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1

Effects of Turbulence on Self-sustained Combustion in Premixed Flame Kernels: A Direct Numerical Simulation (DNS) Study  

Microsoft Academic Search

The effects of mean flame radius and turbulence on self-sustained combustion of turbulent premixed spherical flames in decaying\\u000a turbulence have been investigated using three-dimensional direct numerical simulations (DNS) with single step Arrhenius chemistry.\\u000a Several flame kernels with different initial radius or initial turbulent field have been studied for identical conditions\\u000a of thermo-chemistry. It has been found that for very small

M. Klein; N. Chakraborty; R. S. Cant

2008-01-01

2

Direct Numerical Simulation DNS: Maximum Error as a Function of Mode Number  

SciTech Connect

Numerical errors can be characterized in terms of algebraic polynomial approximation of a sine wave. The magnitude of the error will, therefore, depend on the energy at each mode in a Fourier expansion. Flows with a great deal of energy in the highest modes, such as Turbulence, are therefore the most difficult to approximate.

Jameson, L.

2000-06-01

3

Numerical Errors in DNS: Total Run-Time Error  

Microsoft Academic Search

Understanding numerical errors in simulations is critical for many reasons. First and foremost, one must some estimate concerning the reliability of the final result. Simply put, numerical errors add up over time and in most cases the increase is a linear process. It is quite possible that running a code for a very long time can lead to a solution

2000-01-01

4

Direct Numerical Simulation of Incompressible Axisymmetric Flows.  

National Technical Information Service (NTIS)

In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps...

P. Loulou

1994-01-01

5

Direct Numerical Simulation of Hot Jets.  

National Technical Information Service (NTIS)

The ultimate motivation of this work is to investigate the stability of two dimensional heated jets and its implications for aerodynamic sound generation from data obtained with direct numerical simulations (DNS). As pointed out in our last report, these ...

M. C. Jacob

1993-01-01

6

Numerical Errors in DNS: Total Run-Time Error  

SciTech Connect

Understanding numerical errors in simulations is critical for many reasons. First and foremost, one must some estimate concerning the reliability of the final result. Simply put, numerical errors add up over time and in most cases the increase is a linear process. It is quite possible that running a code for a very long time can lead to a solution which is completely meaningless even though it may look reasonable. This manuscript will begin a technical discussion on these issues.

Jameson, L.

2000-06-06

7

Direct numerical simulation of incompressible axisymmetric flows  

Microsoft Academic Search

In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities

Patrick Loulou

1994-01-01

8

Direct numerical simulation of turbulent flow over a backward-facing step  

NASA Astrophysics Data System (ADS)

Turbulent flow in a channel with a sudden expansion(backward-facing step) is studied by direct numerical simulation (DNS) of incompressible Navier-Stokes equations. Initial results are presented for a 3D DNS of a backward-facing step flow with Reynolds number 6000, based on average bulk upstream velocity and step height. The expansion ratio is 2. Turbulent inflow is provided by regeneration of velocity and pressure fields from a plane downstream from the inflow. Simulations are made using the Semtex DNS spectral element solver. The goal is to generate hi-resolution DNS data of a high Reynolds number flow over a backward-facing step for LES comparisons.

Kopera, Michal A.; Cantwell, Christopher; Kerr, Robert M.; Barkley, Dwight; Blackburn, Hugh

2009-11-01

9

Numerical Investigation of the Control of Separation from Curved and Blunt Trailing Edges Using DNS and LES  

NASA Astrophysics Data System (ADS)

Wall jets over a curved wall geometry (Coanda flows) are investigated using DNS and turbulence modeling. In experiments large coherent structures have enhanced the effectiveness of wall jets in delaying or preventing flow separation on airfoils. Understanding the behavior of these structures is essential for utilizing wall jets for separation control. The research objective is to investigate curvature effects on large coherent structures, in particular the development of longitudinal (Goertler-type) vortices and their interaction with 2D vortices. The focus is on Coanda cylinders using two computational approaches. With the Flow Simulation Methodology (FSM), a turbulent wall jet is computed over a cylinder segment on a body-fitted grid. In FSM, the contribution of the turbulence model depends on the grid resolution relative to a local turbulent length scale. For a flat-plate reference case, FSM is employed as DNS, LES, and URANS. In all cases the large 2D vortices are captured. For the curved-wall geometry, FSM is employed as a DNS. Goertler-type vortices emerge in the simulation but remain weak due to the narrow computational domain. In the second approach, Coanda flows including nozzle and separated region are computed using immersed boundary techniques (IBT). The feasibility of IBT for Coanda Flows is established.

Fasel, Hermann F.

2002-07-01

10

Direct numerical simulation of a momentum driven reacting shear layer  

Microsoft Academic Search

Direct numerical simulations (DNS) were performed of an idealized reacting, momentum driven jet to study effects of heat release and nonequilibrium chemistry in turbulent flames. The spectral element techniques was used to solve the full three-dimensional, unsteady equations of motion for a reacting turbulent jet. A low Mach number approximation was employed that filters out acoustic waves and the time-stepping

Nader Zonouz Pourhassan

1999-01-01

11

Direct numerical simulations of low Reynolds number flow over airfoils with trailing-edge serrations  

Microsoft Academic Search

Direct numerical simulations (DNS) have been conducted of NACA-0012 with serrated and straight flat-plate trailing-edge extensions using a purposely developed immersed boundary method. For the low Reynolds number airfoil flows accessible by DNS, laminar separation bubbles involving laminar-turbulent transition and turbulent reattachment occurs. Comparing results from simulations with serrated and un-serrated trailing-edge extensions, noise reduction for higher frequencies is shown

R. D. Sandberg; L. E. Jones

2011-01-01

12

A numerical method for DNS/LES of turbulent reacting flows  

SciTech Connect

A spatially non-dissipative, implicit numerical method to simulate turbulent reacting flows over a range of Mach numbers, is described. The compressible Navier-Stokes equations are rescaled so that the zero Mach number equations are discretely recovered in the limit of zero Mach number. The dependent variables are co-located in space, and thermodynamic variables are staggered from velocity in time. The algorithm discretely conserves kinetic energy in the incompressible, inviscid, non-reacting limit. The chemical source terms are implicit in time to allow for stiff chemical mechanisms. The algorithm is readily extended to complex chemical mechanisms. Numerical examples using both simple and complex chemical mechanisms are presented.

Doom, Jeff; Hou, Yucheng [Department of Aerospace Engineering and Mechanics, University of Minnesota (United States); Mahesh, Krishnan [Department of Aerospace Engineering and Mechanics, University of Minnesota (United States)], E-mail: mahesh@aem.umn.edu

2007-09-10

13

Three facets of turbulent combustion modelling: DNS of premixed V-flame, LES of lifted nonpremixed flame and RANS of jet-flame  

Microsoft Academic Search

Three aspects of turbulent combustion modelling are discussed to provide an overview of numerical simulation of turbulent flames. The three examples reported concern direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds average Navier–Stokes (RANS) calculations. Recent developments in DNS deal with the possibility of performing a full simulation of a premixed turbulent V-flame evolving in grid turbulence. The

Luc Vervisch; Raphaël Hauguel; Pascale Domingo; Matthieu Rullaud

2004-01-01

14

Three facets of turbulent combustion modelling: DNS of premixed V-flame, LES of lifted nonpremixed flame and RANS of jet-flame  

Microsoft Academic Search

Three aspects of turbulent combustion modelling are discussed to provide an overview of numerical simulation of turbulent flames. The three examples reported concern direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds average Navier-Stokes (RANS) calculations. Recent developments in DNS deal with the possibility of performing a full simulation of a premixed turbulent V-flame evolving in grid turbulence. The

Luc Vervisch; Raphaël Hauguel; Pascale Domingo; Matthieu Rullaud

2004-01-01

15

Direct Simulation of Turbulent Combustion.  

National Technical Information Service (NTIS)

Direct Numerical Simulation (DNS) results obtained for premixed turbulent flames are presented and discussed to provide a description of the DNS possibilities and limitations. Numerical issues and boundary conditions are discussed. The basis of flamelet m...

T. J. Poinsot

1992-01-01

16

Unsteady PTV velocity field past an airfoil solved with DNS: Part 1. Algorithm of hybrid simulation and hybrid velocity field at Re ? 103  

NASA Astrophysics Data System (ADS)

We develop a hybrid unsteady-flow simulation technique combining direct numerical simulation (DNS) and particle tracking velocimetry (PTV) and demonstrate its capabilities by investigating flows past an airfoil. We rectify instantaneous PTV velocity fields in a least-squares sense so that they satisfy the equation of continuity, and feed them to the DNS by equating the computational time step with the frame rate of the time-resolved PTV system. As a result, we can reconstruct unsteady velocity fields that satisfy the governing equations based on experimental data, with the resolution comparable to numerical simulation. In addition, unsteady pressure distribution can be solved simultaneously. In this study, particle velocities are acquired on a laser-light sheet in a water tunnel, and unsteady flow fields are reconstructed with the hybrid algorithm solving the incompressible Navier-Stokes equations in two dimensions. By performing the hybrid simulation, we investigate nominally two-dimensional flows past the NACA0012 airfoil at low Reynolds numbers. In part 1, we introduce the algorithm of the proposed technique and discuss the characteristics of hybrid velocity fields. In particular, we focus on a vortex shedding phenomenon under a deep stall condition (? = 15°) at Reynolds numbers of Re = 1000 and 1300, and compare the hybrid velocity fields with those computed with two-dimensional DNS. In part 2, the extension to higher Reynolds numbers is considered. The accuracy of the hybrid simulation is evaluated by comparing with independent experimental results at various angles of attack and Reynolds numbers up to Re = 104. The capabilities of the hybrid simulation are also compared with two-dimensional unsteady Reynolds-Averaged Navier-Stokes (URANS) solutions in part 2. In the first part of these twin papers, we demonstrate that the hybrid velocity field approaches the PTV velocity field over time. We find that intensive alternate vortex shedding past the airfoil, which is predicted by the two-dimensional DNS, is substantially suppressed in the hybrid simulation and the resultant flow field is similar to the PTV velocity field, which is projection of the three-dimensional velocity field on the streamwise plane. We attempt to identify the motion that originates three-dimensional flow patterns by highlighting the deviation of the PTV velocity field from the two-dimensional governing equations at each snapshot. The results indicate that the intensive spots of the deviation appear in the regions in which three-dimensional instabilities are induced in the shear layer separated from the pressure side.

Suzuki, Takao; Ji, Hui; Yamamoto, Fujio

2009-12-01

17

Direct numerical simulation of turbulent Taylor–Couette flow  

Microsoft Academic Search

The direct numerical simulation (DNS) of the Taylor–Couette flow in the fully turbulent regime is described. The numerical method extends the work by Quadrio and Luchini [M. Quadrio, P. Luchini, Eur. J. Mech. B\\/Fluids 21 (2002) 413–427], and is based on a parallel computer code which uses mixed spatial discretization (spectral schemes in the homogeneous directions, and fourth-order, compact explicit

Davide Pirrò; Maurizio Quadrio

2008-01-01

18

DNS of turbulent channel flow with a higher Reynolds number  

Microsoft Academic Search

With an aid of recent developments in the super and parallel computers, the direct numerical simulation (DNS) of turbulence is now being increasingly performed. It is already more than 10 years ago when Kim-Moin-Moser published their DNS on the turbulent channel flow. Their Reynolds number based on the friction velocity and channel half width was Re_tau=180. In a couple of

Hiroshi Kawamura; Hiroyuki Abe; Yuichi Matsuo

1998-01-01

19

Terascale Direct Numerical Simulations of Turbulent Combustion: Capabilities and Limits (PReSS Talk)  

SciTech Connect

The rapid growth in computational capabilities has provided great opportunities for direct numerical simulations (DNS) of turbulent combustion, a type of simulations without any turbulence model. With the help of terascale high performance supercomputing (HPC) resources, we are now able to provide fundamental insight into turbulence-chemistry interaction in simple laboratory-scale turbulent flames with detailed chemistry using three-dimensional (3D) DNS. However, the actual domain size of 3D-DNS is still limited within {approx} O(10 cm{sup 3}) due to its tremendously high grid resolution required to resolve the smallest turbulent length scale as well as flame structures. Moreover, 3D-DNS will require more computing powers to investigate next-generation engines, of which operating conditions will be characterized by higher pressures, lower temperatures, and higher levels of dilution. In this talk, I will discuss the capabilities and limits of DNS of turbulent combustion and present some results of ignition/extinction characteristics of a highly diluted hydrogen flame counter-flowing against heated air. The results of our recent 3D-DNS of a spatially-developing turbulent lifted hydrogen jet flame in heated coflow will also be presented. The 3D-DNS was performed at a jet Reynolds number of 11,000 with {approx} 1 billion grid points, which required 3.5 million CPU hours on Cray XT3/XT4 at Oak Ridge National Laboratories.

Yoo, Chun Sang (Combustion Research Facility, SNL)

2009-03-26

20

Terascale Direct Numerical Simulations of Turbulent Combustion: Capabilities and Limits (PReSS Talk)  

ScienceCinema

The rapid growth in computational capabilities has provided great opportunities for direct numerical simulations (DNS) of turbulent combustion, a type of simulations without any turbulence model. With the help of terascale high performance supercomputing (HPC) resources, we are now able to provide fundamental insight into turbulence-chemistry interaction in simple laboratory-scale turbulent flames with detailed chemistry using three-dimensional (3D) DNS. However, the actual domain size of 3D-DNS is still limited within {approx} O(10 cm{sup 3}) due to its tremendously high grid resolution required to resolve the smallest turbulent length scale as well as flame structures. Moreover, 3D-DNS will require more computing powers to investigate next-generation engines, of which operating conditions will be characterized by higher pressures, lower temperatures, and higher levels of dilution. In this talk, I will discuss the capabilities and limits of DNS of turbulent combustion and present some results of ignition/extinction characteristics of a highly diluted hydrogen flame counter-flowing against heated air. The results of our recent 3D-DNS of a spatially-developing turbulent lifted hydrogen jet flame in heated coflow will also be presented. The 3D-DNS was performed at a jet Reynolds number of 11,000 with {approx} 1 billion grid points, which required 3.5 million CPU hours on Cray XT3/XT4 at Oak Ridge National Laboratories.

21

Rocket engine numerical simulator  

NASA Astrophysics Data System (ADS)

The topics are presented in viewgraph form and include the following: a rocket engine numerical simulator (RENS) definition; objectives; justification; approach; potential applications; potential users; RENS work flowchart; RENS prototype; and conclusion.

Davidian, Ken

22

Rocket engine numerical simulation  

NASA Astrophysics Data System (ADS)

The topics are presented in view graph form and include the following: a definition of the rocket engine numerical simulator (RENS); objectives; justification; approach; potential applications; potential users; RENS work flowchart; RENS prototype; and conclusions.

Davidian, Ken

1993-12-01

23

Numerical Errors: Reliable Numerical Simulations  

SciTech Connect

Understanding numerical errors in long calculations is a very subtle science and is critical to understanding the reliability of the final answer. We will carefully examine the accumulation of numerical errors over time and discuss how these can lead to reliability estimates. The primary focus will be on a newly uncovered understanding of mode resolution which is at the heart of all numerical computations.

Jameson, L

2001-07-27

24

DNS Operations  

Microsoft Academic Search

\\u000a This chapter describes the operation of a DNS system. Namely, you’ll learn about the following topics:\\u000a \\u000a \\u000a \\u000a \\u000a • \\u000a \\u000a \\u000a DNS queries: How does your browser find www.example.com? How does your mail software know where to send your outgoing e-mail? Such operations\\u000a use DNS queries.\\u000a \\u000a \\u000a \\u000a \\u000a • \\u000a \\u000a \\u000a Reverse mapping: How does your mail software determine your identity? How do you find out who is

Ron Aitchison

25

Spectral structure of stratified turbulence: direct numerical simulations and predictions by large eddy simulation  

NASA Astrophysics Data System (ADS)

Density stratification has a strong impact on turbulence in geophysical flows. Stratification changes the spatial turbulence spectrum and the energy transport and conversion within the spectrum. We analyze these effects based on a series of direct numerical simulations (DNS) of stratified turbulence. To facilitate simulations of real-world problems, which are usually beyond the reach of DNS, we propose a subgrid-scale turbulence model for large eddy simulations of stratified flows based on the Adaptive Local Deconvolution Method (ALDM). Flow spectra and integral quantities predicted by ALDM are in excellent agreement with direct numerical simulation. ALDM automatically adapts to strongly anisotropic turbulence and is thus a suitable tool for studying turbulent flow phenomena in atmosphere and ocean.

Remmler, Sebastian; Hickel, Stefan

2013-06-01

26

Direct numerical simulation of nonpremixed flame-wall interactions  

SciTech Connect

The objective of the present study is to use detailed numerical modeling to obtain basic information on the interaction of nonpremixed flames with cold wall surfaces. The questions of turbulent fuel-air-temperature mixing, flame extinction, and wall-surface heat transfer are studied using direct numerical simulation (DNS). The DNS configuration corresponds to an ethylene-air diffusion flame stabilized in the near-wall region of a chemically inert solid surface. Simulations are performed with adiabatic or isothermal wall boundary conditions and with different turbulence intensities. The simulations feature flame extinction events resulting from excessive wall cooling and convective heat transfer rates up to 90 kW/m{sup 2}. The structure of the simulated wall flames is studied in terms of a classical mass-mixing variable, the fuel-air based mixture fraction, and a less familiar heat loss variable, the excess enthalpy variable, introduced to provide a measure of nonadiabatic behavior due to wall cooling. In addition to the flame structure, extinction events are also studied in detail and a modified flame extinction criterion that combines the concepts of mixture fraction and excess enthalpy is proposed and then tested against the DNS data. (author)

Wang, Yi [Department of Mechanical Engineering, University of Maryland, College Park, MD 20742 (United States); Trouve, Arnaud [Department of Fire Protection Engineering, University of Maryland, College Park, MD 20742 (United States)

2006-02-01

27

Parallel implicit algorithms for direct numerical simulations of hypersonic boundary layer stability and transition  

Microsoft Academic Search

Due to the progress in computer technology in recent years, distributed memory parallel computer systems are rapidly gaining importance in direct numerical simulation (DNS) of the stability and transition of compressible boundary layers. In most works, explicit methods have mainly been used in such simulations to advance the compressible Navier-Stokes equations in time. However, the small wall-normal grid sizes for

Haibo Dong

2003-01-01

28

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

29

Analysis of Thermal Dissipation Rates Based on Direct Numerical and Large–Eddy Simulations of Turbulent Rayleigh–B’enard Convection  

Microsoft Academic Search

Two functions ? and ? are defined to determine quantitatively the role of the turbulent background in thermal convection. Evaluating these functions from the data generated in the Direct Numerical Simulations (DNS) and Large

Olga Shishkina; Claus Wagner

2007-01-01

30

A further study of numerical errors in large-eddy simulations  

Microsoft Academic Search

Numerical errors in large-eddy simulations (LES) arise from aliasing and discretization errors, and errors in the subfilter-scale (SFS) turbulence model. Using a direct numerical simulation (DNS) dataset of stably stratified shear flow to perform a priori tests, we compare the numerical error from several finite difference schemes to the magnitude of the SFS force. This is an extension of Ghosal’s

Fotini Katopodes Chow; Parviz Moin

2003-01-01

31

Numerical simulation of fracture  

SciTech Connect

The Bedded Crack Model (BCM) is a constitutive model for brittle materials. It is based on effective modulus theory and makes use of a generalized Griffith criterion for crack growth. It is used in a solid dynamic computer code to simulate stress wave propagation and fracture in rock. A general description of the model is given and then the theoretical basis for it is presented. Some effects of finite cell size in numerical simulations are discussed. The use of the BCM is illustrated in simulations of explosive fracture of oil shale. There is generally good agreement between the calculations and data from field experiments.

Margolin, L.G.; Adams, T.F.

1982-01-01

32

Dynamic stiffness removal for direct numerical simulations  

SciTech Connect

A systematic approach was developed to derive non-stiff reduced mechanisms for direct numerical simulations (DNS) with explicit integration solvers. The stiffness reduction was achieved through on-the-fly elimination of short time-scales induced by two features of fast chemical reactivity, namely quasi-steady-state (QSS) species and partial-equilibrium (PE) reactions. The sparse algebraic equations resulting from QSS and PE approximations were utilized such that the efficiency of the dynamic stiffness reduction is high compared with general methods of time-scale reduction based on Jacobian decomposition. Using the dimension reduction strategies developed in our previous work, a reduced mechanism with 52 species was first derived from a detailed mechanism with 561 species. The reduced mechanism was validated for ignition and extinction applications over the parameter range of equivalence ratio between 0.5 and 1.5, pressure between 10 and 50 atm, and initial temperature between 700 and 1600 K for ignition, and worst-case errors of approximately 30% were observed. The reduced mechanism with dynamic stiffness removal was then applied in homogeneous and 1-D ignition applications, as well as a 2-D direct numerical simulation of ignition with temperature inhomogeneities at constant volume with integration time-steps of 5-10 ns. The integration was numerically stable and good accuracy was achieved. (author)

Lu, Tianfeng; Law, Chung K. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Yoo, Chun Sang; Chen, Jacqueline H. [Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551 (United States)

2009-08-15

33

Direct numerical simulation of turbulent flow past a trailing edge and the associated noise generation  

Microsoft Academic Search

Direct numerical simulations (DNS) are conducted of turbulent flow passing an infinitely thin trailing edge. The objective is to investigate the turbulent flow field in the vicinity of the trailing edge and the associated broadband noise generation. To generate a turbulent boundary layer a short distance from the inflow boundary, high- amplitude lifted streaks and disturbances that can be associated

RICHARD D. S ANDBERG; NEIL D. S ANDHAM

2008-01-01

34

Direct numerical simulation of transport and electrochemical reaction in battery and fuel cell electrodes  

NASA Astrophysics Data System (ADS)

Batteries and fuel cells are widely used to generate electrical energy, especially in recent applications to electric and hybrid vehicles. To simulate a porous electrode for batteries and fuel cells, macro-homogeneous models are often employed in which the actual morphology of the electrode is ignored, thereby making computations much easier. However, such models are based on the volume-averaging technique, which smears the microscopically complex interfacial structures and has to invoke empirical correlations for describing the effective transport properties in a multiphase system. In this work, a methodology is developed to achieve the description on the pore level based on direct numerical simulation (DNS) method. The DNS solves the accurate point-wise conservation equations on a real micro-structure of the porous electrode and hence utilizes the intrinsic transport properties for each phase. To demonstrate the DNS method, an idealized morphology and further a random microstructure are constructed to represent all the phases composing the porous electrode. A single set of conservation equations of charge and species valid in all phases are developed and numerically solved using a finite volume technique. The present DNS model is first applied to simulate the behavior of an intercalative carbon electrode in the widely used lithium-ion cell. The concentration and potential distributions in both solid and electrolyte phases at the pore level are obtained across the electrode during the discharge. The species and charge transport processes, as well as the electrochemical reactions, are computationally visualized when discharging the electrode. In addition, empirical correlations in porous electrode theory, which describe the dependency of effective properties (diffusion coefficient, conductivity, etc.) on the porosity, are corroborated using the fundamental DNS data. Then the discharge processes of a full lithium ion cell at various rates are simulated with DNS approach and verified by the experimental data. In the application to the cathode catalyst layer of PEM fuel cells, DNS is employed to identify three characteristic voltage losses: kinetics losses, ohmic losses and O2 transport losses. On a constructed random microstructure, DNS is also utilized to optimize the inlet air humidity and the composition design and hence achieve the minimum voltage loss during operation. In summary, the newly developed DNS method has provided an effective method to simulate behavior of thin porous electrodes with microscopically complicated geometries and the fundamentals insight into structure-performance relationships of porous electrodes for the first time.

Wang, Guoqing

35

Direct Numerical Simulations of Rayleigh-Taylor instability  

NASA Astrophysics Data System (ADS)

The development of the Rayleigh-Taylor mixing layer is studied using data from an extensive new set of Direct Numerical Simulations (DNS). This includes a suite of simulations with grid size of 1024^2 x4608 and Atwood number ranging from A=0.04 to 0.9, in order to examine small departures from the Boussinesq approximation as well as large Atwood number effects, and a high resolution simulation of grid size 4096^2 x4032 and Atwood number of 0.75. After the layer width had developed substantially, additional branched simulations have been run under reversed and zero gravity conditions. The results presented address the role of the initial conditions on the mixing layer development and the discrepancy between the growth rates in various experiments and numerical simulations, as well as the changes in Rayleigh-Taylor turbulence properties at large density ratios.

Livescu, Daniel; Wei, Tie; Petersen, Mark

2011-11-01

36

Numerical Simulations of Bubble Dispersion over a Hydrofoil  

NASA Astrophysics Data System (ADS)

The production and entrainment of bubbles in ship wakes is not completely understood despite the fact that it has many practical applications. For example, bubbles trapped in the large vortical structures in the ship wake can form clusters that are able to persist for large distances leaving a long trail of bubbles, which increases the ship's signature; an important consideration in the defence environment. The fundamental mechanisms behind the complicated bubbly flow can be understood using data from numerical simulations. The objective of the study is to investigate the accuracy of current state-of-art numerical models for simulating bubbly flows. A spectral element-Fourier code will be used to carry out direct numerical simulations (DNS) with Lagrangian particle tracking to study the interaction of the upstream bubble distribution with a hydrofoil at different angles of attack and Reynolds numbers, and the effect on the resulting downstream bubble distribution.

