a depth typically extending up to the marine inversion level of several hundred meters above sea level and a diameter on the order of 100--200 km. The Catalina Eddy is produced by the interaction between the synoptic-scale northerly flow and the formidable topography along the southern California coast. A favorable synoptic situation that enhances the increased low-level climatological northerly flow along the central California coastline is the presence of the prominent east-west pressure gradient between the subtropical East Pacific high and the inland thermal low over California. Increased northerlies impinging on the San Rafael mountains north of Santa Barbara result in enhanced mesoscale lee troughing in the bight and establishment of a narrow ridge alongshore, leading to establishment of cyclonic vorticity in the bight. This paper describes numerical simulations and predictions of a Catalina Eddy event with a high-resolution multi-level limited area model. The model is initialized and forced at the lateral boundaries by the National Meteorological Center`s (NMC) 2.5{degree} {times} 2.5{degree} global objective analysis and also by NMC`s medium range forecast model (MRF) 1--10 day forecasts. In the authors previous effort to simulate mesoscale disturbances such as the Catalina Eddy the integrations were performed up to 1 model-day utilizing the NMC analysis as fixed lateral boundary conditions. In this paper they describe the results of continuous 5- to 7-day simulations of the Catalina Eddy event of 26--30 June 1988 by utilizing time-dependent lateral boundary conditions obtained from NMC`s global objective analysis as well as NMC`s MRF forecasts.

Ueyoshi, Kyozo; Roads, J.O. [Scripps Institution of Oceanography, La Jolla, CA (United States); Alpert, J. [National Meteorological Center, Washington, DC (United States)

1991-12-31

184

Numerical Simulations of Hypersonic Boundary Layer Transition

NASA Astrophysics Data System (ADS)

Numerical schemes for supersonic flows tend to use large amounts of artificial viscosity for stability. This tends to damp out the small scale structures in the flow. Recently some low-dissipation methods have been proposed which selectively eliminate the artificial viscosity in regions which do not require it. This work builds upon the low-dissipation method of Subbareddy and Candler which uses the flux vector splitting method of Steger and Warming but identifies the dissipation portion to eliminate it. Computing accurate fluxes typically relies on large grid stencils or coupled linear systems that become computationally expensive to solve. Unstructured grids allow for CFD solutions to be obtained on complex geometries, unfortunately, it then becomes difficult to create a large stencil or the coupled linear system. Accurate solutions require grids that quickly become too large to be feasible. In this thesis a method is proposed to obtain more accurate solutions using relatively local data, making it suitable for unstructured grids composed of hexahedral elements. Fluxes are reconstructed using local gradients to extend the range of data used. The method is then validated on several test problems. Simulations of boundary layer transition are then performed. An elliptic cone at Mach 8 is simulated based on an experiment at the Princeton Gasdynamics Laboratory. A simulated acoustic noise boundary condition is imposed to model the noisy conditions of the wind tunnel and the transitioning boundary layer observed. A computation of an isolated roughness element is done based on an experiment in Purdue's Mach 6 quiet wind tunnel. The mechanism for transition is identified as an instability in the upstream separation region and a comparison is made to experimental data. In the CFD a fully turbulent boundary layer is observed downstream.

Bartkowicz, Matthew David

185

NASA Astrophysics Data System (ADS)

High-resolution direct numerical simulations (DNSs) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier-Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two and three dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring model performance in capturing the range of dynamics on a range of meshes. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. The use of adaptive mesh optimisation is shown to reduce the required element count by approximately two orders of magnitude in comparison with fixed, uniform mesh simulations. This leads to a substantial reduction in computational cost. The computational savings and flexibility afforded by adaptivity along with the flexibility of FE methods make this model well suited to simulating turbidity currents in complex domains.

Parkinson, S. D.; Hill, J.; Piggott, M. D.; Allison, P. A.

2014-09-01

186

Numerical simulations of possible finite time singularities in the incompressible Euler equations for Theoretical Physics I, Ruhr-UniversitÂ¨at Bochum, Germany The numerical simulation of the 3D incompressible: comparison of numerical methods Tobias Grafke, Holger Homann, JÂ¨urgen Dreher, and Rainer Grauer Institute

Grauer, Rainer

187

NASA Astrophysics Data System (ADS)

Twenty years ago there was no experimental access to the velocity gradient tensor for turbulent flows. Without such access, knowledge of fundamental and defining properties of turbulence, such as vorticity dissipation, and strain rates and helicity, could not be studied in the laboratory. Although a few direct simulations at very low Reynolds numbers had been performed, most of these did not focus on properties of the small scales of turbulence defined by the velocity gradient tensor. In 1987 the results of the development and first successful use of a multisensor hot-wire probe for simultaneous measurements of all the components of the velocity gradient tensor in a turbulent boundary layer were published by Balint et al. [Advances in Turbulence: Proceedings of the First European Turbulence Conference (Springer-Verlag, New York, 1987), p. 456]. That same year measurements of all but one of the terms in the velocity gradient tensor were carried out, although not simultaneously, in the self-preserving region of a turbulent circular cylinder wake by Browne et al. [J. Fluid Mech. 179, 307 (1987)], and the first direct numerical simulation (DNS) of a turbulent channel flow was successfully carried out and reported by Kim et al. [J. Fluid Mech. 177, 133 (1987)], including statistics of the vorticity field. Also in that year a DNS of homogeneous shear flow by Rogers and Moin [J. Fluid Mech. 176, 33 (1987)] was published in which the authors examined the structure of the vorticity field. Additionally, Ashurst et al. [Phys. Fluids 30, 2343 (1987)] examined the alignment of the vorticity and strainrate fields using this homogeneous shear flow data as well as the DNS of isotropic turbulence of Kerr [J. Fluid Mech. 153, 31 (1985)] who had initiated such studies. Furthermore, Metcalfe et al. [J. Fluid Mech. 184, 207 (1987)] published results from their direct simulation of a temporally developing planar mixing layer in which they examined coherent vortical states resulting from secondary instabilities. Since then several experimentalists have used multisensor hot-wire probes of increasing complexity in turbulent boundary layers, wakes, jets, mixing layers, and grid flows. Numerous computationalists have employed DNS in a wide variety of turbulent flows at ever increasing Reynolds numbers. Particle image velocimetry and other optical methods have been rapidly developed and advanced during these two decades which have provided other means of access to these fundamental properties of turbulence. This paper reviews highlights of these remarkable developments and points out some of the most important things we have learned about turbulence as a result.

Wallace, James M.

2009-02-01

188

Numerical Simulations of Falling Sphere Viscometry Experiments.

NASA Astrophysics Data System (ADS)

The falling sphere technique based on Stokes' law is widely used to determine the viscosities of geologically relevant melts at high pressures. Stokes' law is valid when a rigid sphere falls slowly and steadily through a stationary and infinite Newtonian medium of uniform properties. High-pressure falling sphere experiments however, usually involve dropping a dense, refractory sphere through a liquid contained by a cylindrical capsule of finite size. The sphere velocity is influenced by the walls (Faxen correction) and ends of the capsule, and possible convective motion of the fluid. Efforts are made to minimize thermal gradients in laboratory experiments, but small temperature differences within the capsule can lead to convection complicating interpretation. We utilize GALE (Moresi et al., 2003;), a finite element particle-in-cell code, to examine these factors in numerical models of conditions similar to those of high-pressure experiments. Our modeling considers a three- dimensional box or cylinder containing a cluster of particles that represent the dense sphere in laboratory experiments surrounded by low viscosity particles representing the melt. GALE includes buoyancy forces, heat flow, and viscosity variations so our model can be used to assess the effects of the capsule's walls and ends, and the consequences of thermal gradients on the sphere's velocity and trajectory. Comparisons between our numerical simulations and real-time falling sphere experiments involving lower viscosity molten komatiite are made to assess the validity of Stokes' law with the standard Faxen correction included, and formulations considering end effects. The modeling also permits an evaluation of the uncertainties in recovering accurate liquid viscosities from Stokes' law when a dense sphere falls through a convecting low viscosity melt. It also allows us to assess acceleration to a terminal velocity that can provide constraints on melt viscosity in experiments in which the terminal velocity was not reached.

O Dwyer, L.; Kellogg, L. H.; Lesher, C. E.

2007-12-01

189

DNSSM: A Large Scale Passive DNS Security Monitoring Framework

anomalies in both online and offline DNS traffic. This framework entitled DNSSM is implemented participating hosts can be identified and malicious backdoor communications can be detected. Any passive DNS domains hosting phishing sites and malware, covert channel communications over DNS to cache poisoning

Paris-Sud XI, UniversitÃ© de

190

ConfiDNS: Leveraging Scale and History to Detect Compromise

While cooperative DNS resolver systems, such as Co- DNS, have demonstrated improved reliability and perfor- mance over standard approaches, their security has been weaker, since any corruption or misbehavior of a single resolver can easily propagate throughout the system. We address this weakness in a new system called Confi- DNS, which augments the cooperative lookup process with configurable policies that

Lindsey Poole; Vivek S. Pai

2008-01-01

191

Numerical Simulation and Validation of Deepwater Spectral Wind-Waves

A numerical simulation study is carried out over Indian Ocean using spectral wind-wave model “WAM.” The surface wind analysis data utilized in this study are generated by assimilation of satellite data in numerical weather prediction models. These winds are used for forcing the ocean WAve Model (WAM) and various spectral and significant wave parameters are simulated. The model simulated outputs

J. K. Panigrahi; J. Swain

2010-01-01

192

Advanced in turbulence physics and modeling by direct numerical simulations

NASA Technical Reports Server (NTRS)

The advent of direct numerical simulations of turbulence has opened avenues for research on turbulence physics and turbulence modeling. Direct numerical simulation provides values for anything that the scientist or modeler would like to know about the flow. An overview of some recent advances in the physical understanding of turbulence and in turbulence modeling obtained through such simulations is presented.

Reynolds, W. C.

1987-01-01

193

Numerical simulations of unsteady flows in turbomachines

NASA Astrophysics Data System (ADS)

The performance of axial and centrifugal turbomachines is significantly affected by the presence of unsteady and viscous flow mechanisms. Most contemporary design systems, however, use steady or linearized unsteady inviscid flow analyses to generate new blade shapes. In an effort to increase the understanding of unsteady viscous flows in turbomachinery blade rows, and to determine the limitations of linearized inviscid flow analyses, a two-part investigation was conducted. In the first portion of this investigation, a nonlinear viscous flow analysis was developed for the prediction of unsteady flows in two dimensional axial turbomachinery blade rows. The boundary conditions were formulated to allow the specification of vortical, entropic and acoustic excitations at the inlet, and acoustic excitations at exit, of a cascade. Numerical simulations were performed for flat plate and compressor exit guide vane cascades, and the predicted results were compared with solutions from classical linearized theory and linearized inviscid flow analysis. The unsteady pressure fields predicted with the current analysis showed close agreement with the linearized solutions for low to moderate temporal frequency vortical and acoustic excitations. As the temporal frequency of the excitations was increased, nonlinear effects caused discrepancies to develop between the linearized and Navier-Stokes solution sets. The inclusion of viscosity had a significant impact on the unsteady vorticity field, but only a minimal effect on the unsteady pressure field. In the second part of this investigation, a quasi-three-dimensional Navier-Stokes analysis was modified and applied to flows in centrifugal turbomachinery blade rows. Inviscid and viscous flow simulations were performed for a centrifugal impeller at three operating conditions. By comparing the predicted and experimental circumferential distributions of the relative frame velocity and flow angle downstream of the impeller, it was hypothesized that in the experiments the end secondary flows energize the impeller suction surface boundary making the local flow behave like an inviscid fluid. The performance curve generated from the viscous calculations showed close agreement with the experimental data.

Dorney, Daniel Joseph

194

Numerical simulation of magma chamber dynamics.

NASA Astrophysics Data System (ADS)

Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective patterns, giving origin to a density-stratified magma chamber.

Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea

2010-05-01

195

Numerical Simulations of Saturn's Polar Cyclones

NASA Astrophysics Data System (ADS)

Shawn R. Brueshaber, Department of Mechanical Engineering, Western Michigan UniversityKunio M. Sayanagi, Atmospheric and Planetary Sciences, Hampton UniversityCassini mission to Saturn has revealed evidences of a warm core cyclone centered on each of the poles of the planet. The morphology of the clouds in these cyclones resembles that of a terrestrial hurricane. The formation and maintenance mechanisms of these large polar cyclones are yet to be explained. Scott (2011, Astrophys. Geophys. Fluid Dyn) proposed that cyclonic vortices beta-drifting poleward can result in a polar cyclone, and demonstrated that beta-drifting cyclonic vortices can indeed cause accumulation of cyclonic vorticity at the pole using a 1-layer quasi-geostrophic model.The objectives of our project is to test Scott's hypothesis using a 1.5-layer shallow-water model and many-layer primitive equations model. We use the Explicit Planetary Isentropic Coordinate (EPIC) model (Dowling et al. 1998, 2004, Icarus) to perform direct numerical simulations of Saturn's polar atmosphere. To date, our project has focused on modifying the model to construct a polar rectangular model grid in order to avoid the problem of polar singularity associated with the conventional latitude-longitude grids employed in many general circulation models. We present our preliminary simulations, which show beta-drifting cyclones cause a poleward flux of cyclonic vorticity, which is consistent with Scott's results.Our study is partially supported by NASA Outer Planets Research Grant NNX12AR38G and NSF Astronomy and Astrophysics Grant 1212216 to KMS.

Brueshaber, Shawn R.; Sayanagi, Kunio M.

2014-11-01

196

DNS AND LES WITH STOCHASTIC MODELLING OF SUBGRID ACCELERATION APPLIED TO SOLID PARTICLES IN A HIGH

DNS AND LES WITH STOCHASTIC MODELLING OF SUBGRID ACCELERATION APPLIED TO SOLID PARTICLES IN A HIGH implications for many environmental systems, from sediment transport to at- mospheric dispersion of pollutants or solid deposition in ma- rine flows. Previous experimental (Kaftori et al., 1995) and numerical

Boyer, Edmond

197

Rotational threshold in global numerical dynamo simulations

NASA Astrophysics Data System (ADS)

Magnetic field observations of low-mass stars reveal an increase of magnetic activity with increasing rotation rate. The so-called activity-rotation relation is usually attributed to changes in the underlying dynamo processes generating the magnetic field. We examine the dependence of the field strength on rotation in global numerical dynamo models and interpret our results on the basis of energy considerations. In agreement with the scaling law proposed by Christensen and Aubert, the field strength in our simulations is set by the fraction of the available power used for the magnetic field generation. This is controlled by the dynamo efficiency calculated as the ratio of ohmic to total dissipation in our models. The dynamo efficiency grows strongly with increasing rotation rate at a Rossby number of 0.1 until it reaches its upper bound of 1 and becomes independent of rotation. This gain in efficiency is related to the strong rotational dependence of the mean electromotive force in this parameter regime. For multipolar models at Rossby numbers clearly larger than 0.1, on the other hand, we do not find a systematic dependence of the field strength on rotation. Whether the enhancement of the dynamo efficiency found in our dipolar models explains the observed activity-rotation relation needs to be further assessed.

Schrinner, M.

2013-04-01

198

Direct numerical simulations of aeolian sand ripples

Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement towards the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by mid-air collisions. Finally, we provide quantitative support for the use the propagation of these ripples as a proxy for remote measurements of sediment transport.

Orencio Duran; Philippe Claudin; Bruno Andreotti

2014-11-07

199

Numerical Simulation of Martian Historical Dynamo

NASA Astrophysics Data System (ADS)

The remnant magnetic field observed from the Mars Global Surveyor (MSG) mission suggested that Mars possessed an active dynamo at least in its early evolution stage. However, not much is known about the physical conditions for the onset and termination of the Martian dynamo, in particular the critical energy required for maintaining the dynamo. Aiming at this problem, we use our MoSST core dynamics model to simulate Martian historical dynamo with the model parameters set except the Rayleigh number (that measures the buoyancy force relative to the Coriolis force). We run model tests in two different directions: (1) decreasing the Rayleigh number from one value at which strong field dynamo solutions are obtained from the model, to the value at which no dynamo solution could be identified in the model; (2) increasing the Rayleigh number from sub-critical values (respect to the onset of pure convection) until a strong field dynamo solution can be identified. With these sets of numerical tests, we intend to identify the minimum energy necessary to maintain the dynamo action in Mars fluid core.

Jiang, W.; Kuang, W.

2006-05-01

200

Direct numerical simulations of aeolian sand ripples.

Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873

Durán, Orencio; Claudin, Philippe; Andreotti, Bruno

2014-11-01

201

Direct Numerical Simulation of Cell Printing

NASA Astrophysics Data System (ADS)

Structural cell printing, i.e., printing three dimensional (3D) structures of cells held in a tissue matrix, is gaining significant attention in the biomedical community. The key idea is to use desktop printer or similar devices to print cells into 3D patterns with a resolution comparable to the size of mammalian cells, similar to that in living organs. Achieving such a resolution in vitro can lead to breakthroughs in areas such as organ transplantation and understanding of cell-cell interactions in truly 3D spaces. Although the feasibility of cell printing has been demonstrated in the recent years, the printing resolution and cell viability remain to be improved. In this work, we investigate one of the unit operations in cell printing, namely, the impact of a cell-laden droplet into a pool of highly viscous liquids using direct numerical simulations. The dynamics of droplet impact (e.g., crater formation and droplet spreading and penetration) and the evolution of cell shape and internal stress are quantified in details.

Qiao, Rui; He, Ping

2010-11-01

202

NASA Astrophysics Data System (ADS)

Sediment transport in nature comprises of bedload and suspended load, and precise modelling of these processes is essential for accurate sediment flux estimation. Traditionally, non-cohesive suspended sediment has been modelled using the advection-diffusion equation (Garcia, 2008), where the success of the model is largely dependent on accurate approximation of the sediment diffusion coefficients. The current study explores the effect of self-stratification on sediment diffusivity using suspended sediment concentration data from direct numerical simulations (DNS) of flows subjected to different levels of stratification, where the level of stratification is dependent on the particle size (parameterized using particle fall velocity ? and volume-averaged sediment concentration (parameterized using shear Richardson number Ri?. Two distinct configurations were explored, first the channel flow configuration (similar to flow in a pipe or a duct) and second, a boundary-layer configuration (similar to open-channel flow). Self-stratification was found to modulate the turbulence intensity (Cantero et al., 2009b), which in turn was found to reduce vertical sediment diffusivity in portions of the domain exposed to turbulence damping. The effect of particle size on vertical sediment diffusivity has been studied in the past by several authors (Rouse, 1937; Coleman, 1970; Nielsen and Teakle, 2004); so in addition to the effect of particle size, the current study also explores the effect of sediment concentration on vertical sediment diffusivity. The results from the DNS simulations were compared with experiments (Ismail, 1952; Coleman, 1986) and field measurements (Coleman, 1970), and were found to agree qualitatively, especially for the case of channel flows. The aim of the study is to understand the effect of stratification due to suspended sediment on vertical sediment diffusivity for different flow configurations, in order to gain insight of the underlying physics, which will eventually help us to improve the existing models for sediment diffusivity.

Dutta, S.; Cantero, M. I.; Garcia, M. H.

2014-08-01

203

1 Natural Ventilation in Buildings: Measurement in a Wind Tunnel and Numerical Simulation of wind tunnel and numerical simulations of airflow around, within and through bluff bodies with openings ventilation in buildings: measurement in a wind tunnel and numerical simulation with large eddy simulation

Chen, Qingyan "Yan"

204

Direct numerical simulation of solid-liquid flow of Newtonian and viscoelastic fluids

NASA Astrophysics Data System (ADS)

The main theme of this work is to enhance the understanding on the behavior of solid particles in flows of Newtonian or viscoelastic fluids by using both two-dimensional and three-dimensional direct numerical simulations (DNS). A large-scale state-of-the-art software package PARTMOVER3D is developed based on an Arbitrary Lagrangian-Eulerian (ALE) technique and an Elastic-Viscous-Stress-Split (EVSS) scheme. Our numerical results are extensively compared with analytical, experimental and numerical ones in the literature. We studied the motion of spheres sedimenting in a cylindrical tube filled with a Newtonian fluid. The hydrodynamic drag and lift on the particle are investigated under various conditions. The effects of the tube wall, in terms of the blockage ratio and the eccentricity ratio, on the particle terminal velocity, migration and rotation are studied. We also investigated the interaction between pair particles released in tandem or side by side at different Reynolds numbers. The migration of particles in a pressure driven flow is the heart of vast number of industrial applications. Using 3-D direct numerical simulations, we systematically investigated the independent parameters controlling the particle migration, which are the blockage ratio, the flow Reynolds number, and the solid-liquid density ratio. During the particle migration, the mechanisms of the fluid inertia, the wall confinement, the local flow shear rate, the particle slip velocity, the particle size, and the particle rotation were extensively examined through the stress distribution on the particle surface under different flow conditions. In the presence of a shear flow, an initially deposited bed of heavy particles will be entrained into the bulk fluid and convected away with the flow. We investigated the mechanism of this particle resuspension by using 2-D direct numerical simulations. Various effects on the lift force on the particle was analyzed by examining the distribution of the stress on the particle surface. We also studied the orientation of an elliptic particle during its resuspension, analyzed the interaction between a pair of particles, and presented the results of the resuspension of a layer of particles. There are striking differences of particle motions in viscoelastic and Newtonian fluids. We explained the mechanism of the anomalous particle behavior due to the elasticity of the viscoelastic fluid. The effects of the Deborah number, the Reynolds number, the retardation-relaxation time ratio, the blockage ratio, and the eccentricity rate on the behavior of the particles were also systemically investigated.

Zhu, Mingyu

205

A numerical model simulation of longshore transport for Galveston Island

The shoreline changes, deposition patterns, and longshore transport rates were calculated for the coast of Galveston Island using a numerical model simulation. The model only simulated changes due to waves creating longshore currents. East Beach...

Gilbreath, Stephen Alexander

2012-06-07

206

Numerical Simulation of Complex Turbomachinery Flows

NASA Technical Reports Server (NTRS)

An unsteady, multiblock, Reynolds Averaged Navier Stokes solver based on Runge-Kutta scheme and Pseudo-time step for turbo-machinery applications was developed. The code was validated and assessed against analytical and experimental data. It was used to study a variety of physical mechanisms of unsteady, three-dimensional, turbulent, transitional, and cooling flows in compressors and turbines. Flow over a cylinder has been used to study effects of numerical aspects on accuracy of prediction of wake decay and transition, and to modify K-epsilon models. The following simulations have been performed: (a) Unsteady flow in a compressor cascade: Three low Reynolds number turbulence models have been assessed and data compared with Euler/boundary layer predictions. Major flow features associated with wake induced transition were predicted and studied; (b) Nozzle wake-rotor interaction in a turbine: Results compared to LDV data in design and off-design conditions, and cause and effect of unsteady flow in turbine rotors were analyzed; (c) Flow in the low-pressure turbine: Assessed capability of the code to predict transitional, attached and separated flows at a wide range of low Reynolds numbers and inlet freestream turbulence intensity. Several turbulence and transition models have been employed and comparisons made to experiments; (d) leading edge film cooling at compound angle: Comparisons were made with experiments, and the flow physics of the associated vortical structures were studied; and (e) Tip leakage flow in a turbine. The physics of the secondary flow in a rotor was studied and sources of loss identified.

Chernobrovkin, A. A.; Lakshiminarayana, B.

1999-01-01

207

Direct numerical simulations of transition and turbulence in smooth-walled Stokes boundary layer

NASA Astrophysics Data System (ADS)

Stokes boundary layer (SBL) is a time-periodic canonical flow that has several environmental, industrial, and physiological applications. Understanding the hydrodynamic instability and turbulence in SBL, therefore, will shed more light on the nature of such flows. Unlike its steady counterpart, the flow in a SBL varies both in space and time, which makes hydrodynamic instability and transition from laminar to turbulent state highly complicated. In this study, we utilized direct numerical simulations (DNS) to understand the characteristics of hydrodynamic instability, the transition from laminar to turbulent state, and the characteristics of intermittent turbulence in a smooth SBL for Re_? in the range of 500-1000. Simulation results show that nonlinear growth plays a critical role on the instability at Re_? = 500 and 600. However, the nonlinear growth does not warrant sustainable transition to turbulence and the outcome is highly dependent on the amplitude and spatial distribution of the initial velocity disturbance in addition to Re_? . Simulation results at Re_? = 500 confirm that instability and subsequent transitional flow will eventually decay. At Re_? = 600 nonlinear growth recurs at every modulation period but such transition does not evolve into fully developed turbulence at any time in the modulation cycle. At Re_? = 700, the flow shows features of fully developed turbulence during some modulation periods and the transitional character of Re_? = 600 at the remaining. Therefore, we conclude that flow in the range of Re_? = 600-700 is to be classified as self-sustaining transitional flow. For higher Reynolds number the flow indeed exhibits features of fully developed boundary layer turbulence for a portion of the wave period, which is known as the intermittently turbulent regime in the literature.