Zhu, Shuang; Ooi, Andrew; Blackburn, Hugh; Anderson, Brendon

2009-11-01

37

Semiconvection: numerical simulations  

NASA Astrophysics Data System (ADS)

A grid of numerical simulations of double-diffusive convection is presented for the astrophysical case where viscosity (Prandtl number Pr) and solute diffusivity (Lewis number Le) are much lower than the thermal diffusivity. As in laboratory and geophysical cases, convection takes place in a layered form. The proper translation of subsonic flows in a stellar interior and an incompressible (Boussinesq) fluid is given, and the validity of the Boussinesq approximation for the semiconvection problem is checked by comparison with fully compressible simulations. The predictions of a simplified theory of mixing in semiconvection given in a companion paper are tested against the numerical results, and used to extrapolate these to astrophysical conditions. The predicted effective He-diffusion coefficient is nearly independent of the double-diffusive layering thickness d. For a fiducial main sequence model (15 M?) the inferred mixing time scale is of the order of 1010 yr. An estimate for the secular increase in d during the semiconvective phase is given. It can potentially reach a significant fraction of the pressure scale height. Movies associated to Figs. 5 and 7 are available in electronic form at http://www.aanda.org

Zaussinger, F.; Spruit, H. C.

2013-06-01

38

Direct Numerical Simulation of the Puffing Phenomenon of an Axisymmetric Thermal Plume  

Microsoft Academic Search

:   A spatial direct numerical simulation of an axisymmetric buoyant thermal plume is presented. The governing flow field equations\\u000a at the centerline are put into a special form to circumvent the axis singularity associated with the cylindrical coordinates\\u000a and the high order accuracy of the numerical scheme is preserved at the centerline. Boundary conditions associated with the\\u000a spatial DNS of

X. Jiang; K. H. Luo

2000-01-01

39

Application and validation of direct numerical simulation for ICF implosion stability analysis  

SciTech Connect

We have recently been applying a powerful computational tool, direct numerical simulation (DNS), to evaluate the stability of imploding inertial confinement fusion (ICF) capsules designed for the National Ignition Facility. In DNS, we explicitly calculate the evolution of realistic surface perturbations far into their nonlinear regimes, using a 2D Lagrangian radiation-hydrodynamics code. Because the mesh may become greatly distorted during the calculation, requiring frequent application of an automatic rezoner, and because we use a 2D code to represent 3D perturbations whose nonlinear behavior is shape- dependent, we have been seeking to assess the accuracy of DNS in as many regimes as possible. For this purpose, we have conducted experimental campaigns to observe the instability of radiatively driven imploding cylinders, deuterated-shell spherical capsules, and radiatively accelerated flat foils perturbed on the unheated surface (``feedout`` experiments). We have compared DNS calculations to data from these experiments, and to theoretical predictions for incompressible Rayleigh-Taylor instability, with satisfactory agreement. Thus we are gradually accumulating confidence in the validity of DNS as applied to ICF.

Hoffman, N.M.; Swenson, F.J.; Varnum, W.S. [and others

1996-07-01

40

Temporal numerical simulations of turbulent Coanda wall jets  

NASA Astrophysics Data System (ADS)

In a novel application of the temporal numerical simulation, an investigation of turbulence modeling techniques is carried for the turbulent wall jet over a convex surface (Coanda wall jet.) The simultaneous presence of multiple instability mechanisms and the interaction with the turbulence dynamics at the solid boundary produces a unique combination of different large turbulent coherent structures that constitutes both a consistent challenge for numerical simulations and an ideal test bed for turbulence models. The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jet restricts the focus from the global turbulent Coanda wall jet to a smaller, local portion of the flow and offers a wide array of advantages to the present work. In particular, the size of the computational domain can be arbitrarily chosen in both the spanwise and the streamwise directions. This allows to either suppress or enhance individual physical mechanisms and, consequently, to selectively reproduce different large coherent structures within the local flow. In the first part, temporal numerical simulations are employed to reproduce four different flow scenarios of the local Coanda wall jet with a level of numerical resolution that, because of the reduced size of the computational domain, cannot be matched by standard DNS of the entire physical flow (spatial DNS, or SDNS .) The TDNS of these four flow scenarios are then used in the second part for an a-posteriori analysis of different turbulence models in order to address common shortcomings shown by Hybrid Turbulence Models (HTM). For each flow scenario, the turbulent flow field is deliberately decomposed in resolved and unresolved flows by the application of different filters in space corresponding to different grid resolution. The behavior of turbulence models can be reproduced from the resolved flow and compared to the turbulent stress tensor directly calculated from the unresolved part of the flow field. Starting from the RANS limit, turbulence models with different levels of complexity are studied. Successively, the performance of these models is analyzed at intermediate numerical resolutions between RANS, LES, and DNS . Finally, an improved formulation of the Flow Simulation Methodology (FSM) is proposed.

Valsecchi, Pietro

41

Direct numerical simulation of salt sheets and turbulence in a double-diffusive shear layer  

Microsoft Academic Search

We describe three-dimensional direct numerical simulations (DNS) of double-diffusively stratified flow interacting with inflectional shear. The extreme difference in diffusivity (and thus minimum length scale) between heat, salt and momentum in seawater is replicated for the first time in a three-dimensional simulation. The primary instability generates salt sheets, which are oriented parallel to the direction of the sheared background flow.

Satoshi Kimura; William Smyth

2007-01-01

42

Direct Numerical Simulation of laminarization in the atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

In the present work the collapse of turbulence in the evening atmosphere is studied by means of direct numerical simulation (DNS). As physical properties of the land surface play a crucial role in either stimulating or moderating the collapse process, emphasis lies on the coupling of the flow model to a realistic surface model. Hereto we apply a heat budget equation at the surface, with contributions from conductive, radiative, and turbulent heat transport. The response of the atmosphere to weak mechanical forcing is studied for various surfaces like: short grass, snow covered surfaces, bare soil and water. Besides numerical simulation also theoretical analysis is used to understand the dynamic feedbacks between the lower stratified atmosphere and the underlying surface. Finally, results are compared with data from various atmospheric field experiments over the world.

Donda, Judith; van de Wiel, Bas; Moene, Arnold; van Heijst, Gert-Jan; Clercx, Herman

2013-04-01

43

CoDNS: Improving DNS Performance and Reliability via Cooperative Lookups  

Microsoft Academic Search

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

44

Numerical simulation of dusty plasmas  

SciTech Connect

The numerical simulation of physical processes in dusty plasmas is reviewed, with emphasis on recent results and unresolved issues. Three areas of research are discussed: grain charging, weak dust-plasma interactions, and strong dust-plasma interactions. For each area, we review the basic concepts that are tested by simulations, present some appropriate examples, and examine numerical issues associated with extending present work.

Winske, D.

1995-09-01

45

Effects of turbulence on the geometric collision rate of sedimenting droplets. Part 1. Results from direct numerical simulation  

Microsoft Academic Search

There have been relatively few studies of turbulent collision rate of sedimenting droplets in the context of cloud physics, for which both the gravitational settling and inertial effects must be simultaneously considered. In this study, direct numerical simulations (DNS) were used to study the geometric collision rates of cloud droplets. Both Stokes drag law and a nonlinear drag law were

Orlando Ayala; Bogdan Rosa; Lian-Ping Wang; Wojciech W. Grabowski

2008-01-01

46

A priori direct numerical simulation assessment of algebraic flame surface density models for turbulent premixed flames in the context of large eddy simulation  

Microsoft Academic Search

Flame surface density (FSD) based reaction rate closure is one of the most important approaches in turbulent premixed flame modeling. The algebraic models for FSD based on power laws often require information about the fractal dimension D and the inner cut-off scale ?i. In the present study, two three-dimensional direct numerical simulation (DNS) databases for freely propagating statistically planar turbulent

Nilanjan Chakraborty; Markus Klein

2008-01-01

47

DNS Rebinding Attacks.  

National Technical Information Service (NTIS)

See Report A Domain Name System (DNS) Rebinding attack compromises the integrity of name resolution in DNS with the goal of controlling the IP address of the host to which the victim ultimately connects. The same origin policy and DNS Pinning techniques w...

G. Kokkinopoulos

2009-01-01

48

DNS of a spatially developing turbulent boundary layer with passive scalar transport  

Microsoft Academic Search

A direct numerical simulation (DNS) of a spatially developing turbulent boundary layer over a flat plate under zero pressure gradient (ZPG) has been carried out. The evolution of several passive scalars with both isoscalar and isoflux wall boundary condition are computed during the simulation. The Navier–Stokes equations as well as the scalar transport equation are solved using a fully spectral

Qiang Li; Philipp Schlatter; Luca Brandt; Dan S. Henningson

2009-01-01

49

Direct numerical simulation of a turbulent wind over a wavy water surface  

NASA Astrophysics Data System (ADS)

Parameterization of the wind-water-waves interaction is a key problem of the air-sea system modeling. Of most importance are water waves with sufficiently large steepness, when nonlinear effects related to the boundary layer separation and vortex generation in the wind flow are well pronounced. Known experimental techniques (contact methods and particle image velocimetry) are not yet able to provide a full, detailed understanding of the wind flow in the viscous sublayer and the buffer region. As an alternative, we consider direct numerical simulations (DNS). In the present paper we discuss numerical algorithm and results of DNS of a turbulent wind flow over a wavy water surface. Waves with maximum steepness of ka = 0.2, wave age 0 < c/u* < 10, and Reynolds number Re = 15,000 are considered. Full, 3-D Navier-Stokes equations are solved in curvilinear coordinates in a reference frame moving with the wave phase speed c. DNS results show that an instantaneous velocity field is characterized by the presence of well-pronounced separation zones in the vicinity of the wave crests whereas the average velocity field is nonseparating. We also perform a comparison of the DNS results with the predictions of a theoretical quasi-linear model of the wind-wave interaction.

Druzhinin, O. A.; Troitskaya, Y. I.; Zilitinkevich, S. S.

2012-11-01

50

Direct numerical simulation of flame stabilization downstream of a transverse fuel jet in cross-flow  

Microsoft Academic Search

A reactive transverse fuel jet in cross-flow (JICF) configuration is studied using three-dimensional direct numerical simulation (DNS) with detailed chemical kinetics in order to investigate the mechanism of flame stabilization in the near field of a fuel jet nozzle. JICF configurations are used in practical applications where high mixing rates are desirable between the jet and the cross-flow fluids such

R. W. Grout; A. Gruber; C. S. Yoo; J. H. Chen

2011-01-01

51

The manipulated transitional backward-facing step flow: an experimental and direct numerical simulation investigation  

Microsoft Academic Search

Results from a joint experimental and direct numerical simulation (DNS) investigation are presented for the flow over a backward-facing step manipulated by low-amplitude time-periodic (harmonic) blowing\\/suction excitation through a narrow slot at the edge of the step. For a Reynolds number of Reh=3000 (based on step height, h, and inflow velocity, Uo) and for laminar inflow, a 33% reduction of

Hans Wengle; André Huppertz; Günter Bärwolff; Gerd Janke

2001-01-01

52

A zonal grid algorithm for DNS of turbulent boundary layers  

Microsoft Academic Search

A zonal grid algorithm for direct numerical simulation (DNS) of incompressible turbulent flows within a Finite-Volume framework is presented. The algorithm uses fully coupled embedded grids and a conservative treatment of the grid-interface variables. A family of conservative prolongation operators is tested in a 2D vortex dipole and a 3D turbulent boundary layer flow. These tests show that both, first-

Michael Manhart

2004-01-01

53

Numerical simulation of Bootstrap Current.  

National Technical Information Service (NTIS)

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 curr...

R. B. White Y. Wu

1993-01-01

54

Numerical simulation of hypersonic flows  

Microsoft Academic Search

Numerical simulation of aerodynamic and chemical kinetic phenomena encountered in the hypersonic flow regime is outlined. In the continuum flow region, the current numerical methods focus on solving the Navier-Stokes equations in conjunction with chemical physics equations, including the non-equilibrium chemical reactions and internal degrees of excitation. In the rarefied gas domain, the state-of-the-art progress using particle simulation which does

J. S. Shang

1992-01-01

55

Numerical simulation of Bootstrap Current  

SciTech Connect

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

56

Numerical simulation of fracture  

SciTech Connect

A constructive model for brittle, and quasi-brittle materials is described. The Bedded Crack Model contains a microphysical description of fracture based on Griffith theory. The effect of cracks on material properties is described by effective modulus theory. Underlying the model is a statistical framework in which the evolution in time of a statistical distribution of cracks is calculated. The theory upon which the model is based is described. The model is implemented in a finite difference computer code. Our model is contrasted with the phenomenologic models usually found in computer codes. A computational simulation of the strain rate dependence of failure stress is presented and compared with laboratory data. A simulation of a gas gun experiment is presented, and the mechanism of spall described.

Margolin, L.G.

1983-01-01

57

Statistical Analysis of Cross Scalar Dissipation Rate Transport in Turbulent Partially Premixed Flames: A Direct Numerical Simulation Study  

Microsoft Academic Search

Statistically planar turbulent partially premixed flames for different initial intensities of decaying turbulence have been\\u000a simulated for global equivalence ratios ??> = 0.7 and ??> = 1.0 using three-dimensional simplified chemistry based Direct Numerical Simulations (DNS). The simulation parameters\\u000a are chosen such that the combustion situation belongs to the thin reaction zones regime and a random bi-modal distribution\\u000a of equivalence

Sean P. Malkeson; Nilanjan Chakraborty

58

Statistical Analysis of Scalar Dissipation Rate Transport in Turbulent Partially Premixed Flames: A Direct Numerical Simulation Study  

Microsoft Academic Search

Statistically planar turbulent premixed and partially premixed flames for different initial turbulence intensities are simulated\\u000a for global equivalence ratios ??>?=?0.7 and ??>?=?1.0 using three-dimensional Direct Numerical Simulations (DNS) with simplified chemistry. For the simulations of partially\\u000a premixed flames, a random distribution of equivalence ratio following a bimodal distribution of equivalence ratio is introduced\\u000a in the unburned reactants ahead of the

Sean P. Malkeson; Nilanjan Chakraborty

2011-01-01

59

Numerical simulations of fission  

SciTech Connect

Hydrodynamic simulation techniques to the fission problem of the lunar origin were applied. It is indicated that, for fluids with the compressibility of stars, dynamic fission instabilities lead to spiral arm ejection of mass and angular momentum in the form of a ring or disk of debris, not as a single body. Some quantitative aspects of these results seem favorable to lunar origin by fission. Fission instabilities in fluid objects with a smaller degree of compressibility, more closely approximating terrestrial material are considered. Although the qualitative features are similar, there are significant quantitative differences for the stiffer equation of state. The implications of the results for the fission hypothesis of lunar origin are discussed. Evolutions illustrating possible approaches to instability are presented.

Durisen, R.H.; Gingold, R.A.; Scott, E.H.

1984-01-01

60

Requirements definition by numerical simulation  

NASA Astrophysics Data System (ADS)

We are investigating the issues involved in requirements definition for narcotics interdiction: how much of a particular signature is possible, how does this amount change for different conditions, and what is the temporal relationship in various scenarios. Our approach has been to simulate numerically the conditions that arise during vapor or particulate transport. The advantages of this approach are that (1) a broad range of scenarios can be rapidly and inexpensively analyzed by simulation, and (2) simulations can display quantities that are difficult or impossible to measure. The drawback of this approach is that simulations cannot include all of the phenomena present in a real measurement, and therefore the fidelity of the simulation results is always an issue. To address this limitation, we will ultimately combine the results of numerical simulations with measurements of physical parameters for inclusion in the simulation. In this paper, we discuss these issues and how they apply to the current problems in narcotics interdictions, especially cargo containers. We also show the results of 1D and 3D numerical simulations, and compare these results with analytical solutions. The results indicate that this approach is viable. We also present data from 3D simulations of vapor transport in a loaded cargo container and some of the issues present in this ongoing work.

Hickman, James J.; Kostas, Chris; Tsang, Kang T.

1994-10-01

61

DNS-based predictive control of turbulence: an optimal benchmark for feedback algorithms  

Microsoft Academic Search

Direct numerical simulations (DNS) and optimal control theory are used in a predictive control setting to determine controls that effectively reduce the turbulent kinetic energy and drag of a turbulent flow in a plane channel at Re[tau] = 100 and Re[tau] = 180. Wall transpiration (unsteady blowing\\/suction) with zero net mass flux is used as the control. The algorithm used

Thomas R. Bewley; Parviz Moin; Roger Temam

2001-01-01

62

DNS of turbulent heat transfer in channel flow with respect to Reynolds and Prandtl number effects  

Microsoft Academic Search

The direct numerical simulation (DNS) of turbulent heat transfer in a channel flow has been carried out to investigate the Reynolds and Prandtl number effects on the turbulent heat transport. The configuration is a fully developed turbulent channel flow with uniform heating from both walls. The Reynolds numbers based on the friction velocity and the channel half width are 180

Hiroshi Kawamura; Hiroyuki Abe; Yuichi Matsuo

1999-01-01

63

DNS of separating, low Reynolds number flow in a turbine cascade with incoming wakes  

Microsoft Academic Search

Three-dimensional direct numerical simulations (DNS) of flow in a low-pressure turbine cascade at high angle of attack have been performed. The large angle of attack is found to cause separation at the leading edge and somewhat upstream of the trailing edge along the suction side of the blade. The separation bubble at the leading edge is small and any disturbances

J. G. Wissink

2003-01-01

64

DNS of Turbulent Flow in a Driven Cavity and Their Analysis Using Proper Orthogonal Decomposition.  

National Technical Information Service (NTIS)

Direct Numerical Simulation (DNS) of 2D and 3D lid-driven cavity flows have been performed. The results have been analyzed using Proper Orthogonal Decomposition (POD). POD has been applied to a 2D driven cavity at Reynolds number 22,000 and to a 3D at Re ...

W. Cazemier R. W. C. P. Verstappen A. E. P. Veldman

1994-01-01

65

DNS and modeling of the turbulent boundary layer over an evaporating liquid film  

Microsoft Academic Search

Contrary to the case of flame interaction with a dry wall, little is known today about liquid film evaporation effects on the physics and structure of the boundary layer and on the flame evolution when approaching a liquid film. In this paper, Direct Numerical Simulation (DNS) is used to study the boundary layer above a liquid evaporating film in the

Gaëtan Desoutter; Chawki Habchi; Bénédicte Cuenot; Thierry Poinsot

2009-01-01

66

DNS of heat transfer increase in a cylinder stagnation region due to wake-induced turbulence  

Microsoft Academic Search

Heat transfer in the stagnation point area of a heated cylinder is investigated using Direct Numerical Simulation (DNS). The heated cylinder is subjected to the turbulent wake of a smaller cylinder placed upstream. Two Reynolds numbers based on the diameter of the heated cylinder of 13,200 and 48,000 are chosen. In accordance with correlations in the literature, an increase in

L. Venema; D. von Terzi; H.-J. Bauer; W. Rodi

2011-01-01

67

Direct Numerical Simulation of Stationary Homogeneous Variable-Density Turbulence  

NASA Astrophysics Data System (ADS)

The turbulence characteristics in statistically stationary turbulent flows composed of two incompressible miscible fluids with different densities are studied using Direct Numerical Simulations (DNS). When the two fluids have very different densities, the differential inertial effects lead to active scalar behavior. To distinguish this from the Boussinesq case, when the two fluids have commensurate densities, we call the former variable-density flows. In order to achieve a statistically stationary state, the velocity field is forced in the real space, using a linear forcing mechanism, while the active scalar field is de-mixed at a rate counteracting the normal diffusion processes using a real-space forcing based on a chemical reaction analogy. The active scalar influence on the turbulence characteristics are discussed as well as the ratios of turbulence to scalar scales for different Atwood, Schmidt, and Reynolds numbers and forcing properties. Finally, the decay of variable-density turbulence from various stationary states is also studied.

Ryu, Jaiyoung; Livescu, Daniel

2011-11-01

68

High-accuracy DNS of supersonic base flows and control of the near wake  

Microsoft Academic Search

Large-scale numerical simulations of axisymmetric, supersonic base flows were conducted at various Reynolds numbers. Direct numerical simulations (DNS) were employed to investigate the hydrodynamic stability behavior of the near-wake region. As a consequence of physical flow instabilities, large coherent structures evolve that have a significant impact on the mean flow wand and are responsible for a considerable amount of base-drag.

Richard D. Sandberg; Hermann F. Fasel

2004-01-01

69

Terascale direct numerical simulations of turbulent combustion using S3D.  

SciTech Connect

Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air co-flow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory intensive loops in the code. Through the careful application of loop transformations, data reuse in cache is exploited thereby reducing memory bandwidth needs, and hence, improving S3D's nodal performance. To enhance collective parallel I/O in S3D, an MPI-I/O caching design is used to construct a two-stage write-behind method for improving the performance of write-only operations. The simulations generate tens of terabytes of data requiring analysis. Interactive exploration of the simulation data is enabled by multivariate time-varying volume visualization. The visualization highlights spatial and temporal correlations between multiple reactive scalar fields using an intuitive user interface based on parallel coordinates and time histogram. Finally, an automated combustion workflow is designed using Kepler to manage large-scale data movement, data morphing, and archival and to provide a graphical display of run-time diagnostics.

Sankaran, Ramanan; Mellor-Crummy, J.; DeVries, M.; Yoo, Chun Sang; Ma, K. L.; Podhorski, N.; Liao, W. K.; Klasky, S.; de Supinski, B.; Choudhary, A.; Hawkes, Evatt R.; Chen, Jacqueline H.; Shende, Sameer

2008-08-01

70

Terascale direct numerical simulations of turbulent combustion using S3D  

SciTech Connect

Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air coflow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory intensive loops in the code. Through the careful application of loop transformations, data reuse in cache is exploited thereby reducing memory bandwidth needs, and hence, improving S3D's nodal performance. To enhance collective parallel I/O in S3D, an MPI-I/O caching design is used to construct a two-stage write-behind method for improving the performance of write-only operations. The simulations generate tens of terabytes of data requiring analysis. Interactive exploration of the simulation data is enabled by multivariate time-varying volume visualization. The visualization highlights spatial and temporal correlations between multiple reactive scalar fields using an intuitive user interface based on parallel coordinates and time histogram. Finally, an automated combustion workflow is designed using Kepler to manage large-scale data movement, data morphing, and archival and to provide a graphical display of run-time diagnostics.

Chen, Jackie [Sandia National Laboratories (SNL); Klasky, Scott A [ORNL; Hawkes, Evatt R [Sandia National Laboratories (SNL); Sankaran, Ramanan [ORNL; Choudhary, Alok [Northwestern University, Evanston; Yoo, Chun S [Sandia National Laboratories (SNL); Liao, Wei-keng [Northwestern University, Evanston; Podhorszki, Norbert [ORNL

2009-01-01

71

Dns-Derived Force Distribution on Flexible Cylinders Subject to Vortex-Induced Vibration  

NASA Astrophysics Data System (ADS)

We use direct numerical simulation (DNS) based on spectral methods to simulate turbulent flow past rigid and flexible cylinders subject to vortex-induced vibrations (VIV). We present comparisons of amplitude, and lift and drag forces, at Reynolds number 1000 for a short and a long cylinder, and we examine differences between a traveling wave response and a standing wave response. The DNS data suggest that the often-used empirical formula proposed by Skop, Griffin & Ramberg in 1977 overpredicts the drag coefficient. We propose an appropriate modification and present preliminary results that indicate that low-dimensional modeling may be an accurate and efficient approach in predicting forces in VIV. Given the lack of any benchmark experiments in VIV currently, the DNS results presented here, both distributions as well as span- and time-averaged quantities, should be helpful to experimentalists and modelers.

Evangelinos, C.; Lucor, D.; Karniadakis, G. E.

2000-04-01

72

A high-order photon Monte Carlo method for radiative transfer in direct numerical simulation  

SciTech Connect

A high-order photon Monte Carlo method is developed to solve the radiative transfer equation. The statistical and discretization errors of the computed radiative heat flux and radiation source term are isolated and quantified. Up to sixth-order spatial accuracy is demonstrated for the radiative heat flux, and up to fourth-order accuracy for the radiation source term. This demonstrates the compatibility of the method with high-fidelity direct numerical simulation (DNS) for chemically reacting flows. The method is applied to address radiative heat transfer in a one-dimensional laminar premixed flame and a statistically one-dimensional turbulent premixed flame. Modifications of the flame structure with radiation are noted in both cases, and the effects of turbulence/radiation interactions on the local reaction zone structure are revealed for the turbulent flame. Computational issues in using a photon Monte Carlo method for DNS of turbulent reacting flows are discussed.

Wu, Y. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States); Modest, M.F. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States); Haworth, D.C. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States)]. E-mail: dch12@psu.edu

2007-05-01

73

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

74

Investigation of Rayleigh-Taylor turbulence and mixing using direct numerical simulation with experimentally-measured initial conditions. I. Comparison to experimental data  

SciTech Connect

A 1152 x 760 x 1280 direct numerical simulation (DNS) using initial conditions, geometry, and physical parameters chosen to approximate those of a transitional, small Atwood number Rayleigh-Taylor mixing experiment [Mueschke, Andrews and Schilling, J. Fluid Mech. 567, 27 (2006)] is presented. The density and velocity fluctuations measured just off of the splitter plate in this buoyantly unstable water channel experiment were parameterized to provide physically-realistic, anisotropic initial conditions for the DNS. The methodology for parameterizing the measured data and numerically implementing the resulting perturbation spectra in the simulation is discussed in detail. The DNS model of the experiment is then validated by comparing quantities from the simulation to experimental measurements. In particular, large-scale quantities (such as the bubble front penetration hb and the mixing layer growth parameter {alpha}{sub b}), higher-order statistics (such as velocity variances and the molecular mixing parameter {theta}), and vertical velocity and density variance spectra from the DNS are shown to be in favorable agreement with the experimental data. Differences between the quantities obtained from the DNS and from experimental measurements are related to limitations in the dynamic range of scales resolved in the simulation and other idealizations of the simulation model. This work demonstrates that a parameterization of experimentally-measured initial conditions can yield simulation data that quantitatively agrees well with experimentally-measured low- and higher-order statistics in a Rayleigh-Taylor mixing layer. This study also provides resolution and initial conditions implementation requirements needed to simulate a physical Rayleigh-Taylor mixing experiment. In Part II [Mueschke and Schilling, Phys. Fluids (2008)], other quantities not measured in the experiment are obtained from the DNS and discussed, such as the integral- and Taylor-scale Reynolds numbers, Reynolds stress anisotropy and two-dimensional density and velocity variance spectra, hypothetical chemical product formation measures, other local and global mixing parameters, and the statistical composition of mixed fluid.

Mueschke, N; Schilling, O

2008-07-23

75

Numerical simulation of atmospheric turbulence  

NASA Astrophysics Data System (ADS)

A review is presented on the application of LES to a simulation of turbulence in the atmospheric boundary layer. First we discuss some historical facts which are interesting from a general perspective because the field of turbulence simulation has its origin in numerical weather forecasting. Instead of giving a standard review of the technique of LES and its various details, we continue by first highlighting some successes of LES in the atmospheric boundary layer and then some failures. The successes are the simulation of the Convective Boundary Layer (CBL) and the Neutral Boundary Layer (NBL). The failures are the simulation of the horizontal velocity fluctuations and the behaviour of the skewness of vertical velocity fluctuations near the surface both in the CBL.

Nieuwstadt, F. T. M.; van Haarlem, B. A.

76

Numerical simulation of Faraday waves  

Microsoft Academic Search

We simulate numerically the full dynamics of Faraday waves in three dimensions for two incompressible and immiscible viscous fluids. The Navier-Stokes equations are solved using a finite-difference projection method coupled with a front-tracking method for the interface between the two fluids. The domain of calculation is periodic in the horizontal directions and bounded in the vertical direction by two rigid

Nicolas Périnet; Damir Juric; Laurette S. Tuckerman

2009-01-01

77

Direct-numerical-simulation-based measurement of the mean impulse response of homogeneous isotropic turbulence  

NASA Astrophysics Data System (ADS)

A technique for measuring the mean impulse response function of stationary homogeneous isotropic turbulence is proposed. Such a measurement is carried out here on the basis of direct numerical simulation (DNS). A zero-mean white-noise volume forcing is used to probe the turbulent flow, and the response function is obtained by accumulating the space-time correlation between the white forcing and the velocity field. This technique to measure the turbulent response in a DNS numerical experiment is a research tool in that field of spectral closures where the linear-response concept is invoked either by resorting to renormalized perturbations theories or by introducing the well-known fluctuation-dissipation relation (FDR). Although the results obtained in the present work are limited to relatively low values of the Reynolds number, a preliminary analysis is possible. Both the characteristic form and the time scaling properties of the response function are investigated in the universal subrange of dissipative wave numbers; a comparison with the response approximation given by the FDR is proposed through the independent DNS measurement of the correlation function. Very good agreement is found between the measured response and Kraichnan’s description of random energy-range advection effects.

Carini, Marco; Quadrio, Maurizio

2010-12-01

78

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

79

Direct numerical and large eddy simulation of longitudinal flow along triangular array of rods using the lattice Boltzmann method  

Microsoft Academic Search

Results of direct numerical (DNS) and large eddy simulation (LES) of turbulent longitudinal flow in rod bundles are presented using the lattice Boltzmann method with the Bhatnagar–Gross–Krook collision operator [P.L. Bhatnagar, E.P. Gross, M. Krook, A model for collision processes in gases. I. Small amplitude processes in charged and neutral one-component systems, Phys. Rev. 94 (1954) 511; Y.H. Qian, d’Humiéres,

Gusztáv Mayer; Gábor Házi

2006-01-01

80

Direct Numerical Simulations of Localised Forced Ignition in Turbulent Mixing Layers: The Effects of Mixture Fraction and Its Gradient  

Microsoft Academic Search

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

81

AGN feedback in numerical simulations  

NASA Astrophysics Data System (ADS)

The passively evolving stellar population in elliptical galaxies (Es) provides a continuous source of fuel for accretion on the central supermassive black hole (SMBH), which is 1) extended over the entire galaxy life (but declining with cosmic time), 2) linearly proportional to the stellar mass of the host spheroid, 3) summing up to a total gas mass that is > 100 times larger than the currently observed SMBH masses, 4) available independently of merging events. The main results of numerical simulations of Es with central SMBH, in which a physically based implementation of radiative and mechanical feedback effects is considered, are presented.

Ciotti, Luca

2010-11-01

82

Numerical Simulation of Frigate Airwakes  

NASA Astrophysics Data System (ADS)

The airwake surrounding the flight deck of a frigate is analysed to better understand the flow field that a helicopter pilot will encounter when operating from this maritime platform. This is a first step in studying the fully coupled helicopter/ship airwake environment. The flow around a simplified scale model of a Canadian patrol frigate is measured experimentally and simulated numerically. The computations were carried out using the structured multi-block flow solver CFD-ACE employing the k-? turbulence model with wall functions. Comparison of experimental and computed velocity and turbulent kinetic energy profiles shows that the simulation captures the flow structures but contains higher spatial gradients. This difference can be partially attributed to the unsteadiness of the flow in the airwake with which a steady-state Navier-Stokes solver will have trouble.

Syms, G. F.

2004-02-01

83

Numerical simulations of galactic wakes  

NASA Astrophysics Data System (ADS)

We have performed a series of numerical simulations which examine the simple but realistic case of a galaxy with a smooth potential corresponding to a King profile, and with no interstellar medium. This corresponds to the case of an early-type cluster galaxy that has previously been stripped of its gas. The simulations provide a numerical basis for future work involving galaxies with interstellar media. We use a time-explicit finite difference code (Lufkin & Hawley 1992, ApJ submitted) to obtain solutions to the nonlinear equations for adiabatic flow in axisymmetry. The computational grid covers a region extending 500 kpc from a stationary galaxy radially and along the symmetry axis. We use a graded mesh, allowing for full resolution near the galaxy. Because the assumed potential has a finite depth, no artificial inner boundary condition is necessary; reflection symmetry at the axis is assumed. With a total grid size of 64 radial x 128 vertical, each run requires approximately 5 minutes of cpu time on the NCSA Cray-2.

Lufkin, Eric A.

1993-01-01

84

Dense magnetized plasma numerical simulations  

NASA Astrophysics Data System (ADS)

The scope for developing the present numerical method was to perform parametric studies for optimization of several configurations in magnetized plasmas. Nowadays there exist several efficient numerical codes in the subject. However, the construction of one's own computational codes brings the following important advantages: (a) to get a deeper knowledge of the physical processes involved and the numerical methods used to simulate them and (b) more flexibility to adapt the code to particular situations in a more efficient way than would be possible for a closed general code. The code includes ion viscosity, thermal conduction (electrons and ions), magnetic diffusion, thermonuclear or chemical reaction, Bremsstrahlung radiation, and equation of state (from the ideal gas to the degenerate electron gas). After each calculation cycle, mesh vertices are moved arbitrarily over the fluid. The adaptive method consists of shifting mesh vertices over the fluid in order to keep a reasonable mesh structure and increase the spatial resolution where the physical solution demands. The code was a valuable tool for parametric study of different physical problems, mainly optimization of plasma focus machine, detonation and propagation of thermonuclear reactions and Kelvin-Helmholtz instabilities in the boundary layer of the terrestrial magnetopause.

Bilbao, L.; Bernal, L.

2010-06-01

85

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

86

DNS of turbulent heat transfer in channel flow with low to medium-high Prandtl number fluid  

Microsoft Academic Search

The direct numerical simulation (DNS) of the turbulent heat transfer for various Prandtl numbers ranging from 0.025 to 5 are performed to obtain statistical quantities such as turbulent heat flux, temperature variance and their budget terms. The configuration is the fully developed channel flow with uniform heating from both walls. The Reynolds number based on the friction velocity and the

Hiroshi Kawamura; Kouichi Ohsaka; Hiroyuki Abe; Kiyoshi Yamamoto

1998-01-01

87

Direct numerical simulation of elastic turbulence and its mixing-enhancement effect in a straight channel flow  

NASA Astrophysics Data System (ADS)

In this paper, we present a direct numerical simulation (DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number (Re=1) in a three-dimensional straight channel flow for the first time, using the Giesekus constitutive model for the fluid. In order to generate and maintain the turbulent fluid motion in the straight channel, a sinusoidal force term is added to the momentum equation, and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field. Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS. The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.

Zhang, Hong-Na; Li, Feng-Chen; Cao, Yang; Kunugi, Tomoaki; Yu, Bo

2013-02-01

88

Numerical simulations of MHD dynamos  

NASA Astrophysics Data System (ADS)

The generation of magnetic fields in space plasmas and in astrophysics is usually described within the framework of magnetohydrodynamics. Turbulent helical flows produce magnetic fields very efficiently, with correlation length scales larger than those characterizing the flow. Within the context of the solar magnetic cycle, a turbulent dynamo is responsible for the so-called alpha effect, while the Omega effect is associated to the differential rotation of the Sun. We present direct numerical simulations of turbulent magnetohydrodynamic dynamos including two-fluid effects such as the Hall current. More specifically, we study the evolution of an initially weak and small-scale magnetic field in a system maintained in a stationary regime of hydrodynamic turbulence, and explore the conditions for exponential growth of the magnetic energy. In all the cases considered, we find that the dynamo saturates at the equipartition level between kinetic and magnetic energy, and the total energy reaches a Kolmogorov power spectrum.

Gómez, Daniel O.; Mininni, Pablo

2005-12-01

89

Numerical simulation of aneurysm hemodynamics  

NASA Astrophysics Data System (ADS)

Rupture of intracranial aneurysms is the leading cause of spontaneous subarachnoid hemorrhage, with high rates of morbidity and mortality. Numerical simulations of flow in a variety of two-dimensional and three-dimensional saccular aneurysm geometries were performed to evaluate possible sites and mechanisms for aneurysm growth and rupture. The governing equations were solved in their finite volume formulation for both steady and pulsatile flows. Recirculation zones and secondary flows were observed in aneurysms and arteries. Regions of elevated and oscillating shear stress were observed, often at the aneurysm's distal shoulder. The influence of several geometric factors, including vessel curvature, branching angle, and aneurysm shape, on flow patterns and fluid mechanical forces was studied, with the goal of assessing the risks posed by given aneurysm geometry.

MacVicar, Stephen; Huynh, Sophia; Rossmann, Jenn

2003-11-01

90

Numerical simulation of Faraday waves  

NASA Astrophysics Data System (ADS)

We simulate numerically the full dynamics of Faraday waves in three dimensions for two incompressible and immiscible viscous fluids. The Navier-Stokes equations are solved using a finite-difference projection method coupled with a front-tracking method for the interface between the two fluids. The domain of calculation is periodic in the horizontal directions and bounded in the vertical direction by two rigid horizontal plates. The critical accelerations and wavenumbers, as well as the temporal behaviour at onset are compared with the results of the linear Floquet analysis of Kumar and Tuckerman [J. Fluid Mech. 279, 49-68 (1994)]. The finite amplitude results are compared with the experiments of Kityk et al. [Phys. Rev. E 72, 036209 (2005)]. In particular we reproduce the detailed spatiotemporal spectrum of both square and hexagonal patterns within experimental uncertainty.

Périnet, Nicolas; Juric, Damir; Tuckerman, Laurette S.

2009-09-01

91

Simulating reionization in numerical cosmology  

NASA Astrophysics Data System (ADS)

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. I present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by various sets of sources. The method requires relatively few time steps and can be employed with simulations of high resolution. First, I explore the reionization history of Helium II by z < 6 quasars. Comparisons between HeII opacities measured observationally and inferred from our analysis reveal that the uncertainties in the empirical luminosity function provide enough leeway to provide a satisfactory match. A property common to all the calculations is that the epoch of Helium II reionization must have occurred between 3?z?4 . I extend my analysis to study the constraints that can be placed on the nature of the cosmic ultraviolet (UV) background in the redshift interval 2.5?z?5 . I find that in order to simultaneously match observational estimates of the HI and HeII opacities, galaxies and quasars must contribute about equally to the ionizing background in HI at z ? 3. Moreover, my analysis requires the stellar component to rise for z > 3 to compensate for the declining contribution from bright quasars at higher redshift. To investigate how stellar source may have reionized the universe at z > 6, I have combined our 3D radiative transfer code with high resolution hydrodynamical simulations to study how population II and III type stars affected the reionization process. The resulting complex reionization histories are presented and comparisons made with observational constraints on the neutral fraction of hydrogen at z ˜ 6 derived from the z = 6.28 SDSS quasar of Becker and coworkers and the recent WMAP measurements of the electron scattering optical depth analysis of Kogut and co-workers.

Sokasian, Aaron

2003-11-01

92

Investigation of boundary condition effects on the propagation of density current using direct numerical simulations  

NASA Astrophysics Data System (ADS)

The propagation of density current in a channel has been studied extensively using theoretical, experimental and numerical tools. For high resolution numerical method, such as direct numerical simulations (DNS), the boundary conditions on the bottom and top of the channel are usually assumed to be no-slip and no-penetration. This study aims to investigate the effects of various boundary conditions encountered in reality, such as shear-stress free top boundary in an open channel, wind shear, suction/blowing bottom due to groundwater flow. The DNS code used in the research implements a revised Kleiser and Schumann (1980) influence-matrix method to treat the Robin type velocity boundary conditions and the related "tau" error corrections. This revised method broadens the applicability of the original Kleiser and Schumann method and is ideal for the purpose of this research. Comparisons of the simulation results reveal that the boundary conditions changes the turbulent flow field and therefore the propagation of the front. The effects on some of the parameters (such as front speed) are investigated and quantified. Further study need to address the scale effects when the vertical scale of the density current is small than or comparable with the channel depth.

Liu, X.

2010-12-01

93

Numerical Simulations of High Speed Turbulent Jets in Crossflow  

NASA Astrophysics Data System (ADS)

This dissertation studies high speed jets in crossflow using numerical simulations. The complexity of this flow makes detailed measurements difficult, and only limited information is provided by past experimental studies. Traditional engineering simulation tools also have difficulties in simulating such flows. Therefore, the current study: 1) develops Large-Eddy Simulation (LES) capability and novel subgrid-scale (SGS) models for high speed flows in complex geometries; 2) realizes multiple methods to generate realistic turbulent boundary layer inflow condition for unstructured compressible flow solver; 3) explores the detailed physics of high speed jets in crossflow; 4) investigates the jet trajectory, entrainment and coherent vortical motions. Large-eddy simulation capability is developed for the base numerical scheme developed by Park & Mahesh (2007) for solving the compressible Navier-Stokes equations on unstructured grids. Large-eddy simulations are performed to study an under-expanded sonic jet injected into a supersonic crossflow and an over-expanded supersonic jet injected into a subsonic crossflow, where the flow conditions are based on Santiago et al.'s (1997) and Beresh et al.'s (2005) experiments, respectively. The simulations successfully reproduce experimentally observed shock systems and vortical structures. The time averaged flow fields are compared to the experimental results, and reasonable agreement is observed. The behavior of the flow is discussed, and the similarities and differences between the two regimes are studied. The trajectory and entrainment of the transverse jet is investigated. A modification to Schetz & Billig's theory (1966) theory is proposed, which yields good prediction of the jet trajectories in the current simulations in the near field. Along the jet center streamline, the jet entrainment grow faster compared to turbulent free jets. In the very far field, the growth rates of jet entrainment decrease to values that are close to those for turbulent free jets. The Strouhal numbers of relevant flow structures are computed from power spectral densities. Many flow motions are observed to be correlated in sonic jet in supersonic crossflow. The frequencies in supersonic injection are observed to be higher than those in sonic injection. A novel eddy-viscosity model, "dynamic k-equation model'', is proposed for the LES of compressible flows with complex flow geometries, where the transport equation for sub-grid scale (SGS) kinetic energy is introduced to predict SGS kinetic energy, instead of using Yoshizawa's model as in standard Dynamic Smagorinsky Model (DSM). The exact SGS kinetic energy transport equation for compressible flows is derived formally. Each of the unclosed terms in the SGS kinetic energy equation is modeled separately and dynamically closed, instead of being grouped into production and dissipation terms, as in the Reynolds Averaged Navier-Stokes (RANS) equations. A priori test using Direct Numerical Simulation (DNS) of decaying isotropic turbulence shows that for Smagorinsky type eddy viscosity model, the correlation between SGS stress and the model is comparable to that from the original model. Also, the suggested model for pressure dilatation term in the SGS kinetic energy equation is found to have high correlation with its actual value. In a posteriori tests, the proposed dynamic k-equation model is applied to decaying isotropic turbulence and normal shock/isotropic turbulence interaction, and yields good agreement with available experimental and DNS data. Compared with the results of Dynamic Smagorinsky Model (DSM), the k-equation model predicts better energy spectra at high wave numbers, similar kinetic energy decay and fluctuations of thermodynamic quantities for decaying isotropic turbulence. For shock/turbulent interaction, &#

Chai, Xiaochuan

94

Particle-Based Direct Numerical Simulation of Contaminant Transport and Deposition in Porous Flow  

SciTech Connect

This work describes an approach to porous flow modeling in which the "micro-length scale to macro-length scale" physical descriptions are addressed as Lagrangian, pore-level flow and transport. The flow features of the physical domain are solved by direct numerical simulation (DNS) with a grid-free, hybrid smoothed particle hydrodynamics (SPH) numerical method (Berry, 2002) based on a local Riemann solution. In addition to being able to handle the large deformation, fluid–fluid and fluid–solid interactions within the contorted geometries of intra- and inter-pore-scale modeling, this Riemann–SPH method should be able to simulate other complexities, such as multiple fluid phases and chemical, particulate, and microbial transport with volumetric and surface reactions. A simple model is presented for the transfer of a contaminant from a carrier fluid to solid surfaces and is demonstrated for flow in a simulated porous media

Ray A. Berry; Richard C. Martineau; Thomas R. Wood

2004-02-01

95

Diversity in DNS performance measures  

Microsoft Academic Search

DNS is a critical component of the operation of Internet applications. However, DNS performance in the wide-area is not well understood. A number of studies present DNS performance measurements [1], [2], [3], [4], but the measurements are out of date, are not collected at client locations (e.g., they are taken at root servers), or are collected at very few client

Richard Liston; Sridhar Srinivasan; Ellen W. Zegura

2002-01-01

96

DNS and BIND Security Issues  

Microsoft Academic Search

Abstract Efforts are underway,to add security to the DNS protocol. We have observed that if BIND would just do what the DNS specifications say it should do, stop crashing, and start checking its inputs, then most of the existing security holes in DNS as practiced would go away. To be sure, attackers would still have a pretty easy time co-opting

Paul Vixie

1995-01-01

97

Direct numerical simulations of Rayleigh-Taylor instability with gravity reversal  

NASA Astrophysics Data System (ADS)

We have conducted high resolution, high Reynolds number Direct Numerical Simulations (DNS) of the Rayleigh-Taylor (RT) instability on the 0.5 petaflop, 150k compute cores BG/L Dawn supercomputer at Lawrence Livermore National Lab. This includes a suite of simulations with Atwood number ranging from 0.04 to 0.9 and grid size of 1024^2 by 4096, and a high resolution simulation of grid size 4096^3 and Atwood number of 0.75. After the layer width has developed substantially, additional branched simulations have been run under reverse gravity and zero gravity conditions. The simulations provide an extensive database to study Rayleigh-Taylor turbulence, including mixing layer growth rate and self-similar behavior, turbulence and mixing asymmetries, and spectral characteristics. Individual terms in the moments transport equations are recorded to develop and validate turbulence closure models.

Petersen, Mark; Livescu, Daniel; Gore, Robert

2010-11-01

98

Numerical Simulations of Thermobaric Explosions  

SciTech Connect

A Model of the energy evolution in thermobaric explosions is presented. It is based on the two-phase formulation: conservation laws for the gas and particle phases along with inter-phase interaction terms. It incorporates a Combustion Model based on the mass conservation laws for fuel, air and products; source/sink terms are treated in the fast-chemistry limit appropriate for such gas dynamic fields. The Model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the fuel (Al or TNT detonation products) with air. Numerical simulations were performed for 1.5-g thermobaric explosions in five different chambers (volumes ranging from 6.6 to 40 liters and length-to-diameter ratios from 1 to 12.5). Computed pressure waveforms were very similar to measured waveforms in all cases - thereby proving that the Model correctly predicts the energy evolution in such explosions. The computed global fuel consumption {mu}(t) behaved as an exponential life function. Its derivative {dot {mu}}(t) represents the global rate of fuel consumption. It depends on the rate of turbulent mixing which controls the rate of energy release in thermobaric explosions.

Kuhl, A L; Bell, J B; Beckner, V E; Khasainov, B

2007-05-04

99

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

100

A multi-zone chemistry mapping approach for direct numerical simulation of auto-ignition and flame propagation in a constant volume enclosure  

Microsoft Academic Search

A direct numerical simulation (DNS) coupling with multi-zone chemistry mapping (MZCM) is presented to simulate flame propagation and auto-ignition in premixed fuel\\/air mixtures. In the MZCM approach, the physical domain is mapped into a low-dimensional phase domain with a few thermodynamic variables as the independent variables. The approach is based on the fractional step method, in which the flow and

M. Jangi; R. Yu; X. S. Bai

2011-01-01

101

A multi-zone chemistry mapping approach for direct numerical simulation of auto-ignition and flame propagation in a constant volume enclosure  

Microsoft Academic Search

A direct numerical simulation (DNS) coupling with multi-zone chemistry mapping (MZCM) is presented to simulate flame propagation and auto-ignition in premixed fuel\\/air mixtures. In the MZCM approach, the physical domain is mapped into a low-dimensional phase domain with a few thermodynamic variables as the independent variables. The approach is based on the fractional step method, in which the flow and

M. Jangi; R. Yu; X. S. Bai

2012-01-01

102

Direct Numerical Simulation of Stability of a Supersonic Mixing Layer Flow  

NASA Astrophysics Data System (ADS)

Linear and nonlinear issue of a mixing layer at Mc=1.2 are studied with a DNS method. Navier-Stokes equations in perturbation form are solved with a finite difference method of the third order accuracy. An approximated boundary condition treatment of small disturbance along the outside boundary is proposed on flow characteristics. This boundary condition is verified to be valid in the numerical case. Linear issue of a mixing layer at Mc=1.2 is simulated. Three modes of instability in the mixing layer have been simulated which are Slow-Mode, Fast-Mode and Mix-Mode. Nonlinear issue pf the mixing layer at Mc=1.2 is also studied. The mode transition of the mixing layer instability is simulated. K-type and H-type secondary instability in supersonic shear layer at Mc=0.5 are simulated.

Shen, Q.; M., F.; G., F.; Wang, Q.

103

A critical comparison of second order closures with direct numerical simulation of homogeneous turbulence  

NASA Astrophysics Data System (ADS)

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.

1991-11-01

104

Inflow and initial conditions for direct numerical simulation based on adjoint data assimilation  

NASA Astrophysics Data System (ADS)

A method for generating inflow conditions for direct numerical simulations (DNS) of spatially-developing flows is presented. The proposed method is based on variational data assimilation and adjoint-based optimization. The estimation is conducted through an iterative process involving a forward integration of a given dynamical model followed by a backward integration of an adjoint system defined by the adjoint of the discrete scheme associated to the dynamical system. The approach's robustness is evaluated on two synthetic velocity field sequences provided by numerical simulation of a mixing layer and a wake flow behind a cylinder. The performance of the technique is also illustrated in a real world application by using noisy large scale PIV measurements. This method denoises experimental velocity fields and reconstructs a continuous trajectory of motion fields from discrete and unstable measurements.

Gronskis, A.; Heitz, D.; Mémin, E.

2013-06-01

105

Direct Numerical Simulation of Boiling Multiphase Flows: State-of-the-Art, Modeling, Algorithmic and Computer Needs  

SciTech Connect

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

106

Direct numerical simulation of ignition front propagation in a constant volume with temperature inhomogeneities, part I : Fundamental analysis and diagnostics.  

SciTech Connect

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry. Parametric studies on the effect of the initial amplitude of the temperature fluctuations, the initial length scales of the temperature and velocity fluctuations, and the turbulence intensity are performed. The combustion mode is characterized using the diagnostic measures developed in Part I of this study. Specifically, the ignition front speed and the scalar mixing timescales are used to identify the roles of molecular diffusion and heat conduction in each case. Predictions from a multizone model initialized from the DNS fields are presented and differences are explained using the diagnostic tools developed.