Ozdemir, Celalettin E.; Hsu, Tian-Jian; Balachandar, S.

2014-04-01

208

Numerical simulation of steam condensation in a nozzle

NASA Astrophysics Data System (ADS)

This paper describes a model of compressible ?ow including homogenous nucleation and consequent growth and evaporation of droplets. Considered ?uid is water vapor with relatively small mass fraction of dispersed water droplets. Main issues of numerical simulation based on this model are discussed. Results of numerical simulation are compared with experimental data.

Halama, Jan; Fort, Jaroslav

2012-04-01

209

NEW NUMERICAL TECHNOLOGIES FOR THE SIMULATION OF ARC WELDING PROCESSES

NEW NUMERICAL TECHNOLOGIES FOR THE SIMULATION OF ARC WELDING PROCESSES Michel Bellet 1 , Makhlouf for arc welding simulation and analysis. The new numerical technologies essentially consist first arc welding processes, named TRANSWELD. It is based on coupled solutions of heat transfer

Paris-Sud XI, UniversitÃ© de

210

NUMERICAL SIMULATIONS OF TRANSVERSE COMPRESSION AND DENSIFICATION IN WOOD

NUMERICAL SIMULATIONS OF TRANSVERSE COMPRESSION AND DENSIFICATION IN WOOD John A. Nairn1 Professor) ABSTRACT Numerical modeling, such as finite element analysis (FEA), of complex structures and complex ma as an anisotropic continuum is used, numerical modeling of realistic wood structures, including details of wood

Nairn, John A.

211

Numerical Simulation of Dynamic Ductile Fracture of SS304

A numerical simulation based on the pressure-sensitive yield criterion of Gurson mesomechanics model is presented for explicit dynamic finite element calculations of SS304 bar under tension at high rates of strain. The necking process, including void nucleation and coalescence, is modeled numerically. The result shows clearly the crack propagation and eventual separation. The numerical analysis is compared with the test,

Zhang Zhongguo; Huang Xicheng

2010-01-01

212

Numerical simulation of tyre\\/road noise

In modern society, traffic noise has become an important issue for mental health. A significant contributor to this noise pollution is exterior tyre\\/road noise, which is caused by the interaction between tyre and road surface and. In order to reduce tyre\\/road noise at the source, accurate numerical prediction models are needed.\\u000aThis research deals with the development of quantitative numerical

Jan Henk Schutte

2011-01-01

213

Numerical simulation of unsteady mixing layers

Time-dependent compressible conservation equations are solved numerically in order to examine the evolution of large-scale structures resulting from the Kelvin-Helmholtz instability. Three two-dimensional configurations are considered: a planar splitter plate, an axisymmetric round jet, and an axisymmetric central dump combustor. The evolution of the axisymmetric gas jet emerging into a quiescent background is numerically studied, and the effects of the

E. S. Oran; J. P. Boris; K. Kailasanath; F. F. Grinstein

1986-01-01

214

Particle Dispersion in a Transitional Axisymmetric Jet: A Numerical Simulation

Numerical simulations are used to study the dynamics and dispersion of particles in the near field of a high velocity transitional axisymmetric jet. A time-dependent finite-difference approach that employs a fourth-order, phase-accurate flux-corrected transport algorithm is used to simulate the flow. Extensive flow visualization and analysis based on numerical simulation are employed to analyze the influence of large-scale vortical structures

J. Uthuppan; S. K. Aggarwalf; F. F. Grinstein; K. Kailasanath

215

Particle dispersion in a transitional axisymmetric jet: A numerical simulation

Numerical simulations are used to study the dynamics and dispersion of particles in the near field of a high velocity transitional axisymmetric jet. A time-dependent finite-difference approach that employs a fourth-order, phase-accurate flux-corrected transport algorithm is used to simulate the flow. Extensive flow visualization and analysis based on numerical simulation are employed to analyze the influence of large-scale vortical structures

J. Uthuppan; S. K. Aggarwal; F. F. Grinstein; K. Kailasanath

1994-01-01

216

Numerical Simulation of Two Phase Flows

NASA Technical Reports Server (NTRS)

Two phase flows can be found in broad situations in nature, biology, and industry devices and can involve diverse and complex mechanisms. While the physical models may be specific for certain situations, the mathematical formulation and numerical treatment for solving the governing equations can be general. Hence, we will require information concerning each individual phase as needed in a single phase. but also the interactions between them. These interaction terms, however, pose additional numerical challenges because they are beyond the basis that we use to construct modern numerical schemes, namely the hyperbolicity of equations. Moreover, due to disparate differences in time scales, fluid compressibility and nonlinearity become acute, further complicating the numerical procedures. In this paper, we will show the ideas and procedure how the AUSM-family schemes are extended for solving two phase flows problems. Specifically, both phases are assumed in thermodynamic equilibrium, namely, the time scales involved in phase interactions are extremely short in comparison with those in fluid speeds and pressure fluctuations. Details of the numerical formulation and issues involved are discussed and the effectiveness of the method are demonstrated for several industrial examples.

Liou, Meng-Sing

2001-01-01

217

61 Numerical Simulation of Vehicle Cooling Systems

Heat management must allow the adjustment of optimal operating temperatures of all components of a vehicle. A comprehensive simulation model will contain all components relevant for heat management. This includes heat sources, heat exchangers, fans etc.. Main aspects of the simulation are air flow and heat transfer analysis. It will be shown that a combination of 1- and 3-dimensional methods

Rudolf REITBAUER; Josef HAGER; Roland MARZY

2000-01-01

218

Numerical simulation of turbulent combustion: Scientific challenges

NASA Astrophysics Data System (ADS)

Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes, improving engine performance, and reducing pollutant emissions. Critical issues as turbulence modeling, turbulence-chemistry interaction, and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for high-fidelity combustion simulation. This paper reviews the current status of the state-of-the-art large eddy simulation (LES)/prob-ability density function (PDF)/detailed chemistry approach that can address the three challenging modelling issues. PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described. Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified. Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.

Ren, ZhuYin; Lu, Zhen; Hou, LingYun; Lu, LiuYan

2014-08-01

219

Numerical error in groundwater flow and solute transport simulation

NASA Astrophysics Data System (ADS)

Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [Voss, 1984] as being a typical finite element code. Our numerical analysis suggests that SUTRA incorporates a numerical dispersion error and that its mass-lumped numerical scheme increases the numerical error. This is confirmed using a Gaussian test problem. A modified SUTRA code, in which the numerical dispersion is calculated and subtracted, produces better results. The much more challenging Elder problem [Elder, 1967; Voss and Souza, 1987] is then considered. Calculation of its numerical dispersion coefficients and numerical stability show that the Elder problem is prone to error. We confirm that Elder problem results are extremely sensitive to the simulation method used.

Woods, Juliette A.; Teubner, Michael D.; Simmons, Craig T.; Narayan, Kumar A.

2003-06-01

220

Numerical simulation of corneal transport processes

This paper presents a numerical study on the transport of ions and ionic solution in human corneas and the corresponding influences on corneal hydration. The transport equations for each ionic species and ionic solution within the corneal stroma are derived based on the transport processes developed for electrolytic solutions, whereas the transport across epithelial and endothelial membranes is modelled by using phenomenological equations derived from the thermodynamics of irreversible processes. Numerical examples are provided for both human and rabbit corneas, from which some important features are highlighted. PMID:16849239

Li, Long-yuan; Tighe, Brian

2005-01-01

221

Numerical simulation of a collapsible nonlinear structure subjected to impacts

A numerical model for the simulation of dynamic compression of a co llapsible multilayer structure subjected to transient compressive excitation is described and tested. It is shown that impacts induce a chaotic collapse of crumple layers. The simulations predict shock pulses and intralaminar forces. Simulated shock pulses that a free -falling impactor is subjected to, and the corresponding animated deformation

Michael A. Sek

222

Coupled numerical simulation of hot stamping process and experimental verification

NASA Astrophysics Data System (ADS)

Hot stamping process is a high non-linear process showing the effect on thermal, mechanical and metallurgical phenomena as they relate to each other. In order to carry out this coupled numerical simulation, fundamental thermal properties such as interfacial heat transfer coefficient and convection heat transfer coefficient as well as crucial mechanics properties were first investigated. Hot stamping tools with cooling system which has been optimized by genetic algorithm were employed in the simulation. The coupled numerical simulation to the whole hot stamping process was built with the ABAQUS/Explicit and FLUENT. Experiment was setup and the results of blank temperature and spring-back were compared with the results of coupled numerical simulation. The comparisons show that the simulation results of numerical model are consistent with experimental results.

Li, Ye; Ying, Liang; Hu, Ping; Shi, Dongyong; Zhao, Xi; Dai, Minghua

2013-05-01

223

Numerical simulations in the development of propellant management devices

NASA Astrophysics Data System (ADS)

Propellant management devices (PMDs) are used for positioning the propellant at the propel-lant port. It is important to provide propellant without gas bubbles. Gas bubbles can inflict cavitation and may lead to system failures in the worst case. Therefore, the reliable operation of such devices must be guaranteed. Testing these complex systems is a very intricate process. Furthermore, in most cases only tests with downscaled geometries are possible. Numerical sim-ulations are used here as an aid to optimize the tests and to predict certain results. Based on these simulations, parameters can be determined in advance and parts of the equipment can be adjusted in order to minimize the number of experiments. In return, the simulations are validated regarding the test results. Furthermore, if the accuracy of the numerical prediction is verified, then numerical simulations can be used for validating the scaling of the experiments. This presentation demonstrates some selected numerical simulations for the development of PMDs at ZARM.

Gaulke, Diana; Winkelmann, Yvonne; Dreyer, Michael

224

Numerical Simulation on Flow in Column Chromatography

NASA Astrophysics Data System (ADS)

Monolithic columns have attracted much attention as a novel platform for high throughput analysis, but there is little information about the fluid profile in the flow channels. In this paper, we presented our approach for the fluid simulation in column chromatography by the lattice Boltzmann method (LBM). To simulate the monolithic column system, the calculation domain was modeled by the 3D channel flow through sphere obstacles. Several types of porous structure were used, with uniform and nonuniform pores. Based on the simulations results, we discussed fluid flow and pressure variation for the optimization of the suitable structure for HPLC system.

Yamamoto, Kazuhiro; Komiyama, Ryo; Umemura, Tomonari

2013-12-01

225

Numerical Simulation of Baroclinic Jovian Vortices

We examine the evolution of baroclinic vortices in a time-dependent, nonlinear numerical model of a Jovian atmosphere. The model uses a normal-mode expansion in the vertical, using the barotropic and first two baroclinic modes. Results for the stability of baroclinic vortices on an f plane in the absence of a mean zonal flow are similar to results of Earth vortex

Richard K. Achterberg; Andrew P. Ingersoll

1994-01-01

226

Polarization transmission at RHIC, numerical simulations

Typical tracking simulations regarding the transmission of the polarization in the proton-proton collider RHIC are discussed. They participate in general studies aimed at understanding and improving polarization performances during polarized proton-proton runs.

Meot F.; Bai, M.; Liu, C.; Minty, M.; Ranjbar, V.

2012-05-20

227

DNS benchmark solution of the fully developed turbulent channel flow with heat transfer

NASA Astrophysics Data System (ADS)

In the present paper direct numerical simulation (DNS) of the fully developed turbulent non-isothermal flow has been study for Re?=150 and for Pr=1.0. The focus is on the role of the thermal boundary condition type on the results. Various types of thermal boundary conditions presented in literature has been considered in this work: isoflux wall boundary conditions, symmetrical isofluxes wall boundary conditions and isothermal b.c. also with combination with adiabatic or isothermal second wall. Turbulence statistics for the fluid flow and thermal field as well turbulence structures are presented and compared. Numerical analysis assuming both zero and non-zero temperature fluctuations at the wall and zero and non-zero temperature gradient in the channel centre shows that thermal structures may differ depend on case and region. Results shows that the type of thermal boundary conditions significantly influence temperature fluctuations while the mean temperature is not affected. Difference in temperature fluctuation generate the difference in turbulent heat fluxes. Presented results are prepared in the form of the benchmark solution data and will be available in the digital form on the website http://home.agh.edu.pl/jaszczur.

Jaszczur, M.

2014-08-01

228

Numerical simulations for MHD coronal seismology

NASA Astrophysics Data System (ADS)

Magnetohydrodynamic (MHD) processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction of transverse structuring into models for the corona modifies the behavior of MHD waves through processes such as dispersion and mode coupling. Exploiting our understanding of MHD waves with the diagnostic tool of coronal seismology relies upon the development of sufficiently detailed models to account for all the features in observations. The development of realistic models appropriate for highly structured and dynamical plasmas is often beyond the domain of simple mathematical analysis and so numerical methods are employed. This paper reviews recent numerical results for seismology of the solar corona using MHD.

Pascoe, David James

2014-07-01

229

Numerical simulation of magmatic hydrothermal systems

The dynamic behavior of magmatic hydrothermal systems entails coupled and nonlinear multiphase flow, heat and solute transport, and deformation in highly heterogeneous media. Thus, quantitative analysis of these systems depends mainly on numerical solution of coupled partial differential equations and complementary equations of state (EOS). The past 2 decades have seen steady growth of computational power and the development of numerical models that have eliminated or minimized the need for various simplifying assumptions. Considerable heuristic insight has been gained from process-oriented numerical modeling. Recent modeling efforts employing relatively complete EOS and accurate transport calculations have revealed dynamic behavior that was damped by linearized, less accurate models, including fluid property control of hydrothermal plume temperatures and three-dimensional geometries. Other recent modeling results have further elucidated the controlling role of permeability structure and revealed the potential for significant hydrothermally driven deformation. Key areas for future reSearch include incorporation of accurate EOS for the complete H2O-NaCl-CO2 system, more realistic treatment of material heterogeneity in space and time, realistic description of large-scale relative permeability behavior, and intercode benchmarking comparisons. Copyright 2010 by the American Geophysical Union.

Ingebritsen, S.E.; Geiger, S.; Hurwitz, S.; Driesner, T.

2010-01-01

230

High order hybrid numerical simulations of two dimensional detonation waves

NASA Technical Reports Server (NTRS)

In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.

Cai, Wei

1993-01-01

231

A Precise and Efficient Evaluation of the Proximity between Web Clients and their Local DNS Servers

and local DNS associations are in the same network-aware cluster [13] (based on BGP routing information from. To determine an FQDN's address, a DNS client sends a request to its local DNS server. The local DNS server resolves the request on behalf of the client by querying a set of authoritative DNS servers. When the local

Mao, Zhuoqing Morley

232

Numerical simulation of powered-lift flows

NASA Technical Reports Server (NTRS)

This article presents work performed at NASA Ames involving the application of computational fluid dynamics (CFD) to the prediction of flows encountered by powered-lift aircraft operating in ground effect. These flows are characterized by jet and jet-induced flows interacting with the ground and aerodynamic surfaces. Over the last five years, work has progressed from simulating the interaction of a single jet impacting on a ground plane, through the simulation of a delta planform with multiple jets in ground effect, to an ongoing effort to simulate the complete flow about a Harrier AV-8B in ground effect. Efforts have also been made to predict the thermal interaction between hot propulsive jets and a landing surface of arbitrary thermal properties. Progress to data in each of these areas is outlined.

Van Dalsem, William R.; Chawla, Kalpana; Smith, Merritt H.; Abeloff, Patricia A.

1990-01-01

233

Numerical simulation of powered-lift flows

NASA Technical Reports Server (NTRS)

This article presents work performed at NASA's Ames Research Center involving the application of Computational Fluid Dynamics (CFD) to the prediction of flows encountered by powered-lift aircraft operating in ground effect. These flows are characterized by jet and jet-induced flows interacting with the ground and aerodynamic surfaces. Over the last five years, work has progressed from simulating the interaction of a single jet impacting on a ground plane, through the simulation of a delta planform with multiple jets in ground effect, to an ongoing effort to simulate the complete flow about a Harrier AV-8B in ground effect. Efforts have also been made to predict the thermal interaction between hot propulsive jets and a landing surface of arbitrary thermal properties. Progress to date in each of these areas will be outlined.

Van Dalsem, William R.; Chawla, Kalpana; Smith, Merritt H.; Abeloff, Patricia A.

1990-01-01

234

SCIT-DNS: Critical Infrastructure Protection through Secure DNS Server Dynamic Updates

framework of DNS servers that voids the above requirement. Our approach, called Self-Cleansing Intrusion rotation and self-cleansing cycles are in the range of minutes, restricting the damages of even undetected assurance, intrusion containment, self-cleansing systems I. INTRODUCTION As the world becomes ever more

Sood, Arun K.

235

Fundamental Study toward Numerical Simulation of Turbulent Combustion Control

Toward the numerical simulation of the total system of turbulent combustion control, fundamental studies on diffusion\\/premixed flames are conducted. In the diffusion flame simulation, the effect of swirled jet on the hydrogen\\/air jet diffusion flame is investigated and it is shown that the lift-off height decreases by the swirl effect. For premixed flame simulations, a non-reacting swirler flow is simulated

Yasuhiro MIZOBUCHI; Ryoji TAKAKI; Shigeru TACHIBANA; Satoru OGAWA

236

Numerical simulation of flow separation control by oscillatory fluid injection

In this work, numerical simulations of flow separation control are performed. The sep-aration control technique studied is called 'synthetic jet actuation'. The developed code employs a cell centered finite volume scheme which handles viscous...

Resendiz Rosas, Celerino

2005-08-29

237

Direct Numerical Simulations of Plunging Airfoils Yves Allaneau

Direct Numerical Simulations of Plunging Airfoils Yves Allaneau and Antony Jameson Stanford plunging airfoils using a low dissipation finite volume scheme that preserves kinetic energy. The kinetic Reynolds numbers plunging airfoils. Results are discussed and compared with experimental data. Nomenclature

Jameson, Antony

238

Numerical Simulation Study on Transpired Solar Air Collector

The unglazed transpired solar air collector is now a well-recognized solar air heater for heating outside air directly. In this article, researchers introduced numerical simulation tools into the solar air collector research area, analyzed...

Wang, C.; Guan, Z.; Zhao, X.; Wang, D.

2006-01-01

239

Numerical simulation of the plasma double layer

A one-dimensional particle-in-cell computer simulation is used to model the formation of an electrostatic double layer. The conditions for the onset of the layer formation are explored and a relation between the length of the layer and the electrostatic potential difference across is found.

Christoph K. Goertz; Glenn Joyce

1975-01-01

240

Numerical Simulations ANSYS FLUENT 14.0

-fin geometry to minimize fabrication issues Â· Determine how variations in fin-tip contact affect thermal tetrahedral cells Â· Uniform incident heat flux of 10 MW/m2 Â· Simulations: realizable k- turbulence model.5104, 9104 Â· Optimization objective Â· Minimize average heated surface (pressure boundary) temperature

California at San Diego, University of

241

Brush seal numerical simulation: Concepts and advances

NASA Technical Reports Server (NTRS)

The development of the brush seal is considered to be most promising among the advanced type seals that are presently in use in the high speed turbomachinery. The brush is usually mounted on the stationary portions of the engine and has direct contact with the rotating element, in the process of limiting the 'unwanted' leakage flows between stages, or various engine cavities. This type of sealing technology is providing high (in comparison with conventional seals) pressure drops due mainly to the high packing density (around 100 bristles/sq mm), and brush compliance with the rotor motions. In the design of modern aerospace turbomachinery leakage flows between the stages must be minimal, thus contributing to the higher efficiency of the engine. Use of the brush seal instead of the labyrinth seal reduces the leakage flow by one order of magnitude. Brush seals also have been found to enhance dynamic performance, cost less, and are lighter than labyrinth seals. Even though industrial brush seals have been successfully developed through extensive experimentation, there is no comprehensive numerical methodology for the design or prediction of their performance. The existing analytical/numerical approaches are based on bulk flow models and do not allow the investigation of the effects of brush morphology (bristle arrangement), or brushes arrangement (number of brushes, spacing between them), on the pressure drops and flow leakage. An increase in the brush seal efficiency is clearly a complex problem that is closely related to the brush geometry and arrangement, and can be solved most likely only by means of a numerically distributed model.

Braun, M. J.; Kudriavtsev, V. V.

1994-01-01

242

NUMERICAL SIMULATION OF GENERALIZED KP TYPE EQUATIONS WITH SMALL DISPERSION

of shallow water waves, a natural generalization of the KdV equation is the 2 + 1 dimensional Kadomtsev be interested in a numerical study of solutions to (1.4), and their corresponding KdV sector, in the regime 1NUMERICAL SIMULATION OF GENERALIZED KP TYPE EQUATIONS WITH SMALL DISPERSION CHRISTIAN KLEIN

Sparber, Christof

243

Numerical Simulation of Extreme Wave Generation Using VOF Method

Numerical simulations of extreme wave generation are carried out by using the Volume Of Fluid (VOF) method. Extreme waves are generated based on wave focusing in a 2-D numerical model. To validate the capability of the VOF-based model described in this article, the propagation of regular waves is computed and compared with the theoretical results. By adjusting the phases of

Xi-zeng ZHAO; Chang-hong HU; Zhao-chen SUN

2010-01-01

244

Numerical simulation of a supercritical CO 2 geothermosiphon

The thermo-hydraulic performance of a CO2 geothermosiphon has been numerically investigated using the commercially available software CFX. A simple Engineered (or Enhanced) Geothermal System, EGS, consisting of an injection and a production well as well as a reservoir is numerically simulated. Both water and carbon dioxide have been examined as the working fluid. While the former fluid has been very

M. Haghshenas Fard; K. Hooman; H. T. Chua

245

Numerical simulation of ceramic breeder pebble bed thermal creep behavior

Numerical simulation of ceramic breeder pebble bed thermal creep behavior Alice Ying *, Hulin Huang Abstract The evolution of ceramic breeder pebble bed thermal creep deformation subjected to an external load and a dif- ferential thermal stress was studied using a modified discrete numerical code

Abdou, Mohamed

246

Numerical simulations of a diode laser BPH treatment system

Numerical simulations are presented of the laser-tissue interaction of a diode laser system for treating benign prostate hyperplasia. The numerical model includes laser light transport, heat transport, cooling due to blood perfusion, thermal tissue damage, and enthalpy of tissue damage. Comparisons of the stimulation results to clinical data are given. We report that a reasonable variation from a standard set

Richard A. London; Victor C. Esch; Stephanos Papademetriou

1999-01-01

247

NUMERICAL SIMULATION OF IVlULTIPOLE PLASMA CONFINEMENT

and gun injected plasmas can also be studied. The numerical predictions and comparisons with experimentalNUMERICAL SIMULATION OF IVlULTIPOLE PLASMA CONFINEMENT by J. C. Sprott February 1973 PLP 505 Plasma averaged quantities. It has been used mostly to study cw microwave heated plasmas, but pulsed microwave

Sprott, Julien Clinton

248

NUMERICAL SIMULATION OF COMPRESSIBLE TWO-PHASE FLUID FLOW

NUMERICAL SIMULATION OF COMPRESSIBLE TWO-PHASE FLUID FLOW : Ghost fluid method vs Saurel Abgrall Discretization Â Saurel-Abgrall Approach Â "Real" Ghost Fluid Method Â· Numerical Results Â Shock Mathieu Bachmann 2 #12;Motivation Cavitation near a Solid2 rapid collapse, jet formation near boundaries

Helluy, Philippe

249

Numerical Simulation of Mud-Filtrate Invasion in Deviated Wells

of deviated wells. We simulate numerically the physics of mud-filtrate invasion in vertical, horizontal by introducing an effective-flow-rate function that describes the evo- lution in time of the rate of invasion (numerically and in the laboratory) the physics of mud-filtrate invasion. Drilling variables such as mud

Torres-VerdÃn, Carlos

250

. This modification of the nonlinear SchrÂ¨odinger equation has been used to model pulse propagation in some modeProject: Numerical errors GOALS 1. To characterize and understand numerical error in simulations of the nonlinear SchrÂ¨odinger equation and modifications of it. REFERENCES 1. O. E. Martinez, R. L. Fork, and J. P

Maryland, Baltimore County, University of

251

Numerical Simulations of Acoustically Driven, Burning Droplets

NASA Astrophysics Data System (ADS)

The burning characteristics of fuel droplets exposed to external acoustical excitation within a microgravity environment are investigated numerically. The issue of acoustic excitation of flames in microgravity is especially pertinent to understanding the behavior of accidental fires which could occur in spacecraft crew quarters and which could be affected by pressure perturbations as result from ventilation fans or engine vibrations. Combustion of methanol fuel droplets is considered here using a full chemical reaction mechanism.(Marchese, A.J., et al., 26th Symp. (Int.) on Comb., p. 1209, 1997) The droplet and surrounding diffusion flame are situated within a cylindrical acoustic waveguide where standing waves are generated with varying frequency and amplitude. Applied sound pressure levels are limited at present to magnitudes for which the droplet shape remains spherical. A third order accurate, essentially-non-oscillatory (ENO) numerical scheme is employed to accurately resolve the spatial and temporal evolution of the flame front. Acoustically excited vs. non-excited external conditions for the burning droplet in microgravity are compared, and the effects of acoustic frequency, sound pressure level, and relative position of the droplet with respect to pressure and velocity nodes are explored.