Sankaran, Ramanan; Mason, Scott D. (Lockheed Martin Corportation, Sunnyvale, CA); Chen, Jacqueline H.; Hawkes, Evatt R.; Im, Hong G.

2005-01-01

107

Direct numerical simulation of ignition front propagation in a constant volume with temperature inhomogeneities. II. Parametric study  

SciTech Connect

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry. Parametric studies on the effect of the initial amplitude of the temperature fluctuations, the initial length scales of the temperature and velocity fluctuations, and the turbulence intensity are performed. The combustion mode is characterized using the diagnostic measures developed in Part I of this study. Specifically, the ignition front speed and the scalar mixing timescales are used to identify the roles of molecular diffusion and heat conduction in each case. Predictions from a multizone model initialized from the DNS fields are presented and differences are explained using the diagnostic tools developed. (author)

Hawkes, Evatt R.; Sankaran, Ramanan; Pebay, Philippe P.; Chen, Jacqueline H. [Reacting Flow Research Department, Combustion Research Facility, Sandia National Laboratories, P.O. Box 969 MS 9051, Livermore, CA 94551-0969 (United States)

2006-04-15

108

Direct numerical simulation of ignition front propagation in a constant volume with temperature inhomogeneities, Part II : Parametric study.  

SciTech Connect

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry. Parametric studies on the effect of the initial amplitude of the temperature fluctuations, the initial length scales of the temperature and velocity fluctuations, and the turbulence intensity are performed. The combustion mode is characterized using the diagnostic measures developed in Part I of this study. Specifically, the ignition front speed and the scalar mixing timescales are used to identify the roles of molecular diffusion and heat conduction in each case. Predictions from a multizone model initialized from the DNS fields are presented and differences are explained using the diagnostic tools developed.

Sankaran, Ramanan; Chen, Jacqueline H.; Hawkes, Evatt R.; Pebay, Philippe Pierre

2005-01-01

109

Investigation of Rayleigh-Taylor turbulence and mixing using direct numerical simulation with experimentally measured initial conditions. I. Comparison to experimental data  

NASA Astrophysics Data System (ADS)

A 1152×760×1280 direct numerical simulation (DNS) using initial conditions, geometry, and physical parameters chosen to approximate those of a transitional, small Atwood number Rayleigh-Taylor mixing experiment [Mueschke et al., J. Fluid Mech. 567, 27 (2006)] is presented. In particular, the Atwood number is 7.5×10-4, and temperature diffusion is modeled by mass diffusion with an equivalent Schmidt number of 7. The density and velocity fluctuations measured just off of the splitter plate in this buoyantly unstable water channel experiment were parametrized to provide physically realistic, anisotropic initial conditions for the DNS. The methodology for parametrizing the measured data and numerically implementing the resulting perturbation spectra in the simulation is discussed in detail. The DNS is then validated by comparing quantities from the simulation to experimental measurements. In particular, large-scale quantities (such as the bubble front penetration hb and the mixing layer growth parameter ?b), higher-order statistics (such as velocity variances and the molecular mixing parameter ? on the center plane), and vertical velocity and density variance spectra from the DNS are shown to be in favorable agreement with the experimental data. The DNS slightly underestimates the growth of the bubble front hb but predicts ?b~0.07 at the latest time, in excellent agreement with the experimental measurement. While the molecular mixing parameter ? is also slightly underestimated by the DNS during the nonlinear and weakly turbulent growth phases, the late-time value ?~0.55 compares favorably with the value ?~0.6 measured in the experiment. The one-dimensional density and vertical velocity variance spectra are in excellent agreement between the DNS and experimental measurements. Differences between the quantities obtained from the DNS and from experimental measurements are related to limitations in the dynamic range of scales resolved in the DNS and other idealizations of the simulation. Specifically, the statistical convergence of the DNS results and confidence interval bounds are discussed. This work demonstrates that a parametrization of experimentally measured initial conditions can yield simulation data that quantitatively agrees well with experimentally measured low- and higher-order statistics in a Rayleigh-Taylor mixing layer. This study also provides resolution and initial conditions implementation requirements needed to simulate a physical Rayleigh-Taylor mixing experiment. In Paper II [Mueschke and Schilling, Phys. Fluids 21, 014107 (2009)], other quantities not measured in the experiment are obtained from the DNS and discussed, such as the integral- and Taylor-scale Reynolds numbers, Reynolds stress and dissipation anisotropy, two-dimensional density and velocity variance spectra, hypothetical chemical product formation measures, other local and global mixing parameters, and the statistical composition of mixed fluid. These quantities are valuable for assessing the predictions of Reynolds-averaged Navier-Stokes and large-eddy simulation models of Rayleigh-Taylor turbulent mixing.

Mueschke, Nicholas J.; Schilling, Oleg

2009-01-01

110

Performance of numerical spray combustion simulation  

Microsoft Academic Search

The aim of this study is to examine the performance of numerical spray combustion simulation. A numerical simulation for the prediction of local properties of heavy oil spray flames stabilized by a baffle plate is described. Time-averaged governing conservation equations are solved to estimate the combustion gas flow, gas composition and temperature fields in the experimental combustor. The ?-? turbulence

T. Furuhata; S. Tanno; T. Miura; Y. Ikeda; T. Nakajima

1997-01-01

111

The Numerical Simulation of Turbulence  

Microsoft Academic Search

In this contribution, I give an overview of the various approaches toward the numerical modelling of turbulence, particularly, in the interstellar medium. The discussion is placed in a physical context, i. e. computational problems are motivated from basic physical considerations. Presenting selected examples for solutions to these problems, I introduce the basic ideas of the most commonly used numerical methods.

W. Schmidt

2007-01-01

112

Numerical simulation of underground explosions  

Microsoft Academic Search

This paper presents a numerical method to calculate stress wave propagation in rock mass and to estimate damage zone around an underground borehole generated by explosion. Numerical calculations are carried out by using a commercial software AUTODYN2D, which is a finite difference code with Lagrange, Euler and combined Lagrange-Euler processors, and is especially suitable for modelling high velocity nonlinear dynamic

Hong Hao; Guowei Ma; Yingxin Zhou

1998-01-01

113

Numerical simulation of backdraft phenomena  

Microsoft Academic Search

This paper reports preliminary computational fluid dynamics (CFD) simulations of backdraft observed in an experimental rig at Lund University. The analysis was performed with the CFX software using the Detached Eddy Simulation (DES) turbulence model, a hybrid of Large Eddy Simulation (LES) and RANS, in combination with the EDM combustion model. The DES model uses a RANS formulation in wall

Andrej Horvat; Yehuda Sinai

2007-01-01

114

Numerical Simulations of Maritime Frontogenesis  

Microsoft Academic Search

A hydrostatic primitive equation model initialized in a highly baroclinically unstable state was used to simulate maritime cyclogenesis and frontogenesis. In order to identify boundary layer physical processes important in maritime frontogenesis, several different simulations were performed. In an effort to isolate impacts due solely to the boundary layer, moist processes were not included. An adiabatic and inviscid simulation provided

William T. Thompson; R. T. Williams

1997-01-01

115

Numerical simulation of a high Mach number jet flow  

NASA Astrophysics Data System (ADS)

The recent efforts to develop accurate numerical schemes for transition and turbulent flows are motivated, among other factors, by the need for accurate prediction of flow noise. The success of developing high speed civil transport plane (HSCT) is contingent upon our understanding and suppression of the jet exhaust noise. The radiated sound can be directly obtained by solving the full (time-dependent) compressible Navier-Stokes equations. However, this requires computational storage that is beyond currently available machines. This difficulty can be overcome by limiting the solution domain to the near field where the jet is nonlinear and then use acoustic analogy (e.g., Lighthill) to relate the far-field noise to the near-field sources. The later requires obtaining the time-dependent flow field. The other difficulty in aeroacoustics computations is that at high Reynolds numbers the turbulent flow has a large range of scales. Direct numerical simulations (DNS) cannot obtain all the scales of motion at high Reynolds number of technological interest. However, it is believed that the large scale structure is more efficient than the small-scale structure in radiating noise. Thus, one can model the small scales and calculate the acoustically active scales. The large scale structure in the noise-producing initial region of the jet can be viewed as a wavelike nature, the net radiated sound is the net cancellation after integration over space. As such, aeroacoustics computations are highly sensitive to errors in computing the sound sources. It is therefore essential to use a high-order numerical scheme to predict the flow field. The present paper presents the first step in a ongoing effort to predict jet noise. The emphasis here is in accurate prediction of the unsteady flow field. We solve the full time-dependent Navier-Stokes equations by a high order finite difference method. Time accurate spatial simulations of both plane and axisymmetric jet are presented. Jet Mach numbers of 1.5 and 2.1 are considered. simulations was about a million. &Our numerical model is based on the 2-4 scheme by Gottlieb & Turkel. Bayliss et al. applied the 2-4 scheme in boundary layer computations. This scheme was also used by Ragab and Sheen to study the nonlinear development of supersonic instability waves in a mixing layer. *In this study, we present two dimensional direct simulation results for both plane and axisymmetric jets. -These results are compared with linear theory predictions. These computations were made for near nozzle exit region and velocity in spanwise/azimuthal direction was assumed to be zero.

Hayder, M. Ehtesham; Turkel, Eli; Mankbadi, Reda R.

1993-01-01

116

Direct numerical simulations of low Reynolds number flow over airfoils with trailing-edge serrations  

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) have been conducted of NACA-0012 with serrated and straight flat-plate trailing-edge extensions using a purposely developed immersed boundary method. For the low Reynolds number airfoil flows accessible by DNS, laminar separation bubbles involving laminar-turbulent transition and turbulent reattachment occurs. Comparing results from simulations with serrated and un-serrated trailing-edge extensions, noise reduction for higher frequencies is shown using power spectra and one-third octave averaged pressure contours. The effect of the trailing-edge serrations on an acoustic feedback loop observed in previous simulations and the subsequent effect on the laminar separation bubble is studied via cross-correlations, probability density functions of skin friction and spanwise wavenumber spectra. The results show that the presence of serrations leads to some spanwise variation of transitional structures in the separated shear layer, but does not significantly affect the overall hydrodynamic field on the airfoil upstream of the serrations. Two reasons for why the hydrodynamic field is not considerably affected by the presence of serrations are suggested.

Sandberg, R. D.; Jones, L. E.

2011-08-01

117

Turbulent flame-wall interaction: a DNS study  

SciTech Connect

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

118

The multiscale formulation of large eddy simulation: Decay of homogeneous isotropic turbulence  

Microsoft Academic Search

The variational multiscale method is applied to the large eddy simulation (LES) of homogeneous, isotropic flows and compared with the classical Smagorinsky model, the dynamic Smagorinsky model, and direct numerical simulation (DNS) data. Overall, the multiscale method is in better agreement with the DNS data than both the Smagorinsky model and the dynamic Smagorinsky model. The results are somewhat remarkable

Thomas J. R. Hughes; Luca Mazzei; Assad A. Oberai; Alan A. Wray

2001-01-01

119

Direct numerical simulations of turbulent flow over a permeable wall using a direct and a continuum approach  

NASA Astrophysics Data System (ADS)

A direct numerical simulation (DNS) has been performed of turbulent channel flow over a three-dimensional Cartesian grid of 30×20×9 cubes in, respectively, the streamwise, spanwise, and wall-normal direction. The grid of cubes mimics a permeable wall with a porosity of 0.875. The flow field is resolved with 600×400×400 mesh points. To enforce the no-slip and no-penetration conditions on the cubes, an immersed boundary method is used. The results of the DNS are compared with a second DNS in which a continuum approach is used to model the flow through the grid of cubes. The continuum approach is based on the volume-averaged Navier-Stokes (VANS) equations [S. Whitaker, ``The Forchheimer equation: a theoretical development,'' Transp. Porous Media 25, 27 (1996)] for the volume-averaged flow field. This method has the advantage that it requires less computational power than the direct simulation of the flow through the grid of cubes. More in general, for complex porous media one is usually forced to use the VANS equations, because a direct simulation would not be possible with present-day computer facilities. A disadvantage of the continuum approach is that in order to solve the VANS equations, closures are needed for the drag force and the subfilter-scale stress. For porous media, the latter can often be neglected. In the present work, a relation for the drag force is adopted based on the Irmay [``Modèles théoriques d'écoulement dans les corps poreux,'' Bulletin Rilem 29, 37 (1965)] and the Burke-Plummer model [R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena (Wiley, New York, 2002)], with the model coefficients determined from simulations reported by W. P. Breugem, B. J. Boersma, and R. E. Uittenbogaard [``Direct numerical simulation of plane channel flow over a 3D Cartesian grid of cubes,'' Proceedings of the Second International Conference on Applications of Porous Media, edited by A. H. Reis and A. F. Miguel (Évora Geophysics Center, Évora, 2004), p. 27]. The results of the DNS with the grid of cubes and the second DNS in which the continuum approach is used, agree very well.

Breugem, W. P.; Boersma, B. J.

2005-02-01

120

Assessment of closure schemes in second-order conditional moment closure against DNS with extinction and ignition  

SciTech Connect

The performance of second-order conditional moment closure (CMC) depends on models to evaluate conditional variances and covariances of temperature and species mass fractions. In this paper the closure schemes based on the steady laminar flamelet model (SLFM) are validated against direct numerical simulation (DNS) involving extinction and ignition. Scaling is performed to reproduce proper absolute magnitudes, irrespective of the origin of mismatch between local flamelet structures and scalar dissipation rates. DNS based on the pseudospectral method is carried out to study hydrogen-air combustion with a detailed kinetic mechanism, in homogeneous, isotropic, and decaying turbulent media. Lewis numbers are set equal to unity to avoid complication of differential diffusion. The SLFM-based closures for correlations among fluctuations of reaction rate, scalar dissipation rate, and species mass fractions show good comparison with DNS. The variance parameter in lognormal PDF and the constants in the dissipation term have been estimated from DNS results. Comparison is made for the resulting conditional profiles from DNS, first-order CMC, and second-order CMC with correction to the most critical reaction step according to sensitivity analysis. Overall good agreement ensures validity of the SLFM-based closures for modeling conditional variances and covariances in second-order CMC.

Sreedhara, S.; Huh, Kang Y. [Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784 (Korea, Republic of)

2005-12-01

121

Numerical simulations of the solar atmosphere  

Microsoft Academic Search

In this thesis several aspects of the solar atmosphere are investigated using numerical simulations. Simulations and observations of reversed solar granulation are compared. It is concluded that reversed granulation is a hydrodynamical process and is a consequence of convection reversal. Images are synthesized from simulations of solar magnetoconvection to study the quality of different proxy-magnetometry diagnostics. It is concluded that

J. Leenaarts

2007-01-01

122

Untangling the Web from DNS  

Microsoft Academic Search

The Web relies on the Domain Name System (DNS) to resolve the hostname portion of URLs into IP addresses. This marriage-of-convenience enabled the Web's mete- oric rise, but the resulting entanglement is now hinder- ing both infrastructures—the Web is overly constrained by the limitations of DNS, and DNS is unduly burdened by the demands of the Web. There has been

Michael Walfish; Hari Balakrishnan; Scott J. Shenker

2004-01-01

123

Numerical wind speed simulation model  

SciTech Connect

A relatively simple stochastic model for simulating wind speed time series that can be used as an alternative to time series from representative locations is described in this report. The model incorporates systematic seasonal variation of the mean wind, its standard deviation, and the correlation speeds. It also incorporates systematic diurnal variation of the mean speed and standard deviation. To demonstrate the model capabilities, simulations were made using model parameters derived from data collected at the Hanford Meteorology Station, and results of analysis of simulated and actual data were compared.

Ramsdell, J.V.; Athey, G.F.; Ballinger, M.Y.

1981-09-01

124

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

125

Numerical simulations of detonation transmission  

Microsoft Academic Search

The complex, dynamic shock-detonation structure formed by the glancing interaction of a primary detonation with a secondary explosive is studied using time-dependent two-dimensional simulations and related experiments. The materials considered in the simulations are stoichiometric and lean mixtures of hydrogen and oxygen diluted with argon. Related experiments have used undiluted hydrogen and oxygen as well as other gases. The conditions

Elaine S. Oran; David A. Jones; Martin Sichel

1991-01-01

126

Shock interaction with a deformable particle: Direct numerical simulation and point-particle modeling  

NASA Astrophysics Data System (ADS)

The interaction of shock waves with deformable particles is an important fundamental problem. In some applications, e.g., the detonation of explosives loaded with metal particles, the pressure behind the shock wave can be significantly larger than the yield strength of the particle material. This means that particles can deform severely during their interaction with the shock wave. The experimental and theoretical studies of shock interaction with deformable particles (SIDP) are extremely challenging because of its highly transient nature. As a result, no accurate model exists yet that can be used in simulations. The objective of this paper is to develop a simple point-particle model that accurately captures the unsteady force and heat-transfer in SIDP. In the development of this model, we build on earlier models by Ling et al. (Int. J. Multiphase Flow 37, 1026-1044 (2011)) for the unsteady force and heat-transfer contributions for rigid particles. Insights gained from direct numerical simulations (DNS) guide the extension of these models to deforming particles. Results obtained with the extended model for the interaction of a deforming particle with a shock wave and a Chapman-Jouguet detonation wave compare well with DNS results and therefore offer significant improvements over standard models.

Ling, Y.; Haselbacher, A.; Balachandar, S.; Najjar, F. M.; Stewart, D. S.

2013-01-01

127

Numerical Simulation on Laser Fusion in China  

SciTech Connect

Numerical simulation is a powerful tool to get insight into the physics of laser fusion. Much effort has been devoted to develop the numerical simulation code series named LARED in China. The code series LARED are composed of six parts and enable us to have the simulation capability for the key processes in laser fusion. In recent years, a number of numerical simulations using LARED have been carried out and the simulation is checked by experiments done at the laser facility SG-II and SG-III prototype. In the present talk, some details of LARED code series will be introduced, and some simulation results, especially recent work on the opacities, will be shown.

Zhu Shaoping; Pei Wenbing; Xu Yan; Gu Peijun; Lan Ke; Ye Wenhua; Wu Junfeng; Li Jinghong; Gao Yaoming; Zheng Chunyang; Li Shuanggui; Mo Zeyao; Yan Jun [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China); Zhang Weiyan [National High-Tech Inertial Confinement Fusion Committee of China, Beijing 100088 (China)

2009-05-02

128

DNS of high speed boundary layers over ablating surfaces  

NASA Astrophysics Data System (ADS)

Ablation of thermal protection shields is an important design problem in developing reentry vehicles. Development of predictive computational models for this problem will enable optimization of the size and hence weight of the protective layer. In this work, direct numerical simulation (DNS) of a compressible ablating boundary layer is used to understand the modeling issues in the context of Reynolds-averaged Navier Stokes (RANS) equations. The DNS is performed at conditions obtained from a detailed RANS study of a reentry vehicle. The free stream conditions of the two simulations are Mach 0.6, temperature 5940 K, and Re? 1000; and Mach 1.2, temperature 5580 K, and Re? 2000. The surface ablation of a graphite ablator is modeled using a locally 1-D, quasi-steady state formulation with control volume mass and energy balances over the interior of the ablator. A 10-species gas phase chemistry mechanism is used. A priori studies are used to evaluate scalar flux models and the reaction source term closure in RANS.

Braman, Kalen; Raman, Venkat; Upadhyay, Rochan; Ezekoye, Ofodike

2010-11-01

129

Effects of Lewis number on conditional fluid velocity statistics in low Damköhler number turbulent premixed combustion: A direct numerical simulation analysis  

NASA Astrophysics Data System (ADS)

The effects of global Lewis number Le on the statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damköhler number and Lewis number ranging from 0.34 to 1.2. The conditional velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damköhler number flames. It has been shown that the Lewis number substantially affects the mean velocity and the velocity fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean velocity and the velocity fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture.

Chakraborty, Nilanjan; Lipatnikov, Andrei N.

2013-04-01

130

Dns Extensions To Network Address Translators (dns_alg)  

Microsoft Academic Search

Abstract: Domain Name Service (DNS) provides name to address mapping within arouting class (ex: IP). Network Address Translators (NATs) attempt toprovide transparent routing between hosts in disparate address realmsof the same routing class. Typically, NATs exist at the border of astub domain, hiding private addresses from external addresses. Thisdocument identifies the need for DNS extensions to NATs and outlineshow a

P Srisuresh; G Tsirtsis; P Akkiraju; A Heffernan

1999-01-01

131

Numerical simulation of heat exchanger  

SciTech Connect

Accurate and detailed knowledge of the fluid flow field and thermal distribution inside a heat exchanger becomes invaluable as a large, efficient, and reliable unit is sought. This information is needed to provide proper evaluation of the thermal and structural performance characteristics of a heat exchanger. It is to be noted that an analytical prediction method, when properly validated, will greatly reduce the need for model testing, facilitate interpolating and extrapolating test data, aid in optimizing heat-exchanger design and performance, and provide scaling capability. Thus tremendous savings of cost and time are realized. With the advent of large digital computers and advances in the development of computational fluid mechanics, it has become possible to predict analytically, through numerical solution, the conservation equations of mass, momentum, and energy for both the shellside and tubeside fluids. The numerical modeling technique will be a valuable, cost-effective design tool for development of advanced heat exchangers.

Sha, W.T.

1985-01-01

132

Numerical simulation of a guitar  

Microsoft Academic Search

The purpose of this study is to present a time-domain numerical modeling of the guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard and the sound radiation in the air. We use a specific spectral method for solving the Kirchhoff–Love’s dynamic plate model for orthotropic material, a fictitious

Eliane Bécache; Antoine Chaigne; Gregoire Derveaux; Patrick Joly

2005-01-01

133

Numerical simulation of axisymmetric turbulent jets  

NASA Astrophysics Data System (ADS)

The flow in axisymmetric turbulent jets is numerically simulated with the use of a semi-empirical second-order turbulence model including differential transport equations for the normal Reynolds stresses. Calculated results are demonstrated to agree with experimental data.

Demenkov, A. G.; Ilyushin, B. B.; Chernykh, G. G.

2008-09-01

134

Numerical Simulation of Plasmas at Princeton I.  

National Technical Information Service (NTIS)

A program on numerical plasma simulation was undertaken. The following codes were developed: One- and two-dimensional models using finite-sized particles and including only electrostatic interactions between particles; One, one and a half (two velocities ...

J. M. Dawson W. L. Kruer J. P. Boris J. H. Orens C. Oberman

1969-01-01

135

Numerical simulation of turbulent reacting flows  

SciTech Connect

A multidimensional, transient computational fluid dynamics algorithm has been developed for simulation of reacting flows in automotive engines. We describe the basic features of the method and present several numerical solutions obtained with it.

Cloutman, L.D.

1984-01-01

136

Numerical simulations of elliptical galaxies  

NASA Astrophysics Data System (ADS)

For the formation of elliptical galaxies, two scenarios, monolithic collapse vs. major merger, have been debated. We simulate the formation and chemodynamical evolution of 128 Es from the CDM initial fluctuations, using the GRAPE-SPH code that include star formation, supernovae feedback, and chemical enrichment. In our CDM-based scenario, galaxies form through the successive merging of subgalaxies with various masses.

Kobayashi, Chiaki

2010-11-01

137

Direct numerical simulation of heat release and NO{sub x} formation in turbulent nonpremixed flames  

SciTech Connect

Attempts to use complex chemistry and transport in direct numerical simulations (DNS) of premixed combustion (even for kinetically simple systems, such as H{sub 2}/air and CH{sub 4}/air) often result in excessive needs of memory and CPU time. This paper presents a methodology (integrated combustion chemistry [ICC]) capable of integrating complex chemistry effects into DNS while maintaining computational efficiency. The methodology includes the use of a limited number of species and reactions with parameters which are derived to match a number of flame properties. It is illustrated through a four-step reaction mechanism appropriate for a stoichiometric methane/air flame, and which compares favorably with predictions of the detailed GRI 2.11 mechanism. The proposed scheme includes one reaction for the methane oxidation, one for the thermal, one for the Fenimore, and one for the nonpremixed reburn chemical NO{sub x} routes. The kinetic parameters for the hydrocarbon oxidation were determined by matching the GRI 2.11 predictions for laminar burning velocity and adiabatic flame temperature, main reactants concentrations, and extinction strain rates for both premixed (steady) and nonpremixed (steady and unsteady) strained laminar flames. The chemical parameters for the three steps corresponding to NO{sub x} chemistry were determined by matching the NO{sub x} profiles obtained for strained diffusion flames with GRI 2.11. Finally, this four-step mechanism was used in DNS of two- and three-dimensional turbulent nonpremixed combustion to assess the validity of flamelet approaches. While the flamelet approaches were found to perform well for heat release, their extension to NO{sub x} formation appears to be not as successful because of the existence of compressed zones where products accumulate and increase the No{sub x} production.

Bedat, B.; Egolfopoulos, F.N.; Poinsot, T.

1999-10-01

138

Numerical simulation of hydraulic transients  

NASA Astrophysics Data System (ADS)

A numerical method suitable for the analysis of hydraulic transients in one-dimensional pipelines as well as some applications of the method are presented in this thesis. In the present method one-dimensional flow equations are solved in a characteristic form using a finite difference technique. A nonequilibrium two-phase flow model is used, which makes it possible to analyze the effect of vaporization. The motion of the pipe-wall, which is important in some types of hydraulic transients, can be taken into account approximately. The main application of the method has been the piping of nuclear reactors.

Siikonen, T.

139

Numerical Simulations of HH 555  

NASA Astrophysics Data System (ADS)

We present three-dimensional (3D) gasdynamic simulations of the Herbig Haro object HH 555. HH 555 is a bipolar jet emerging from the tip of an elephant trunk entering the Pelican Nebula from the adjacent molecular cloud. Both beams of HH 555 are curved away from the center of the H II region. This indicates that they are being deflected by a sidewind probably coming from a star located inside the nebula or by the expansion of the nebula itself. HH 555 is most likely an irradiated jet emerging from a highly embedded protostar, which has not yet been detected. In our simulations we vary the incident photon flux, which in one of our models is equal to the flux coming from a star 1 pc away emitting 5×1048 ionizing (i.e., with energies above the H Lyman limit) photons per second. An external, plane-parallel flow (a ``sidewind'') is coming from the same direction as the photoionizing flux. We have made four simulations, decreasing the photon flux by a factor of 10 in each simulation. We discuss the properties of the flow, and we compute H? emission maps (integrated along lines of sight). We show that the level of the incident photon flux has an important influence on the shape and visibility of the jet. If the flux is very high, it causes a strong evaporation of the neutral clump, producing a photoevaporated wind traveling in the direction opposite to the incident flow. The interaction of the two flows creates a double shock ``working surface'' around the clump, protecting it and the jet from the external flow. The jet only starts to curve when it penetrates through the working surface.

Kajdi?, P.; Raga, A. C.

2007-12-01

140

Direct numerical simulations of turbulence  

Microsoft Academic Search

Due to exceptional possibilities offered by large scientific calculators, the direct, unstationary resolution of Navier-Stokes equations in situations pertaining to turbulence and transition is now at hand. In this paper, we develop very high resolution simulations of three-dimensional incompressible and compressible mixing layers, developed isotropic turbulence, and rotating turbulence. We focus on coherent structures and large-scale intermittency. In the mixing-layer

M. Lesieur; P. Comte; O. Metals

1992-01-01

141

Numerical tools for atomistic simulations.  

SciTech Connect

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

142

Eruption Morphologies from Numerical Simulations  

NASA Astrophysics Data System (ADS)

Eruptive processes in nature produce a wide variety of morphologies, including cone sheets, dykes, sills, and pipes. The choice of a particular eruptive style is determined partly by local inhomogeneities, and partly by the gross overall properties of the country rock and the physical properties of the eruptive fluid. We have performed two-dimensional simulations designed to capture a range of morphologies in an eruptive system, using the finite-volume code Sage, originally developed at Science Applications International. In these simulations, we supply a mixture of basaltic magma, supercritical water, and carbon dioxide at a given pressure and zero velocity into a 2-km deep fill of basaltic country rock. We vary the supply pressure and the material properties of the country rock in a parameter study. All simulation runs are followed until the volatile-rich mixture breaks out at the surface. Pipes are produced at high pressures with softer backgrounds, cone sheets at lower pressures and stiffer backgrounds, while sills are produced in intermediate regimes.

Gisler, Galen

2013-04-01

143

NUMERICAL SIMULATIONS OF VIBRATION ASSISTED MACHINING  

Microsoft Academic Search

A two-dimensional (2-D) finite element model (FEM) has been developed to perform numerical simulations of vibration assisted machining (VAM). The model is based on an updated Lagrangian formulation, with adaptive remeshing. The model is capable of simulating the amplitude and frequency independently of the tool in the cutting (x) and thrust (y) force directions over a wide range of values.

John A. Patten; Andre Williams

144

Numerical simulations of ultrafine powder coating systems  

Microsoft Academic Search

Numerical simulations for gas–solid two-phase flows were conducted for an experimental coating booth and an industrial coating booth to study the effect of the coating powder size on the performance of the coating process. To optimize coating parameters, simulations were conducted for different coating parameters, such as the size of the coating part, the distance between the coating part and

Z. Li; J. Zhu; C. Zhang

2005-01-01

145

A new methodology for the numerical simulation of wall bounded turbulent flows  

NASA Astrophysics Data System (ADS)

Research is presented on the development and testing of a new procedure for the time dependent, spatially varying numerical simulation of wall bounded turbulent flows. The Flow Simulation Methodology (FSM), as it is now known, was originally proposed by Speziale (1996a) for the purpose of computing complex, non-equilibrium flows which are currently beyond the reach of Smagorinsky based Large-Eddy Simulations (LES). The new method represents a hybrid approach that combines favorable aspects of Reynolds stress modeling [used for Reynolds Averaged Navier-Stokes (BANS) calculations] with the underlying principles of LES. For instance, Reynolds stress models developed for non-equilibrium, anisotropic, and/or rotational flows can be utilized in the unsteady manner of LES, i.e. where the flow field is decomposed into resolved-scale (calculated) and subgrid-scale (modeled) components, thereby reducing computational requirements. The key to the FSM is a contribution function which provides a degree of local turbulence modeling that is dependent upon the ratio of the numerical resolution to the Kolmogorov length-scale, an estimate for the smallest scales of turbulent motion. With this approach, a calculation resolved to the level of a Direct Numerical Simulation (DNS) can proceed continuously to a Reynolds Averaged Navier-Stokes calculation as the numerical resolution is decreased and/or the Reynolds number is increased. In between these two limits, an "untraditional" LES is recovered. The method is untraditional because it replaces the commonly employed Smagorinsky subgrid-scale model, which is known to have considerable limitations, with a more capable Reynolds stress model. A detailed evaluation of the Flow Simulation Methodology is made for the test case of a transitional and turbulent flat plate boundary layer with zero pressure gradient. The relatively simple geometry is chosen because the technical issues associated with combining elements of RANS calculations and LES must be established and the FSM itself must be validated before more complex flows can be attempted. The Reynolds stresses needed for the new method are computed using the two-equation Algebraic Stress Model (ASM) of Gatski & Speziale (1993) developed for non-equilibrium turbulent flows. Results of FSM calculations are compared with results obtained from coarse grid DNS, traditional LES based on the Smagorinsky subgrid-scale model, and RANS, all of which are implemented using an identical core computer code. This approach is extremely valuable to the evaluation of the FSM since a common code allows for certain behaviors to be more easily attributed to the turbulence models as opposed to numerical effects. Further validation is achieved through comparisons of FSM results with various direct numerical simulations and experiments available in the literature.

Bachman, Cary Robert

2001-10-01

146

Direct numerical simulation of turbulent free-surface high Prandtl number fluid flows in fusion reactors  

NASA Astrophysics Data System (ADS)

A high Pr fluid flow, such as FLiBe, has less heat transport capability because of low thermal conductivity and very thin thermal boundary layer. Until today, turbulent flow and heat transfer feature of high Pr fluid, especially as for a free-surface flow configuration, is not so clear because of the difficulties in velocity and temperature measurements in such a very thin boundary layer. In the present study, Direct Numerical Simulation (DNS) of turbulent free-surface flow of various Pr fluids has been carried out with a constant heat flux from the free surface and an adiabatic condition imposed on the wall. From the DNS, turbulent statistics have been obtained and the flow structure has been investigated via computational flow visualization technique. One of the highlights of this study is that the turbulent diffusivity near the free-surface increases when Pr increase and it leads to a very high-temperature region which could appear there, and then eventually a ``laminarization'' of fluid flow could occurr because of less turbulent heat flux there. This means that it is necessary to consider some turbulent heat transfer and thermal mixing augmentation for high Pr fluid flows.

Kunugi, T.; Satake, S.; Sagara, A.

2001-05-01

147

Direct numerical simulation of the mixing tab flow  

NASA Astrophysics Data System (ADS)

The trapezoidal mixing tab has attracted growing attention due to its ability to generate hairpin vortices to enhance cross-stream mixing (Gretta & Smith, 1993; Elavarasan & Meng, 2000). In spite of several previous experimental studies, the physics pertaining to the topological, dynamical and statistical characteristics of the trapezoidal-tab wake is still poorly understood. A major difficulty is the highly three-dimensional nature of the tab wake. The objective of this work is to provide a comprehensive physical picture of the topological, dynamical and statistical features of the tab flow by using direct numerical simulations (DNS), and to elucidate several unresolved fundamental questions about the trapezoidal tab wake. The current work considers a trapezoidal tab mounted on a flat plate. Simulations are conducted for three tab inclination angles ? = 12.25°, 24.5° and 49° with the Reynolds number Re = 600 based on the free-stream velocity and the tab height. A finite-volume discretization scheme involving about 2.6 × 106 control volumes is employed for the simulation and the results are compared with PIV experimental data. The simulation results are shown to reproduce all the flow features as observed in experiments and reveal several new phenomena. It is shown that the hairpin vortex comprises clustered flat-plate boundary-layer vortex lines from various streamwise locations. The hairpin vortex is found to be capable of lifting up and entraining new vortex lines from the local boundary layer, thereby increasing its strength to counter vorticity diffusion. This characteristic provides a self-sustaining mechanism for the hairpin structure. It is also shown that the turbulence production is mostly accomplished by the hairpin heads/arches, while the highest turbulent kinetic energy is associated with the hairpin legs. The topological characteristics of the vortex structures, the statistical characteristics and the mixing mechanisms of the flow are discussed in detail. Simulations also show that a larger inclination angle results in more enhanced mixing in the tab wake; however, with the penalty of a larger pressure drop across the tab.

Dong, Suchuan

148

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

NASA Astrophysics Data System (ADS)

The objective of this research is to make use of Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) for the computational analyses of high speed reacting flows. Our efforts in the first phase of this research conducted within the past three years have been directed in several issues pertaining to intricate physics of turbulent reacting flows. In our previous 5 semi-annual reports submitted to NASA LaRC, as well as several technical papers in archival journals, the results of our investigations have been fully described. In this progress report which is different in format as compared to our previous documents, we focus only on the issue of LES. The reason for doing so is that LES is the primary issue of interest to our Technical Monitor and that our other findings were needed to support the activities conducted under this prime issue. The outcomes of our related investigations, nevertheless, are included in the appendices accompanying this report. The relevance of the materials in these appendices are, therefore, discussed only briefly within the body of the report. Here, results are presented of a priori and a posterior analyses for validity assessments of assumed Probability Density Function (PDF) methods as potential subgrid scale (SGS) closures for LES of turbulent reacting flows. Simple non-premixed reacting systems involving an isothermal reaction of the type A + B yields Products under both chemical equilibrium and non-equilibrium conditions are considered. A priori analyses are conducted of a homogeneous box flow, and a spatially developing planar mixing layer to investigate the performance of the Pearson Family of PDF's as SGS models. A posteriori analyses are conducted of the mixing layer using a hybrid one-equation Smagorinsky/PDF SGS closure. The Smagorinsky closure augmented by the solution of the subgrid turbulent kinetic energy (TKE) equation is employed to account for hydrodynamic fluctuations, and the PDF is employed for modeling the effects of scalar fluctuations. The implementation of the model requires the knowledge of the local values of the first two SGS moments. These are provided by additional modeled transport equations. In both a priori and a posteriori analyses, the predicted results are appraised by comparison with subgrid averaged results generated by DNS. Based on these results, the paths to be followed in future investigations are identified.

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

149

DNS of turbulent flow in a driven cavity and their analysis using proper orthogonal decomposition  

NASA Astrophysics Data System (ADS)

Direct Numerical Simulation (DNS) of 2D and 3D lid-driven cavity flows have been performed. The results have been analyzed using Proper Orthogonal Decomposition (POD). POD has been applied to a 2D driven cavity at Reynolds number 22,000 and to a 3D at Re = 10,000. The POD-basis-functions have been computed using the so-called 'snapshot' method of Sirovich. The 2D basisfunctions are used for a Galerkin projection of the Navier-Stokes equations. This results in a relatively low (20 to 80) dimensional dynamical behavior, that shows (almost) the same dynamical behavior, in short and long term, as the DNS. Moreover, if the Reynolds number is set to 11,000, the 80-dimensional dynamical system has (almost) the same periodic solution as the 2D Navier-Stokes equations have at Re = 11,000.

Cazemier, W.; Verstappen, R. W. C. P.; Veldman, A. E. P.

1994-12-01

150

Probing space-time through numerical simulations  

NASA Astrophysics Data System (ADS)

Einstein's equations describe gravity using an elegant but complicated set of equations. Finding astrophysically relevant solutions to these equations requires the most sophisticated numerical algorithms and powerful supercomputers available. The search for astrophysical solutions has made numerical relativity one of the most active areas of research in gravitational physics. Of particular interest in numerical relativity has been simulating the inspiral and coalescence of compact binaries involving black holes and neutrons stars. The outcome from these simulations will bring general relativity into harmony with the observations of gravitational radiation that are expected to take place in the immediate future. This article highlights current progress in numerical relativity. It also attempts to envision the future of this field and its integration with gravitational wave astronomy.

Laguna, Pablo

2005-11-01

151

Numerical simulations of strong incompressible magnetohydrodynamic turbulence  

SciTech Connect

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

152

Numerical simulation of textile flexibility testing  

Microsoft Academic Search

A non-linear numerical simulation of a standard procedure for textile flexibility testing is performed using discretised beam bending model. Geometric non-linearity due to large deflections is traced using incremental method. Linear moment-curvature response is assumed, as well as constant curvature of a finite element of the beam. Numerical procedure is incorporated into a PC programme producing graphical results for the

Željko Šomodi; Anica Hursa; Dubravko Rogale

2003-01-01

153

DNS of Unsteady Heat Transfer Increase on a Curved Surface Due to Wake-Induced Turbulence  

Microsoft Academic Search

\\u000a From experimental studies it is well established that free-stream and wake-induced turbulence can increase the heat transfer\\u000a on curved surfaces such as turbine blades or cylinders even if the mean flow matches corresponding laminar velocity profiles.\\u000a Here, preliminary results of an investigation using (embedded) Direct Numerical Simulation (DNS) are reported that aim at\\u000a identifying the responsible physical mechanisms for this

D. von Terzi; L. Venema; H.-J. Bauer; W. Rodi

154

Numerically simulating the sandwich plate system structures  

NASA Astrophysics Data System (ADS)

Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.

Feng, Guo-Qing; Li, Gang; Liu, Zhi-Hui; Niu, Huai-Lei; Li, Chen-Feng

2010-09-01

155

Numerical simulation of radial compressor stage  

NASA Astrophysics Data System (ADS)

Article describes numerical simulations of air flow in radial compressor stage in NUMECA CFD software. In simulations geometry variants with and without seals are used. During tasks evaluating was observed seals influence on flow field and performance parameters of compressor stage. Also is described CFDresults comparison with results from design software based on experimental measurements and monitoring of influence of seals construction on compressor stage efficiency.

Syka, T.; Lu?á?ek, O.

2013-04-01

156

Numerical simulation of underwater explosion loads  

Microsoft Academic Search

Numerical simulation of TNT underwater explosion was carried out with AUTODYN software. Influences of artificial viscosity\\u000a and mesh density on simulation results were discussed. Detonation waves in explosive and shock wave in water during early\\u000a time of explosion are high frequency waves. Fine meshes (less than 1,mm) in explosive and water nearby, and small linear viscosity\\u000a coefficients and quadratic viscosity

Chunliang Xin; Gengguang XU; Kezhong Liu

2008-01-01

157

Numerical simulations of iced airfoils and wings  

Microsoft Academic Search

A numerical study was conducted to understand the effects of simulated ridge and leading-edge ice shapes on the aerodynamic performance of airfoils and wings. In the first part of this study, a range of Reynolds numbers and Mach numbers, as well as ice-shape sizes and ice-shape locations were examined for various airfoils with the Reynolds-Averaged Navier-Stokes approach. Comparisons between simulation

Jianping Pan

2004-01-01

158

Numerical Simulations of Disk-Planet Interactions  

Microsoft Academic Search

The aim of this thesis is the study the dynamical interactions occurring between a forming planet and its surrounding protostellar environment. This task is accomplished by means of both 2D and 3D numerical simulations. The first part of this work concerned global simulations in 3D. These were intended to investigate large-scale effects caused by a Jupiter-size body still in the

Gennaro D'Angelo

2003-01-01

159

Numerical Simulations of Solar Acoustic Field  

NASA Astrophysics Data System (ADS)

We present numerical simulations of propagation of acoustic waves in the upper convection zone using a standard solar model and realistic equation of state (OPAL model). The main goals are to study properties of solar waves for various excitation sources and interaction of these waves with spatial inhomogeneities, and also to generate artificial wave fields for testing local helioseismic diagnostics of the solar interior, currently used for SOHO/MDI and GONG data. In our numerical model, non-reflecting boundary conditions based on absorbing 3D perfectly matched layer (PML) are imposed at all boundaries of the computational domain in Cartesian geometry. This prevents spurious reflection of acoustic waves from boundaries back to the computational domain. The top non-reflecting boundary is set in the solar atmosphere above the temperature minimum. This allowed us to realistically model the wave reflection from the solar atmosphere. We have developed a special PLM model, numerically stable in the case of a stratified medium with gravity, and investigated and tested various numerical schemes (including high-order dispersion-relation-preserving scheme). Numerical simulations have been carried out on parallel computers for different kinds of acoustic sources(force and energy sources). Single point sources are used to calculate realistic Green functions required for holographic seismic imaging. Simulated acoustic field from multiple sources randomly distributed below the photosphere is used as artificial data for testing helioseismic inversions, accuracy of Born and ray approximations.

Parchevsky, K. V.; Kosovichev, A. G.

2005-12-01

160

Numerical Simulation of Pulse Detonation Engine Phenomena  

Microsoft Academic Search

This paper describes one- and two-dimensional numerical simulations, with simplified as well as full reaction kinetics, of a single cycle pulse detonation engine (PDE). The present studies explore the igni- tion energies associated with the initiation of a det- onation in the PDE tube, and quantify reactive flow phenomena, performance parameters, and noise gen- eration associated with full and simplified

Xing He; Ann R. Karagozian

2003-01-01

161

Numerical recipes for mold filling simulation  

Microsoft Academic Search

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

Doug Kothe; Damir Juric; Kin Lam; B. Lally

1998-01-01

162

Numerical simulation of molecular uptake via electroporation  

Microsoft Academic Search

A numerical study of electroporation-mediated molecular delivery is presented. The model consists of the Nernst–Planck equations for species transport, coupled with an asymptotic Smoluchowski equation for membrane permeabilization. The transfer of calcium ions into a Chinese Hamster Ovary cell is simulated. The results reveal important physical insights. First, for this particular case, ion electrophoresis plays an important role, and is

Jianbo Li; Hao Lin

2011-01-01

163

Numerical simulation of magnetotelluric fields at Stromboli  

Microsoft Academic Search

1 Summary Stromboli is a small volcanic island in the Mediterranean Sea off the west coast of Italy. It is famous for its characteristic Strombolian eruptions. To get a better understanding of these processes further explorations of the inner structure of the volcano are essential. By carrying out numerical simulations, we aim at showing that the

A. Franke; S. Kütter; R.-U. Börner; K. Spitzer

164

Numerical simulation of axisymmetric turbulent jets  

Microsoft Academic Search

The flow in axisymmetric turbulent jets is numerically simulated with the use of a semi-empirical second-order turbulence\\u000a model including differential transport equations for the normal Reynolds stresses. Calculated results are demonstrated to\\u000a agree with experimental data.

A. G. Demenkov; B. B. Ilyushin; G. G. Chernykh

2008-01-01

165

NUMERICAL SIMULATION OF WATER ABSORPTION IN SOFTWOOD  

Microsoft Academic Search

Whereas water can frequently come in contact with wood-based building envelope components, little work has tried to measure and model moisture uptake in orthotropic wood. This paper presents experimental results and numerical simulations of water uptake in softwood. Water absorption coefficients were measured and shown to vary according to the orientation of the fiber grain. Helium pycnometry was employed to

Luis Candanedo; Dominique Derome

2005-01-01

166

Numerical simulation of direct energy conversion  

Microsoft Academic Search

Use of numerical simulation to study Post's (1970) electrostatic scheme for direct conversion of fusion energy to electricity. Using a two-dimensional electrostatic approach, it is shown that useful efficiency information may be obtained from monoenergetic low-density (ratio of ion number density to critical density much less than 1) ion beams. Using the generated efficiency function, it is possible to find

S. J. Gitomer; C. K. Krishnan

1974-01-01

167

Numerical simulation of plasma opening switches  

SciTech Connect

Plasma Opening Switches have been examined numerically with the aid of the ANTHEM plasma simulation model. A generic bi-cylindrical switch is studied. The switching of generator pulses ranging from 50 ns to 1 ..mu..sec is reviewed, for a variety of plasma fill lengths and densities, and for a range of resistive loads. 7 refs., 9 figs.

Mason, R.J.; Jones, M.E.; Bergman, C.D.

1989-01-01

168

Numerical Simulation of Compressible Plane Jets  

Microsoft Academic Search

Spatial direct numerical simulation of compressible plane jets exhausting into a parallel stream has been performed. The mathematical model is inviscid and captures large-scale mixing events, such as vortex roll-up and multiple pairings. These are the most dynamically important features, even in the fully developed turbulent region in free shear flows such as the plane jet. Application and performance of

R. S. Reichert; S. Biringen

1996-01-01

169

Even a small stenosis asymmetry can trigger post-stenotic transition to turbulence: Implications for modeling and simulation  

Microsoft Academic Search

Direct numerical simulations (DNS) were employed to illustrate that even a small stenosis asymmetry can trigger post-stenotic transition to turbulence. DNS predicted a laminar flow field downstream of an axisymmetric stenosis but the introduction of a geometric perturbation at the stenosis throat, in the form of an eccentricity that was only 5% of the main vessel diameter, resulted in stenotic

Sonu S Varghese

2006-01-01

170

Direct numerical simulation of supercritical annular electroconvection.  

PubMed

We use direct numerical simulation to study electrically driven convection in an annular thin film. The simulation models a laboratory experiment that consists of a weakly conducting, submicron thick liquid crystal film suspended between two concentric electrodes. The film is driven to convect by imposing a sufficiently large voltage across it. The flow is driven by a surface charge density inversion which is unstable to the imposed electrical force. This mechanism is closely analogous to the mass density inversion which is unstable to the buoyancy force in conventional, thermally driven Rayleigh-Bénard convection. The simulation uses a pseudospectral method with Chebyshev polynomials in the radial direction and Fourier modes in the azimuthal direction. The numerical results, which are in good agreement with previous experimental data and theoretical predictions, reveal several insights. The mode competition near a codimension-two point exhibits hysteresis. The primary bifurcation is supercritical for a broad range of fluid and geometrical parameters. PMID:17930140

Tsai, Peichun; Daya, Zahir A; Deyirmenjian, Vatche B; Morris, Stephen W

2007-08-10

171

Numerical well test simulations in heterogeneous reservoirs  

SciTech Connect

The poster presents a software package which is devoted to the numerical simulation of well tests. The package is made of three main modules: (1) PRE PROCESSOR - The user friendly front end to be used to input the reservoir model characteristics and the test data. This module is running on PC`s under MS-Windows. (2) SIMULATOR - The numerical simulator which can be run on any kind of computer from PC`s to mainframe. (3) POST PROCESSOR - The graphical post processor which displays the results of the simulation. Either pressure maps and well results are managed. This module is also running on PC`s under MS-Windows. The simulator provides several advanced features to help the user to identify the reservoir model which best fits the well model pressure to the field recorded data: (1) INVESTIGATION AREA - The location of the investigation area and its apparent permeability can be computed all along the test period thus giving the user a better understanding of the well pressure behavior. (2) FACIES IDENTIFICATION - Whenever the reservoir description is made of reservoir facies coming from geostatistical simulation, the gradients of the well pressure versus the facies permeabilities can be computed. A non linear constrained optimization process can then be used to compute the facies properties which give the best model restitution of the recorded test pressure.

Blanc, G.; Guerillot, D.; Rahon, D. [Institut Francais du Petrole, Pau (France)

1995-08-01

172

Direct numerical simulation of turbulent, chemically reacting flows  

NASA Astrophysics Data System (ADS)

This dissertation: (i) develops a novel numerical method for DNS/LES of compressible, turbulent reacting flows, (ii) performs several validation simulations, (iii) studies auto-ignition of a hydrogen vortex ring in air and (iv) studies a hydrogen/air turbulent diffusion flame. The numerical method is spatially non-dissipative, implicit and applicable over a range of Mach numbers. The compressible Navier-Stokes equations are rescaled so that the zero Mach number equations are discretely recovered in the limit of zero Mach number. The dependent variables are co--located in space, and thermodynamic variables are staggered from velocity in time. The algorithm discretely conserves kinetic energy in the incompressible, inviscid, non--reacting limit. The chemical source terms are implicit in time to allow for stiff chemical mechanisms. The algorithm is readily applicable to complex chemical mechanisms. Good results are obtained for validation simulations. The algorithm is used to study auto-ignition in laminar vortex rings. A nine species, nineteen reaction mechanism for H2/air combustion proposed by Mueller et al. [37] is used. Diluted H 2 at ambient temperature (300 K) is injected into hot air. The simulations study the effect of fuel/air ratio, 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 MR (Mastorakos et al. [32]). Subsequent evolution of the flame is not predicted by zetaMR; a most reactive temperature TMR 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 towards 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. We then study auto-ignition of turbulent H2/air diffusion flames using the Mueller et al. [37] mechanism. Isotropic turbulence is superimposed on an unstrained diffusion flame where diluted H 2 at ambient temperature interacts with hot air. Both, unity and non-unity Lewis number are studied. The results are contrasted to the homogeneous mixture problem and laminar diffusion flames. Results show that auto-ignition occurs in fuel lean, low vorticity, high temperature regions with low scalar dissipation around a most reactive mixture fraction, zetaMR (Mastorakos et al. [32]). However, unlike the laminar flame where auto-ignition occurs at zetaMR, the turbulent flame auto-ignites over a very broad range of zeta around zetaMR, which cannot completely predict the onset of ignition. The simulations also study the effects of three-dimensionality. Past two--dimensional simulations (Mastorakos et al. [32]) show that when flame fronts collide, extinction occurs. However, our three dimensional results show that when flame fronts collide; they can either increase in intensity, combine without any appreciable change in intensity or extinguish. This behavior is due to the three--dimensionality of the flow.