Kim, Heon-Chang; Karagozian, Ann R.; Smith, Owen I.

1999-11-01

252

Radiative Transfer in 3D Numerical Simulations

We simulate convection near the solar surface, where the continuum optical depth is of order unity. Hence, to determine the radiative heating and cooling in the energy conservation equation, we must solve the radiative transfer equation (instead of using the diffusion or optically thin cooling approximations). A method efficient enough to calculate the radiation for thousands of time steps is needed. We assume LTE and a non-gray opacity grouped into 4 bins according to strength. We perform a formal solution of the Feautrier equation along a vertical and four straight, slanted, rays (at four azimuthal angles which are rotated 15 deg. every time step). We present details of our method. We also give some results: comparing simulated and observed line profiles for the Sun, showing the importance of 3D transfer for the structure of the mean atmosphere and the eigenfrequencies of p-modes, illustrating Stokes profiles for micropores, and analyzing the effect of radiation on p-mode asymmetries.

Robert Stein; Aake Nordlund

2002-09-24

253

Numerical Simulation of Pulsed Meander Coil Emat

NASA Astrophysics Data System (ADS)

Electro magnetic acoustic transducers (EMATs) are now being widely investigated for non-contact non-destructive testing (NDT) of solid materials. This type of transducer can generate and/or detect ultrasound in electrically conductive or magnetic materials through the Lorentz force principle and/or magneto-elastic effects. This work describes about the Meander coil EMAT that is modeled using finite element method. A 2-D finite element model was developed to calculate the induced current inside the medium, and subsequently the Lorentz force density in the medium. The calculated Lorentz force density values are applied for simulating the transient ultrasonic wave generation within the medium. Meander coil EMATs that were designed using the model were used for experimental studies. Several case studies will be reported which include Rayleigh waves, Shear waves, Longitudinal and Lamb wave modes using pulsed mode of excitation. The experimental results were agreed well with the simulation results.

Dhayalan, R.; Balasubramaniam, Krishnan; Krishnamurthy, C. V.

2010-02-01

254

Numerical Simulations Using the Immersed Boundary Technique

NASA Technical Reports Server (NTRS)

The immersed-boundary method can be used to simulate flows around complex geometries within a Cartesian grid. This method has been used quite extensively in low Reynolds-number flows, and is now being applied to turbulent flows more frequently. The technique will be discussed, and three applications of the method will be presented, with increasing complexity. to illustrate the potential and limitations of the method, and some of the directions for future work.

Piomelli, Ugo; Balaras, Elias

1997-01-01

255

Numerical Simulation of Ion Thruster Optics

NASA Technical Reports Server (NTRS)

A three-dimensional simulation code (ffx) designed to analyze ion thruster optics is described. It is an extension of an earlier code and includes special features like the ability to model a wide range of grid geometries, cusp details, and mis-aligned aperture pairs to name a few. However, the principle reason for advancing the code was in the study of ion optics erosion. Ground based testing of ion thruster optics, essential to the understanding of the processes of grid erosion, can be time consuming and costly. Simulation codes that can accurately predict grid lifetimes and the physical mechanisms of grid erosion can be of great utility in the development of future ion thruster optics designed for more ambitious applications. Results of simulations are presented that describe wear profiles for several standard and nonstandard aperture geometries, such as those grid sets with square- or slotted-hole layout patterns. The goal of this paper will be to introduce the methods employed in the ffx code and to briefly demonstrate their use.

Rawlin, Vincent K. (Technical Monitor); Farnell, Cody C.; Williams, John D.; Wilbur, Paul J.

2003-01-01

256

Sound Generation by a Turbulent Flow in Musical Instruments - Multiphysics Simulation Approach -

Total computational costs of scientific simulations are analyzed between direct numerical simulations (DNS) and multiphysics simulations (MPS) for sound generation in musical instruments. In order to produce acoustic sound by a turbulent flow in a simple recorder-like instrument, compressible fluid dynamic calculations with a low Mach number are required around the edges and the resonator of the instrument in DNS, while incompressible fluid dynamic calculations coupled with dynamics of sound propagation based on the Lighthill's acoustic analogy are used in MPS. These strategies are evaluated not only from the viewpoint of computational performances but also from the theoretical points of view as tools for scientific simulations of complicated systems.

Kobayashi, Taizo; Takahashi, Kin'ya; Mibu, Ryota; Aoyagi, Mutsumi

2007-01-01

257

Scramjet Propulsive Flowpath Design and Numerical Simulation

NASA Astrophysics Data System (ADS)

The integrated propulsive flowpath of scramjet configuration was preliminarily designed and analyzed in this paper. The flow-fields characteristics and performance of the designed two-dimensional integrated propulsive flowpath were numerically calculated under various equivalent fuel-air ratio conditions, using computational fluid dynamics methods. The calculation results were then compared with the experimental data on some typical conditions, and the flow-field and performance of the integrated scramjet flowpath with different equivalent fuel-air ratios were analyzed and discussed in detail. The investigation results from these efforts showed that: (1) the inlet function was beyond disturbances by combustion induced shock wave and pressure fluctuations under the equivalent fuel-air ratio condition of 1.0, which well satisfied the design requirements; (2) with the increasing equivalent fuel-air ratio, the combustion intensity in the combustor was significantly enhanced, resulting in an increasing net-thrust of the propulsive flowpath.

Li, Jian-ping; Song, Wen-yan; Liu, Xin

2014-06-01

258

Numerical simulation of icing, deicing, and shedding

NASA Technical Reports Server (NTRS)

An algorithm has been developed to numerically model the concurrent phenomena of two-dimensional transient heat transfer, ice accretion, ice shedding and ice trajectory which arise from the use of electrothermal pad. The Alternating Direction Implicit method is used to simultaneously solve the heat transfer and accretion equations occurring in the multilayered body covered with ice. In order to model the phase change between ice and water, a technique was used which assumes a phase for each node. This allows the equations to be linearized such that a direct solution is possible. This technique requires an iterative procedure to find the correct phase at each node. The computer program developed to find this solution has been integrated with the NASA-Lewis flow/trajectory code LEWICE.

Wright, W. B.; Dewitt, K. J.; Keith, T. G., Jr.

1991-01-01

259

Numerical Simulation of Viscous Accretion Disks

NASA Astrophysics Data System (ADS)

A two-dimensional numerical hydrodynamics code is developed to model viscous accretion discs, employing the method of smoothed particle hydrodynamics. The effective shear viscosity present in the code is evaluated. Using a polytropic equation of state, models of self-gravitating accretion disks are evolved with a range of physical parameters, including viscosity. From these models it is found that a characteristic mass accretion rate, constant with time, tends to be maintained by the accretion disks, and that mass accretion is inversely proportional to the strength of the local shear viscous force. This is a consequence of the damping effect of local viscous forces upon the global non-axisymmetric modes that primarily drive accretion in these disks. In addition, the formation of satellites is observed in models which also develop a dominating m=1 tidal mode. The relevance of these satellites to planet formation is speculated.

Drimmel, Ronald

1995-12-01

260

Numerical simulation of an axial blood pump.

The axial blood pump with a magnetically suspended impeller is superior to other artificial blood pumps because of its small size. In this article, the distributions of velocity, path line, pressure, and shear stress in the straightener, the rotor, and the diffuser of the axial blood pump, as well as the gap zone were obtained using the commercial software, Fluent (version 6.2). The main focus was on the flow field of the blood pump. The numerical results showed that the axial blood pump could produce 5.14 L/min of blood at 100 mm Hg through the outlet when rotating at 11,000 rpm. However, there was a leakage flow of 1.06 L/min in the gap between the rotor cylinder and the pump housing, and thus the overall flow rate the impeller could generate was 6.2 L/min. The numerical results showed that 75% of the scalar shear stresses (SSs) were less than 250 Pa, and 10% were higher than 500 Pa within the whole pump. The high SS region appeared around the blade tip where a large variation of velocity direction and magnitude was found, which might be due to the steep angle variation at the blade tip. Because the exposure time of the blood cell at the high SS region within the pump was relatively short, it might not cause serious damage to the blood cells, but the improvement of blade profile should be considered in the future design of the axial pump. PMID:17584481

Chua, Leok Poh; Su, Boyang; Lim, Tau Meng; Zhou, Tongming

2007-07-01

261

The halo model and numerical simulations

Recently there has been a lot of attention focussed on a virialized halo-based approach to understanding the properties of the matter and galaxy power spectrum. A key ingredient in this model is the number and distribution of galaxies within dark matter halos as a function of mass. This quantity has been predicted from semi-analytic modeling and from fits to observational data. Here we present predictions for the occupation number and spatial distribution of sub-halos based on a high-resolution hydrodynamical simulation including cooling, star-formation and feedback.

Martin White; Lars Hernquist; Volker Springel

2000-12-28

262

A Posteriori Study of a DNS Database Describing Super critical Binary-Species Mixing

NASA Technical Reports Server (NTRS)

Currently, the modeling of supercritical-pressure flows through Large Eddy Simulation (LES) uses models derived for atmospheric-pressure flows. Those atmospheric-pressure flows do not exhibit the particularities of high densitygradient magnitude features observed both in experiments and simulations of supercritical-pressure flows in the case of two species mixing. To assess whether the current LES modeling is appropriate and if found not appropriate to propose higher-fidelity models, a LES a posteriori study has been conducted for a mixing layer that initially contains different species in the lower and upper streams, and where the initial pressure is larger than the critical pressure of either species. An initially-imposed vorticity perturbation promotes roll-up and a double pairing of four initial span-wise vortices into an ultimate vortex that reaches a transitional state. The LES equations consist of the differential conservation equations coupled with a real-gas equation of state, and the equation set uses transport properties depending on the thermodynamic variables. Unlike all LES models to date, the differential equations contain, additional to the subgrid scale (SGS) fluxes, a new SGS term that is a pressure correction in the momentum equation. This additional term results from filtering of Direct Numerical Simulation (DNS) equations, and represents the gradient of the difference between the filtered pressure and the pressure computed from the filtered flow field. A previous a priori analysis, using a DNS database for the same configuration, found this term to be of leading order in the momentum equation, a fact traced to the existence of high-densitygradient magnitude regions that populated the entire flow; in the study, models were proposed for the SGS fluxes as well as this new term. In the present study, the previously proposed constantcoefficient SGS-flux models of the a priori investigation are tested a posteriori in LES, devoid of or including, the SGS pressure correction term. The present pressure-correction model is different from, and more accurate as well as less computationally intensive than that of the a priori study. The constant-coefficient SGS-flux models encompass the Smagorinsky (SMC), in conjunction with the Yoshizawa (YO) model for the trace, the Gradient (GRC) and the Scale Similarity (SSC) models, all exercised with the a priori study constant coefficients calibrated at the transitional state. The LES comparison is performed with the filtered- and-coarsened (FC) DNS, which represents an ideal LES solution. Expectably, an LES model devoid of SGS terms is shown to be considerably inferior to models containing SGS effects. Among models containing SGS effects, those including the pressure-correction term are substantially superior to those devoid of it. The sensitivity of the predictions to the initial conditions and grid size are also investigated. Thus, it has been discovered that, additional to the atmospheric-pressure models currently used, a new model is necessary to simulate supercritical-pressure flows. This model depends on the thermodynamic characteristics of the chemical species involved.

Bellan, Josette; Taskinoglu, Ezgi

2012-01-01

263

Linking Intrinsic GRB Properties with Numerical Simulations

NASA Astrophysics Data System (ADS)

Since their discovery in the late 1960s, gamma-ray bursts (GRBs) have established a reputation of being mysterious astrophysical phenomena. This well-deserved reputation is a result of complex physical processes hidden from observation, and extreme energies previously unobserved. GRB observations have provided measurements of several physical parameters, including information about the energy and the dynamics of these events. From the several decades of observational data, it is widely believed that GRBs have beamed emission, leading to their association with relativistic jets. The progenitor of the observed emission is still unknown, although recent clues have advanced our understanding. Due to observational limitations, we must rely on theoretical studies and computational simulations to further understand the complex physical processes. In this paper we discuss the link between GRB observable parameters and those required for computational simulations. Following the spirit of this conference on AGN, Microquasar and GRB jets, this information is intended for an audience with a wide appreciation of jets, but without detailed knowledge of GRBs.

Richardson, G. A.

2006-09-01

264

Numerical simulations of moon-ringlet interaction

NASA Astrophysics Data System (ADS)

Nonaxisymmetric ring features excited by perturbations of shepherd satellites are studied in terms of direct particle simulations using Aarseth's N-body integrator combined with the calculation of particle-particle impacts. Interaction parameters typical to Saturn's F-ring are investigated. The generation of clumps by external satellites is verified, but the interparticle collisions tend to smooth sharp features. Using F-ring parameters the clumps are observed to cover the total azimuthal length, but it is not clear whether these azimuthally overlapping clumps would be detectable in the actual F-ring. Gravitational scattering by ring particles increases the velocity dispersion, smearing regular azimuthal features at least in the rings of low optical depths. Considerable accretion is observed to occur, particles sticking pairwise to each other, even if the tendency of the particles to accrete is artificially reduced in the simulations. A new explanation for the braided appearance of the F-ring is proposed, based on the interaction between the shepherding satellites and the ring containing embedded moonlets. In our model the braiding is a dynamic phenomenon: the braids are destroyed and recreated in a cyclical manner.

Hanninen, J.

1993-05-01

265

Numerical simulation of the SOFIA flow field

NASA Technical Reports Server (NTRS)

This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity runs the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.

Klotz, Stephen P.

1995-01-01

266

Numerical simulation of the SOFIA flowfield

NASA Technical Reports Server (NTRS)

This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity run the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.

Klotz, Stephen P.

1994-01-01

267

Numerical and laboratory simulations of auroral acceleration

The existence of parallel electric fields is an essential ingredient of auroral physics, leading to the acceleration of particles that give rise to the auroral displays. An auroral flux tube is modelled using electrostatic Vlasov simulations, and the results are compared to simulations of a proposed laboratory device that is meant for studies of the plasma physical processes that occur on auroral field lines. The hot magnetospheric plasma is represented by a gas discharge plasma source in the laboratory device, and the cold plasma mimicking the ionospheric plasma is generated by a Q-machine source. In both systems, double layers form with plasma density gradients concentrated on their high potential sides. The systems differ regarding the properties of ion acoustic waves that are heavily damped in the magnetosphere, where the ion population is hot, but weakly damped in the laboratory, where the discharge ions are cold. Ion waves are excited by the ion beam that is created by acceleration in the double layer in both systems. The efficiency of this beam-plasma interaction depends on the acceleration voltage. For voltages where the interaction is less efficient, the laboratory experiment is more space-like.

Gunell, H.; De Keyser, J. [1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, B-1180 Brussels (Belgium)] [1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, B-1180 Brussels (Belgium); Mann, I. [EISCAT Scientific Association, P.O. Box 812, SE-981 28 Kiruna, Sweden and Department of Physics, Umeå University, SE-901 87 Umeå (Sweden)] [EISCAT Scientific Association, P.O. Box 812, SE-981 28 Kiruna, Sweden and Department of Physics, Umeå University, SE-901 87 Umeå (Sweden)

2013-10-15

268

Investigation of transient redox electrochemical MHD using numerical simulations

To advance numerical simulation capabilities of electrochemical magnetohydrodynamics (ECMHD), we employed potential step and potential sweep voltammetry in simulations of the ECMHD of a redox couple. Using time-varying boundary conditions based on the Butler–Volmer electrode kinetics model, we studied the interplay of Lorentz force, convection and redox species concentration distribution. Parametric studies of potential sweep rate, standard rate constant, solution

D. Sen; K. M. Isaac; N. Leventis; I. Fritsch

2011-01-01

269

Numerical simulations of katabatic flow in Coats Land,

Numerical simulations of katabatic flow in Coats Land, Antarctica A thesis submitted to the School winds play a crucial role in the surface wind regime of Antarctica. This thesis presents simulated case, focusing on the vertical resolution, the boundary-layer scheme, the stability functions and the roughness

Renfrew, Ian

270

Numerical simulation of transition in a rotating disk flow

NASA Technical Reports Server (NTRS)

An investigation of the laminar-turbulence transition process in a three-dimensional boundary layer on a rotating disk is initiated. Preliminary results from a direct numerical simulation using spectral collocation method are presented. The simulation results in the linear regime is tested against linear stability theory. Saturation of the primary disturbance energy suggests the importance of modal interaction in initiating transition.

Balachandar, S.; Streett, C. L.

1990-01-01

271

Numerical simulations of reactive flows in ram accelerators

Reactive flows around accelerating projectiles in ram accelerators are numerically simulated using a newly developed code for time-dependent flows in noninertial frames. Two different modes of operations, the thermally choked mode and the superdetonative mode have been investigated. The simulations show that, in both modes, a significant acceleration (up to 10(exp 5) g) can be achieved with projectiles of different

C. Li; A. M. Landsberg; K. Kailasanath; E. S. Oran; J. P. Boris

1992-01-01

272

Characterizing electron temperature gradient turbulence via numerical simulation

Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation

W. M. Nevins; J. Candy; S. Cowley; T. Dannert; A. Dimits; W. Dorland; C. Estrada-Mila; G. W. Hammett; F. Jenko; M. J. Pueschel; D. E. Shumaker

2006-01-01

273

Numerical Convergence of Hydrodynamical SPH Simulations of Cooling Clusters

The results from hydrodynamical TREESPH simulations of galaxy clusters are used to investigate the dependence of the final cluster X-ray properties upon the numerical resolution and the assumed star formation models for the cooled gas. A comparison between runs with different star formation methods shows that the results of simulations, based on star formation methods in which gas conversion into

Riccardo Valdarnini

2002-01-01

274

3D numerical simulation of transient processes in hydraulic turbines

An approach for numerical simulation of 3D hydraulic turbine flows in transient operating regimes is presented. The method is based on a coupled solution of incompressible RANS equations, runner rotation equation, and water hammer equations. The issue of setting appropriate boundary conditions is considered in detail. As an illustration, the simulation results for runaway process are presented. The evolution of

S. Cherny; D. Chirkov; D. Bannikov; V. Lapin; V. Skorospelov; I. Eshkunova; A. Avdushenko

2010-01-01

275

Particle acceleration in solar flares: observations versus numerical simulations

Particle acceleration in solar flares: observations versus numerical simulations A O Benz, P C@astro.phys.ethz.ch Abstract. Solar flares are generally agreed to be impulsive releases of magnetic energy. ReconnectionÂray observations, transitÂtime damping simulation, reconnection, astrophysics #12; 2 1. Introduction Solar flares

276

Numerical simulations of pyroclastic surge in eruptions of Usu Volcano

Pyroclastic surge developed during explosive volcanic eruption can cause hazardous damage as serious as other phenomena such as blast waves or eruptive fragments. A numerical code is developed for simulating the pyroclastic surge. The code is an extension of a shock capturing code that treats shock wave propagation and other complex wave interactions (Saito, 2002). It is applied for simulating

M. Saba; T. Saito; H. Oshima

2006-01-01

277

Numerical simulations of volcanic jets: Importance of vent overpressure

the effects of shock waves on the gas-thrust region. These simulations are of free-jet decompression atmospheric pressure, the gas-thrust region is overpressured and develops a jet-like structure of standing shock waves. Using a pseudogas approximation for a mixture of tephra and gas, we numerically simulate

278

Using DHTs to Untangle the Web from DNS Michael Walfish

Computer Science Institute (ICSI), Berkeley CA). This research is part of the IRIS project and supportedUsing DHTs to Untangle the Web from DNS Michael Walfish MIT Laboratory for Computer Science practicality as the dominant force shaping DNS. Legal wran- gling over domain ownership is commonplace

279

Using DHTs to Untangle the Web from DNS Michael Walfish

(International Computer Science Institute (ICSI), Berkeley CA). This research is part of the IRIS projectUsing DHTs to Untangle the Web from DNS Michael Walfish #3; MIT Laboratory for Computer Science practicality as the dominant force shaping DNS. Legal wranÂ gling over domain ownership is commonplace

280

Numerical Simulation of Bioparticle Manipulation Using Dielectrophoresis

NASA Astrophysics Data System (ADS)

The manipulation of biological particles (cells, viruses DNA, proteins) is an important research subject in microfluidics. The dielectrophoresis (DEP) based on AC electrokinetics became one of the most widely used tools in particle separation, due to the low operating voltage (1-20 V), which significantly diminishes the Joule heating of the suspension. The present paper presents a 2-D model for the DEP-based separation microsystem consisting of a microchannel controlled with an interdigitated electrode array. The dielectrophoretic force produced by the nonuniform electric field acts on the bioparticles in suspension in fluid medium inducing spatial movement. The force depends on a number of parameters such as the geometry of the electrodes, the frequency of the applied electric field, as well as dielectric properties of the particles and the surrounding medium. The behavior of this type of system is numerically investigated. The electrical field distribution, the DEP force and the concentration profile in the microchannel are computed using a code based on the finite element technique. The analysis of the role of different problem parameters confirms the potential applications of DEP in handling and separation of particles.

Neculae, A.; Bunoiu, O. M.; Lungu, M.

2010-08-01

281

Numerical Simulation of Viscous Accretion Disks

NASA Astrophysics Data System (ADS)

A two-and three-dimensional numerical hydrodynamics FORTRAN code is developed to model viscous accretion disks, employing the method of smoothed particle hydrodynamics. The effective shear viscosity present in the code is evaluated. Using a polytropic equation of state, models of self-gravitating accretion disks are evolved with central mass to disk ratios of 1 and 3, with ratios of specific heats of 2 and 5/3, and with an artificial viscosity parameter of 1, 0.5, 0.25. From these models it is found that a characteristic mass accretion rate, constant with time, is maintained by the accretion disks, and that mass accretion is inversely proportional to the strength of the local shear viscous force. This is a consequence of the effect of local viscous forces upon the global non-axisymmetric modes that primarily drive accretion in these disks. In addition, the formation of satellites is observed in models which also develop a dominating m = 1 mode. The relevance of these satellites to planet formation is speculated.

Drimmel, Ronald Eugene

1995-01-01

282

AGN feedback in elliptical galaxies: numerical simulations

The importance of feedback (radiative and mechanical) from massive black holes at the centers of elliptical galaxies is not in doubt, given the well established relation among black hole mass and galaxy optical luminosity. Here, with the aid of high-resolution hydrodynamical simulations, we discuss how this feedback affects the hot ISM of isolated elliptical galaxies of different mass. The cooling and heating functions include photoionization plus Compton heating, the radiative transport equations are solved, and the mechanical feedback due to the nuclear wind is also described on a physical basis; star formation is considered. In the medium-high mass galaxies the resulting evolution is highly unsteady. At early times major accretion episodes caused by cooling flows in the recycled gas produced by stellar evolution trigger AGN flaring: relaxation instabilities occur so that duty cycles are small enough to account for the very small fraction of massive ellipticals observed to be in the QSO-phase, when the accr...

Ciotti, L

2011-01-01

283

Numerical simulations on the magnetopause current layer

One-dimensional particle simulations are carried out in order to study the current layer between a plasma and magnetic field such as seen at the magnetopause boundary layer. When a subsonic solar wind plasma flow impinges upon a vacuum dipole magnetic field, the width of the current layer is found much smaller than the ion gyroradius and is close to theoretically predicted geometric mean of the ion and electron gyroradii. The width remains essentially the same when the magnetic field is filled with a thermal plasma whose density is smaller than the incoming solar wind density. The width, therefore, remains much smaller than the ion gyroradius. It is found that a similar sharp current layer develops in a plasma confined in a magnetic field such as seen in laboratory and space plasmas. 15 refs., 11 figs.