Doom, Jeffrey Joseph

173

Numerical simulation of an electroweak oscillon  

SciTech Connect

Numerical simulations of the bosonic sector of the SU(2)xU(1) electroweak standard model in 3+1 dimensions have demonstrated the existence of an oscillon--an extremely long-lived, localized, oscillatory solution to the equations of motion--when the Higgs mass is equal to twice the W{sup {+-}} boson mass. It contains total energy roughly 30 TeV localized in a region of radius 0.05 fm. A detailed description of these numerical results is presented.

Graham, N. [Department of Physics, Middlebury College, Middlebury, Vermont 05753 (United States)

2007-10-15

174

Interpreting Observations of GRBs with Numerical Simulations  

NASA Astrophysics Data System (ADS)

We show how numerical simulations have triggered the interpretation of GRB 101225A, so-called, the “Christmas burst.” This event is unusual because of its extremely long ?-ray emission and optical counterpart. The X-ray spectrum shows a black-body component which is present on a handful of nearby gamma-ray bursts (GRBs). Numerical models have shown that the atypical properties of this GRB can be explained by the interaction between an ultrarelativistic jet and high-density ejecta, which naturally results after the dynamical common-envelope phase of the merger between a neutron star and the He core of a red giant binary system.

Aloy, M. A.; Cuesta-Martínez, C.; Mimica, P.; Obergaulinger, M.; Thöne, C. C.; Ugarte Postigo, A.; Fryer, C.; Page, K. L.; Gorosabel, J.; Perley, D. A.; Kouveliotou, C.; Janka, H. T.; Racusin, J. L.; Christmas Burts Collaboration

2013-04-01

175

Numerical simulations for transonic aerodynamic flows  

NASA Astrophysics Data System (ADS)

Transonic flow is an important aerodynamic phenomenon that occurs in the high subsonic Mach number flight regime. This paper presents the development of a numerical simulation for three-dimensional transonic aerodynamic flows around an isolated wing. The mathematical formulation is based on a transonic small-disturbance equation, which is a nonlinear and mixed elliptic-hyperbolic partial-differential equation. A Newton-like iterative scheme is developed for solving the transonic equation, and it is used in conjunction with a preconditioned minimal-residual algorithm. The numerical technique is proven to be efficient and reliable. Computational results for transonic flows around the ONERA M6 wing are presented.

Wong, Yau Shu; Jiang, Hong

1991-04-01

176

Numerical simulation of groundwater flow on MPPs  

SciTech Connect

Mathematical models are often used to aid in the design and management of engineered remediation procedures. This paper discusses the numerical simulation of groundwater flow in three-dimensional heterogeneous porous media. A portable and scalable code called PARFLOW is being developed for massively parallel computers to enable the detailed modeling of large sites. This code uses a turning bands algorithm to generate a statistically accurate subsurface realization, and preconditioned conjugate gradients to solve the linear system that yields the flow velocity field. Preliminary numerical results for the LLNL site are presented.

Ashby, S.; Falgout, R.; Tompson, A. [Lawrence Livermore National Lab., CA (United States); Fogwell, T. [International Technology Corp., Martinez, CA (United States)

1994-03-01

177

Numerical simulation of centrifugal casting of pipes  

NASA Astrophysics Data System (ADS)

A numerical simulation model for the horizontal centrifugal pipe casting process was developed with the commercial simulation package Flow3D. It considers - additionally to mass, energy and momentum conservation equations and free surface tracking - the fast radial and slower horizontal movement of the mold. The iron inflow is not steady state but time dependent. Of special importance is the friction between the liquid and the mold in connection with the viscosity and turbulence of the iron. Experiments with the mold at controlled revolution speeds were carried out using a high-speed camera. From these experiments friction coefficients for the description of the interaction between mold and melt were obtained. With the simulation model, the influence of typical process parameters (e.g. melts inflow, mold movement, melt temperature, cooling media) on the wall thickness of the pipes can be studied. The comparison to results of pipes from production shows a good agreement between simulation and reality.

Kaschnitz, E.

2012-07-01

178

Numerical simulations of iced airfoils and wings  

NASA Astrophysics Data System (ADS)

A numerical study was conducted to understand the effects of simulated ridge and leading-edge ice shapes on the aerodynamic performance of airfoils and wings. In the first part of this study, a range of Reynolds numbers and Mach numbers, as well as ice-shape sizes and ice-shape locations were examined for various airfoils with the Reynolds-Averaged Navier-Stokes approach. Comparisons between simulation results and experimental force data showed favorable comparison up to stall conditions. At and past stall condition, the aerodynamic forces were typically not predicted accurately for large upper-surface ice shapes. A lift-break (pseudo-stall) condition was then defined based on the lift curve slope change. The lift-break angles compared reasonably with experimental stall angles, and indicated that the critical ice-shape location tended to be near the location of minimum pressure and the location of the most adverse pressure gradient. With the aim of improving the predictive ability of the stall behavior for iced airfoils, simulations using the Detached Eddy Simulation (DES) approach were conducted in the second part of this numerical investigation. Three-dimensional DES computations were performed for a series of angles of attack around stall for the iced NACA 23012 and NLF 0414 airfoils. The simulations for both iced airfoils provided the maximum lift coefficients and stall behaviors qualitatively consistent with experiments.

Pan, Jianping

179

Numerical simulation for hydrogen magnetic refrigeration  

NASA Astrophysics Data System (ADS)

We have built active magnetic regenerator (AMR) test apparatuses operated with a gas displacer to transfer the heat from magnetic material unit (AMR bed). Because finding an optimum parameter by experiment is not easy, numerical simulation is necessary to confirm the experimental conditions. As the first step of the project, we developed a 1-dimensional porous media model for hydrogen magnetic refrigerator with a Brayton-likeoperation cycle. This model has been calculated separately for heat exchange fluid and magnetic material. The results using two different magnetic materials have been compared.We confirmed that the simulation results agreed with experimental data of the internal gas displacer system.

Zhu, Yiyin; Hattori, Hideyuki; Matsumoto, Koichi; Yanagisawa, Yoshinori; Nakagome, Hideki; Numazawa, Takenori

2012-06-01

180

Issues in Numerical Simulation of Fire Suppression  

SciTech Connect

This paper outlines general physical and computational issues associated with performing numerical simulation of fire suppression. Fire suppression encompasses a broad range of chemistry and physics over a large range of time and length scales. The authors discuss the dominant physical/chemical processes important to fire suppression that must be captured by a fire suppression model to be of engineering usefulness. First-principles solutions are not possible due to computational limitations, even with the new generation of tera-flop computers. A basic strategy combining computational fluid dynamics (CFD) simulation techniques with sub-grid model approximations for processes that have length scales unresolvable by gridding is presented.

Tieszen, S.R.; Lopez, A.R.

1999-04-12

181

Numerical Simulation in a Supercirtical CFB Boiler  

NASA Astrophysics Data System (ADS)

The dimension of the hot circulation loop of the supercritical CFB boiler is large, and there are many unknowns and challenges that should be identified and resolved during the development. In order to realize a reasonable and reliable design of the hot circulation loop, numerical simulation of gas-solid flow in a supercritical CFB boiler was conducted by using FLUENT software. The working condition of hot circulation loop flow field, gas-solid flow affected by three unsymmetrical cyclones, air distribution and pressure drop in furnace were analyzed. The simulation results showed that the general arrangement of the 600MWe supercritical CFB boiler is reasonable.

Zhang, Yanjun; Gaol, Xiang; Luo, Zhongyang; Jiang, Xiaoguo

182

Numerical simulations of viscous Faraday waves  

NASA Astrophysics Data System (ADS)

We conduct a numerical exploration of the nonlinear dynamics of surface gravity-capillary waves in a fluid layer oscillating vertically in a gravitational field (i.e. the Faraday system). A number of intriguing experimental observations still cannot be explained by available theory, although progress has been made by incorporating the complex interplay between streaming flows generated by oscillating boundary layers and the oscillations that are responsible for them. We perform numerical simulations of the time-dependent incompressible Navier-Stokes equations describing the free surface flow that includes surface tension and the complex moving fluid interface. The numerical approach uses an arbitrary-Lagrangian-Eulerian formulation of a parallel spectral element solver. We explore a two-dimensional fluid layer with periodic and finite lateral boundary conditions, and use the results to quantify the resulting streaming flows which we relate to the overall wave dynamics and available theoretical predictions.

O'Connor, Nicholas; Knobloch, Edgar; Fischer, Paul; Paul, Mark

2007-11-01

183

Numerical simulation of gridded electrostatic lens.  

PubMed

Gridded electrostatic lenses are frequently used in extraction systems and low energy ion beam transport line. Typically, for numerical simulation the grid is treated as a metal plate transparent for beam particles. The influence of real grid geometry on the beam dynamics in the gridded lens has been investigated by KOBRA-3d code. Beam emittance growth for different lens parameters has been investigated. Approximating expressions for obtained results are presented. The grid geometry providing minimal beam distortions is proposed. PMID:22380339

Kropachev, G N; Alexeev, N N; Balabin, A I; Kulevoy, T V; Nikolaev, V I

2012-02-01

184

Numerical simulation of gridded electrostatic lens  

NASA Astrophysics Data System (ADS)

Gridded electrostatic lenses are frequently used in extraction systems and low energy ion beam transport line. Typically, for numerical simulation the grid is treated as a metal plate transparent for beam particles. The influence of real grid geometry on the beam dynamics in the gridded lens has been investigated by KOBRA-3d code. Beam emittance growth for different lens parameters has been investigated. Approximating expressions for obtained results are presented. The grid geometry providing minimal beam distortions is proposed.

Kropachev, G. N.; Alexeev, N. N.; Balabin, A. I.; Kulevoy, T. V.; Nikolaev, V. I.

2012-02-01

185

Numerical simulations for transonic aerodynamic flows  

Microsoft Academic Search

Transonic flow is an important aerodynamic phenomenon that occurs in the high subsonic Mach number flight regime. This paper presents the development of a numerical simulation for three-dimensional transonic aerodynamic flows around an isolated wing. The mathematical formulation is based on a transonic small-disturbance equation, which is a nonlinear and mixed elliptic-hyperbolic partial-differential equation. A Newton-like iterative scheme is developed

Yau Shu Wong; Hong Jiang

1991-01-01

186

Numerical simulation of gridded electrostatic lens  

SciTech Connect

Gridded electrostatic lenses are frequently used in extraction systems and low energy ion beam transport line. Typically, for numerical simulation the grid is treated as a metal plate transparent for beam particles. The influence of real grid geometry on the beam dynamics in the gridded lens has been investigated by KOBRA-3d code. Beam emittance growth for different lens parameters has been investigated. Approximating expressions for obtained results are presented. The grid geometry providing minimal beam distortions is proposed.

Kropachev, G. N.; Alexeev, N. N.; Balabin, A. I.; Kulevoy, T. V.; Nikolaev, V. I [Institute for Theoretical and Experimental Physics, Moscow (Russian Federation)

2012-02-15

187

Numerical simulations on ion acoustic double layers  

SciTech Connect

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

188

Numerical Simulations of a Relativistic Inverted Magnetron  

Microsoft Academic Search

A new design for an inverted magnetron is presented and modeled both analytically, using a single particle smooth bore relativistic approach, and numerically, using a massively parallel electromagnetic particle-in-cell code, Improved Concurrent Electromagnetic Particle-In-Cell (ICEPIC) code. Analysis and simulation confirm that the inverted magnetron design presented here is capable of oscillating in the ? mode at axial magnetic fields of

Timothy P. Fleming; Michael R. Lambrecht; Keith L. Cartwright

2010-01-01

189

Numerical simulation and nasal air-conditioning  

PubMed Central

Heating and humidification of the respiratory air are the main functions of the nasal airways in addition to cleansing and olfaction. Optimal nasal air conditioning is mandatory for an ideal pulmonary gas exchange in order to avoid desiccation and adhesion of the alveolar capillary bed. The complex three-dimensional anatomical structure of the nose makes it impossible to perform detailed in vivo studies on intranasal heating and humidification within the entire nasal airways applying various technical set-ups. The main problem of in vivo temperature and humidity measurements is a poor spatial and time resolution. Therefore, in vivo measurements are feasible only to a restricted extent, solely providing single temperature values as the complete nose is not entirely accessible. Therefore, data on the overall performance of the nose are only based on one single measurement within each nasal segment. In vivo measurements within the entire nose are not feasible. These serious technical issues concerning in vivo measurements led to a large number of numerical simulation projects in the last few years providing novel information about the complex functions of the nasal airways. In general, numerical simulations merely calculate predictions in a computational model, e.g. a realistic nose model, depending on the setting of the boundary conditions. Therefore, numerical simulations achieve only approximations of a possible real situation. The aim of this review is the synopsis of the technical expertise on the field of in vivo nasal air conditioning, the novel information of numerical simulations and the current state of knowledge on the influence of nasal and sinus surgery on nasal air conditioning.

Keck, Tilman; Lindemann, Jorg

2011-01-01

190

Numerical simulation of premixed turbulent methane combustion  

Microsoft Academic Search

With adaptive-grid computational methodologies and judicious use of compressible and low Mach number combustion models, we are carrying out three-dimensional, time-dependent direct numerical simulations of a laboratory-scale turbulent premixed methane burner. In the laboratory experiment, turbulence is generated by a grid located in the throat of a 50mm diameter circular nozzle; swirl is be introduced by four tangential air jets

Marc S. Day; John B. Bell; Ann S. Almgren; Vincent E. Beckner; Michael J. Lijewski; Robert Cheng; Ian Shepherd; Matthew Johnson

2003-01-01

191

Direct numerical simulation of a recorder.  

PubMed

The aeroacoustics of a recorder are studied using a direct numerical simulation based on the Navier-Stokes equations in two dimensions. Spatial maps for the air pressure and velocity give a detailed picture of vortex shedding near the labium. Changes in the spectrum as a result of variations in the blowing speed are also investigated. The results are in good semi-quantitative agreement with general results for these phenomena from experiments. PMID:23363126

Giordano, N

2013-02-01

192

Numerical simulation of multi-species diffusion  

Microsoft Academic Search

A numerical model has been developed to simulate the transport of several ionic species across a saturated concrete or mortar\\u000a sample. The chloride binding as well as the electrical coupling between the different ionic fluxes are included in the model\\u000a by using the Nernst-Planck system of equations. This model highlights which parameters affect substantially chloride penetration\\u000a into reinforced concrete structures

O. Truc; J.-P. Ollivier; L. O. Nilsson

2000-01-01

193

Numerical simulation for fan broadband noise prediction  

Microsoft Academic Search

In order to elucidate the broadband noise of fan, the numerical simulation of fan operating at two different rotational speeds\\u000a is carried out using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The computed results\\u000a are compared to experiment to estimate its accuracy and are found to show good agreement with experiment. A method is proposed\\u000a to evaluate the turbulent kinetic

Takaaki Hase; Nobuhiko Yamasaki; Tsutomu Ooishi

2011-01-01

194

Numerical Simulation of Riblet Controlled Spatial Transition  

Microsoft Academic Search

\\u000a To analyze the fundamental physical mechanism which determines the damping effect of a riblet surface on three-dimensional\\u000a transition several numerical simulations of spatial transition in a flat plate zero-pressure gradient boundary layer above\\u000a a riblet wall are performed in this study. Two types of transition are investigated. The first type of transition, namely\\u000a K-type transition, is induced by a dominant

Stephan Klumpp; Matthias Meinke; Wolfgang Schröder

195

Numerical Simulation of Two-Phase Flow in Severely Damaged Core Geometries  

SciTech Connect

In the event of a severe accident in a nuclear reactor, the oxidation, dissolution and collapse of fuel rods is likely to change dramatically the geometry of the core. A large part of the core would be damaged and would look like porous medium made of randomly distributed pellet fragments, broken claddings and relocated melts. Such a complex medium must be cooled in order to stop the accident progression. IRSN investigates the effectiveness of the water re-flooding mechanism in cooling this medium where complex two-phase flows are likely to exist. A macroscopic model for the prediction of the cooling sequence was developed for the ICARE/CATHARE code (IRSN mechanistic code for severe accidents). It still needs to be improved and assessed. It appears that a better understanding of the flow at the pore scale is necessary. As a result, a direct numerical simulation (DNS) code was developed to investigate the local features of a two-phase flow in complex geometries. In this paper, the Cahn-Hilliard model is used to simulate flows of two immiscible fluids in geometries representing a damaged core. These geometries are synthesized from experimental tomography images (PHEBUS-FP project) in order to study the effects of each degradation feature, such as displacement and fragmentation of the fuel rods and claddings, on the two-phase flow. For example, the presence of fragmented fuel claddings is likely to enhance the trapping of the residual phase (either steam or water) within the medium which leads to less flow fluctuations in the other phase. Such features are clearly shown by DNS calculations. From a series of calculations where the geometry of the porous medium is changed, conclusions are drawn for the impact of rods damage level on the characteristics of two-phase flow in the core. (authors)

Meekunnasombat, Phongsan; Fichot, Florian [Institute of Radioprotection and Nuclear Safety - IRSN, BP 17 - 92262 Fontenay-aux-Roses Cedex 31, avenue de la Division Leclerc 92260 Fontenay-aux-Roses (France); Quintard, Michel [Institut de Mecanique des Fluides de Toulouse, 1 Allee du Professeur Camille Soula, 31400 Toulouse (France)

2006-07-01

196

Direct Numerical Simulation on a Cartesian Mesh of the Flow through a Tube Bundle  

NASA Astrophysics Data System (ADS)

In this paper, we present a three-dimensional direct numerical simulation (DNS) of a turbulent flow through a staggered tube bundle. The Navier-Stokes equations are discretized on a staggered Cartesian grid with the help of the finite-volume approach. The complex geometry of the tube bundle is implemented by the diagonal cartesian method (DCM). The advantage of this method, in comparison with body-fitted coordinate approaches, is that it leads to less complicated algorithms and, therefore, to more efficient computations. The principle of this method is described in this paper. Simulations of the flow through a tube bundle are carried out at Re=6000 on four different meshes with various grid spacings. Results of the simulations on the finest mesh are compared with the experimental data of Simonin and Barcouda [Measurements of fully developed turbulent flow across tube bundle. In 3ème Conférence Internationale sur les Applications de l'Anéemometrie Laser à la Mécanique des Fluides, 1986] and with the large-eddy simulations (LES) of Rollet-Miet et al. ["LES and RANS of turbulent flow in tube bundles", Int. J. Heat Fluid Flow, 20 (1999) pp. 241-254]. Based on this comparison we conclude that an accurate simulation of a flow through a tube bundle can be performed with the DCM.

Moulinec, C.; Pourquié, M. J. B. M.; Boersma, B. J.; Buchal, T.; Nieuwstadt, F. T. M.

2004-01-01

197

Linear stability analysis and direct numerical simulation of a miscible two-fluid channel flow  

NASA Astrophysics Data System (ADS)

The temporal evolution of an initially laminar two-fluid channel flow is investigated using linear stability analysis and direct numerical simulation. The stability of a two-fluid shear flow is encountered in numerous situations, including water wave generation by wind, atomization of fuels, aircraft deicing and nuclear reactor cooling. The application of particular interest in this study is liquefying hybrid combustion, for which the two-fluid channel flow is used as a model problem to characterize the relevant mixing and entrainment mechanisms. The two fluids are miscible with dissimilar densities and viscosities. The thickness of one of the fluid layers is much smaller than that of the other, with the denser and more viscous fluid comprising the thin layer. Linear stability analysis is used to identify possibly unstable modes in the two-fluid configuration. The analysis is considered for two different situations. In one case, the fluid density and viscosity change discontinuously across a sharp interface, while in the other, the fluids are separated by a finite thickness transition layer, over which the fluid properties vary continuously. In the sharp interface limit, the linear stability is governed by an Orr-Sommerfeld equation in each fluid layer, coupled by boundary conditions at the interface. A numerical solution of the system of equations is performed using a Chebyshev spectral collocation method. In the case where the fluids are separated by a finite thickness transition zone, an Orr-Sommerfeld-type equation is solved with the compound matrix method. The non-linear stages of the flow evolution are investigated by direct numerical simulation. In a temporal simulation, two of the three spatial dimensions are periodic. Fourier spectral discretization is used in these dimensions, while a compact finite difference scheme is utilized in the non-periodic direction. The time advancement is performed by a projection method with a third order Adams-Bashforth-Moulton predictor-corrector scheme. Initial conditions for the DNS are supplied by the linear stability analysis. Linear stability analysis indicates that the thickness of the transition zone between the fluids has a significant impact on the amplification of the two least stable modes present in the two-fluid channel flow. Compared to the sharp interface limit, one of the modes is damped and the other one is either amplified or damped depending on the Reynolds number. Two dissimilar entrainment mechanisms are observed in the DNS calculations, corresponding to these two modes. One results in significantly more entrainment and mixing between the two fluids. This mechanism exhibits a greater degree of vorticity generation, particularly due to the baroclinic effect.

Haapanen, Siina Ilona

198

Numeric Simulation Tools of the IMPEx Infrastructure  

NASA Astrophysics Data System (ADS)

The EU-FP7 Project "Integrated Medium for Planetary Exploration" (IMPEx) was established as a result of scientific collaboration between institutions across Europe and is working on the integration of a set of interactive data analysis and modeling tools in the field of space plasma physics. These tools are comprised of numerical Hybrid/MHD and analytical Paraboloid magnetospheric models from the simulation sector as well as AMDA, ClWeb and 3DView from the data analysis and visualization sector. The basic feature of IMPEx consists in connection of different data sources, including archived computational simulation results and observational data, in order to analyse and visualize scientific data by means of interactive web-based tools. In this presentation we introduce Hybrid and Magnetohydrodynamic Modelling (HMM) environment which is an example of simulation services within IMPEx. HMM includes two global numerical hybrid models (a hybrid model HYB from FMI and a hybrid model from LATMOS) and magnetohydrodynamic model (GUMICS) from FMI. Especially, we introduce the web service, Hybrid Web Archive[1] which enables access to the simulation runs made by HYB and GUMICS models in the IMPEx HMM environment.

Kallio, E. J.; Khodachenko, M. L.; Génot, V.; Schmidt, W.; Jarvinen, R.; Häkkinen, L.; Al-Ubaidi, T.; Topf, F.; Modolo, R.; Hess, S.; Alexeev, I. I.

2012-09-01

199

Direct numerical simulations and modeling of jets in crossflow  

NASA Astrophysics Data System (ADS)

Jets in crossflow are central to a variety of applications such as fuel injection, gas turbine combustion and film-cooling. Direct Numerical Simulations are used to study the different aspects of round jets in a crossflow. The first problem studies the effect of jet and crossflow velocity profiles on jet trajectories and the near-field. A new scaling law for the jet trajectory is proposed, that accounts for these parameters. The proposed scaling is shown to be a significant improvement over current scaling laws. DNS of a turbulent jet in crossflow is performed at conditions corresponding to an experiment (Su & Mungal 2004). Detailed comparison shows good agreement with experiment, and additional quantities, not available experimentally, are presented. Turbulent kinetic energy budget is computed, and is used to suggest possible reasons for the difficulty experienced by current engineering models in predicting this complex flow. A predictor-corrector approach is implemented to compute passive scalar transport. This ensures that the local scalar concentration is always within bounds. The passive scalar is introduced along with the jet fluid, once the velocity field is statistically stationary. Mean scalar profiles show a good agreement when compared to the experiment. The scalar field is used to compute entrainment of the crossflow fluid by the jet, which is greater than that in a regular jet. The reasons for a transverse jet's enhanced entrainment are explained in terms of the pressure field in the vicinity of the jet. A two-dimensional model problem is used to study jet cross-section deformation. The model jet deforms at its trailing edge, exhibits the Kelvin-Helmholtz instability at its outer edges, and---later---yields a counter-rotating vortex pair (CVP). The model jet experiences constant acceleration in its initial stages, and moves at constant velocity at longer times. Deformation of the jet cross-section may be explained in terms of the pressure field that the crossflow fluid imposes on the jet, and the acceleration that the jet experiences. It is shown that the CVP is formed even in two dimensions, and that the pipe is not necessary.

Muppidi, Suman

200

Development and parallelization of a direct numerical simulation to study the formation and transport of nanoparticle clusters in a viscous fluid  

NASA Astrophysics Data System (ADS)

The direct numerical simulation (DNS) offers the most accurate approach to modeling the behavior of a physical system, but carries an enormous computation cost. There exists a need for an accurate DNS to model the coupled solid-fluid system seen in targeted drug delivery (TDD), nanofluid thermal energy storage (TES), as well as other fields where experiments are necessary, but experiment design may be costly. A parallel DNS can greatly reduce the large computation times required, while providing the same results and functionality of the serial counterpart. A D2Q9 lattice Boltzmann method approach was implemented to solve the fluid phase. The use of domain decomposition with message passing interface (MPI) parallelism resulted in an algorithm that exhibits super-linear scaling in testing, which may be attributed to the caching effect. Decreased performance on a per-node basis for a fixed number of processes confirms this observation. A multiscale approach was implemented to model the behavior of nanoparticles submerged in a viscous fluid, and used to examine the mechanisms that promote or inhibit clustering. Parallelization of this model using a masterworker algorithm with MPI gives less-than-linear speedup for a fixed number of particles and varying number of processes. This is due to the inherent inefficiency of the master-worker approach. Lastly, these separate simulations are combined, and two-way coupling is implemented between the solid and fluid.

Sloan, Gregory James

201

Direct numerical simulation of ignition front propagation in a constant volume with temperature inhomogeneities. I. Fundamental analysis and diagnostics  

SciTech Connect

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry with a view to providing better understanding and modeling of combustion processes in homogeneous charge compression-ignition engines. Numerical diagnostics are developed to analyze the mode of combustion and the dependence of overall ignition progress on initial mixture conditions. The roles of dissipation of heat and mass are divided conceptually into transport within ignition fronts and passive scalar dissipation, which modifies the statistics of the preignition temperature field. Transport within ignition fronts is analyzed by monitoring the propagation speed of ignition fronts using the displacement speed of a scalar that tracks the location of maximum heat release rate. The prevalence of deflagrative versus spontaneous ignition front propagation is found to depend on the local temperature gradient, and may be identified by the ratio of the instantaneous front speed to the laminar deflagration speed. The significance of passive scalar mixing is examined using a mixing timescale based on enthalpy fluctuations. Finally, the predictions of the multizone modeling strategy are compared with the DNS, and the results are explained using the diagnostics developed. (author)

Chen, Jacqueline H.; Hawkes, Evatt R.; Sankaran, Ramanan [Reacting Flow Research Department, Combustion Research Facility, Sandia National Laboratories, P.O. Box 969 MS 9051, Livermore, CA 94551-0969 (United States); Mason, Scott D. [Lockheed Martin Corporation, Sunnyvale, CA 94089 (United States); Im, Hong G. [Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125 (United States)

2006-04-15

202

Numerical Simulation of Fluid Mud Gravity Currents  

NASA Astrophysics Data System (ADS)

Fluid mud bottom gravity currents are simulated numerically using a commercial computational fluid dynamics software, ANSYS-Fluent. In this study, Eulerian-Eulerian multi-fluid method is selected since this method treats all phases in a multiphase system as interpenetrated continua. There are three different phases in the computational model constructed for this study: water, fluid mud, and air. Water and fluid mud are defined as two miscible fluids and the mass and momentum transfers between these two phases are taken into account. Fluid mud, which is a dense suspension of clay particles and water, is defined as a single-phase non-Newtonian fluid via user-defined-functions. These functions define the physical characteristics (density, viscosity, etc.) of the fluid mud and these characteristics vary with changing suspension concentration due to mass transfer between the fluid mud and the water phase. Results of this two-dimensional numerical model are verified with data obtained from experiments conducted in a laboratory flume with a lock-release set-up. Numerical simulations are currently being conducted to elucidate turbulent entrainment of ambient water into fluid mud gravity currents. This study is motivated by coastal dredge disposal operations.

Yilmaz, N. A.; Testik, F. Y.

2011-12-01

203

Numerical Simulation of Extreme European Windstorms  

NASA Astrophysics Data System (ADS)

Extreme synoptic storms present a significant economic risk in Europe mostly due to high wind gusts. This study focuses on understanding the most extreme storms that hit the European continent in terms of their dynamic and thermodynamic properties, utilizing high resolution numerical simulations of storms extracted from GCM runs. We have performed an ensemble of GCM simulations of over 2000 years, extracted tracks of storms produced by the GCM, downscaled these storms with WRF at a relatively high resolution (50km), and finally estimated their incurred economic loss using our proprietary catastrophe model. We choose a small set of the most extreme storms (in terms of economic loss) to analyze in more detail in the following way: 1. Identify common characteristics between extreme storms in terms of their evolution, vertical and horizontal structure, and the synoptic situation in which they are embedded. 2. Perform a series of numerical experiments with increasing WRF resolution and investigate changes in the storm intensity, size, and structure. The overall objective of this paper is to provide a clear understanding of the nature of extreme events and the numerical means needed to investigate them.

Mitas, C.

2010-12-01

204

Influence of polymer additives on turbulent energy cascading in forced homogeneous isotropic turbulence studied by direct numerical simulations  

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) were performed for the forced homogeneous isotropic turbulence (FHIT) with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading influenced by drag-reducing effects. The finite elastic non-linear extensibility-Peterlin model (FENE-P) was used as the conformation tensor equation for the viscoelastic polymer solution. Detailed analyses of DNS data were carried out in this paper for the turbulence scaling law and the topological dynamics of FHIT as well as the important turbulent parameters, including turbulent kinetic energy spectra, enstrophy and strain, velocity structure function, small-scale intermittency, etc. A natural and straightforward definition for the drag reduction rate was also proposed for the drag-reducing FHIT based on the decrease degree of the turbulent kinetic energy. It was found that the turbulent energy cascading in the FHIT was greatly modified by the drag-reducing polymer additives. The enstrophy and the strain fields in the FHIT of the polymer solution were remarkably weakened as compared with their Newtonian counterparts. The small-scale vortices and the small-scale intermittency were all inhibited by the viscoelastic effects in the FHIT of the polymer solution. However, the scaling law in a fashion of extended self-similarity for the FHIT of the polymer solution, within the presently simulated range of Weissenberg numbers, had no distinct differences compared with that of the Newtonian fluid case.

Li, Feng-Chen; Cai, Wei-Hua; Zhang, Hong-Na; Wang, Yue

2012-11-01

205

Characteristics of a numerical fluid dynamics simulator  

SciTech Connect

John von Neumann envisioned scientists and mathematicians analyzing and controlling their numerical experiments on nonlinear dynamic systems interactively. We describe our concept of a real-time Numerical Fluid Dynamics Simulator NFDS, and derive its characteristics adopting the following as guiding principles: (a) that the performance characteristics (information output, throughput and storage) of the NFDS be defined by the maximum rate at which the researcher can absorb the results of his/her simulation, thus establishing an impedance match between man and machine, (b) that the NFDS off-load from the researcher's brain in every way possible the routine tasks of data analysis that can be done automatically, and (c) that the NFDS is operated as a dedicated experimental device, much as a wind tunnel, and that the researcher has complete control over the apparatus and experiment. We envision the NFDS to be composed of simulation processors, data storage devices, and image processing devices of extremely high power and capacity, interconnected by very high throughput communication channels. We present individual component performance requirements for both real-time and playback operating modes of the NFDS, using problems of current interest in fluid dynamics as examples.

Winkler, K.H.A.; Norman, M.L.; Norton, J.L.

1985-01-01

206

Toward Realistic Galaxy Formation by Numerical Simulations  

NASA Astrophysics Data System (ADS)

In most of numerical simulations of spiral galaxy formation, mass/spatial resolution is ~ 105-6 M_? and kpc or sub-kpc, therefore inhomogeneous structure of the ISM in galaxies is not resolved. This is the most serious defect in simulating star formation and its feedback during galaxy formation/evolution. Here we show an intrinsic structures of the ISM using 3-D high resolution hydrodynamic simulations of galactic disks. We show that the PDFs in globally stable, inhomogeneous ISM in galactic disks are well fitted by a single log-normal function over a wide density range. The dispersion of the log-normal PDF (LN-PDF) is larger for more gas-rich systems. Using the LN-PDF, we give a generalized version of Schmidt-Kennicutt law, i.e. SFR as a function of average gas density, a critical local density for star formation, and star formation efficiency. We also introduce our new project, “Project Milky Way”, in which we aim to resolve properly the cold, dense ISM, as found in above simulations, by ultra-high resolution during galaxy formation. We are planning to construct a special cluster for simulating formation of “Milky Way” using the next generation GRAPE.

Wada, K.; Saitoh, T. R.; Daisaka, H.; Norman, C. A.

207

Numerical simulation of platelet margination in microcirculation  

NASA Astrophysics Data System (ADS)

The adhesion of platelets to vascular walls is the first step in clotting. This process critically depends on the preferential concentration of platelets near walls. The presence of red blood cells, which are the predominant blood constituents, is known to affect the steady state platelet concentration and the dynamic platelet margination, but the underlying mechanism is not well understood to-day. We use a direct numerical simulation to study the platelet margination process, with particular emphasis on the Stokesian hydrodynamic interactions among red cells, platelets, and vessel walls. Well-known mechanical models are used for the shearing and bending stiffness of red cell membranes, and the stiffer platelets are modeled as rigid discoids. A boundary integral formulation is used to solve the flow field, where the numerical solution procedure is accelerated by a parallel O(N N) smooth particle-mesh Ewald method. The effects of red cell hematocrit and deformability will be discussed.

Zhao, Hong; Shaqfeh, Eric

2009-11-01

208

Numerical Simulations of Lithospheric Mantle Delamination  

NASA Astrophysics Data System (ADS)

Sudden uplift, extension, and increased igneous activity are often explained by rapid mechanical thinning of the lithospheric mantle (e.g., Kay and Kay (1993)). Two main thinning mechanisms have been proposed, convective removal of a thickened lithospheric root or delamination at the favor of a crustal decoupling level. The latter mechanism was first defined by Bird (1979) as the whole mantle lithosphere peeling away from the crust by the horizontal propagation of a shear zone at the crust mantle boundary. We performed 2-D numerical simulations of convection using a viscoplastic rheology with an effective viscosity depending strongly on temperature, depth, composition (crust/mantle), and stress. The simulations develop in four steps. (1) We first obtain "classical" sublithospheric convection for a long time period (~100~Myrs), yielding a slightly heterogeneous lithospheric temperature structure. (2) At some time, in some simulations, a strong thinning of the mantle occurs progressively in a small area (~100~km wide). This process puts the asthenosphere in direct contact with the lower crust. (3) Large pieces of mantle lithosphere then quickly sink into the mantle, by the horizontal propagation of a detachment level away from the "asthenospheric conduit". (4) Delamination recesses or stops when the lithospheric mantle slab break off. We determine the parameters (crustal thicknesses, activation energies, and friction coefficients) leading to the initiation of delamination (step 2). We find that delamination initiates where the Moho temperature is the higher, as soon as the crust and mantle viscosities are sufficiently low. Delamination may thus occur on Earth in orogenic settings when the crust is thick and the Moho temperature exceeds ~8000C. Simulations preformed with variable crustal thicknesses show that delamination initiates at the base of the deeper crust, but does not propagate along the base of the shallower crust. A few 3-D numerical simulation have been performed using a Newtonian rheology with a viscosity depending strongly on temperature. A sharp viscosity increase is imposed within the lithosphere at a given depth to simulate a decupling level at the crust/mantle boundary. We then compare these 3-D simulations to 2-D simulations performed in the same conditions, to highlight differences between 2-D and 3-D delamination geometries. References: Bird, P., Continental delamination and the Colorado Plateau, \\it J. Geophys. Res., 84, 7561-7571, 1979. Kay, R. W. and Kay, S. M., Delamination and delamination magmatism, \\it Tectonophysics, 219, 177-189, 1993.

Morency, C.; Doin, M.

2002-12-01

209

Common DNS Operational and Configuration Errors  

Microsoft Academic Search

This memo describes errors often found in both the operation of Domain Name System (DNS) servers, and in the data that these DNS servers contain. This memo tries to summarize current Internet requirements as well as common practice in the operation and configuration of the DNS. This memo also tries to summarize or expand upon issues raised in (RFC 1537).

D. Barr

1996-01-01

210

DNScup: Strong Cache Consistency Protocol for DNS  

Microsoft Academic Search

Effective caching in Domain Name System (DNS) is crit- ical to its performance and scalability. Existing DNS only supports weak cache consistency by using the Time-To-Live (TTL) mechanism, which functions reasonably well in nor- mal situations. However, maintaining strong cache con- sistency in DNS as an indispensable exceptional handling mechanismhasbecomemore andmoredemandingfor three important objectives: (1) to quickly respond and handle

Xin Chen; Haining Wang; Shansi Ren; Xiaodong Zhang

211

Comprehensive Numerical Simulation of Laser Materials Processing  

NASA Astrophysics Data System (ADS)

The previous chapter concluded the physical discussion of laser materials processing (LMP). In this chapter no new physical concepts or theory of physical phenomena will be introduced. The objective of this chapter is rather to give an overview of how to analyse the complex system that is LaserMaterials Processing. As has been shown in great detail, the physical level of complexity is deep and analysis becomes extremely cumbersome if it is pursued on an analytical level. Albeit giving great insight into the detailed phenomena, whole processes and their sensitivity to ambient conditions and changes in process parameters or physical setup cannot be investigated using these methods alone. Here numerical simulation comes into play for the scientist investigating processes from an engineering point of view. Numerical simulation has an almost endless scope for system complexity and is only limited by the resources available and the time the investigator is prepared to wait for results. This final chapter should be read as a guide to how to get started.Some fundamental principles of discrete numerical modelling will be introduced and reference made to work by other authors. This, in the space available, can by no means be a comprehensive review, or a textbook of all the methods available and required. Nevertheless it should be seen as a starting point for investigators, at the doctoral student level, trying to get to terms with the task ahead, or for the researcher trying to move from practice to theory, from experiment to simulation, looking for a guide on what to look out for, where to go and which pitfalls to avoid.

Gross, Markus

212

Universality of the Kolmogorov Constant in Numerical Simulations of Turbulence.  

National Technical Information Service (NTIS)

Motivated by a recent survey of experimental data, we examine data on the Kolmogorov spectrum constant in numerical simulations of isotropic turbulence, using results both from previous studies and from new direct numerical simulations over a range of Rey...

P. K. Yeung Y. Zhou

1997-01-01

213

Direct numerical simulations of the double scalar mixing layer. Part II: Reactive scalars  

SciTech Connect

The reacting double scalar mixing layer (RDSML) is investigated as a canonical multistream flow and a model problem for simple piloted diffusion flames. In piloted diffusion flames, the reacting fuel and oxidizer streams are initially separated by a central pilot stream at stoichiometric composition. The primary purpose of this pilot is to delay the mixing of the pure streams until a stable flame base can develop. In such multistream systems, the modeling of turbulent scalar mixing is complicated by the multiple feed streams, leading to more complex fine-scale statistics, which remain as yet an unmet modeling challenge compared to the simpler two-feed system. In Part I we described how multimodal mixture fraction probability density functions (PDFs) and conditional scalar dissipation rates can be modeled with a presumed mapping function approach. In this work we present an efficient and robust extension of the modeling to a general multistream reacting flow and compare predictions to three-dimensional direct numerical simulations (DNS) of the RDSML with a single-step reversible chemistry model and varying levels of extinction. With high extinction levels, the interaction with the pilot stream is described. Additionally, state-of-the-art combustion modeling calculations including conditional moment closure (CMC) and stationary laminar flamelet modeling (SLFM) are performed with the newly developed mixing model. Excellent agreement is found between the DNS and modeling predictions, even where the PDF is essentially a triple-delta shape near the flame base, so long as extinction levels are moderate to low. The suggested approach outlined in this paper is strictly valid only for flows that can be described by a single mixture fraction. For these flows the approach should provide engineers with fine-scale models that are of accuracy comparable to those already available for binary mixing, at only marginally higher complexity and cost. (author)

Mortensen, Mikael [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, 2006 Sydney NSW (Australia); de Bruyn Kops, Stephen M. [Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003 (United States); Cha, Chong M. [Department of Mechanical Engineering, Indiana University-Purdue University, Indianapolis, IN 46202 (United States)

2007-06-15

214

Numerical simulations unravel the cosmic web.  

PubMed

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

215

Tornado structure interaction: a numerical simulation  

SciTech Connect

The effects of tornadoes on buildings are examined to determine the wind forces on structures. The American National Standards Institute (ANSI) has developed guidelines for building code requirements for the minimum wind loads a building must be designed to withstand. The conservatism or nonconservatism on the ANSI approach is evaluated by simulating tornado-structure interaction numerically with a two-dimensional fluid dynamics computer code and a vortex model. Only external pressures are considered. The computer calculations yield the following percentages of the ANSI design pressures: rigid frame, 50 to 90%; individual wall panels, 75 to 200%; and wall corners, 50 to 75%.

Wilson, T.

1977-05-20

216

Direct numerical simulation of turbulent mixing.  

PubMed

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

2013-10-21

217

Numerical simulation for fan broadband noise prediction  

NASA Astrophysics Data System (ADS)

In order to elucidate the broadband noise of fan, the numerical simulation of fan operating at two different rotational speeds is carried out using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The computed results are compared to experiment to estimate its accuracy and are found to show good agreement with experiment. A method is proposed to evaluate the turbulent kinetic energy in the framework of the Spalart-Allmaras one equation turbulence model. From the calculation results, the turbulent kinetic energy is visualized as the turbulence of the flow which leads to generate the broadband noise, and its noise sources are identified.

Hase, Takaaki; Yamasaki, Nobuhiko; Ooishi, Tsutomu

2011-03-01

218

Numerical simulation of flow through biofluid devices  

NASA Astrophysics Data System (ADS)

The results of a numerical simulation of flow through an artificial heart and through an artificial tilting-disk heart valve are presented. The simulation involves solving the incompressible Navier-Stokes equations; the solution process is described. The details and difficulties of modeling these particular geometries are discussed. The artificial heart geometry uses a single moving grid, and the valve computation uses an overlaid-grid approach with one moving grid and one stationary grid. The equations must be solved iteratively for each discrete time step of the computations, requiring a significant amount of computing time. It is particularly difficult to analyze and present the fluid physics represented by these calculations because of the time-varying nature of the flow, and because the flows are internal. Three-dimensional graphics and scientific visualization techniques have become instrumental in solving these problems.

Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin; Chang, I.-Dee

219

Numerical simulation of large fabric filter  

NASA Astrophysics Data System (ADS)

Fabric filters are used in the wide range of industrial technologies for cleaning of incoming or exhaust gases. To achieve maximal efficiency of the discrete phase separation and long lifetime of the filter hoses, it is necessary to ensure uniform load on filter surface and to avoid impacts of heavy particles with high velocities to the filter hoses. The paper deals with numerical simulation of two phase flow field in a large fabric filter. The filter is composed of six chambers with approx. 1600 filter hoses in total. The model was simplified to one half of the filter, the filter hoses walls were substituted by porous zones. The model settings were based on experimental data, especially on the filter pressure drop. Unsteady simulations with different turbulence models were done. Flow field together with particles trajectories were analyzed. The results were compared with experimental observations.

Sedlá?ek, Jan; Kova?ík, Petr

2012-04-01

220

Numerical simulation of attosecond nanoplasmonic streaking  

NASA Astrophysics Data System (ADS)

The characterization of the temporal profile of plasmonic fields is important both from the fundamental point of view and for potential applications in ultrafast nanoplasmonics. It has been proposed by Stockman et al (2007 Nat. Photonics 1 539) that the plasmonic electric field can be directly measured by the attosecond streaking technique; however, streaking from nanoplasmonic fields differs from streaking in the gas phase because of the field localization on the nanoscale. To understand streaking in this new regime, we have performed numerical simulations of attosecond streaking from fields localized in nanoantennas. In this paper, we present simulated streaked spectra for realistic experimental conditions and discuss the plasmonic field reconstruction from these spectra. We show that under certain circumstances when spatial averaging is included, a robust electric field reconstruction is possible.

Skopalová, E.; Lei, D. Y.; Witting, T.; Arrell, C.; Frank, F.; Sonnefraud, Y.; Maier, S. A.; Tisch, J. W. G.; Marangos, J. P.

2011-08-01

221

Numerical simulation of flow through biofluid devices  

SciTech Connect

The results of a numerical simulation on a Cray-2 supercomputer of flow through an artificial heart and through an artificial tilting-disk heart valve are presented. The simulation involves solving the incompressible Navier-Stokes equations; the solution process is described. The details and difficulties of modeling these particular geometries are discussed. The artificial heart geometry uses a single moving grid, and the valve computation uses an overlaid-grid approach with one moving grid and one stationary grid. The equations must be solved iteratively for each discrete time step of the computations, requiring a significant amount of computing time. It is particularly difficult to analyze and present the fluid physics represented by these calculations because of the time-varying nature of the flow, and because the flows are internal. The use of three-dimensional graphics and scientific visualization techniques have become instrumental in solving these problems.

Rogers, S.E.; Kwak, D. (NASA Ames Research Center, Moffett Field, CA (US)); Kiris, C.; Chang, I.D. (Stanford Univ., Stanford, CA (US))

1990-01-01

222

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

223

DNS Security Introduction and Requirements  

Microsoft Academic Search

The Domain Name System Security Extensions (DNSSEC) add data origin authentication and data integrity to the Domain Name System. This document introduces these extensions and describes their capabilities and limitations. This document also discusses the services that the DNS security extensions do and do not provide. Last, this document describes the interrelationships between the documents that collectively describe DNSSEC.

R. Austein; M. Larson

2003-01-01

224

Detuned resonances of Tollmien-Schlichting waves in an airfoil boundary layer: Experiment, theory, and direct numerical simulation  

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

225

Visualization techniques in plasma numerical simulations  

NASA Astrophysics Data System (ADS)

Numerical simulations of plasma processes usually yield a huge amount of raw numerical data. Information about electric and magnetic fields and particle positions and velocities can be typically obtained. There are two major ways of elaborating these data. First of them is called plasma diagnostics. We can calculate average values, variances, correlations of variables, etc. These results may be directly comparable with experiments and serve as the typical quantitative output of plasma simulations. The second possibility is the plasma visualization. The results are qualitative only, but serve as vivid display of phenomena in the plasma followed-up. An experience with visualizing electric and magnetic fields via Line Integral Convolution method is described in the first part of the paper. The LIC method serves for visualization of vector fields in two dimensional section of the three dimensional plasma. The field values can be known only in grid points of three-dimensional grid. The second part of the paper is devoted to the visualization techniques of the charged particle motion. The colour tint can be used for particle’s temperature representation. The motion can be visualized by a trace fading away with the distance from the particle. In this manner the impressive animations of the particle motion can be achieved.

Kulhánek, P.; Smetana, M.

2004-03-01

226

Direct numerical simulation of axisymmetric jets  

NASA Astrophysics Data System (ADS)

Results from numerical simulations of the evolution of the Kelvin-Helmholtz instability are presented for an unforced, subsonic, compressible, axisymmetric, spatially-evolving shear layer. In addition, the effect of small, random pressure fluctuations at the nozzle orifice on the growth of the mixing layer is studied. These fluctuations model inflow perturbations in experimental flows arising from turbulence and boundary layers in the nozzle. The finite-difference numerical model used to perform the simulations solves the two-dimensional time-dependent conservation equations for an ideal fluid using the Flux-Corrected Transport algorithm and timestep-splitting techniques. No subgrid turbulence model has been included. In the absence of perturbations, the calculations indicate that the large scale development of the unforced jet shear layer has an underlying degree of organization. This is the result of a feedback mechanism in which the shear layer ahead of the nozzle edge is modulated by the far field that is induced by the mergings downstream, near the end of the potential core of the jet. The studies with random high frequency perturbations on the inflow velocity show that they effectively tend to break the temporal correlations between the structures.

Grinstein, F. F.; Oran, E. S.; Boris, J. P.

1986-01-01

227

Numerical and theoretical study on the relative diffusion of particle pairs in isotropic turbulence  

Microsoft Academic Search

The Lagrangian statistics of the motion of a pair of fluid particles are studied by high-resolution direct numerical simulation (DNS) of quasi-stationary and isotropic 3D turbulence with 1024^3 grid points. The Taylor-scale Reynolds number is 283, and the energy spectrum exhibits an inertial subrange. The DNS suggests that the mean square distance grows with time t as ~ C? t^3

Takashi Ishihara; Yukio Kaneda

2001-01-01

228

Numerical Simulations of Crater Formation with Dilatancy  

NASA Astrophysics Data System (ADS)

The most characteristic geophysical signature of an impact crater is a circular negative gravity anomaly, centered over the crater. The cause of the gravity low is dilatancy: fracturing and brecciation, induced by the passage of the shock wave and comminution during crater formation, creates pore space between fragments and fractures, reducing the bulk density of the sub-crater material. Calculation of damage accumulation is routine in modern numerical impact simulations; accounting for dilatancy is not. As a result, most impact simulations do not correctly predict density changes beneath an impact crater, which limits the scope for comparison of model results with geophysical data. A simple approach to account for dilation during shear failure in impact simulations is to supplement the pressure computed by the equation of state with a "dilatancy pressure," representing the outward force of grains moving passed one another, in cells where shear failure has occurred (Johnson and Holmquist, 1994; doi:10.1063/1.46199). This additional pressure effectively shifts the pressure-density relationship for the dilatant material up (to a higher pressure) so that when the material unloads to atmospheric pressure the density drops to a (dilated) bulk density that is below the reference density of the pristine material. A limitation of this approach is that the bulk modulus of the dilated material is the same as that of the pristine material and, consequently, that an unrealistically large dilatancy pressure is required to achieve typical bulk densities of fractured rock. Here we propose an improvement to this approach where both the distension (porosity) and the pressure are modified during shear failure, which allows for the correct reduction in bulk modulus with increasing dilation. In our approach, shear failure leads to a prescribed decrease in the reference density of the dilatant material. The ratio of this reference density to the current density is used to compute a distension (porosity), which through the ?-? porosity model acts to increase the pressure by the amount required to shift the material from its current equation of state surface to that of the more distended, dilatant material. We show that simulations of crater formation using our dilatancy model are in good agreement with observed density and porosity variations beneath terrestrial simple craters and make predictions about the role of dilatancy in the formation of larger, complex craters. Our new dilatancy model will allow future numerical impact simulations to be directly compared with geophysical observations, such as gravity and seismic velocity anomalies, providing much greater observational constraint on simulation results. This is of particular significance for models of terrestrial craters where the surface expression has been removed by erosion and the geophysical signature is the only vestige of impact. Moreover, numerical simulations of cratering with dilatancy will aid in the interpretation of high-resolution gravity data soon to be collected over lunar craters by GRAIL.