Okuda, H.

1990-12-01

284

Direct numerical simulation of flow and heat transfer in a turbine cascade with incoming wakes

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) of flow in a turbine cascade with heat transfer have been performed. The set-up of the simulations was chosen in close accordance with previous experiments. Three of the experimental situations were simulated: one without free-stream turbulence and two with periodically incoming wakes of different frequency and with different levels of background fluctuation. Hence, the calculations allow us to study the influence of impinging wakes and background fluctuations on the development of the boundary layers and the local Nusselt number along the surfaces of the heated blade. Along the suction side, the pressure gradient is first favourable and then turns adverse near the trailing edge and the boundary layer remains laminar for the case without free-stream turbulence with the Nusselt number showing the typical decay from the leading to the trailing edge. With periodic wakes and background turbulence, transition occurs when the pressure gradient turns adverse, but intermittency persists so that the boundary layer is not fully turbulent when the trailing edge is reached. In this region, the heat transfer is increased significantly by an amount comparable to that found in the experiments. In the pre-transitional region with favourable pressure gradient, the flow acceleration stretches the free-stream vortices, aligning their axis with the flow direction, thereby forming streamwise vortical structures. These increase the laminar heat transfer in this region by 20 30%, which is, however, much less than observed in the experiments. On the pressure side, the pressure gradient is favourable along the entire blade so that the boundary layer remains laminar. Here, the wakes, through their impingement, also generate streamwise vortical structures which, because of the low convection speed on this side, have a very long lifetime compared to the structures along the suction side. Also these structures increase the laminar heat transfer by about 30%, which for the case with the highest wake frequency is again much less than in the experiments. The simulated average level of fluctuations in the laminar parts of the boundary layers is comparable or even higher than that in the experiments so that it seems likely that a difference in the spectral contents causes the discrepancies. The wake turbulence entering the calculation domain corresponds to that in far wakes with relatively small-scale structures, whereas in the experiments the wakes most probably still carried some large-scale fluctuations of the size of the wake width, which have been found to be more effective in increasing laminar heat transfer.

Wissink, Jan G.; Rodi, Wolfgang

2006-12-01

285

Constraints on the universe as a numerical simulation

NASA Astrophysics Data System (ADS)

Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation and investigate potentially observable consequences. Among the observables that are considered are the muon g - 2 and the current differences between determinations of , but the most stringent bound on the inverse lattice spacing of the universe, GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest-energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice.

Beane, Silas R.; Davoudi, Zohreh; J. Savage, Martin

2014-09-01

286

Numerical simulation of baroclinic Jovian vortices

NASA Astrophysics Data System (ADS)

We examine the evolution of baroclinic vortices in a time-dependent, nonlinear numerical model of a Jovian atmosphere. The model uses a normal-mode expansion in the vertical, using the barotropic and first two baroclinic modes. Results for the stability of baroclinic vortices on an f plane in the absence of a mean zonal flow are similar to results of Earth vortex models, although the presence of a fluid interior on the Jovian planets shifts the stability boundaries to smaller length scales. The presence of a barotropic mean zonal flow in the interior stabilizes vortices against instability and significantly modifies the finite amplitude form of baroclinic instabilities. The effect of a zonal flow on a form of barotropic instability produces periodic oscillations in the latitude and longitude of the vortex as observed at the level of the cloud tops. This instability may explain some, but not all, observations of longitudinal oscillations of vortices on the outer planets. Oscillations in aspect ratio and orientation of stable vortices in a zonal shear flow are observed in this baroclinic model, as in simpler two-dimensional models. Such oscillations are also observed in the atmospheres of Jupiter and Neptune. The meridional propagation and decay of vortices on a beta plane is inhibited by the presence of a mean zonal flow. The direction of propagation of a vortex relative to the mean zonal flow depends upon the sign of the meridional potential vorticity gradient; combined with observations of vortex drift rates, this may provide a constraint on model assumption for the flow in the deep interior of the Jovian planets.

Achterberg, R. K.; Ingersoll, A. P.

1994-02-01

287

Numerical simulation of fundamental trapped sausage modes

Context: We integrate the 2D MHD ideal equations of a straight slab to simulate observational results associated with fundamental sausage trapped modes. Aims: Starting from a non-equilibrium state with a dense chromospheric layer, we analyse the evolution of the internal plasma dynamics of magnetic loops, subject to line-tying boundary conditions, and with the coronal parameters described in Asai et al. (2001) and Melnikov et al. (2002) to investigate the onset and damping of sausage modes. Methods: To integrate the equations we used a high resolution shock-capturing (HRSC) method specially designed to deal appropriately with flow discontinuities. Results: Due to non-linearities and inhomogeneities, pure modes are difficult to sustain and always occur coupled among them so as to satisfy, e.g., the line-tying constraint. We found that, in one case, the resonant coupling of the sausage fundamental mode with a slow one results in a non-dissipative damping of the former. Conclusions: In scenarios of thick and den...

Cécere, M; Reula, O

2011-01-01

288

Introduction Adaptive wavelet numerical simulation Turbulence modelling Summary Calculating for turbulence #12;Introduction Adaptive wavelet numerical simulation Turbulence modelling Summary Collaborators for turbulence #12;Introduction Adaptive wavelet numerical simulation Turbulence modelling Summary Outline

Kevlahan, Nicholas

289

Numerical Simulations of Wave Generation by a Vertical Plunger Using RANS and SPH Models

uses the smoothed particle hydrodynamics SPH method. Numerical simulations using several differentNumerical Simulations of Wave Generation by a Vertical Plunger Using RANS and SPH Models S. C. Yim Database subject headings: Simulation; Numerical models; Hydrodynamics; Wave generation. Introduction

Yim, Solomon C.

290

Numerical Simulations of the Wardle Instability

NASA Astrophysics Data System (ADS)

In dense interstellar clouds, the ionisation fraction is so low that the material may be considered to be made up of two fluids: a perfectly conducting fluid consisting of the ions and electrons and a neutral fluid consisting of atomic hydrogen. These interact via collisions, but the imperfect coupling leads to a finite resistivity (ambi-polar diffusion). Under these conditions, there exist shock structures, called C-shocks, in which the dissipation is due to resistivity rather than viscosity (Draine 1980). Wardle (1990, 1991a,b) showed that C-shocks with Alfven Mach numbers greater than ? 5 are subject to a transverse corrugation instability and nonlinear calculations have shown that this leads to the formation of dense fingers of neutral gas (Toth 1995a,b; Stone 1997; Neufeld & Stone 1997; MacLow & Smith 1997). However, the instability relies on a separation between the conducting fluid and the neutral fluid, which does not occur if timescale for ionisation equilibrium is short compared to the flow time through the shock structure. The ionisation fraction is then simply a function of neutral density and our simulations show that this does indeed suppress the instability. Since the timescale for ionisation equilibrium is always short compared to the flow time in dense clouds, this means that the instability does not occur unless charged grains play a significant role. Instability is possible in this case because a fluid composed of charged grains does undergo separation from the neutrals and the grain mass fraction influences the ionisation fraction. We use the multi-fluid code described in Falle (2003), which includes the grain fluid, to show that the instability can occur in such cases.

Falle, S. A. E. G.; Hartquist, T. W.; van Loo, S.

2009-04-01

291

Turbulence in the highly restricted dynamics of a closure at second order: comparison with DNS

NASA Astrophysics Data System (ADS)

S3T (Stochastic Structural Stability Theory) employs a closure at second order to obtain the dynamics of the statistical mean turbulent state. When S3T is implemented as a coupled set of equations for the streamwise mean and perturbation states, nonlinearity in the dynamics is restricted to interaction between the mean and perturbations. The S3T statistical mean state dynamics can be approximately implemented by similarly restricting the dynamics used in a direct numerical simulation (DNS) of the full Navier-Stokes equations (referred to as the NS system). Although this restricted nonlinear system (referred to as the RNL system) is greatly simplified in its dynamics in comparison to the associated NS, it nevertheless self-sustains a turbulent state in wall-bounded shear flow with structures and dynamics comparable to those observed in turbulence. Moreover, RNL turbulence can be analysed effectively using theoretical methods developed to study the closely related S3T system. In order to better understand RNL turbulence and its relation to NS turbulence, an extensive comparison is made of diagnostics of structure and dynamics in these systems. Although quantitative differences are found, the results show that turbulence in the RNL system closely parallels that in NS and suggest that the S3T/RNL system provides a promising reduced complexity model for studying turbulence in wall-bounded shear flows.

Constantinou, N. C.; Lozano-Durán, A.; Nikolaidis, M.-A.; Farrell, B. F.; Ioannou, P. J.; Jiménez, J.

2014-04-01

292

Numerical Simulation of SNCR Technology with Simplified Chemical Kinetics Model

NASA Astrophysics Data System (ADS)

The paper deals with numerical simulation of SNCR method. For numerical modelling was used CFD code Ansys/CFX. SNCR method was described by dominant chemical reaction, which were look up NIST Chemical database. The reactions including reduction of NOx and concentration change of pollutants, like N2O and CO in flue gas too. Proposed chemical kinetics and CFD model was applied to two boilers. Both simulations were compared with experimental measurements. First simulation was used to validation of chemical mechanism. Second simulation was based on first simulation and it was used to verification of compiled SNCR chemical mechanism. Next the new variant of the reagent penetration lance was proposed and compared with the original variants.

Blejcha?, T.; Dolní?ková, D.

2013-04-01

293

Geometric issues in reverse osmosis: numerical simulation and experimentation.

This investigation is a synergistic combination of laboratory experimentation and numerical simulation to quantify the practical impact of geometric imperfections in the flow channels of a reverse osmosis (RO) system. To this end, carefully executed experiments are performed to quantify the fluid flow in a system containing feed spacers which are embedded in the RO membrane. In a complementary activity, numerical simulations were performed both for an ideal geometric situation (without embedments) and the actual geometric configuration including the embedments. It was found that the presence of unaccounted embedments affected the pressure drop predictions for the system by 14-19%. When account was taken of the embedments, the simulation results were found to be virtually coincident with the experimental results. This outcome suggests that deviations between experimental and simulation results encountered in the literature might well have been due to geometrical deviations of the type investigated here. The numerical simulation of the feedwater fluid flow was based on the often-used but unverified assumption that the velocity field experiences the geometric periodicity of the feed spacer. This assumption was lent support by results from a non-periodic simulation model and by the excellent agreement between the numerically based predictions and the experimental data. PMID:25353939

Srivathsan, G; Sparrow, Ephraim; Gorman, John

2014-10-01

294

Direct numerical simulation of auto-ignition of a hydrogen vortex ring reacting with hot air

Direct numerical simulation (DNS) is used to study chemically reacting, laminar vortex rings. A novel, all-Mach number algorithm developed by Doom et al. [J. Doom, Y. Hou, K. Mahesh, J. Comput. Phys. 226 (2007) 1136-1151] is used. The chemical mechanism is a nine species, nineteen reaction mechanism for H{sub 2}/air combustion proposed by Mueller et al. [M.A. Mueller, T.J. Kim, R.A. Yetter, F.L. Dryer, Int. J. Chem. Kinet. 31 (1999) 113-125]. Diluted H{sub 2} at ambient temperature (300 K) is injected into hot air. The simulations study the effect of fuel/air ratios, oxidizer temperature, Lewis number and stroke ratio (ratio of piston stroke length to diameter). Results show that auto-ignition occurs in fuel lean, high temperature regions with low scalar dissipation at a 'most reactive' mixture fraction, {zeta}{sub MR} (Mastorakos et al. [E. Mastorakos, T.A. Baritaud, T.J. Poinsot, Combust. Flame 109 (1997) 198-223]). Subsequent evolution of the flame is not predicted by {zeta}{sub MR}; a most reactive temperature T{sub MR} is defined and shown to predict both the initial auto-ignition as well as subsequent evolution. For stroke ratios less than the formation number, ignition in general occurs behind the vortex ring and propagates into the core. At higher oxidizer temperatures, ignition is almost instantaneous and occurs along the entire interface between fuel and oxidizer. For stroke ratios greater than the formation number, ignition initially occurs behind the leading vortex ring, then occurs along the length of the trailing column and propagates toward the ring. Lewis number is seen to affect both the initial ignition as well as subsequent flame evolution significantly. Non-uniform Lewis number simulations provide faster ignition and burnout time but a lower maximum temperature. The fuel rich reacting vortex ring provides the highest maximum temperature and the higher oxidizer temperature provides the fastest ignition time. The fuel lean reacting vortex ring has little effect on the flow and behaves similar to a non-reacting vortex ring. (author)

Doom, Jeff; Mahesh, Krishnan [Department of Aerospace Engineering and Mechanics, University of Minnesota, 107 Akerman Hall, Minneapolis, MN (United States)

2009-04-15

295

Numerical simulation of surface barriers for shrub-steppe ecoregions

Surface barriers, constructed of earthen materials, are being proposed for the long-term management of vadose-zone buried waste and subsurface contamination for sites within the shrub-steppe ecoregion of North America. Field experiments of a prototype barrier on a shrub-steppe site have been ongoing since 1994, providing water balance data, which includes drainage from the sideslopes. Design and licensing of surface barriers will require a demonstrated understanding of the nonisothermal geohydrologic and coupled ground surface to atmosphere water mass and energy transport processes that control water infiltration to the subsurface. As a prelude to inverse numerical modeling to estimate critical parameters for the prototype barrier, this paper describes and demonstrates a numerical simulator for modeling the prototype barrier for shrub-steppe environments. The numerical simulator comprises a nonisothermal multifluid subsurface flow and transport simulator fully coupled to a modified nonlinear sparsely vegetated (bare substrate to closed canopy) evapotranspiration module that mechanistically predicts evaporation.

White, Mark D.; Ward, Andy L.

2006-02-11

296

Numerical Convergence of Hydrodynamical SPH Simulations of Cooling Clusters

The results from hydrodynamical TREESPH simulations of galaxy clusters are used to investigate the dependence of the final cluster X-ray properties upon the numerical resolution and the assumed star formation models for the cooled gas. A comparison between runs with different star formation methods shows that the results of simulations, based on star formation methods in which gas conversion into stars is controlled by an efficiency parameter c_{star}, are sensitive to the simulation numerical resolution. In this respect star formation methods based instead on a local density threshold, are shown to give more stable results. Final X-ray luminosities are found to be numerically stable, with uncertainties of a factor 2.

R. Valdarnini

2001-11-05

297

Numerical Simulations of Vertical Oscillations of a Curved Coronal Loop

NASA Astrophysics Data System (ADS)

We consider an impulsively-started, vertical excitation of a solar coronal loop that is embedded into a potential arcade. The two-dimensional numerical model we implement includes the effects of line curvature and allows us to explore the effect of varying the initial pulse position. The results of the numerical simulations reveal kink mode oscillations with waveperiods that are reasonably close to the observational findings of Wang and Solanki (2004).

Murawski, K.; Selwa, M.; Rossmanith, J. A.

2005-09-01

298

A numerical simulation on the perforation of reinforced concrete targets

The perforation of steel-bar-reinforced concrete target is studied numerically in this paper using LS-DYNA code and the modified Taylor–Chen–Kuszmaul continuum damage model. The crater diameters on both the front and back surfaces of the concrete target and the residual velocity of the projectile predicted by the numerical simulation are in good agreement with the experimental results reported by Hanchak et

Fenglei Huang; Haijun Wu; Qiankun Jin; Qingming Zhang

2005-01-01

299

Numerical Models and Simulations in Sailing Yacht Design

In this note, we describe the numerical methodology developed in the framework of the collaboration between the Ecole Polytechnique\\u000a Fédérale de Lausanne (EPFL) and the Alinghi Team, in preparation to the 32nd edition of the America’s Cup which took place\\u000a in Valencia (Spain) in summer 2007. The mathematical and numerical models adopted to simulate different design aspects (such\\u000a as appendage

Davide Detomi; Nicola Parolini; Alfio Quarteroni

300

Numerical simulation of the countercurrent flow in a gas centrifuge

A finite difference method is presented for the numerical simulation of the axisymmetric countercurrent flows in gas centrifuge. A time-marching technique is used to relax an arbitrary initial condition to the desired steady-state solution. All boundary layers may be resolved, and nonlinear effects may be included. Numerical examples are presented. It is concluded that this technique is capable of accurately predicting the performance of a wide variety of machines under all operating conditions of interest.

Cloutman, L.D.; Gentry, R.A.

1981-01-01

301

Numerical modeling and simulation of carburized and nitrided quenching process

In order to study metallo-thermo-mechanical behavior during carburized and nitrided quenching, a numerical model when considering quantitative effects of diffused carbon and nitrogen gradients and kinetics of phase transformation is proposed. Coupled calculations of diffusion, phase transformation and stress\\/strain give the final distributions of carbon and nitrogen contents as well as residual stress and distortion. Within the numerical simulation method,

Dong-Ying Ju; Chuncheng Liu; Tatsuo Inoue

2003-01-01

302

Data from a 1152X760X1280 direct numerical simulation (DNS) [N. J. Mueschke and O. Schilling, Phys. Fluids 21, 014106 (2009)] of a transitional Rayleigh-Taylor mixing layer modeled after a small Atwood number water channel experiment is used to comprehensively investigate the structure of mean and turbulent transport and mixing. The simulation had physical parameters and initial conditions approximating those in the experiment. The budgets of the mean vertical momentum, heavy-fluid mass fraction, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate equations are constructed using Reynolds averaging applied to the DNS data. The relative importance of mean and turbulent production, turbulent dissipation and destruction, and turbulent transport are investigated as a function of Reynolds number and across the mixing layer to provide insight into the flow dynamics not presently available from experiments. The analysis of the budgets supports the assumption for small Atwood number, Rayleigh/Taylor driven flows that the principal transport mechanisms are buoyancy production, turbulent production, turbulent dissipation, and turbulent diffusion (shear and mean field production are negligible). As the Reynolds number increases, the turbulent production in the turbulent kinetic energy dissipation rate equation becomes the dominant production term, while the buoyancy production plateaus. Distinctions between momentum and scalar transport are also noted, where the turbulent kinetic energy and its dissipation rate both grow in time and are peaked near the center plane of the mixing layer, while the heavy-fluid mass fraction variance and its dissipation rate initially grow and then begin to decrease as mixing progresses and reduces density fluctuations. All terms in the transport equations generally grow or decay, with no qualitative change in their profile, except for the pressure flux contribution to the total turbulent kinetic energy flux, which changes sign early in time (a countergradient effect). The production-to-dissipation ratios corresponding to the turbulent kinetic energy and heavy-fluid mass fraction variance are large and vary strongly at small evolution times, decrease with time, and nearly asymptote as the flow enters a self-similar regime. The late-time turbulent kinetic energy production-to-dissipation ratio is larger than observed in shear-driven turbulent flows. The order of magnitude estimates of the terms in the transport equations are shown to be consistent with the DNS at late-time, and also confirms both the dominant terms and their evolutionary behavior. These results are useful for identifying the dynamically important terms requiring closure, and assessing the accuracy of the predictions of Reynolds-averaged Navier-Stokes and large-eddy simulation models of turbulent transport and mixing in transitional Rayleigh-Taylor instability-generated flow.

Schilling, Oleg [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Mueschke, Nicholas J. [Texas A and M Univ., College Station, TX (United States)

2010-10-18

303

Data exploration of turbulence simulations using a database cluster

We describe a new environment for the exploration of tur- bulent flows that uses a cluster of databases to store com- plete histories of Direct Numerical Simulation (DNS) results. This allows for spatial and temporal exploration of high- resolution data that were traditionally too large to store and too computationally expensive to produce on demand. We perform analysis of these

Eric A. Perlman; Randal C. Burns; Yi Li; Charles Meneveau

2007-01-01

304

Numerical simulation of the interaction between flow and flexible nets

NASA Astrophysics Data System (ADS)

A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid-structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests.

Bi, Chun-Wei; Zhao, Yun-Peng; Dong, Guo-Hai; Xu, Tiao-Jian; Gui, Fu-Kun

2014-02-01

305

Astrophysical jets: Observations, numerical simulations, and laboratory experiments

This paper provides summaries of ten talks on astrophysical jets given at the HEDP/HEDLA-08 International Conference in St. Louis. The talks are topically divided into the areas of observation, numerical modeling, and laboratory experiment. One essential feature of jets, namely, their filamentary (i.e., collimated) nature, can be reproduced in both numerical models and laboratory experiments. Another essential feature of jets, their scalability, is evident from the large number of astrophysical situations where jets occur. This scalability is the reason why laboratory experiments simulating jets are possible and why the same theoretical models can be used for both observed astrophysical jets and laboratory simulations.

Bellan, P. M. [Caltech, Pasadena, California 91125 (United States); Livio, M. [Space Telescope Science Institute, Baltimore, Maryland 21218 (United States); Kato, Y. [University of Tsukuba, Ibaraki 3058577 (Japan); Lebedev, S. V. [Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom); Ray, T. P. [Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2 (Ireland); Ferrari, A. [Dipartimento di Fisica, Universita di Torino, via Pietro Giuria 1, 10125 Torino, Italy and Department of Astronomy and Astrophysics, University of Chicago, Chicago, Illinois 60637 (United States); Hartigan, P. [Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892 (United States); Frank, A. [Department of Physics and Astronomy and Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14627 (United States); Foster, J. M. [AWE Aldermaston, Reading RG7 4PR (United Kingdom); Nicolaie, P. [Centre Lasers Intenses et Applications, Universite Bordeaux 1-CEA-CNRS, 33405 Talence (France)

2009-04-15

306

Numerical simulation of tornado wind loading on structures

NASA Technical Reports Server (NTRS)

A numerical simulation of a tornado interacting with a building was undertaken in order to compare the pressures due to a rotational unsteady wind with that due to steady straight winds used in design of nuclear facilities. The numerical simulations were performed on a two-dimensional compressible hydrodynamics code. Calculated pressure profiles for a typical building were then subjected to a tornado wind field and the results were compared with current quasisteady design calculations. The analysis indicates that current design practices are conservative.

Maiden, D. E.

1976-01-01

307

Numerical simulation of water flow around a rigid fishing net

This paper is devoted to the simulation of the flow around and inside a rigid axisymmetric net. We describe first how experimental data have been obtained. We show in detail the modelization. The model is based on a Reynolds Averaged Navier-Stokes turbulence model penalized by a term based on the Brinkman law. At the out-boundary of the computational box, we have used a "ghost" boundary condition. We show that the corresponding variational problem has a solution. Then the numerical scheme is given and the paper finishes with numerical simulations compared with the experimental data.

Roger Lewandowski; Géraldine Pichot

2006-12-20

308

Numerical simulation of tethered DNA in shear flow

NASA Astrophysics Data System (ADS)

The behavior of tethered DNA in shear flow is investigated numerically by the smoothed dissipative particle dynamics (SDPD) method. Unlike numerical methods used in previous studies, SDPD models the solvent explicitly, takes into account the fully coupled hydrodynamic interactions and is free of the numerical artifact of wall sticking. Based on numerical simulations the static and dynamic properties of a tethered DNA is studied both qualitatively and quantitatively. The observed properties are in general agreement with previous experimental, numerical and theoretical work. Furthermore, the cyclic-motion phenomenon is studied by power spectrum density and cross-correlation function analysis, which suggest that there is only a very weak coherent motion of tethered DNA for a characteristic timescale larger than the relaxation time. Cyclic motion is more likely relevant as an isolated event than a typical mode of DNA motion.

Litvinov, S.; Hu, X. Y.; Adams, N. A.

2011-05-01

309

Building Blocks for Reliable Complex Nonlinear Numerical Simulations. Chapter 2

NASA Technical Reports Server (NTRS)

This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.

Yee, H. C.; Mansour, Nagi N. (Technical Monitor)

2001-01-01

310

Building Blocks for Reliable Complex Nonlinear Numerical Simulations

NASA Technical Reports Server (NTRS)

This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations.

Yee, H. C.

2005-01-01

311

Building Blocks for Reliable Complex Nonlinear Numerical Simulations

NASA Technical Reports Server (NTRS)

This talk describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.

Yee, H. C.; Mansour, Nagi N. (Technical Monitor)

2002-01-01

312

Numerical simulation of double-diffusive finger convection

A hybrid finite element, integrated finite difference numerical model is developed for the simulation of double-diffusive and multicomponent flow in two and three dimensions. The model is based on a multidimensional, density-dependent, saturated-unsaturated transport model (SUTRA), which uses one governing equation for fluid flow and another for solute transport. The solute-transport equation is applied sequentially to each simulated species. Density coupling of the flow and solute-transport equations is accounted for and handled using a sequential implicit Picard iterative scheme. High-resolution data from a double-diffusive Hele-Shaw experiment, initially in a density-stable configuration, is used to verify the numerical model. The temporal and spatial evolution of simulated double-diffusive convection is in good agreement with experimental results. Numerical results are very sensitive to discretization and correspond closest to experimental results when element sizes adequately define the spatial resolution of observed fingering. Numerical results also indicate that differences in the molecular diffusivity of sodium chloride and the dye used to visualize experimental sodium chloride concentrations are significant and cause inaccurate mapping of sodium chloride concentrations by the dye, especially at late times. As a result of reduced diffusion, simulated dye fingers are better defined than simulated sodium chloride fingers and exhibit more vertical mass transfer. Copyright 2005 by the American Geophysical Union.

Hughes, J.D.; Sanford, W.E.; Vacher, H.L.

2005-01-01

313

Numerical simulation of double-diffusive finger convection

NASA Astrophysics Data System (ADS)

A hybrid finite element, integrated finite difference numerical model is developed for the simulation of double-diffusive and multicomponent flow in two and three dimensions. The model is based on a multidimensional, density-dependent, saturated-unsaturated transport model (SUTRA), which uses one governing equation for fluid flow and another for solute transport. The solute-transport equation is applied sequentially to each simulated species. Density coupling of the flow and solute-transport equations is accounted for and handled using a sequential implicit Picard iterative scheme. High-resolution data from a double-diffusive Hele-Shaw experiment, initially in a density-stable configuration, is used to verify the numerical model. The temporal and spatial evolution of simulated double-diffusive convection is in good agreement with experimental results. Numerical results are very sensitive to discretization and correspond closest to experimental results when element sizes adequately define the spatial resolution of observed fingering. Numerical results also indicate that differences in the molecular diffusivity of sodium chloride and the dye used to visualize experimental sodium chloride concentrations are significant and cause inaccurate mapping of sodium chloride concentrations by the dye, especially at late times. As a result of reduced diffusion, simulated dye fingers are better defined than simulated sodium chloride fingers and exhibit more vertical mass transfer.

Hughes, Joseph D.; Sanford, Ward E.; Vacher, H. Leonard

2005-01-01

314

Numerical Simulation of the Double Slit Interference with Ultracold Atoms

We present a numerical simulation of the double slit interference experiment realized by F. Shimizu, K. Shimizu and H. Takuma with ultracold atoms. We show how the Feynman path integral method enables the calculation of the time-dependent wave function. Because the evolution of the probability density of the wave packet just after it exits the slits raises the issue of the interpreting the wave/particle dualism, we also simulate trajectories in the de Broglie-Bohm interpretation.

Michel Gondran; Alexandre Gondran

2007-12-05

315

Numerical Convergence of Hydrodynamical SPH Simulations of Cooling Clusters

The results from hydrodynamical TREESPH simulations of galaxy clusters are\\u000aused to investigate the dependence of the final cluster X-ray properties upon\\u000athe numerical resolution and the assumed star formation models for the cooled\\u000agas. A comparison between runs with different star formation methods shows that\\u000athe results of simulations, based on star formation methods in which gas\\u000aconversion into

Riccardo Valdarnini

2001-01-01

316

3D numerical simulation of transient processes in hydraulic turbines

NASA Astrophysics Data System (ADS)

An approach for numerical simulation of 3D hydraulic turbine flows in transient operating regimes is presented. The method is based on a coupled solution of incompressible RANS equations, runner rotation equation, and water hammer equations. The issue of setting appropriate boundary conditions is considered in detail. As an illustration, the simulation results for runaway process are presented. The evolution of vortex structure and its effect on computed runaway traces are analyzed.

Cherny, S.; Chirkov, D.; Bannikov, D.; Lapin, V.; Skorospelov, V.; Eshkunova, I.; Avdushenko, A.

2010-08-01

317

Solid freeform fabrication of aluminum alloy components: Numerical simulations

A heat transfer model has been developed to simulate the evolution of temperature during semi-solid metal (SSM) solid freeform\\u000a fabrication (SFF) process. The governing equations were solved numerically using finite difference method. Deposition of simple\\u000a cubic components of A356 (Al-7%Si-0.45%Mg) aluminum alloy have been simulated. The effect of process parameters such as deposition\\u000a pattern, deposition velocity, slurry cross-section and slurry

G. Vijh; A. Gokhale; S. Mishra; V. Singh; N. N. Viswanathan

2009-01-01

318

Experimental and numerical investigation of inertial particle clustering in isotropic turbulence

NASA Astrophysics Data System (ADS)

This paper presents the first detailed comparisons between experiments and direct numerical simulations (DNS) of inertial particle clustering in nearly isotropic . The experimental system consists of a box 38cm in each dimension with fans in the eight corners that sustain nearly isotropic turbulence in the centre of the box. We inject hollow glass spheres with a mean diameter of 6 preferential concentration’). The radial distribution function (RDF), a statistical measure of clustering, has been calculated from the particle position field. We select this measure because of its relevance to the collision kernel for particles. DNS of the equivalent system, with nearly perfect parameter overlap, have also been performed. We observe good agreement between the RDF predictions of the DNS and the experimental observations, despite some challenges in the interpretation of the experiments. The results provide important guidance on ways to improve the measurement.

Salazar, Juan P. L. C.; de Jong, Jeremy; Cao, Lujie; Woodward, Scott H.; Meng, Hui; Collins, Lance R.

319

Radioluminescence in Al : C analytical and numerical simulation results

, for example, Aznar et al [2]). These experimental studies have established several empirical results for RL is one of the main dosimetric materials. In this work, we study RL using a kinetic model involving two with the occupancies of the relevant traps and centres are simulated numerically. The set of differential equations

Chen, Reuven

320

Numerical simulation and experimental observations of initial friction transients

Experiments were performed to better understand the sliding frictional behavior between metals under relatively high shear and normal forces. Microstructural analyses were done to estimate local near-surface stress and strain gradients. The numerical simulation of the observed frictional behavior was based on a constitutive model that uses a state variable approach.

Hughes, D.A.; Weingarten, L.I.; Dawson, D.B.

1995-07-01

321

Interference microscopy of subnanometer depth resolution: Numerical simulation

NASA Astrophysics Data System (ADS)

We present results of numerical simulation performed with the aim to study the possibility of measuring subnanometer-range roughness parameters using an automated interference Linnik microscope with a white-light source. It is shown that reconstruction noises of phase images can be reduced to 0.1 nm when using averaging of interferograms and phase images.

Vishnyakov, G. N.; Levin, G. G.; Minaev, V. L.; Tsel'mina, I. Yu.

2013-12-01

322

Numerical Simulation in Applied Geophysics. From de Messocale to ...

spaces in 1D, 2D and 3D. ... method in the 1D and 2D cases. Global ... saturated porous materials. ... 4: Numerical simulation of 2D wave propagation in Biot's media. ... sor of a fractured medium with harmonic experiments, Computer Methods.

2013-10-09

323

Numerical Simulations for spiral crystal growth with impurity, interlaced spiral

Numerical Simulations for spiral crystal growth with impurity, interlaced spiral and variable, then the crystal may need extremely high driving force around screw dislocation. #12;Hollow core type growth r Â·Variable driving force by distance from a screw dislocation Â·Wisker like growth Â·Hollow core like growth

Ishii, Hitoshi

324

Numerical Simulation of Interfacial Transport Processes using OpenFOAM

Numerical Simulation of Interfacial Transport Processes using OpenFOAMÂ® Fundamentals/matrix coupling) Figure 1: Growing droplet at sin- gle capillary; interface covered by multiple surfactants. OpenFOAM to the conventional mathematical notation for tensors and partial differential equations. Thus, OpenFOAM renders

Heermann, Dieter W.

325

Numerical simulation of cooling gas injection using adaptive multiscale techniques

with experimental data. The influence of varying rate of cooling gas, injection angle etc. on the cooling efficiency stream Mach numbers in the range of 0.02 to 0.2]. The interaction of the injected cooling gasNumerical simulation of cooling gas injection using adaptive multiscale techniques Wolfgang Dahmen

326

A Computational Model for the Numerical Simulation of FSW Processes

In this paper a computational model for the numerical simulation of Friction Stir Welding (FSW) processes is presented. FSW is a new method of welding in solid state in which a shouldered tool with a profile probe is rotated and slowly plunged into the joint line between two pieces of sheet or plate material which are butted together. Once the

C. Agelet de Saracibar; M. Chiumenti; D. Santiago; M. Cervera; N. Dialami; G. Lombera

2010-01-01

327

Comparison of numerical simulations and laboratory studies of laser thrombolysis

We compare Los Alamos numerical simulations with Oregon Medical Laser Center laser deposition experiments conducted with gelatin thrombus surrogates specifically chosen for relevance to clinical laser thrombolysis. Initial idealized calculations suggest that a surprisingly large fraction of the absorbed laser energy appears as acoustic radiation. We build on these results here by investigating geometrical affects, material property variations, and sources

Edward J. Chapyak; Robert P. Godwin; Scott A. Prahl; Hanqun Shangguan

1997-01-01

328

Contemporary Mathematics Numerical Simulation of Gas Bubbles Rising in Viscous

Contemporary Mathematics Numerical Simulation of Gas Bubbles Rising in Viscous Liquids at High- duced in the context of gas bubbles rising in viscous liquids, e.g. air bubbles rising in water. Key on a supercomputer. Finally, the use of a non-inertial, moving reference frame attached to the rising bubble

Lin, Ping

329

Numerical simulations of unsteady reactive flows in a combustion chamber

Time-dependent, compressible numerical simulations have been performed for the flowfield in an idealized ramjet that consists of an axisymmetric inlet and combustor and a choked nozzle, in order to study the instability induced by the interactions between large-scale vortex structures, acoustic waves, and chemical energy release. Nonreactive flow calculations show complex interactions; vortex shedding occurs at the natural instability frequency

K. Kailasanath; J. H. Gardner; E. S. Oran; J. P. Boris

1991-01-01

330

Fibreoptic communication lines with distributed Raman amplification: Numerical simulation

The properties of optical solitons in variable-dispersion fibreoptic communication lines in which distributed Raman amplification of optical signals is used are studied by numerical simulation. It is shown that solitons can serve as carriers of information in communication systems with a data transmission rate exceeding 10 Gbit s{sup -1}. (optical solitons)

Nasieva, I O [Novosibirsk State University, Novosibirsk (Russian Federation); Fedoruk, Mikhail P [Institute of Computational Techologies, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

2003-10-31

331

A review of numerical simulation of hydrothermal systems.

Many advances in simulating single and two-phase fluid flow and heat transport in porous media have recently been made in conjunction with geothermal energy research. These numerical models reproduce system thermal and pressure behaviour and can be used for other heat-transport problems, such as high-level radioactive waste disposal and heat-storage projects. -Authors

Mercer, J.W.; Faust, C.R.

1979-01-01

332

Numerical simulation of transpiration cooling through porous , T. Gotzen1

55, 52056 Aachen SUMMARY Transpiration cooling using ceramic matrix composite (CMC) materials to facilitate such numerical simulations for a carbon/carbon material mounted in the side wall of a hot gas against high thermal loads by coating it with special materials. In contrast, active systems, which

333

VORTEX FORMATION BY SUCCESSIVE THERMALS: A NUMERICAL SIMULATION

The purpose of this research is to investigate, by means of numerical simulation experiments, the complex inter- actions between consecutive toroidally circulating buoyant elements (thermals) when these occur in either rotating or nonrotating environments. The study includes both the vortex formation process and the effect that this process has on the properties of the one or more buoyant elements involved

EUGENE M. WILKINS; YOSHIKAZU SASAKI; ROGER H. SCHAUSS

1971-01-01

334

Multiscale Numerical Simulation of Radiation Heat Transfer in Participating Media

In this paper, a numerical method for the simulation of radiative heat transfer is presented. The multiscale radiative exchange method (MREM) calculates the radiative source terms in a mesh structure that is coarser than the structures that are typically used in computational fluid flow calculations. To consider the effects of smaller scales on the overall predictions of the model, two

Mohammad Hadi Bordbar; Timo Hyppänen

2013-01-01

335

Numerical Simulation on Flow Fields of the Blockerless Thrust Reverser

The flow fields of a blockerless thrust reverser model were studied using computational fluid dynamic (CFD). The numerical simulations were performed with the bypass ratio of 9. The effects of cascade flow ratio and the injection flow ratio with variation of injection parameters at different fan nozzle pressure ratio (FNPR) were studied. According to detailed analysis of the thrust reverser

Yun-Hao Zhang; Qitai Eri; Xiao-Xing Li

2011-01-01

336

Numerical Simulations of Wing-Body Junction Flows

NASA Technical Reports Server (NTRS)

The goal of the research project is to contribute to the optimized design of fan bypass systems in advanced turbofan engines such as the Advanced Ducted Propulsors (ADP). The immediate objective is to perform numerical simulation of duct-strut interactions to elucidate the loss mechanisms associated with this configuration that is characteristic of ADP. These numerical simulations would complement an experimental study being undertaken at Purdue University. As the first step in the process, a numerical study of wing-body junction flow is being undertaken as it shares a number of characteristics with the duct-strut interaction flow. The presence of the characteristic horseshoe vortex and the associated secondary flow are the salient features that contribute to making this flow a challenge to predict numerically. The simulations will be performed with the NPARC code on the CRAY Y-MP platform at LeRC. The grids for the simulation have been generated using an algebraic mapping technique with a multisurface algorithm.

Krishnamurthy, R.; Cagle, C.; Chandra, S.

1996-01-01

337

Experimental and Numerical Simulations of Tsunami-Structures Interaction

Recently, with the support of the Network for Earthquake Engineering Simulation Program of the National Science Foundation in the US, Oregon State University (OSU) has completed the upgrading of a Tsunami Wave Basin Facility to support experimental and computational tsunami research. This paper briefly describes the physical experimental facility and selected experimental and numerical models at OSU for tsunami structure

Solomon C. Yim

338

Numerical simulation of fracture in experiments with compressed shells

NASA Astrophysics Data System (ADS)

The acceleration dynamics and fracture of 12Kh18N10T steel shells loaded by the detonation of a spherical explosive layer are numerically simulated. NAG-type and some other fracture calculation techniques are shown to correctly describe the experimental results obtained in this work.

Anoshin, M. A.; Gabzetdinova, L. Ya.; Kozlov, E. A.; Kuratov, S. E.; Ol'khov, O. V.; Sokolov, S. S.; Tarzhanov, V. I.; Shuvalova, E. V.

2012-04-01

339

Numerical simulation of plugging failure in ballistic penetration

A coupled computational material model of viscoplasticity and ductile damage has been developed and implemented in LS-DYNA. This model gives good agreement between numerical simulations and experimental observations of plugging failure in ballistic penetration, without the use of inverse modelling or predefined defects. However, even if the model constants can be determined from relatively simple uniaxial tensile tests, the computational

T. Børvik; O. S. Hopperstad; T. Berstad; M. Langseth

2001-01-01

340

Numerical simulation of thrust reverser for rear mounted engine

The objectives of the study were to establish the feasibility of the evaluation of the performances of thrust reverser systems through numerical simulations, with Onera's Cedre computation code. Two configurations were retained, the first one was an isolated engine and the second one was an installed engine in a rear mounted generic configuration. The first configuration concerns the aft part

G. TURPIN; F. VUILLOT; C. CROISY; D. BERNIER

341

Numerical simulation of cohesive powder behavior in a fluidized bed

A numerical simulation model was developed for wet powder fluidization in the scope of investigation on cohesive powder behavior. The model was developed based on the discrete element method (DEM) with the inter-particle cohesive interaction due to liquid bridging. To take into account the liquid bridge force between particles and between a particle and a wall, a regression expression for

Takafumi Mikami; Hidehiro Kamiya; Masayuki Horio

1998-01-01

342

General physics motivations for numerical simulations of quantum field theory

In this introductory article a brief description of Quantum Field Theories (QFT) is presented with emphasis on the distinction between strongly and weakly coupled theories. A case is made for using numerical simulations to solve QCD, the regnant theory describing the interactions between quarks and gluons. I present an overview of what these calculations involve, why they are hard, and

Rajan Gupta

1999-01-01

343

Numerical Simulation of the Perrin-Like Experiments

ERIC Educational Resources Information Center

A simple model of the random Brownian walk of a spherical mesoscopic particle in viscous liquids is proposed. The model can be solved analytically and simulated numerically. The analytic solution gives the known Einstein-Smoluchowski diffusion law r[superscript 2] = 2Dt, where the diffusion constant D is expressed by the mass and geometry of a…

Mazur, Zygmunt; Grech, Dariusz

2008-01-01

344

Numerical Simulation on Pharmaceutical Powder Compaction Lianghao Han1,a

Numerical Simulation on Pharmaceutical Powder Compaction Lianghao Han1,a , James Elliott1,b Department of Materials Science and Metallurgy, University of Cambridge, CB2 3QZ,UK 2 Pfizer Global R elasticity law developed to describe the compaction behavior of pharmaceutical powders. The model

Elliott, James

345

A numerical simulation of the phenomena in Be plasma

In this paper, we present the numerical simulation of the Be deposition phenomena using the Thermionic Vacuum Arc (TVA) method. The Be marker layer must be adherent to the substrate and compact to resemble bulk beryllium. Thermionic Vacuum Arc (TVA) is an externally heated cathode arc which can be established in high vacuum condition, in vapors of the anode material.

Camelia Gavrila; Cristian P. Lungu; Ion Gruia

2011-01-01

346

Numerical simulation of selective laser sintering transient temperature field

A numerical simulation pattern based on finite element algorithm is proposed for calculation of selective laser sintering transient temperature field. The patter is based on the transient thermal radiation and the boundary conditions is concerned soundly, particularly during the transient sintering the relation between thermal conductivity and transient sintering temperature is set up on the basis of practical test to

Jian Xing; Xiaogang Sun

2009-01-01

347

NUMERICAL SIMULATION OF THREE-DIMENSIONAL TUFT CORONA AND ELECTROHYDRODYNAMICS

The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of in...

348

Numerical simulation of moving rigid body in rarefied gases

In this paper we present a numerical scheme to simulate a moving rigid body with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated by solving the Boltzmann equation using a DSMC particle method. The motion of the rigid body is governed by the Newton-Euler equations, where the force and the torque on the rigid body is computed from the momentum transfer of the gas molecules colliding with the body. On the other hand, the motion of the rigid body influences the gas flow in its surroundings. We validate the numerical results by testing the Einstein relation for Brownian motion of the suspended particle. The translational as well as the rotational degrees of freedom are taken into account. It is shown that the numerically computed translational and rotational diffusion coefficients converge to the theoretical values.

Samir Shrestha; Sudarshan Tiwari; Axel Klar; Steffen Hardt

2014-06-19

349

Numerical simulation of moving rigid body in rarefied gases

In this paper we present a numerical scheme to simulate a moving rigid body with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated by solving the Boltzmann equation using a DSMC particle method. The motion of the rigid body is governed by the Newton-Euler equations, where the force and the torque on the rigid body is computed from the momentum transfer of the gas molecules colliding with the body. On the other hand, the motion of the rigid body influences the gas flow in its surroundings. We validate the numerical results by testing the Einstein relation for Brownian motion of the suspended particle. The translational as well as the rotational degrees of freedom are taken into account. It is shown that the numerically computed translational and rotational diffusion coefficients converge to the theoretical values.

Shrestha, Samir; Klar, Axel; Hardt, Steffen

2014-01-01

350

Numerical relativity simulations in the era of the Einstein Telescope

Numerical-relativity (NR) simulations of compact binaries are expected to be an invaluable tool in gravitational-wave (GW) astronomy. The sensitivity of future detectors such as the Einstein Telescope (ET) will place much higher demands on NR simulations than first- and second-generation ground-based detectors. We discuss the issues facing compact-object simulations over the next decade, with an emphasis on estimating where the accuracy and parameter space coverage will be sufficient for ET and where significant work is needed.

Mark Hannam; Ian Hawke

2009-08-21

351

A Numerical Formulation for Simulating Free-Surface Hydrodynamics

Cartesian-grid methods in combination with immersed-body and volume-of-fluid methods are ideally suited for simulating breaking waves around ships. A surface panelization of the ship hull is used as input to impose body-boundary conditions on a three-dimensional cartesian grid. The volume-of-fluid portion of the numerical algorithm is used to capture the free-surface interface, including the breaking of waves. The numerical scheme is implemented on a parallel computer. Recent improvements to the numerical scheme are discussed, including implementation of a new multigrid procedure and conversion to MPI communication. Numerical predictions are compared to laboratory measurements of a towed transom-stern model.

O'Shea, Thomas T; Dommermuth, Douglas G; Wyatt, Donald C

2014-01-01

352

A Precise and Efficient Evaluation of the Proximity between Web Clients and their Local DNS Servers

, since only 16% of the client and local DNS associations are in the same networkÂaware cluster [13 sends a request to its local DNS server. The local DNS server resolves the request on behalfA Precise and Efficient Evaluation of the Proximity between Web Clients and their Local DNS Servers

Mao, Zhuoqing Morley

353

Benchmarks and numerical methods for the simulation of boiling flows

NASA Astrophysics Data System (ADS)

Comparisons of different numerical methods suited to the simulations of phase changes are presented in the framework of interface capturing computations on structured fixed computational grids. Due to analytical solutions, we define some reference test-cases that every numerical technique devoted to phase change should succeed. Realistic physical properties imply some drastic interface jump conditions on the normal velocity or on the thermal flux. The efficiencies of Ghost Fluid and Delta Function Methods are compared to compute the normal velocity jump condition. Next, we demonstrate that high order extrapolation methods on the thermal field allow performing accurate and robust simulations for a thermally controlled bubble growth. Finally, some simulations of the growth of a rising bubble are presented, both for a spherical bubble and a deformed bubble.

Tanguy, Sébastien; Sagan, Michaël; Lalanne, Benjamin; Couderc, Frédéric; Colin, Catherine

2014-05-01

354

A DNS Reflection Method for Global Traffic Management Cheng Huang

A DNS Reflection Method for Global Traffic Management Cheng Huang Microsoft Research Nick Holt Microsoft Corporation Y. Angela Wang Polytechnic Institute of NYU Albert Greenberg Microsoft Research Jin Li

Chou, Philip A.

355

Configuration Management File Manager Developed for Numerical Propulsion System Simulation

NASA Technical Reports Server (NTRS)

One of the objectives of the High Performance Computing and Communication Project's (HPCCP) Numerical Propulsion System Simulation (NPSS) is to provide a common and consistent way to manage applications, data, and engine simulations. The NPSS Configuration Management (CM) File Manager integrated with the Common Desktop Environment (CDE) window management system provides a common look and feel for the configuration management of data, applications, and engine simulations for U.S. engine companies. In addition, CM File Manager provides tools to manage a simulation. Features include managing input files, output files, textual notes, and any other material normally associated with simulation. The CM File Manager includes a generic configuration management Application Program Interface (API) that can be adapted for the configuration management repositories of any U.S. engine company.

Follen, Gregory J.

1997-01-01

356

Numerical simulation of the unsteady behaviour of cavitating flows

NASA Astrophysics Data System (ADS)

A 2D numerical model is proposed to simulate unsteady cavitating flows. The Reynolds-averaged Navier-Stokes equations are solved for the mixture of liquid and vapour, which is considered as a single fluid with variable density. The vapourization and condensation processes are controlled by a barotropic state law that relates the fluid density to the pressure variations. The numerical resolution is a pressure-correction method derived from the SIMPLE algorithm, with a finite volume discretization. The standard scheme is slightly modified to take into account the cavitation phenomenon. That numerical model is used to calculate unsteady cavitating flows in two Venturi type sections. The choice of the turbulence model is discussed, and the standard RNG k-model is found to lead to non-physical stable cavities. A modified k-model is proposed to improve the simulation. The influence of numerical and physical parameters is presented, and the numerical results are compared to previous experimental observations and measurements. The proposed model seems to describe the unsteady cavitation behaviour in 2D geometries well.

Coutier-Delgosha, O.; Reboud, J. L.; Delannoy, Y.

2003-06-01

357

Thermal numerical simulator for laboratory evaluation of steamflood oil recovery

A thermal numerical simulator running on an IBM AT compatible personal computer is described. The simulator was designed to assist laboratory design and evaluation of steamflood oil recovery. An overview of the historical evolution of numerical thermal simulation, NIPER's approach to solving these problems with a desk top computer, the derivation of equations and a description of approaches used to solve these equations, and verification of the simulator using published data sets and sensitivity analysis are presented. The developed model is a three-phase, two-dimensional multicomponent simulator capable of being run in one or two dimensions. Mass transfer among the phases and components is dictated by pressure- and temperature-dependent vapor-liquid equilibria. Gravity and capillary pressure phenomena were included. Energy is transferred by conduction, convection, vaporization and condensation. The model employs a block centered grid system with a five-point discretization scheme. Both areal and vertical cross-sectional simulations are possible. A sequential solution technique is employed to solve the finite difference equations. The study clearly indicated the importance of heat loss, injected steam quality, and injection rate to the process. Dependence of overall recovery on oil volatility and viscosity is emphasized. The process is very sensitive to relative permeability values. Time-step sensitivity runs indicted that the current version is time-step sensitive and exhibits conditional stability. 75 refs., 19 figs., 19 tabs.

Sarathi, P.

1991-04-01

358

Numerical Propulsion System Simulation (NPSS) 1999 Industry Review

NASA Technical Reports Server (NTRS)

The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia, and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective, high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. In addition, the paper contains a summary of the feedback received from industry partners in the development effort and the actions taken over the past year to respond to that feedback. The NPSS development was supported in FY99 by the High Performance Computing and Communications Program.

Lytle, John; Follen, Greg; Naiman, Cynthia; Evans, Austin

2000-01-01

359

The modelling of the tangential strain rate term in the Flame Surface Density (FSD) transport equation in the context of Reynolds Averaged Navier–Stokes (RANS) simulations of turbulent premixed combustion has been addressed by a priori analysis of a Direct Numerical Simulation (DNS) database of statistically planar freely propagating flames with wide variations of Damköhler number Da, heat release parameter ?

Mohit Katragadda; Sean P. Malkeson; Nilanjan Chakraborty

2011-01-01

360

Numerical simulation of the deformation and breakup of droplets subjected to complex, time been carried out. A volumeoffluid (VOF) method, previously used to simulate numerically firstly to generate strain rate histories that droplets experience and secondly to simulate the effect

Renardy, Yuriko

361

Expert System Architecture for Rocket Engine Numerical Simulators: A Vision

NASA Technical Reports Server (NTRS)

Simulation of any complex physical system like rocket engines involves modeling the behavior of their different components using mostly numerical equations. Typically a simulation package would contain a set of subroutines for these modeling purposes and some other ones for supporting jobs. A user would create an input file configuring a system (part or whole of a rocket engine to be simulated) in appropriate format understandable by the package and run it to create an executable module corresponding to the simulated system. This module would then be run on a given set of input parameters in another file. Simulation jobs are mostly done for performance measurements of a designed system, but could be utilized for failure analysis or a design job such as inverse problems. In order to use any such package the user needs to understand and learn a lot about the software architecture of the package, apart from being knowledgeable in the target domain. We are currently involved in a project in designing an intelligent executive module for the rocket engine simulation packages, which would free any user from this burden of acquiring knowledge on a particular software system. The extended abstract presented here will describe the vision, methodology and the problems encountered in the project. We are employing object-oriented technology in designing the executive module. The problem is connected to the areas like the reverse engineering of any simulation software, and the intelligent systems for simulation.

Mitra, D.; Babu, U.; Earla, A. K.; Hemminger, Joseph A.

1998-01-01

362

Numerical simulations of solar disturbances and their interplanetary consequences

NASA Technical Reports Server (NTRS)

Time-dependent MHD numerical simulations are used to study responses of the solar atmosphere and interplanetary medium to simulated solar disturbances. A number of 2D and 3D examples of coronal mass ejection (CME) simulations and some current controversies concerning the basic processes of CME initiation are discussed. Footpoint shearing motion is tested to determine whether it can provide a reasonable mechanism for CME development from arch filament configurations. Possible interplanetary consequences to CME-like disturbances are demonstrated by using 3D simulations to determine the dynamic response of the solar wind to a plasmoid injection from an eruptive filament or prominence. The possibility that a plasmoid may be generated in the interplanetary medium by a solar-generated shock that propagates through a heliospheric current sheet is discussed. Application of the 3D model for the interpretation of interplanetary scintillation observations is addressed.

Dryer, M.; Wu, S. T.; Detman, T. R.

1990-01-01

363

Numerical Simulation of Multi-CME Events in the Heliosphere

NASA Astrophysics Data System (ADS)

The ENLIL-based modeling system enables faster-than-real time simulations of corotating and transient heliospheric disturbances. This “hybrid” system does not simulate origin of coronal mass ejections (CMEs) but uses appearance in coronagraphs, ?ts geometric and kinematic parameters, and launches a CME-like structure into the solar wind computed using the Wang-Sheeley-Arge (WSA) coronal model. Numerical heliospheric simulation then provides global context of CMEs propagating in the inner heliosphere and interacting with structured background solar wind and with other CMEs. In this presentation, we introduce the recent improvements that support modeling of the evolving background solar wind and continuous modeling of multiple-CME events. We simulated over 700 CMEs in 2011-2013 to validate and calibrate our new modeling system. In this presentation, we will show examples of multi-CME events in March 2012 and July 2012 periods of enhanced solar activity. We will present results of 3D numerical magnetohydrodynamic (MHD) simulations and compare them with remote white-light observations, with in-situ measurements of plasma parameters and detection of solar energetic particles (SEPs) at various spacecraft.

Odstrcil, Dusan; Luhmann, Janet G.; Jian, Lan; Mays, Leila; Xie, Hong; Taktakishvilli, Aleksandre

364

Characterizing electron temperature gradient turbulence via numerical simulation

Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s<0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.

Nevins, W. M.; Candy, J.; Cowley, S.; Dannert, T.; Dimits, A.; Dorland, W.; Estrada-Mila, C.; Hammett, G. W.; Jenko, F.; Pueschel, M. J.; Shumaker, D. E. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); General Atomics, San Diego, California 92186 (United States); Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547 (United States); Centre de Recherches en Physique des Plasmas (CRPP), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); University of Maryland, College Park, Maryland 20742 (United States); Department of Mechanical and Aerospace Engineering, UCSD, San Diego, California 92093 (United States); Princeton Plasma Physics Laboratory, Princeton, New Jersey 08536 (United States); Max-Planck Institut fuer Plasmaphysik, D-85748 Garching (Germany); Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2006-12-15

365

Characterizing Electron Temperature Gradient Turbulence Via Numerical Simulation

Numerical simulations of electron temperature gradient (ETG) turbulence are presented which characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasmaoperating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s < 0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.

Nevins, W M; Candy, J; Cowley, S; Dannert, T; Dimits, A; Dorland, W; Estrada-Mila, C; Hammett, G W; Jenko, F; Pueschel, M J; Shumaker, D E

2006-05-22

366

Numerical simulation of electrothermal de-icing systems

NASA Technical Reports Server (NTRS)

Transient simulations of de-icing of composite aircraft components by electrothermal heating have been computed for both one and two-dimensional rectangular geometries. The implicit Crank-Nicolson formulation is used to insure stability of the finite-differenced heat conduction equations and the phase change in the ice layer is simulated using the Enthalpy method. Numerical solutions illustrating de-icer performance for various composite aircraft blades and environmental conditions are presented. Comparisons are made with previous studies and with available experimental data. Initial results using a coordinate mapping technique to describe the actual blade geometry are discussed.

De Witt, K. J.; Keith, T. G.; Chao, D. F.; Masiulaniec, K. C.

1983-01-01

367

A numerical simulation of the phenomena in Be plasma

NASA Astrophysics Data System (ADS)

In this paper, we present the numerical simulation of the Be deposition phenomena using the Thermionic Vacuum Arc (TVA) method. The Be marker layer must be adherent to the substrate and compact to resemble bulk beryllium. Thermionic Vacuum Arc (TVA) is an externally heated cathode arc which can be established in high vacuum condition, in vapors of the anode material. The arc is ignited between a heated cathode provided with a Whenelt cylinder and the anode which is a crucible containing the material to be evaporated [1]. We have used the COMSOL software to simulate the Be deposition phenomena using the TVA method.

Gavrila, Camelia; Lungu, Cristian P.; Gruia, Ion

2011-05-01

368

Numerical simulations of a diode laser BPH treatment system

Numerical simulations are presented of the laser-tissue interaction of a diode laser system for treating benign prostate hyperplasia. The numerical model includes laser light transport, heat transport, cooling due to blood perfusion, thermal tissue damage, and enthalpy of tissue damage. Comparisons of the simulation results to clinical data are given. We report that a reasonable variation from a standard set of input data produces heating times which match those measured in the clinical trials. A general trend of decreasing damage volume with increasing heating time is described. We suggest that the patient-to- patient variability seen in the data can be explained by differences in fundamental biophysical properties such as the optical coefficients. Further work is identified, including the measurement and input to the model of several specific data parameters such as optical coefficients, blood perfusion cooling rate, and coagulation rates.

Esch, V; London, R A; Papademetriou, S

1999-02-23

369

Numerical simulation of the circulation of the atmosphere of Titan

NASA Technical Reports Server (NTRS)

A three dimensional General Circulation Model (GCM) of Titan's atmosphere is described. Initial results obtained with an economical two dimensional (2D) axisymmetric version of the model presented a strong superrotation in the upper stratosphere. Because of this result, a more general numerical study of superrotation was started with a somewhat different version of the GCM. It appears that for a slowly rotating planet which strongly absorbs solar radiation, circulation is dominated by global equator to pole Hadley circulation and strong superrotation. The theoretical study of this superrotation is discussed. It is also shown that 2D simulations systemically lead to instabilities which make 2D models poorly adapted to numerical simulation of Titan's (or Venus) atmosphere.

Hourdin, F.; Levan, P.; Talagrand, O.; Courtin, Regis; Gautier, Daniel; Mckay, Christopher P.

1992-01-01

370

Simulating Prosthetic Heart Valve Hemodynamics: Numerical Model Development

NASA Astrophysics Data System (ADS)

Since the first successful implantation of a prosthetic heart valve four decades ago, over 50 different designs have been developed including both mechanical and bio-prosthetic valves. Valve implants, however, are associated with increased risk of blood clotting, a trend which is believed to be linked to the complex hemodynamics induced by the prosthesis. To understand prosthetic valve hemodynamics under physiological conditions, we develop a numerical method capable of simulating flows in realistic prosthetic heart valves in anatomical geometries. The method employs a newly developed hybrid numerical technique that integrates the chimera overset grid approach with a Cartesian, sharp-interface immersed boundary methodology. The capabilities of the method are demonstrated by applying it to simulate pulsatile flow in both bileaflet and tri-leaflet valves moving with prescribed leaflet kinematics.

Ge, Liang

2005-11-01

371

Numerical studies towards practical large-eddy simulation

Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and "low-cost" shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.

Boudet, Jérôme; Shao, L; Lévêque, Emmanuel

2008-01-01

372

Numerical studies towards practical large-eddy simulation

NASA Astrophysics Data System (ADS)

Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and “low-cost” shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.

Boudet, J.; Caro, J.; Shao, L.; Lévêque, E.

2007-11-01

373

PROBING BROWNSTEIN-MOFFAT GRAVITY VIA NUMERICAL SIMULATIONS

In the standard scenario of the Newtonian gravity, a late-type galaxy (i.e., a spiral galaxy) is well described by a disk and a bulge embedded in a halo mainly composed of dark matter. In Brownstein-Moffat gravity, there is a claim that late-type galaxy systems would not need to have halos, avoiding as a result the dark matter problem, i.e., a modified gravity (non-Newtonian) would account for the galactic structure with no need of dark matter. In the present paper, we probe this claim via numerical simulations. Instead of using a 'static galaxy', where the centrifugal equilibrium is usually adopted, we probe the Brownstein-Moffat gravity dynamically via numerical N-body simulations.

Brandao, C. S. S.; De Araujo, J. C. N., E-mail: claudio@das.inpe.b, E-mail: jcarlos@das.inpe.b [Divisao de Astrofisica, Instituto Nacional de Pesquisas Espaciais, S. J. Campos, SP 12227-010 (Brazil)

2010-07-10

374

Direct numerical simulation of the dynamics of sliding rough surfaces

NASA Astrophysics Data System (ADS)

The noise generated by the friction of two rough surfaces under weak contact pressure is usually called roughness noise. The underlying vibration which produces the noise stems from numerous instantaneous shocks (in the microsecond range) between surface micro-asperities. The numerical simulation of this problem using classical mechanics requires a fine discretization in both space and time. This is why the finite element method takes much CPU time. In this study, we propose an alternative numerical approach which is based on a truncated modal decomposition of the vibration, a central difference integration scheme and two algorithms for contact: The penalty algorithm and the Lagrange multiplier algorithm. Not only does it reproduce the empirical laws of vibration level versus roughness and sliding speed found experimentally but it also provides the statistical properties of local events which are not accessible by experiment. The CPU time reduction is typically a factor of 10.

Dang, Viet Hung; Perret-Liaudet, Joel; Scheibert, Julien; Le Bot, Alain

2013-11-01

375

Large Eddy Simulations of Magnetohydrodynamic Turbulence

NASA Astrophysics Data System (ADS)

Increases in computer power, while important, are not likely to have a large impact on the problem of simulating turbulence at high Reynolds number. The energy and anisotropy are contained predominantly in the larger scales of motion, but most of the computational effort in a direct numerical simulation (DNS) is expended on the smallest dissipative motions. We present preliminary results from a large eddy simulation (LES) with periodic cubic geometry, where we do not attempt to simulate all the wavenumber modes up to the viscous cut-off. Only the large scales are explicitly resolved, while the interaction of the large scales with the smaller scales is modeled. The model is localized by dynamical calculation of the closure parameters. The performance of different models is evaluated by comparison of LES results with data from a higher resolution DNS. We intend this study to form a basis for the implementation of the large eddy simulation technique in a global simulation of the solar wind.

Chhiber, R.; Matthaeus, W. H.; Wan, M.; Usmanov, A. V.

2013-12-01

376

Direct numerical simulation (DNS) of the near field of a three-dimensional spatially developing turbulent lifted hydrogen jet flame in heated coflow is performed with a detailed mechanism to determine the stabilization mechanism and the flame structure. The DNS was performed at a jet Reynolds number of 11,000 with over 940 million grid points. The results show that auto-ignition in a fuel-lean mixture at the flame base is the main source of stabilization of the lifted jet flame. A chemical flux analysis shows the occurrence of near-isothermal chemical chain branching preceding thermal runaway upstream of the stabilization point, indicative of hydrogen auto-ignition in the second limit. The Damkoehler number and key intermediate-species behaviour near the leading edge of the lifted flame also verify that auto-ignition occurs at the flame base. At the lifted-flame base, it is found that heat release occurs predominantly through ignition in which the gradients of reactants are opposed. Downstream of the flame base, both rich-premixed and non-premixed flames develop and coexist with auto-ignition. In addition to auto-ignition, Lagrangian tracking of the flame base reveals the passage of large-scale flow structures and their correlation with the fluctuations of the flame base. In particular, the relative position of the flame base and the coherent flow structure induces a cyclic motion of the flame base in the transverse and axial directions about a mean lift-off height. This is confirmed by Lagrangian tracking of key scalars, heat release rate and velocity at the stabilization point.

Chen, Jackie [Sandia National Laboratories (SNL); Sankaran, Ramanan [ORNL; Yoo, Chun S [Sandia National Laboratories (SNL)

2009-01-01

377

Numerical simulations of the pyrolysis of 1, 2 dichloroethane

Numerical simulations of 1, 2 dichloroethane (EDC) pyrolysis are conducted to understand the process in the production of\\u000a the vinyl chloride monomer (VCM) and by-products. A chemical kinetic mechanism is developed, with the adopted scheme involving\\u000a 44 gas-phase species and 260 elementary forward and backward reactions. Detailed sensitivity analyses and the rates of production\\u000a analysis are performed on each of

Ki Yong Lee

2002-01-01

378

A mesh-free approach to numerical rock mechanics simulations

NASA Astrophysics Data System (ADS)

Numerical simulation of the nucleation, growth, and coalescence of fracture networks is a fundamental aspect of lithospheric geodynamics and engineering applications such as enhanced geothermal systems, hydraulic fracturing and CO2 sequestration. Modeling the underlying mechanics is challenging because of several numerical difficulties. In particular, fracture path evolution predicted by mesh-based models can be heavily affected by numerical resolution of the chosen discretization scheme. Additionally, large deformations can lead to numerical errors associated with highly deformed elements. We are developing algorithms that simulate fracture nucleation and growth using mesh-free methods that overcome the difficulties arising from the mesh-sensitivity of conventional mesh-based methods. We implemented a mesh-free local Petrov-Galerkin method (MLPG), which is based on the local weak form of the problem under consideration. This method requires no mesh for interpolation or integration, and thus may be well-suited to handle strain localization occurring during fracture development. Interpolation is performed using moving least squares approximation (MLS) shape functions, and since nodal integration is performed locally, this approach can be parallelized efficiently. We present a mesh-free 2D elasto-plastic model for geomaterials that includes frictional hardening and cohesion softening using the Mohr-Coulomb failure criterion to simulate fracture network evolution and dynamic fracture propagation. Model performance is further enhanced through parallelization by utilising a hybrid CPU/GPU cluster using the PETSc library. We outline the implementation of the developed code, and evaluate its performance from a series of benchmark simulations.

Jansen, Gunnar; Galvan, Boris; Miller, Stephen

2014-05-01

379

Numerical Simulation of Blood Flow Through Microvascular Capillary Networks

A numerical method is implemented for computing blood flow through a branching microvascular capillary network. The simulations\\u000a follow the motion of individual red blood cells as they enter the network from an arterial entrance point with a specified\\u000a tube hematocrit, while simultaneously updating the nodal capillary pressures. Poiseuille’s law is used to describe flow in\\u000a the capillary segments with an

C. Pozrikidis

2009-01-01

380

Numerical simulation of wavy falling film flow using VOF method

Surface wave dynamics of vertical falling films under monochromatic-frequency flowrate-forcing perturbations is computed by the direct simulation of Navier–Stokes equations using the Volume of Fluid (VOF) method to track free surfaces and the Continuum Surface Force (CSF) model to account for dynamic boundary conditions at free surfaces. The numerical VOF–CSF model is completely formulated, and more attention is given to

D. Gao; N. B. Morley; V. Dhir

2003-01-01

381

Mobile phone as a platform for numerical simulation

NASA Astrophysics Data System (ADS)

In this work numerical simulations performed on mobile devices equipped with ARM microprocessors are shown. Calculations include: light propagation in linear and nonlinear media based on one-dimensional Schrödinger equation and molecules reorientation in nematic liquid crystals. The purpose of this publication is to show advantages and disadvantages of using mobile devices as a platform for education and research. Discussion about software development is provided.

Sala, Filip A.

2012-01-01

382

Numerical Simulation of Coherent Structures over Plant Canopy

This paper reports large eddy simulations of the interaction between an atmospheric boundary layer and a canopy (representing\\u000a a forest cover). The problem is studied for a homogeneous configuration representing the situation encountered above a continuous\\u000a forest cover, as well as for a heterogeneous configuration representing the situation similar to an edge or a clearing in\\u000a a forest. The numerical

Konstantin Gavrilov; Gilbert Accary; Dominique Morvan; Dmitry Lyubimov; Sofiane Méradji; Oleg Bessonov

2011-01-01

383

Numerical Simulations of the Metallicity Distribution in Dwarf Spheroidal Galaxies

Recent observations show that the number of stars with very low metallicities in the dwarf spheroidal satellites of the Milky Way is low, despite the low average metallicities of stars in these systems. We undertake numerical simulations of star formation and metal enrichment of dwarf galaxies in order to verify whether this result can be reproduced with ''standard'' assumptions. The answer is likely to be negative, unless some selection bias against very low metallicity stars is present in the observations.

Ripamonti, Emanuele; Tolstoy, E.; Helmi, A.; Battaglia, G.; /Kapteyn Astron. Inst., Groningen; Abel, T.; /KIPAC, Menlo Park

2006-12-12

384

Numerical simulations of unsteady reactive flows in a combustion chamber

This paper reports on a potentially important source of large-pressure oscillations in combustors that is an instability induced by the interactions between large-scale vortex structures, acoustic waves, and chemical energy release. To study these interactions, we have performed time-dependent, compressible numerical simulations of the flow field in an idealized ramjet consisting of an axisymmetric inlet and combustor and a choked

K. Kailasanath; J. H. Gardner; E. S. Oran; J. P. Boris

1991-01-01

385

Three-dimensional numerical simulations of unsteady reactive square jets

Results of finite-difference, time-dependent numerical studies of the near field of subsonic, reactive square jets are presented. The simulations model space\\/time-developing compressible (subsonic) jets, using species- and temperature-dependent diffusive transport, and finite-rate chemistry appropriate for H2 combustion. Comparative measurements of entrainment for square jets are obtained based on evaluations of streamwise mass-flux to obtain an assessment on how the jet

F. F. Grinstein; K. Kailasanath

1995-01-01

386

Three-dimensional numerical simulations of unsteady reactive square jets

Results of finite-difference, time-dependent numerical studies of the near field of subsonic, reactive square jets were presented. The simulations model space\\/time-developing compressible (subsonic) jets, using species- and temperature-dependent diffusive transport, and finite-rate chemistry appropriate for H2 combustion. Comparative measurements of entrainment for square jets were obtained based on evaluations of streamwise mass-flux to obtain an assessment on how the jet

F. F. Grinstein; K. Kailasanath

1995-01-01

387

Numerical simulation of particle transport in planar shear layers

Numerical simulations of particle dispersion in a planar shear dominated by large scale vortical structures are reported. The shear layer is formed by two co-flowing streams past a splitter plate. The emphasis of this work is on examining how the particle dynamics are affected by the large-scale coherent structures in the initial development of the instabilities in a spatially-developing mixing

S. K. Aggarwal; J. B. Yapo; F. F. Grinstein; K. Kailasanath

1996-01-01

388

Redistribution of thermoelastic stresses in shaped crystals: Numerical simulation

The shape of crystals was considered for the first time as an important factor controlling thermoelastic stresses during crystal\\u000a growth. It was found on the basis of numerical simulation that thermoelastic stresses can be redistributed by varying the\\u000a shape of a crystal during growth. In this way, large weakly stressed regions can be obtained in the crystal owing to the

L. L. Kuandykov; S. I. Bakholdin

2004-01-01

389

A numerical simulation of boundary-layer flows near shelterbelts

We have developed a shelterbelt boundary-layer numerical model to study the patterns and dynamic processes relating to flow interaction with shelterbelts. The model simulates characteristics of all three zones of airflow passing over and through shelterbelts: the windward windspeed-reduction zone, the overspeeding zone above the shelterbelt, and the leeward windspeed-reduction zone. Locations of the maximum windspeed reduction and recirculation zone,

Hao Wang; Eugene S. Takle

1995-01-01

390

EXTENDED SCALING LAWS IN NUMERICAL SIMULATIONS OF MAGNETOHYDRODYNAMIC TURBULENCE

Magnetized turbulence is ubiquitous in astrophysical systems, where it notoriously spans a broad range of spatial scales. Phenomenological theories of MHD turbulence describe the self-similar dynamics of turbulent fluctuations in the inertial range of scales. Numerical simulations serve to guide and test these theories. However, the computational power that is currently available restricts the simulations to Reynolds numbers that are significantly smaller than those in astrophysical settings. In order to increase computational efficiency and, therefore, probe a larger range of scales, one often takes into account the fundamental anisotropy of field-guided MHD turbulence, with gradients being much slower in the field-parallel direction. The simulations are then optimized by employing the reduced MHD equations and relaxing the field-parallel numerical resolution. In this work we explore a different possibility. We propose that there exist certain quantities that are remarkably stable with respect to the Reynolds number. As an illustration, we study the alignment angle between the magnetic and velocity fluctuations in MHD turbulence, measured as the ratio of two specially constructed structure functions. We find that the scaling of this ratio can be extended surprisingly well into the regime of relatively low Reynolds number. However, the extended scaling easily becomes spoiled when the dissipation range in the simulations is underresolved. Thus, taking the numerical optimization methods too far can lead to spurious numerical effects and erroneous representation of the physics of MHD turbulence, which in turn can affect our ability to identify correctly the physical mechanisms that are operating in astrophysical systems.

Mason, Joanne; Cattaneo, Fausto [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637 (United States); Perez, Jean Carlos; Boldyrev, Stanislav, E-mail: jmason@flash.uchicago.edu, E-mail: cattaneo@flash.uchicago.edu, E-mail: jcperez@wisc.edu, E-mail: boldyrev@wisc.edu [Department of Physics, University of Wisconsin at Madison, 1150 University Ave, Madison, WI 53706 (United States)

2011-07-10

391

Numerical simulation of droplet impacting liquid surface by SPH

Droplet impacting liquid surface is not only the extremely prevalent phenomenon in the nature and industrial production but\\u000a also the extremely complicated problem of strong non-linear transient impact and free-surface flow. On the basis of the two-dimensional\\u000a viscous incompressible N-S equations, this paper conducts a study of numerical simulation on the problem of droplet impacting\\u000a liquid surface (water beads) of

DaMing Li; XiaoYu Li; Yi Lin

2011-01-01

392

Study on the numerical schemes for hypersonic flow simulation

Hypersonic flow is full of complex physical and chemical processes, hence its investigation needs careful analysis of existing\\u000a schemes and choosing a suitable scheme or designing a brand new scheme. The present study deals with two numerical schemes\\u000a Harten, Lax, and van Leer with Contact (HLLC) and advection upstream splitting method (AUSM) to effectively simulate hypersonic\\u000a flow fields, and accurately

S. P. Nagdewe; G. R. Shevare; Heuy-Dong Kim

2009-01-01

393

Numerical simulation of a planing vessel at high speed

NASA Astrophysics Data System (ADS)

Planing vessels are applied widely in civil and military situations. Due to their high speed, the motion of planning vessels is complex. In order to predict the motion of planning vessels, it is important to analyze the hydrodynamic performance of planning vessels at high speeds. The computational fluid dynamic method (CFD) has been proposed to calculate hydrodynamic performance of planning vessels. However, in most traditional CFD approaches, model tests or empirical formulas are needed to obtain the running attitude of the planing vessels before calculation. This paper presents a new CFD method to calculate hydrodynamic forces of planing vessels. The numerical method was based on Reynolds-Averaged Navier-Stokes (RANS) equations. The volume of fluid (VOF) method and the six-degrees-of-freedom equation were applied. An effective process was introduced to solve the numerical divergence problem in numerical simulation. Compared with experimental results, numerical simulation results indicate that both the running attitude and hydrodynamic performance can be predicted well at high speeds.

Su, Yumin; Chen, Qingtong; Shen, Hailong; Lu, Wei

2012-06-01

394

The calibration of numerically simulated color and material change processes

NASA Astrophysics Data System (ADS)

As shown in the past, the first steps of product changing processes within extrusion dies can be observed through numerical simulations using transient calculations and the volume of fluid (VOF) approach. However, in the later part of the changing process, influences from the system, such as surface properties of the die channel or particle types in the polymer, govern the progress of the melt flow directly at the wall. Recently an approach allows these effects to be implemented into the numerical simulation despite the complexity of the whole flow system. In general it is common to assume a zero velocity at the channel wall in fluid dynamic calculations. In reality the exchange of materials during the extrusion process can be observed. Therefore, a finite velocity at the wall has to exist. Although this velocity is very low, it cannot be ignored for product changes as for most other calculations, because the velocity of the source material at the wall dominates the time or the amount of target material needed to complete the change. To calibrate the numerical calculation considering the effects near the channel wall a correcting function based on the experimental data is used. Therefore a wall velocity is calculated analytically and implemented as boundary condition in the numerical computation. This function is based on experimental data from color and material changes of several low density polyethylene (LDPE) types.

Szöke, L.; Wortberg, J.

2014-05-01

395

NASA Technical Reports Server (NTRS)

The numerical simulation of transitional and turbulent processes in hypersonic boundary layers often involves a physical process of a shock-disturbance wave interaction in complex two-dimensional and three-dimensional flow fields. For such simulations, it is required that there be a high order of accuracy in capturing both the shock and the small disturbances. The purpose of this paper is to evaluate the viability of using high order shock capturing schemes to track small disturbances in a multi-dimensional steady hypersonic flow. The numerical methods that are to be studied are the Total Variation Diminishing (TVD) scheme, and Essentially Non-Oscillatory (ENO) scheme. This paper shows that the presence of numerical oscillations in the flow field solution may drastically hinder any attempt at tracking the propagation of any physical disturbances. It has been found that the numerical oscillations that exist for shock capturing methods may be significant enough to pollute a flow field containing small physical disturbances. The effects of the refinement of the grid do not reduce the oscillations, but rather they decrease the wavelength of the oscillations. It is shown that by aligning the shock with the grid, the amplitude of these spurious oscillations may be greatly reduced.

Lee, Theodore K.; Zhong, Xiao-Lin

1998-01-01

396

Transient productivity index for numerical well test simulations

The most difficult aspect of numerical simulation of well tests is the treatment of the Bottom Hole Flowing (BHF) Pressure. In full field simulations, this pressure is derived from the Well-block Pressure (WBP) using a numerical productivity index which accounts for the grid size and permeability, and for the well completion. This productivity index is calculated assuming a pseudo-steady state flow regime in the vicinity of the well and is therefore constant during the well production period. Such a pseudo-steady state assumption is no longer valid for the early time of a well test simulation as long as the pressure perturbation has not reached several grid-blocks around the well. This paper offers two different solutions to this problem: (1) The first one is based on the derivation of a Numerical Transient Productivity Index (NTPI) to be applied to Cartesian grids; (2) The second one is based on the use of a Corrected Transmissibility and Accumulation Term (CTAT) in the flow equation. The representation of the pressure behavior given by both solutions is far more accurate than the conventional one as shown by several validation examples which are presented in the following pages.

Blanc, G.; Ding, D.Y.; Ene, A. [Institut Francais du Petrole, Pau (France)] [and others

1997-08-01

397

Numerical Simulation of Microbiological Growth in the Capillary Fringe

NASA Astrophysics Data System (ADS)

The capillary fringe (CF) is a highly dynamic zone in a porous media at the interface between water-saturated aquifer and vadose zone, where steep biogeochemical gradients and thus high bioactivities are expected. In recent years, considerable effort has been undertaken to deepen the understanding of the physical (flow, diffusion, dispersion), geochemical (dissolution, precipitation) and biological (metabolism, excretion, biofilm formation) processes in the CF. We developed a numerical simulator for multiphase multicomponent flow in porous media which is able to consider simultaneously multiphase flow, component transport, phase exchange, geochemical reactions and microbiological processes. A splitting approach for phase transport, component transport and reaction/phase exchanges allows the usage of higher-order discretizations for the component transport. This reduces numerical dispersion significantly, which is especially important in the simulation of reactive flow. In a flow-through laboratory experiment performed at the Karlsruhe Institute of Technology, Germany, within the project "Dynamic Capillary Fringes - A Multidisciplinary Approach", the oxygen phase transfer, the growth and the transport of a bacteria (green fluorescent Escherichia coli) were investigated. The results of numerical simulations of the E. coli growth in the CF with a high nutrient supply under steady-state and transient flow conditions are compared to the experimental data.

Hron, P.; Jost, D.; Engwer, C.; Ippisch, O.; Bastian, P.

2012-04-01

398

AN EQUATION-FREE, REDUCED-ORDER MODELING APPROACH TO TROPICAL PACIFIC SIMULATION

, which may be evolved using Direct Numerical Simulations (DNS) and by restriction, we can obtain. In this paper we apply the EF POD-assisted method to the reduced modeling of a large-scale upper ocean in 1946 (see [3]) and Loeve in 1945 (see [4]), and the method has been extensively used in research within

Navon, Michael

399

Study of natural ventilation in buildings by large eddy simulation Yi Jiang and Qingyan Chen*

regarding the distribution of air velocity and pressure around and inside buildings. Although a wind tunnel is computational fluid dynamics (CFD), which is becoming popular due to the Jiang, Y. and Chen, Q. 2001. "Study of computing capacity and speed. Three CFD methods are available: direct numerical simulation (DNS), large eddy

Chen, Qingyan "Yan"

400

Numerical simulations of localized high field 1H MR spectroscopy

NASA Astrophysics Data System (ADS)

The limited bandwidths of volume selective RF pulses in localized in vivo MRS experiments introduce spatial artifacts that complicate spectral quantification of J-coupled metabolites. These effects are commonly referred to as a spatial interference or "four compartment" artifacts and are more pronounced at higher field strengths. The main focus of this study is to develop a generalized approach to numerical simulations that combines full density matrix calculations with 3D localization to investigate the spatial artifacts and to provide accurate prior knowledge for spectral fitting. Full density matrix calculations with 3D localization using experimental pulses were carried out for PRESS (TE = 20, 70 ms), STEAM (TE = 20, 70 ms) and LASER (TE = 70 ms) pulse sequences and compared to non-localized simulations and to phantom solution data at 4 T. Additional simulations at 1.5 and 7 T were carried out for STEAM and PRESS (TE = 20 ms). Four brain metabolites that represented a range from weak to strong J-coupling networks were included in the simulations (lactate, N-acetylaspartate, glutamate and myo-inositol). For longer TE, full 3D localization was necessary to achieve agreement between the simulations and phantom solution spectra for the majority of cases in all pulse sequence simulations. For short echo time (TE = 20 ms), ideal pulses without localizing gradients gave results that were in agreement with phantom results at 4 T for STEAM, but not for PRESS (TE = 20). Numerical simulations that incorporate volume localization using experimental RF pulses are shown to be a powerful tool for generation of accurate metabolic basis sets for spectral fitting and for optimization of experimental parameters.

Kaiser, Lana G.; Young, Karl; Matson, Gerald B.

2008-11-01

401

A Simulation and Decision Framework for Selection of Numerical Solvers in Scientific Computing

A Simulation and Decision Framework for Selection of Numerical Solvers in Scientific Computing and deeper knowl- edge in numerical analysis. In this paper we propose a model-driven combined decision-simulation. Â· The efficiency of numerical simulation is strongly influenced by a correct choice of the numerical method

Burns, Peter

402

A parallel implicit method for the direct numerical simulation of wall-bounded compressible-order accurate implicit temporal numerical scheme for the direct numerical simulation of turbulent flows. The numerical simulation results are compared with the results given by explicit RungeÂKutta schemes

MartÃn, Pino

403

Studying Turbulence Using Numerical Simulation Databases. No. 7; Proceedings of the Summer Program

NASA Technical Reports Server (NTRS)

The Seventh Summer Program of the Center for Turbulence Research took place in the four-week period, July 5 to July 31, 1998. This was the largest CTR Summer Program to date, involving thirty-six participants from the U. S. and nine other countries. Thirty-one Stanford and NASA-Ames staff members facilitated and contributed to most of the Summer projects. A new feature, and perhaps a preview of the future programs, was that many of the projects were executed on non-NASA computers. These included supercomputers located in Europe as well as those operated by the Departments of Defense and Energy in the United States. In addition, several simulation programs developed by the visiting participants at their home institutions were used. Another new feature was the prevalence of lap-top personal computers which were used by several participants to carry out some of the work that in the past were performed on desk-top workstations. We expect these trends to continue as computing power is enhanced and as more researchers (many of whom CTR alumni) use numerical simulations to study turbulent flows. CTR's main role continues to be in providing a forum for the study of turbulence for engineering analysis and in facilitating intellectual exchange among the leading researchers in the field. Once again the combustion group was the largest. Turbulent combustion has enjoyed remarkable progress in using simulations to address increasingly complex and practically more relevant questions. The combustion group's studies included such challenging topics as fuel evaporation, soot chemistry, and thermonuclear reactions. The latter study was one of three projects related to the Department of Energy's ASCI Program (www.llnl.gov/asci); the other two (rocket propulsion and fire safety) were carried out in the turbulence modeling group. The flow control and acoustics group demonstrated a successful application of the so-called evolution algorithms which actually led to a previously unknown forcing strategy for jets yielding increased spreading rate. A very efficient algorithm for flow in complex geometries with moving boundaries based on the immersed boundary forcing technique was tested with very encouraging results. Also a new strategy for the destruction of aircraft trailing vortices was introduced and tested. The Reynolds Averaged Modeling (RANS) group demonstrated that the elliptic relaxation concept for RANS calculations is also applicable to transonic flows with shocks; however, prediction of laminar/turbulent transition remains an important pacing item. A large fraction of the LES effort was devoted to the development and testing of a new algorithmic procedure (as opposed to phenomenological model) for subgrid scale modeling based on regularized de-filtering of the flow variables. This appears to be a very promising approach, and a significant effort is currently underway to assess its robustness in high Reynolds number flows and in conjunction with numerical methods for complex flows. As part of the Summer Program two review tutorials were given on Turbulent structures in hydrocarbon pool fires (Sheldon Tieszen), and Turbulent combustion modeling: from RANS to LES via DNS (Luc Vervisch); and two seminars entitled Assessment of turbulence models for engineering applications (Paul Durbin) and Subgrid-scale modeling for non-premixed, turbulent reacting flows (James Riley) were presented. A number of colleagues from universities, government agencies, and industry attended the final presentations of the participants on July 31 and participated in the discussions. There are twenty-six papers in this volume grouped in five areas. Each group is preceded with an overview by its coordinator.

1998-01-01

404

AI-Based Simulation: An Alternative to Numerical Simulation and Modeling

AI-Based Simulation: An Alternative to Numerical Simulation and Modeling Shahab D. Mohaghegh1,2 1- tern recognition technologies collectively known as Artificial Intelligence and Data Mining (AI to several prolif- ic reservoirs in the Middle East and in the Gulf of Mexico. #12;AI-Based reservoir models

Mohaghegh, Shahab

405

Common envelope numerical simulations: What are we missing?

NASA Astrophysics Data System (ADS)

The common envelope (CE) interaction is a very fast astrophysical process (it lasts about a year) whereby a close binary star temporarily becomes one large star. What happens next is anybody's guess. The two stars may merge, explode or transform into a compact binary. The main way to study this phenomenon is through numerical simulations, but nowadays the works that have been performed in this context fail to explain various important questions about the CE. By carrying out three-dimensional (3D) simulations of the CE interaction using a 3D hydrodynamic plus gravity code, we are trying to push the simulations a step further. We are adding additional ingredients that could be relevant to solve those important questions. In particular, we are analysing the effects of the interaction preceding the CE on the CE itself and of the stellar rotation.

Iaconi, Roberto

2014-09-01

406

Numerical simulation of radiative heat loss in an experimental burner

We describe the numerical algorithm used in the COYOTE two-dimensional, transient, Eulerian hydrodynamics program to allow for radiative heat losses in simulations of reactive flows. The model is intended primarily for simulations of industrial burners, but it is not confined to that application. It assumes that the fluid is optically thin and that photons created by the fluid immediately escape to free space or to the surrounding walls, depending upon the application. The use of the model is illustrated by simulations of a laboratory-scale experimental burner. We find that the radiative heat losses reduce the local temperature of the combustion products by a modest amount, typically on the order of 50 K. However, they have a significant impact on NO{sub x} production.

Cloutman, L.D. [Lawrence Livermore National Lab., CA (United States); Brookshaw, L. [California Univ., Davis, CA (United States). Dept. of Physics

1993-09-01

407

Numerical Simulation of Delamination Growth in Composite Materials

NASA Technical Reports Server (NTRS)

The use of decohesion elements for the simulation of delamination in composite materials is reviewed. The test methods available to measure the interfacial fracture toughness used in the formulation of decohesion elements are described initially. After a brief presentation of the virtual crack closure technique, the technique most widely used to simulate delamination growth, the formulation of interfacial decohesion elements is described. Problems related with decohesion element constitutive equations, mixed-mode crack growth, element numerical integration and solution procedures are discussed. Based on these investigations, it is concluded that the use of interfacial decohesion elements is a promising technique that avoids the need for a pre-existing crack and pre-defined crack paths, and that these elements can be used to simulate both delamination onset and growth.

Camanho, P. P.; Davila, C. G.; Ambur, D. R.

2001-01-01

408

[A numerical simulation of the aerodynamics of the nasal cavity].

We present the results of the numerical simulation of the flow in the nasal cavity, going from the tip of the nostril to the nasopharyngeal region. The volume of the nasal cavity, obtained from axial and coronal scans, takes into account the geometries of the nasal valve and turbinates. The simulation is carried out with the FLUENT code which solves the equations of fluid mechanics. The obtained results for the inspiratory phase are analyzed from the velocities and pressures, paying special attention to the separation of the streamlines in the region located between the middle meatus and the olfactory area. The presented results show the potential of simulation when used in parallel with the clinical approach. PMID:10739999

Chometon, F; Ebbo, D; Gillieron, P; Koïfman, P; Lecomte, F; Sorrel-Dejerine, N

2000-03-01

409

Numerical simulation of space debris impacts on the Whipple shield

NASA Astrophysics Data System (ADS)

The authors carried out three series of experimental tests of the first bumper perforation and main wall cratering processes directly caused by three types of projectiles with about 2, 4 and 7 km s -1 impact velocities but comparable initial kinetic energies, by using three different accelerators (one-stage powder gun, two-stage light-gas gun and rail gun), for the purpose of investigating space debris hypervelocity impacts onto single-walled Whipple bumper shields [1]. In the present study, after reviewing the numerical simulation method of hydrocode for both Eulerian and Lagrangian descriptions, a number of parametric numerical simulation analyses using multiple material Eulerian methods were performed in order to optimize the material properties of bumper and main wall materials through comparison with experimental results of single target impacts by the projectiles. In particular, the material data on the dynamic fracture phenomena are discussed in detail in the first part. Then a couple of numerical calculations using the interactive Lagrangian rezoning method to simulate the overall impact process against the single walled Whipple shield were performed and compared with the corresponding experimental results. Both results indicated fairly good agreement with each other. Moreover, it was demonstrated that the present method is helpful and efficient in understanding the impact phenomena and fracture mechanism in the space debris hypervelocity impact problem. Finally the multiple material Eulerian method was applied to the same problems modeled by the interactive Lagrangian rezoning method used previously, because the former is much easier to use for almost all users, although it is more diffusive and unclear of material boundaries than the latter. Those two kinds of numerical results also indicated fairly good agreements with each other.

Katayama, M.; Toda, S.; Kibe, S.

1997-06-01

410

Numerical Simulation of Turbulent Flows in Complex Geometries using the Coherent Vortex

Numerical Simulation of Turbulent Flows in Complex Geometries using the Coherent Vortex Simulation turbulence from a Direct Numerical Simulation. Henning Bockhorn Institute for Technical Chemistry and Polymer;2 H. Bockhorn et al. Even more than in the incompressible regime, the numerical simulation of fully

Ã?cole Normale SupÃ©rieure

411

Numerical simulations of the Lagrangian averaged NavierÂStokes equations for homogeneous isotropic numerical simulation of turbulent flows at small to moderate Reynolds numbers has been a valuable asset for numerical simulations of high Reynolds number flows. Alternative approaches to simulations of turbulent

Shkoller, Steve

412

Optical nonlinear properties for solids and nanostructures: theory and numerical simulations

Optical nonlinear properties for solids and nanostructures: theory and numerical simulations) and associated numerical tools for the calculation of second harmonic in the presence of a static electric

Botti, Silvana

413

Numerical simulations of pyroclastic surge in eruptions of Usu Volcano

NASA Astrophysics Data System (ADS)

Pyroclastic surge developed during explosive volcanic eruption can cause hazardous damage as serious as other phenomena such as blast waves or eruptive fragments. A numerical code is developed for simulating the pyroclastic surge. The code is an extension of a shock capturing code that treats shock wave propagation and other complex wave interactions (Saito, 2002). It is applied for simulating imaginary eruptions of Usu volcano, one of the most active volcano in Japan. The eruption is modeled as a high-speed jet ejected from a vent opened at the ground into a stationary atomosphere. The governing equations of mass, momentum and energy are solved by finite volume methods known as WAF(Weighed Averaged Flux) method with the HLLC approximate Riemann solver(Toro, 1997). The numerical grids of the terrain are generated from a digital elevation map. Preliminary numerical tests are carried out and followings are found: a) At the beginning of eruption, a blast wave is generated and propagates rather quickly(supersonic propagation). b) After the blast wave, a column of of high density erupting as developes. c) In about 100 sec from the beginning of the eruption, it is observed that high density gas flow spreads out along the ground as pyroclastic surge. The correlation between the gas ejection speed and the speed of the pyroclastic surge is also investigated. Saito, T. (2002), Numerical analysis of dusty-gas flows, J. Comput. Phys., 176, 129-144. Toro, E. F. (1997), Riemann solvers and numerical methods for fluid dynamics, Springer-Verlag, Heidelberg.

Saba, M.; Saito, T.; Oshima, H.

2006-12-01

414

Numerical simulation and experimental verification of extended source interferometer

NASA Astrophysics Data System (ADS)

Extended source interferometer, compared with the classical point source interferometer, can suppress coherent noise of environment and system, decrease dust scattering effects and reduce high-frequency error of reference surface. Numerical simulation and experimental verification of extended source interferometer are discussed in this paper. In order to provide guidance for the experiment, the modeling of the extended source interferometer is realized by using optical design software Zemax. Matlab codes are programmed to rectify the field parameters of the optical system automatically and get a series of interferometric data conveniently. The communication technique of DDE (Dynamic Data Exchange) was used to connect Zemax and Matlab. Then the visibility of interference fringes can be calculated through adding the collected interferometric data. Combined with the simulation, the experimental platform of the extended source interferometer was established, which consists of an extended source, interference cavity and image collection system. The decrease of high-frequency error of reference surface and coherent noise of the environment is verified. The relation between the spatial coherence and the size, shape, intensity distribution of the extended source is also verified through the analysis of the visibility of interference fringes. The simulation result is in line with the result given by real extended source interferometer. Simulation result shows that the model can simulate the actual optical interference of the extended source interferometer quite well. Therefore, the simulation platform can be used to guide the experiment of interferometer which is based on various extended sources.

Hou, Yinlong; Li, Lin; Wang, Shanshan; Wang, Xiao; Zang, Haijun; Zhu, Qiudong

2013-12-01

415

Stochastic algorithms for the analysis of numerical flame simulations

Recent progress in simulation methodologies and high-performance parallel computers have made it is possible to perform detailed simulations of multidimensional reacting flow phenomena using comprehensive kinetics mechanisms. As simulations become larger and more complex, it becomes increasingly difficult to extract useful information from the numerical solution, particularly regarding the interactions of the chemical reaction and diffusion processes. In this paper we present a new diagnostic tool for analysis of numerical simulations of reacting flow. Our approach is based on recasting an Eulerian flow solution in a Lagrangian frame. Unlike a conventional Lagrangian view point that follows the evolution of a volume of the fluid, we instead follow specific chemical elements, e.g., carbon, nitrogen, etc., as they move through the system . From this perspective an ''atom'' is part of some molecule of a species that is transported through the domain by advection and diffusion. Reactions cause the atom to shift from one chemical host species to another and the subsequent transport of the atom is given by the movement of the new species. We represent these processes using a stochastic particle formulation that treats advection deterministically and models diffusion and chemistry as stochastic processes. In this paper, we discuss the numerical issues in detail and demonstrate that an ensemble of stochastic trajectories can accurately capture key features of the continuum solution. The capabilities of this diagnostic are then demonstrated by applications to study the modulation of carbon chemistry during a vortex-flame interaction, and the role of cyano chemistry in rm NO{sub x} production for a steady diffusion flame.

Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski, Michael J.

2004-04-26

416

Stochastic algorithms for the analysis of numerical flame simulations

Recent progress in simulation methodologies and new, high-performance parallel architectures have made it is possible to perform detailed simulations of multidimensional combustion phenomena using comprehensive kinetics mechanisms. However, as simulation complexity increases, it becomes increasingly difficult to extract detailed quantitative information about the flame from the numerical solution, particularly regarding the details of chemical processes. In this paper we present a new diagnostic tool for analysis of numerical simulations of combustion phenomena. Our approach is based on recasting an Eulerian flow solution in a Lagrangian frame. Unlike a conventional Lagrangian viewpoint in which we follow the evolution of a volume of the fluid, we instead follow specific chemical elements, e.g., carbon, nitrogen, etc., as they move through the system. From this perspective an ''atom'' is part of some molecule that is transported through the domain by advection and diffusion. Reactions ca use the atom to shift from one species to another with the subsequent transport given by the movement of the new species. We represent these processes using a stochastic particle formulation that treats advection deterministically and models diffusion as a suitable random-walk process. Within this probabilistic framework, reactions can be viewed as a Markov process transforming molecule to molecule with given probabilities. In this paper, we discuss the numerical issues in more detail and demonstrate that an ensemble of stochastic trajectories can accurately capture key features of the continuum solution. We also illustrate how the method can be applied to studying the role of cyanochemistry on NOx production in a diffusion flame.

Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski, Michael J.

2001-12-14

417

High order DNS for late flow transition

NASA Astrophysics Data System (ADS)

In this report, a new high order scheme for boundary points is introduced when calculating the derivative of smooth functions by Compact Scheme. The primitive function reconstruction method of ENO schemes is applied to obtain the conservative form of the Compact Scheme. Meanwhile, modified compact scheme is developed by using an effective shock detector to block upwinding compact scheme to cross the shock, a control function, and an adaptive scheme which uses some WENO flux near the shock. The new scheme makes the original upwinding compact scheme able to capture the shock sharper than WENO and, more important, keep high order accuracy and high resolution in the smooth area which is particularly important for shock, shock boundary layer interaction and shock acoustic interaction. This report is also devoted to a DNS study of late nonlinear stages of laminar-turbulent transition on a flat plate. A number of new mechanisms about turbulence generation are presented as following. It includes mechanism of the large coherent vortex structure formation, small length scale generation and flow randomization, etc. It is shown that the energy transfer from large vortices to small vortices is carried out by multiple level sweeps, and all small length scales (turbulence) are generated by shear layer instability which is produced by large vortex structure with multiple level vortex rings, multiple level sweeps, and multiple level positive spikes near the laminar sub-layers. Also, it reveals that multiple vortex rings are also consequences of shear layer instability produced by momentum deficit which is formed by vortex ejections. In additional, the U-shaped vortex, which is not a secondary but tertiary vortex, serves as an additional channel to support the multiple ring structure. It is found that the loss of symmetry and randomization are caused by internal property of the boundary layer. Moreover, the loss of symmetry starts from the second level ring cycle in the middle of the flow field and spreads to the bottom of the boundary layer and then the whole flow field. More other new mechanisms have been discussed as well.

Lu, Ping

418

Numerical Simulation of Viscous Flow by Smoothed Particle Hydrodynamics

NASA Astrophysics Data System (ADS)

Smoothed particle hydrodynamics (SPH) is an effective numerical method to solve various problems, especially in astrophysics, but its applications have been limited to inviscid flows since it is considered not to yield ready solutions to fluid equations with second-order derivatives. Here we present a new SPH method that can be used to solve the Navier-Stokes equations for constant viscosity. The method is applied to two-dimensional Poiseuille flow, three-dimensional Hagen-Poiseuille flow and two-dimensional isothermal flows around a cylinder. In the former two cases, the temperature of fluid is assumed to be linearly dependent on a coordinate variable x along the flow direction. The numerical results agree well with analytic solutions, and we obtain nearly uniform density distributions and the expected parabolic and paraboloid velocity profiles. The density and velocity field in the latter case are compared with the results obtained using a finite difference method. Both methods give similar results for Reynolds number Re = 6, 10, 20, 30 and 55, and the differences in the total drag coefficients are about 2 ~ 4%. Our numerical simulations indicate that SPH is also an effective numerical method for calculation of viscous flows.

Takeda, H.; Miyama, S. M.; Sekiya, M.

1994-11-01

419

Numerical simulation of free water surface in pump intake

NASA Astrophysics Data System (ADS)

The purpose of this paper is to verify the volume of fluid (VOF) method for simulating the free water surface flow in pump intake. With the increasing computer power, VOF method has been becoming a more flexible and accurate choice to replace the conventional fixed water surface method, because it does not require assumptions on the nature of air-water interface. Two examples are presented in this paper. The first example is presented for simulating the growth of air-entrained vortices. LES (Large Eddy Simulation) model, instead of RANS (Reynolds averaged Navier-Stokes) turbulence model, is used to capture the peak of circular velocity around the vortex core. Numerical result shows good agreement with the benchmark experiment carried by the Turbomachinery Society of Japan. The second example predicts the flow rate distribution in the pump intake consisting of one opened and two closed channels. VOF result is compared with the conventional fixed water surface method assuming free-slip boundary condition on the fluid interface. The difference of flow pattern in the opened channel indicates that numerical flow field is affected remarkably by the setup of boundary condition at air-water interface.

Zhao, L. J.; Nohmi, M.

2012-11-01

420

Numerical simulation of the non-Newtonian mixing layer

NASA Technical Reports Server (NTRS)

This work is a continuing effort to advance our understanding of the effects of polymer additives on the structures of the mixing layer. In anticipation of full nonlinear simulations of the non-Newtonian mixing layer, we examined in a first stage the linear stability of the non-Newtonian mixing layer. The results of this study show that, for a fluid described by the Oldroyd-B model, viscoelasticity reduces the instability of the inviscid mixing layer in a special limit where the ratio (We/Re) is of order 1 where We is the Weissenberg number, a measure of the elasticity of the flow, and Re is the Reynolds number. In the present study, we pursue this project with numerical simulations of the non-Newtonian mixing layer. Our primary objective is to determine the effects of viscoelasticity on the roll-up structure. We also examine the origin of the numerical instabilities usually encountered in the simulations of non-Newtonian fluids.

Azaiez, Jalel; Homsy, G. M.

1993-01-01

421

Using Numerical Modeling to Simulate Space Capsule Ground Landings

NASA Technical Reports Server (NTRS)

Experimental work is being conducted at the National Aeronautics and Space Administration s (NASA) Langley Research Center (LaRC) to investigate ground landing capabilities of the Orion crew exploration vehicle (CEV). The Orion capsule is NASA s replacement for the Space Shuttle. The Orion capsule will service the International Space Station and be used for future space missions to the Moon and to Mars. To evaluate the feasibility of Orion ground landings, a series of capsule impact tests are being performed at the NASA Langley Landing and Impact Research Facility (LandIR). The experimental results derived at LandIR provide means to validate and calibrate nonlinear dynamic finite element models, which are also being developed during this study. Because of the high cost and time involvement intrinsic to full-scale testing, numerical simulations are favored over experimental work. Subsequent to a numerical model validated by actual test responses, impact simulations will be conducted to study multiple impact scenarios not practical to test. Twenty-one swing tests using the LandIR gantry were conducted during the June 07 through October 07 time period to evaluate the Orion s impact response. Results for two capsule initial pitch angles, 0deg and -15deg , along with their computer simulations using LS-DYNA are presented in this article. A soil-vehicle friction coefficient of 0.45 was determined by comparing the test stopping distance with computer simulations. In addition, soil modeling accuracy is presented by comparing vertical penetrometer impact tests with computer simulations for the soil model used during the swing tests.

Heymsfield, Ernie; Fasanella, Edwin L.

2009-01-01

422

An Object Model for a Rocket Engine Numerical Simulator

NASA Technical Reports Server (NTRS)

Rocket Engine Numerical Simulator (RENS) is a packet of software which numerically simulates the behavior of a rocket engine. Different parameters of the components of an engine is the input to these programs. Depending on these given parameters the programs output the behaviors of those components. These behavioral values are then used to guide the design of or to diagnose a model of a rocket engine "built" by a composition of these programs simulating different components of the engine system. In order to use this software package effectively one needs to have a flexible model of a rocket engine. These programs simulating different components then should be plugged into this modular representation. Our project is to develop an object based model of such an engine system. We are following an iterative and incremental approach in developing the model, as is the standard practice in the area of object oriented design and analysis of softwares. This process involves three stages: object modeling to represent the components and sub-components of a rocket engine, dynamic modeling to capture the temporal and behavioral aspects of the system, and functional modeling to represent the transformational aspects. This article reports on the first phase of our activity under a grant (RENS) from the NASA Lewis Research center. We have utilized Rambaugh's object modeling technique and the tool UML for this purpose. The classes of a rocket engine propulsion system are developed and some of them are presented in this report. The next step, developing a dynamic model for RENS, is also touched upon here. In this paper we will also discuss the advantages of using object-based modeling for developing this type of an integrated simulator over other tools like an expert systems shell or a procedural language, e.g., FORTRAN. Attempts have been made in the past to use such techniques.

Mitra, D.; Bhalla, P. N.; Pratap, V.; Reddy, P.

1998-01-01

423

Droughts and floods over China: Observation and numerical simulation

By analyzing the spatial and temporal distribution of the observations of the Chinese 336-station rainfall data in the 1980`s, two distinctly opposite rainfall types over East China in summer are discovered. On the 500hPa geopotential height anomaly fields in spring and summer, the variations of the general atmospheric circulation in the previous spring are closely correlated to the two kinds of conversely distributed rainfall. Furthermore, these two types of rainfall also have a certain relationship with two types of conversely distributed sea surface temperature anomalies (SSTA) in the equatorial Pacific. To verify these observational results, eight numerical model runs are carried out by IAP 2-L AGCM, with observed monthly mean global SSTs as external forcings and observed atmospheric data on February 15 as initial conditions. The simulated distributions of rainfall anomalies over East China in summer agree well with observations. With conversely distributed SSTA in the equatorial Pacific, the simulated 500hPa geopotential height anomalies are also conversely distributed, and they are closely related to the two types of simulated rainfall anomaly over East China. The simulated distributions of anomalous 500hPa geopotential height in spring are quite similar to observations. Finally, in order to evaluate the ability of IAP 2-L AGCM in the modelling of droughts and floods and short-term climate change, an objective analysis is completed between simulated results and observational data.

Yang Fanglin; Yuan Chongguang [Chinese Academy of Sciences, Beijing (China). Inst. of Atmospheric Physics

1994-12-31

424

Numerical simulations for plasma-based dry reforming

NASA Astrophysics Data System (ADS)

The conversion of greenhouse gases (CO2 and CH4) to more valuable chemicals is one of the challenges of the 21st century. The aim of this study is to describe the plasma chemistry occurring in a DBD for the dry reforming of CO2/CH4 mixtures, via numerical simulations. For this purpose we apply the 0D simulation code ``Global/kin,'' developed by Kushner, in order to simulate the reaction chemistry and the actual reaction conditions for a DBD, including the occurrence of streamers. For the chemistry part, we include a chemistry set consisting of 62 species taking part in 530 reactions. First we describe the reaction chemistry during one streamer, by simulating one discharge pulse and its afterglow, to obtain a better understanding of the reaction kinetics. Subsequently, we expand these results to real time scale simulations, i.e., 1 to 10 seconds, where we analyze the effects of the multiple discharges (streamers) and input energy on the conversion and the selectivity of the reaction products, as well as on the energy efficiency of the process. The model is validated based on experimental data from literature.

Snoeckx, Ramses; Aerts, Robby; Bogaerts, Annemie

2012-10-01

425

Hydrodynamics of Hypersonic Jets: Experiments and Numerical Simulations

Stars form in regions of the galaxy that are denser and cooler than the mean interstellar medium. These regions are called Giant Molecular Clouds. At the beginning of their life, up to $10^5-10^6$ years, stars accrete matter from their rich surrounding environment and are origin of a peculiar phenomenon that is the jet emission. Jets from Young Stellar Objects (YSOs) are intensively studied by the astrophysical community by observations at different wavelengths, analytical and numerical modeling and laboratory experiments. Indications about the jet propagation and its resulting morphologies are here obtained by means of a combined study of hypersonic jets carried out both in the laboratory and by numerical simulations.

Belan, Marco; Tordella, Daniela; Massaglia, Silvano; Ferrari, Attilio; Mignone, Andrea; Bodenschatz, Eberhard

2011-01-01

426

INEX (integrated numerical experiment) simulations of the Boeing FEL system

The INEX (integrated numerical experiment) numerical model is applied to the 0.6 {mu}m FEL oscillator at Boeing Aerospace and Electronics Company in Seattle, WA. This system consists of a 110 MeV L-band rf linac, a beam transport line from the accelerator to the entrance of the wiggler, the 5.0 meter THUNDER variable taper wiggler, and a near concentric two mirror optical oscillator. Many aspects of the model for the electron beam accelerator and transport line agree with experimental measurements. Predictions for lasing performance are compared with data obtained in May and June 1989 using a mild tapered wiggler. We obtain good agreement with the achieved extraction efficiency, while 1D pulse simulations reproduce the observed sideband instability. 15 refs., 11 figs.

Tokar, R.L.; Young, L.M.; Lumpkin, A.H.; McVey, B.D.; Thode, L.E.; Bender, S.C.; Chan, K.C.D. (Los Alamos National Lab., NM (USA)); Yeremian, A.D.; Dowell, D.H.; Lowrey, A.R. (Boeing Aerospace and Electronics, Seattle, WA (USA))

1989-01-01

427

A Numerical simulation of transition in plane channel flow

NASA Technical Reports Server (NTRS)

A numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500 is described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 by 33 by 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), implementation of subgrid-scale terms are necessary to obtain proper turbulent statistics.

Goglia, G.; Biringen, S.

1982-01-01

428

Numerical simulations of electrostatically driven jets from nonviscous droplets.

The evolution of a perfectly conducting and nonviscous fluid, under the action of an electric field (uniform at infinity), is studied numerically. Level set techniques are employed to develop an Eulerian potential flow model that can follow the drop evolution past breakup, while the free surface fluid velocity and the electric field force are obtained via axisymmetric boundary integral calculations. Numerical results are presented for neutral and charged droplets and for free charged droplets. In all cases, the evolution droplet aspect ratio, progeny droplet size, Taylor cone angles, jet shapes, and self-similar scaling exponents are reported. In particular, for free charged water droplets, the bursting frequency and other jetting characteristics have been carefully analyzed. Wherever possible, these results are compared with previously reported experiments and simulations. PMID:24730941

Garzon, M; Gray, L J; Sethian, J A

2014-03-01

429

Numerical simulations of a diode laser BPH treatment system

NASA Astrophysics Data System (ADS)

Numerical simulations are presented of the laser-tissue interaction of a diode laser system for treating benign prostate hyperplasia. The numerical model includes laser light transport, heat transport, cooling due to blood perfusion, thermal tissue damage, and enthalpy of tissue damage. Comparisons of the stimulation results to clinical data are given. We report that a reasonable variation from a standard set of input data produces heating times which match those measured in the clinical trials. A general trend of decreasing damage volume with increasing heating time is described. We suggest that the patient-to-patient variability seen in the data can be explained by differences in fundamental biophysical properties such as the optical coefficients. Further work is identified, including the measurement and input to the model of several specific data parameters such as optical coefficients, blood perfusion cooling rate, and coagulation rates.

London, Richard A.; Esch, Victor C.; Papademetriou, Stephanos

1999-06-01

430

Numerical simulations of electrostatically driven jets from nonviscous droplets

NASA Astrophysics Data System (ADS)

The evolution of a perfectly conducting and nonviscous fluid, under the action of an electric field (uniform at infinity), is studied numerically. Level set techniques are employed to develop an Eulerian potential flow model that can follow the drop evolution past breakup, while the free surface fluid velocity and the electric field force are obtained via axisymmetric boundary integral calculations. Numerical results are presented for neutral and charged droplets and for free charged droplets. In all cases, the evolution droplet aspect ratio, progeny droplet size, Taylor cone angles, jet shapes, and self-similar scaling exponents are reported. In particular, for free charged water droplets, the bursting frequency and other jetting characteristics have been carefully analyzed. Wherever possible, these results are compared with previously reported experiments and simulations.

Garzon, M.; Gray, L. J.; Sethian, J. A.

2014-03-01

431

Unsteady numerical simulations of the stability and dynamics of flames

NASA Technical Reports Server (NTRS)

In this report we describe the research performed at the Naval Research Laboratory in support of the NASA Microgravity Science and Applications Program over the past three years (from Feb. 1992) with emphasis on the work performed since the last microgravity combustion workshop. The primary objective of our research is to develop an understanding of the differences in the structure, stability, dynamics and extinction of flames in earth gravity and in microgravity environments. Numerical simulations, in which the various physical and chemical processes can be independently controlled, can significantly advance our understanding of these differences. Therefore, our approach is to use detailed time-dependent, multi-dimensional, multispecies numerical models to perform carefully designed computational experiments. The basic issues we have addressed, a general description of the numerical approach, and a summary of the results are described in this report. More detailed discussions are available in the papers published which are referenced herein. Some of the basic issues we have addressed recently are (1) the relative importance of wall losses and gravity on the extinguishment of downward-propagating flames; (2) the role of hydrodynamic instabilities in the formation of cellular flames; (3) effects of gravity on burner-stabilized flames, and (4) effects of radiative losses and chemical-kinetics on flames near flammability limits. We have also expanded our efforts to include hydrocarbon flames in addition to hydrogen flames and to perform simulations in support of other on-going efforts in the microgravity combustion sciences program. Modeling hydrocarbon flames typically involves a larger number of species and a much larger number of reactions when compared to hydrogen. In addition, more complex radiation models may also be needed. In order to efficiently compute such complex flames recent developments in parallel computing have been utilized to develop a state-of-the-art parallel flame code. This is discussed below in some detail after a brief discussion of the numerical models.

Kailasanath, K.; Patnaik, G.; Oran, E. S.

1995-01-01

432

Numerical Simulation of Tangling in Jet Engine Turbines

NASA Astrophysics Data System (ADS)

The numerical analysis of certain safety related problems presents serious difficulties, since the large number of components present leads to huge finite element models that can only be solved by using large and expensive computers or by making rough approaches to the problem. Tangling, or clashing, in the turbine of a jet engine airplane is an example of such problems. This is caused by the crash and friction between rotor and stator blades in the turbine after an eventual shaft failure. When facing the study of an event through numerical modelling, the accurate simulation of this problem would require the engineer to model all the rotor and stator blades existing in the turbine stage, using a small element size in all pieces. Given that the number of stator and rotor blades is usually around 200, such simulations would require millions of elements. This work presents a new numerical methodology, specifically developed for the accurate modelling of the tangling problem that, depending on the turbine configuration, is able to reduce the number of nodes up to an order of magnitude without losing accuracy. The methodology, which benefits from the cyclic configuration of turbines, is successfully applied to the numerical analysis of a hypothetical tangling event in a turbine, providing valuable data such as the rotating velocity decrease of the turbine, the braking torque and the damage suffered by the blades. The methodology is somewhat general and can be applied to any problem in which damage caused by the interaction between a rotating and static piece is to be analysed.

Cendón, David A.; Erice, Borja; Gálvez, Francisco; Sánchez-Gálvez, Vicente

2012-12-01

433

Numerical simulation of a liquid propellant rocket motor

NASA Astrophysics Data System (ADS)

This work presents a numerical simulation of the flow field in a liquid propellant rocket engine chamber and exit nozzle using techniques to allow the results to be taken as starting points for designing those propulsive systems. This was done using a Finite Volume method simulating the different flow regimes which usually take place in those systems. As the flow field has regions ranging from the low subsonic to the supersonic regimes, the numerical code used, initially developed for compressible flows only, was modified to work proficiently in the whole velocity range. It is well known that codes have been developed in CFD, for either compressible or incompressible flows, the joint treatment of both together being complex even today, given the small number of references available in this area. Here an existing code for compressible flow was used and primitive variables, the pressure, the Cartesian components of the velocity and the temperature instead of the conserved variables were introduced in the Euler and Navier-Stokes equations. This was done to permit the treatment at any Mach number. Unstructured meshes with adaptive refinements were employed here. The convective terms were treated with upwind first and second order methods. The numerical stability was kept with artificial dissipation and in the spatial coverage one used a five stage Runge-Kutta scheme for the Fluid Mechanics and the VODE (Value of Ordinary Differential Equations) scheme along with the Chemkin II in the chemical reacting solution. During the development of this code simulating the flow in a rocket engine, comparison tests were made with several different types of internal and external flows, at different velocities, seeking to establish the confidence level of the techniques being used. These comparisons were done with existing theoretical results and with other codes already validated and well accepted by the CFD community.

Salvador, Nicolas M. C.; Morales, Marcelo M.; Migueis, Carlos E. S. S.; Bastos-Netto, Demétrio

2001-03-01

434

Computer-based numerical simulations of adsorption in nanostructures

NASA Astrophysics Data System (ADS)

Zeolites are crystalline oxides with uniform, molecular-pore diameters of 3-14Å. Significant developments since 1950 made production of synthetic zeolites with high purity and controlled chemical composition possible. In powder-form, zeolites are major role-players in high-tech, industrial catalysis, adsorption, and ion exchange applications. Understanding properties of thin-film zeolites has been a focus of recent research. The ability to fine-tune desired macroscopic properties by controlled alteration at the molecular level is paramount. The relationships between macroscopic and molecular-level properties are established by experimental research. Because generating macroscopic, experimental data in a controlled laboratory can be prohibitively costly and time-consuming, reliable numerical simulations, which remove such difficulties, are an attractive alternative. Using a Configurational Biased Monte Carlo (CBMC) approach in grand canonical ensemble, numerical models for pure component and multicomponent adsorption processes were developed. Theoretical models such as ideal (IAST) and real adsorbed solution theory (RAST) to predict mixture adsorption in nanopores were used for comparison. Activity coefficients used in RAST calculations were determined from the Wilson, spreading pressure and COSMO-RS models. Investigative testing of the method on known materials, represented by all-silica zeolites such as MFI (channel type) and DDR (cage type), proved successful in replicating experimental data on adsorption of light hydrocarbons - alkanes, such as methane, ethane, propane and butane. Additionally, adsorption of binary and ternary mixtures was simulated. The given numerical approach developed can be a powerful, cost and time saving tool to predict process characteristics for different molecular-structure configurations. The approach used here for simulating adsorption properties of nanopore materials including process characteristics, may have great potential for other properties of interest.

Khashimova, Diana

2014-08-01

435

Numerical simulations of volume holographic imaging system resolution characteristics

NASA Astrophysics Data System (ADS)

Because of the Bragg selectivity of volume holographic gratings, it helps VHI system to optically segment the object space. In this paper, properties of point-source diffraction imaging in terms of the point-spread function (PSF) are investigated, and characteristics of depth and lateral resolutions in a VHI system is numerically simulated. The results show that the observed diffracted field obviously changes with the displacement in the z direction, and is nearly unchanged with displacement in the x and y directions. The dependence of the diffracted imaging field on the z-displacement provides a way to possess 3-D image by VHI.

Sun, Yajun; Jiang, Zhuqing; Liu, Shaojie; Tao, Shiquan

2009-05-01

436

Numerical simulation of electron cyclotron current drive characteristics on EAST

NASA Astrophysics Data System (ADS)

Electron cyclotron current drive (ECCD) will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been carried out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron (EC) wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.

Wei, Wei; Ding, Bo-Jiang; Zhang, Xin-Jun; Wang, Xiao-Jie; Li, Miao-Hui; Kong, Er-Hua; Zhang, Lei

2014-05-01

437

A new representation of wells in numerical reservoir simulation

Numerical PI's are used to relate wellblock and wellbore pressures and the flow rate of a well in reservoir simulations by finite difference. This approach is based on an equivalent wellblock radius'', r[sub eq,o]. When nonuniform grids are used, r[sub eq,o] may create an error in wellbore pressure or oil rate. This paper presents a new well representation. The analytical solution for near-well pressure is included by modifying the transmissibilities between gridblocks so that flow around as well is described fully. The new method is applicable to non-uniform grids and nonisolated wells.

Yu Ding; Renard, G. (Inst. Francais du Petrole, Rueil Malmaison (France))

1994-05-01

438

Diffusive mesh relaxation in ALE finite element numerical simulations

The theory for a diffusive mesh relaxation algorithm is developed for use in three-dimensional Arbitary Lagrange/Eulerian (ALE) finite element simulation techniques. This mesh relaxer is derived by a variational principle for an unstructured 3D grid using finite elements, and incorporates hourglass controls in the numerical implementation. The diffusive coefficients are based on the geometric properties of the existing mesh, and are chosen so as to allow for a smooth grid that retains the general shape of the original mesh. The diffusive mesh relaxation algorithm is then applied to an ALE code system, and results from several test cases are discussed.

Dube, E.I.

1996-06-01

439

Numerical Simulation of Low-Density Shock-Wave Interactions

NASA Technical Reports Server (NTRS)

Computational Fluid Dynamics (CFD) numerical simulations of low-density shock-wave interactions for an incident shock impinging on a cylinder have been performed. Flow-field density gradient and surface pressure and heating define the type of interference pattern and corresponding perturbations. The maximum pressure and heat transfer level and location for various interaction types (i.e., shock-wave incidence with respect to the cylinder) are presented. A time-accurate solution of the Type IV interference is employed to demonstrate the establishment and the steadiness of the low-density flow interaction.

Glass, Christopher E.

1999-01-01

440

Numerical simulations of the accretion-ejection instability

The Accretion-Ejection Instability (AEI) is explored numerically using a global 2d model of the inner region of a magnetised accretion disk. The disk is initially currentless but threaded by an external vertical magnetic field created by external currents, and frozen in the flow. In agreement with the theory a spiral instability, similar in many ways to those observed in self-gravitating disks, but driven by magnetic stresses, develops when the magnetic field is close to equipartition with the disk thermal pressure. The present non-linear simulations give good evidence that such an instability can occur in the inner region of accretion disks.

Stuart Caunt; Michel Tagger

2000-11-17