Collins, G. S.; Melosh, H. J.; Wilson, C. R.; Wuennemann, K.

2011-12-01

229

Characteristics of a numerical fluid dynamics simulator  

NASA Astrophysics Data System (ADS)

A concept of a real time Numerical Fluid Dynamics Simulator (NFDS) is described, and its characteristics are derived. The following characteristics are adopted as guiding principles: (1) that the performance characteristics (information output, throughput and storage) of the NFDS be defined by the maximum rate at which the research can absorb the results of his/her simulator, thus establishing an impedance match between man and machine; (2) that the NFDS off-load from the researcher's brain in every way possible the routine tasks of data analysis that can be done automatically; and (3) that the NFDS is operated as a dedicated experimental device and that the researcher has complete control over the apparatus and experiment. The NFDS is envisioned to be composed of simulation processors, data storage devices, and image processing devices of extremely high power and capacity, interconnected by very high throughput communication channels. Individual component performance requirements are presented for both real time and playback operating models of the NFDS, using problems of current interest in fluid dynamics as examples.

Winkler, K. H. A.; Norman, M. L.; Norton, J. L.

1985-08-01

230

Numerical simulation of premixed turbulent methane combustion  

SciTech Connect

In this paper we study the behavior of a premixed turbulent methane flame in three dimensions using numerical simulation. The simulations are performed using an adaptive time-dependent low Mach number combustion algorithm based on a second-order projection formulation that conserves both species mass and total enthalpy. The species and enthalpy equations are treated using an operator-split approach that incorporates stiff integration techniques for modeling detailed chemical kinetics. The methodology also incorporates a mixture model for differential diffusion. For the simulations presented here, methane chemistry and transport are modeled using the DRM-19 (19-species, 84-reaction) mechanism derived from the GRIMech-1.2 mechanism along with its associated thermodynamics and transport databases. We consider a lean flame with equivalence ratio 0.8 for two different levels of turbulent intensity. For each case we examine the basic structure of the flame including turbulent flame speed and flame surface area. The results indicate that flame wrinkling is the dominant factor leading to the increased turbulent flame speed. Joint probability distributions are computed to establish a correlation between heat release and curvature. We also investigate the effect of turbulent flame interaction on the flame chemistry. We identify specific flame intermediates that are sensitive to turbulence and explore various correlations between these species and local flame curvature. We identify different mechanisms by which turbulence modulates the chemistry of the flame.

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

2001-12-14

231

A priori direct numerical simulation assessment of algebraic flame surface density models for turbulent premixed flames in the context of large eddy simulation  

NASA Astrophysics Data System (ADS)

Flame surface density (FSD) based reaction rate closure is one of the most important approaches in turbulent premixed flame modeling. The algebraic models for FSD based on power laws often require information about the fractal dimension D and the inner cut-off scale ?i. In the present study, two three-dimensional direct numerical simulation (DNS) databases for freely propagating statistically planar turbulent premixed flames are analyzed among which the flame in one case belongs to the corrugated flamelet (CF) regime, whereas the other falls well within the thin reaction zone (TRZ) regime. It is found that D for the flame in the TRZ regime is greater than the value obtained for the flame in the CF regime. For the flame within the TRZ regime, the fractal dimension is found to be 7/3, which is the same as D for a material surface in a turbulent environment. For the flame in the CF regime, ?i is found to scale with the Gibson scale, whereas ?i is found to scale with the Kolmogorov length scale for the flame in the TRZ regime. Based on these observations a new algebraic model for FSD is proposed, where D and ?i are expressed as functions of Karlovitz number. The performances of the new and existing algebraic models for FSD are compared with the corresponding values obtained from DNS databases.

Chakraborty, Nilanjan; Klein, Markus

2008-08-01

232

Numerical simulations of black-hole spacetimes  

NASA Astrophysics Data System (ADS)

This thesis covers various aspects of the numerical simulation of black-hole spacetimes according to Einstein's general theory of relativity, using the Spectral Einstein Code developed by the Caltech-Cornell-CITA collaboration. The first topic is improvement of binary-black-hole initial data. One such issue is the construction of binary-black-hole initial data with nearly extremal spins that remain nearly constant during the initial relaxation in an evolution. Another concern is the inclusion of physically realistic tidal deformations of the black holes to reduce the high-frequency components of the spurious gravitational radiation content, and represents a first step in incorporating post-Newtonian results in constraint-satisfying initial data. The next topic is the evolution of black-hole binaries and the gravitational waves they emit. The first spectral simulation of two inspiralling black holes through merger and ringdown is presented, in which the black holes are nonspinning and have equal masses. This work is extended to perform the first spectral simulations of two inspiralling black holes with moderate spins and equal masses, including the merger and ringdown. Two configurations are considered, in which both spins are either anti-aligned or aligned with the orbital angular momentum. Highly accurate gravitational waveforms are computed for all these cases, and are used to calibrate waveforms in the effective-one-body model. The final topic is the behavior of quasilocal black-hole horizons in highly dynamical situations. Simulations of a rotating black hole that is distort ed by a pulse of ingoing gravitational radiation are performed. Multiple marginally outer trapped surfaces are seen to appear and annihilate with each other during the evolution, and the world tubes th ey trace out are all dynamical horizons. The dynamical horizon and angular momentum flux laws are evaluated in this context, and the dynamical horizons are contrasted with the event horizon. The format ion of multiple marginally outer trapped surfaces in the Vaidya spacetime is also treated.

Chu, Tony

233

3D Numerical simulations of oblique subduction  

NASA Astrophysics Data System (ADS)

In the past 2D numerical studies (e.g. Gerya et al., 2002; Gorczyk et al., 2007; Malatesta et al., 2012) provided evidence that during intraoceanic subduction a serpentinite channel forms above the downgoing plate. This channel forms as a result of hydration of the mantle wedge by uprising slab-fluids. Rocks buried at high depths are finally exhumed within this buoyant low-viscosity medium. Convergence rate in these 2D models was described by a trench-normal component of velocity. Several present and past subduction zones worldwide are however driven by oblique convergence between the plates, where trench-normal motion of the subducting slab is coupled with trench-parallel displacement of the plates. Can the exhumation mechanism and the exhumation rates of high-pressure rocks be affected by the shear component of subduction? And how uprise of these rocks can vary along the plate margin? We tried to address these questions performing 3D numerical models that simulate an intraoceanic oblique subduction. The models are based on thermo-mechanical equations that are solved with finite differences method and marker-in-cell techniques combined with multigrid approach (Gerya, 2010). In most of the models a narrow oceanic basin (500 km-wide) surrounded by continental margins is depicted. The basin is floored by either layered or heterogeneous oceanic lithosphere with gabbro as discrete bodies in serpentinized peridotite and a basaltic layer on the top. A weak zone in the mantle is prescribed to control the location of subduction initiation and therefore the plate margins geometry. Finally, addition of a third dimension in the simulations allowed us to test the role of different plate margin geometries on oblique subduction dynamics. In particular in each model we modified the dip angle of the weak zone and its "lateral" geometry (e.g. continuous, segmented). We consider "continuous" weak zones either parallel or increasingly moving away from the continental margins. Moreover, we tested the effect on subduction/exhumation dynamics of several values of the trench-parallel component of convergence-rate vector. Gerya T., Stöckhert B., Perchuk A.L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: a numerical simulation. Tectonics, vol. 21, n. 6, 1056. Gerya, T. V., 2010. Introduction to numerical geodynamic modelling. Cambridge University Press, Cambridge. Gorczyk W., Guillot S., Gerya T.V., Hattori K. (2007a). Asthenospheric upwelling, oceanic slab retreat, and exhumation of UHP mantle rocks: insights from Greater Antilles. Geophysical research letters, vol. 34, L21309. Malatesta C., Gerya T., Scambelluri M., Federico L., Crispini L., Capponi G. (2012). Intraoceanic subduction of "heterogeneous" oceanic lithosphere in narrow basins: 2D numerical modeling. Lithos, http://dx.doi.org/10.1016/j.lithos.2012.01.003

Malatesta, C.; Gerya, T.; Scambelluri, M.; Crispini, L.; Federico, L.; Capponi, G.

2012-04-01

234

Numerical simulations of icing in turbomachinery  

NASA Astrophysics Data System (ADS)

Safety concerns over aircraft icing and the high experimental cost of testing have spurred global interest in numerical simulations of the ice accretion process. Extensive experimental and computational studies have been carried out to understand the icing on external surfaces. No parallel initiatives were reported for icing on engine components. However, the supercooled water droplets in moist atmosphere that are ingested into the engine can impinge on the component surfaces and freeze to form ice deposits. Ice accretion could block the engine passage causing reduced airflow. It raises safety and performance concerns such as mechanical damage from ice shedding as well as slow acceleration leading to compressor stall. The current research aims at developing a computational methodology for prediction of icing phenomena on turbofan compression system. Numerical simulation of ice accretion in aircraft engines is highly challenging because of the complex 3-D unsteady turbomachinery flow and the effects of rotation on droplet trajectories. The aim of the present research focuses on (i) Developing a computational methodology for ice accretion in rotating turbomachinery components; (ii) Investigate the effect of inter-phase heat exchange; (iii) Characterize droplet impingement pattern and ice accretion at different operating conditions. The simulations of droplet trajectories are based on a Eulerian-Lagrangian approach for the continuous and discrete phases. The governing equations are solved in the rotating blade frame of reference. The flow field is computed by solving the 3-D solution of the compressible Reynolds Averaged Navier Stokes (RANS) equations. One-way interaction models simulate the effects of aerodynamic forces and the energy exchange between the flow and the droplets. The methodology is implemented in the cool, TURBODROP and applied to the flow field and droplet trajectories in NASA Roto-67r and NASA-GE E3 booster rotor. The results highlight the variation of impingement location and temperature with droplet size. It also illustrates the effect of rotor speed on droplet temperature rise. The computed droplet impingement statistics and flow properties are used to calculate ice shapes. It was found that the mass of accreted ice and maximum thickness is highly sensitive to rotor speed and radial location.

Das, Kaushik

235

Numerical Simulations of Turbulent MHD Reconnection  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a very important process in a large number of laboratory, space, and astrophysical plasmas. It is usually believed that in the resistive MHD regime, the reconnection rate obeys the classical Sweet-Parker scaling, proportional to the square root of the resistivity, and is thus very slow. Whether reconnection can be significantly accelerated in the presence of MHD turbulence is still an unresolved question. In this study, we use high-resolution incompressible resistive magnetohydrodynamic numerical simulations to investigate the effect of externally imposed small-scale turbulence on the reconnection of a large-scale magnetic field. We characterize the turbulent enhancement of the reconnection rate over the laminar Sweet-Parker rate as a function of the resistivity, turbulent driving scale and amplitude. A. Lazarian & E. Vishniac, ApJ, 517, 700 (1999).

Loureiro, Nuno; Uzdensky, Dmitri; Schekochihin, Alexander; Yousef, Tarek

2008-11-01

236

Numerical simulations of a stellar intensity interferometer  

NASA Astrophysics Data System (ADS)

The revival of stellar intensity interferometry may allow large arrays of gamma ray telescopes to reconstruct high resolution images of stars. Intensity interferometry measurements rely on the fact that the different Fourier components of the light collected at each telescope produce low frequency beats resulting in small intensity fluctuations displaying correlation between the different telescopes in an array. The correlations provide access to the squared degree of mutual coherence of the light at the different telescopes, which is related to the size and shape of the star via the Cittert-Zernike theorem. Here, we discuss our work toward a detailed and realistic numerical simulation of intensity interferometry with two telescopes, which provides insight into the effects of the finite size of the telescopes, the photodetectors and electronics response, and excess noise on the performances of future intensity interferometry experiments.

Rou, Janvida; Nunez, Paul; Kieda, David; Lebohec, Stephan

2011-10-01

237

DNS of vibrating grid turbulence  

Microsoft Academic Search

Direct numerical simulation of the turbulence generated at a grid vibrating normally to itself using spectral code [1] is presented. Due to zero mean shear there is no production of turbulence apart from the grid. Action of the grid is mimiced by the function implemented in the middle of the simulation box:f_i (x_1 ,x_2 ) = {n^2 S}\\/2left{ {left| {{delta

G. Khujadze; M. Oberlack

2009-01-01

238

Numerical relativity simulations of binary neutron stars  

NASA Astrophysics Data System (ADS)

We present a new numerical relativity code designed for simulations of compact binaries involving matter. The code is an upgrade of the BAM code to include general relativistic hydrodynamics and implements state-of-the-art high-resolution-shock-capturing schemes on a hierarchy of mesh refined Cartesian grids with moving boxes. We test and validate the code in a series of standard experiments involving single neutron star spacetimes. We present test evolutions of quasiequilibrium equal-mass irrotational binary neutron star configurations in quasicircular orbits which describe the late inspiral to merger phases. Neutron star matter is modeled as a zero-temperature fluid; thermal effects can be included by means of a simple ideal gas prescription. We analyze the impact that the use of different values of damping parameter in the Gamma-driver shift condition has on the dynamics of the system. The use of different reconstruction schemes and their impact in the post-merger dynamics is investigated. We compute and characterize the gravitational radiation emitted by the system. Self-convergence of the waves is tested, and we consistently estimate error bars on the numerically generated waveforms in the inspiral phase.

Thierfelder, Marcus; Bernuzzi, Sebastiano; Brügmann, Bernd

2011-08-01

239

a Study on Correlation Moments of Two-Phase Fluctuating Velocity Using Direct Numerical Simulation  

NASA Astrophysics Data System (ADS)

Existing models of two-phase fluctuating velocity correlation moments are unsatisfactory because of their inability to clearly identify the dependency of two-phase velocity covariance on fluid- and particle-phase velocity second moments. This is especially true of wall-bounded turbulent flows. In this paper, the statistical fluctuating velocity of both phases in particle-laden turbulent channel flows were obtained numerically by means of direct numerical simulation (DNS) coupled to the Lagrangian particle trajectory method. The effects of particle Stokes number on the scaling of two-phase fluctuating velocity correlation moments were analyzed considering effects of flow inhomogeneity. An improved two-phase correlation closure model of exponential decay with emphasis on the particle-phase kinetic energy was then proposed based on the results of an evaluation of five existing models. This new model was found to be better than previous models, which used local equilibrium assumption. The present investigations may facilitate understanding of two-phase flow physics and the construction of models capable of predicting the movements of particle-laden turbulent flows accurately using Reynolds-averaged Navier-Stokes (RANS) methods.

Wang, Bing; Wei, Wei; Zhang, Huiqiang

2013-10-01

240

Numerical simulation of premixed turbulent methane combustion  

SciTech Connect

With adaptive-grid computational methodologies and judicious use of compressible and low Mach number combustion models, we are carrying out three-dimensional, time-dependent direct numerical simulations of a laboratory-scale turbulent premixed methane burner. In the laboratory experiment, turbulence is generated by a grid located in the throat of a 50mm diameter circular nozzle; swirl is be introduced by four tangential air jets spaced uniformly around the circumference of the nozzle just above the turbulence grid. A premixed methane flame is stabilized above the nozzle in the central core region where a velocity deficit is induced7the swirling flow. The time-dependent flow field inside the nozzle, from the turbulence grid and the high-speed jets, to the nozzle exit plane is simulated using an adaptive-grid embedded-boundary compressible Navier-Stokes solver. The compressible calculation then provides time-dependent boundary conditions for an adaptive low Mach number model of the swirl-stabilized premixed flame. The low Mach model incorporates detailed chemical kinetics and species transport using 20 species and 84 reactions. Laboratory diagnostics available for comparisons include characterizations of the flow field just down stream of the nozzle exit plane, and flame surface statistics, such as mean location, wrinkling and crossing frequencies.

Day, Marc S.; Bell, John B.; Almgren, Ann S.; Beckner, Vincent E.; Lijewski, Michael J.; Cheng, Robert; Shepherd, Ian; Johnson, Matthew

2003-06-14

241

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

242

DNS and Linear Stability Analyses of Unsteady 3-D Hypersonic Wall- Bounded Flows with Real-Gas Effects.  

National Technical Information Service (NTIS)

The goal of this research project is to develop new advanced numerical methods and to perform DNS studies of transient hypersonic reacting flows over full 3-D maneuvering vehicles. The DNS tools and supporting theoretical approaches are used to gain new f...

X. Zhong

2000-01-01

243

Numerical Simulation and Experimental Test on Muzzle Brake Efficiency  

Microsoft Academic Search

Numerical simulation and firing test of a gun was performed to give the muzzle brake efficiency and pressure of muzzle blast wave for evaluating the muzzle brake performance. Two models of muzzle flow were given respectively with Euler equations ignore initial flow field and Navier-Stokes equations with turbulence model consider initial flow field. Numerical simulation was carried out and simulation

Kun Jiang; Hao Wang

2011-01-01

244

Numerical simulation of ballistic impact on composite laminates  

Microsoft Academic Search

The paper reports experimental and numerical simulation of ballistic impact problems on thin composite laminated plates reinforced with Kevlar 29. Ballistic impact was imparted with simulated fragments designed in accordance with STANAG-2920 on plates of different thickness. Numerical modelling was developed and used to obtain an estimate for the limit perforation velocity (V50) and simulate failure modes and damage. Computations

M. A. G. Silva; C. Cisma?iu; C. G. Chiorean

2005-01-01

245

Numerical simulation of a magnetron plasma sputtering system using VORPAL  

Microsoft Academic Search

Three-dimensional numerical simulation is conducted for a magnetron sputtering plasma using the particle in cell code VORPAL. Numerical simulation of sputtering process requires accurate models of nuclear stopping in materials, particle dynamics and self-consistent electromagnetic fields. VORPAL can simulate cold dense plasma sputtering system under many different electromagnetic configurations. The dynamics of both incident particles and sputtered neutral atoms are

Chuandong Zhou; Peter H. Stoltz

2010-01-01

246

Numerical simulation of mesospheric gravity waves  

NASA Astrophysics Data System (ADS)

Recently, first three-dimensionally resolved observations of polar mesospheric winter echeos (PMWEs) by a multi-beam experiment of the Middle Atmosphere Alomar Radar system (MAARSY) were published by Rapp et al. (2011). The observed PMWE at about 75 km altitude was tilted in the main flow direction (west to east). The origin of the PMWE was explained by two disparate concepts of gravity wave dynamics. On the one hand, the tilted PMWE was assumed to be aligned with the phase line of a linear gravity wave (?z ? 23 km, ?x ? 460 km) propagating at an intrinsic phase speed of - 73 m/s against the westerly wind. On the other hand, turbulence generated by breaking gravity waves was a necessary element to explain the existence of backscattering fluctuations. In addition to a thorough analysis of the synoptic meteorological conditions, high-resolution numerical simulations are performed with the all-scale geophysical flow solver EULAG (Prusa et al., 2008). The anelastic and pseudo-incompressible approximated equations are solved in a 3D computational domain covers a 1500 km long slice of Scandinavia and spans from the surface to 100 km altitude. Multiple numerical experiments are performed to explore the origin of the observed PMWE. Various hypotheses are tested. The presentation will discuss if the PMWEs were the result of breaking mountain waves excited by the flow over Scandinavia or if dynamical instabilities occuring in the highly sheared mesospheric flow led to the observed turbulence. Rapp, M., R. Latteck, G. Stober, et al., 2011: First three-dimensional observations of polar mesosphere winter echoes: Resolving space-time ambiguity. J. Geophys. Res., 116, A11307, doi:10.1029/2011JA016858. Prusa, J.M., P.K. Smolarkiewicz, A.A. Wyszogrodzki, 2008: EULAG, a computational model for multiscale flows, Comput. Fluids 37, 1193-1207.

Dörnbrack, Andreas; Rapp, Markus; Latteck, Ralph

2013-04-01

247

Direct numerical simulations of turbulent thermal boundary layers subjected to adverse streamwise pressure gradients  

NASA Astrophysics Data System (ADS)

An innovative method for prescribing turbulent thermal inflow information in spatially developing boundary layers under streamwise pressure gradients is introduced for attached flows. The approach is tested and validated in a suite of Direct Numerical Simulations (DNS) of thermal boundary layers for zero (ZPG) and adverse (APG) pressure gradients with momentum thickness Reynolds numbers (Re?) up to 3000. The turbulent thermal data are generated based on the dynamic multi-scale approach proposed by Araya et al. [``A dynamic multi-scale approach for turbulent inflow boundary conditions in spatially evolving flows,'' J. Fluid Mech. 670, 581-605 (2011)], which is extended to include thermal field simulations in the present article. The approach is based on the original rescaling-recycling method developed by Lund, Wu, and Squires [``Generation of turbulent inflow data for spatially developing boundary layer simulations,'' J. Comput. Phys. 140, 233-258 (1998)] for ZPG flows. Isothermal walls are considered for the thermal field and the molecular Prandtl number is 0.71. In addition, only inlet momentum/thermal boundary layer thicknesses must be prescribed while other flow parameters such as the inlet friction velocity, u?, and friction temperature, ??, are computed dynamically based on the flow solution obtained downstream by means of a test plane. This plane is located between the inlet and recycle stations. Based on the unique and extensive DNS results of heat transfer obtained in this investigation, the effects of Reynolds numbers and adverse pressure gradients on the flow and thermal parameters are also explored and visualized. The principal outcome of adverse pressure gradient on the flow parameters has been determined as a secondary peak, particularly on the streamwise velocity fluctuations in the outer region, which shows clear evidence of energy production in the outer flow and not only in the buffer layer as traditionally known. Nevertheless, this peak is not so obvious on the thermal fluctuations but it is hypothesized that the reason is mainly attributed to the absence of a freestream thermal gradient, as imposed in the velocity field. Furthermore, the high-speed streaks in the buffer layer are observed to be notably shorter and wider in a Strong APG than in the ZPG case. Finally, a significant decrease of the turbulent Prandtl number is attributed to the presence of a Strong APG.

Araya, Guillermo; Castillo, Luciano

2013-09-01

248

Numerical simulation of "An American Haboob"  

NASA Astrophysics Data System (ADS)

A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High resolution numerical models are required for accurate simulation of the small-scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM with 3.5 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the Normalized Difference Vegetation Index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~ 25 km), the model PM10 surface dust concentration reached ~ 2500 ?g m-3, but underestimated the values measured by the PM10stations within the city. Model results are also validated by the MODIS aerosol optical depth (AOD), employing deep blue (DB) algorithms for aerosol loadings. Model validation included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), equipped with the lidar instrument, to disclose the vertical structure of dust aerosols as well as aerosol subtypes. Promising results encourage further research and application of high-resolution modeling and satellite-based remote sensing to warn of approaching severe dust events and reduce risks for safety and health.

Vukovic, A.; Vujadinovic, M.; Pejanovic, G.; Andric, J.; Kumjian, M. R.; Djurdjevic, V.; Dacic, M.; Prasad, A. K.; El-Askary, H. M.; Paris, B. C.; Petkovic, S.; Nickovic, S.; Sprigg, W. A.

2013-10-01

249

A numerical simulation of the backward Raman amplifying in plasma  

NASA Astrophysics Data System (ADS)

This paper describe a numerical simulation method for the interaction between laser pulses and low density plasmas based on hydrodynamic approximation. We investigate Backward Raman Amplifying (BRA) experiments and their variants. The numerical results are in good agreement with experiments.

Wang, Hong-Yu; Huang, Zu-Qia

2005-12-01

250

Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry  

SciTech Connect

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

251

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

252

Impulscytophotometrische DNS-Untersuchungen bei Blasenkarzinomen  

Microsoft Academic Search

Zusammenfassung Die Anwendbarkeit und die Bedeutung quantitativer zellularer DNS-Bestimmungen mit Hilfe rascher durchflußzytofluorometrischer Technik werden bei neudiagnostizierten Tumoren sowie der Behandlung des Carcinoma in situ der Blase diskutiert. Aus den DNS-Histogram-men lassen sich Ploidiegrad u?d Anteil von S-Phase-Zellen, welcher die Proliferationsaktivität des Tumors wiedergibt, bestimmen. Diploi-de DNS-Verteilungen finden sich bei 60 % von T 1-Tumoren, während alle anderen Tumoren einschließlich

B. Tribukait; H. Gustafson

1980-01-01

253

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

254

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

255

Numerical simulations of a nanodusty RF plasma  

NASA Astrophysics Data System (ADS)

The nucleation, growth, charging and transport of nanoparticles in a low-pressure RF plasma have profound effects on the plasma. In previous work we developed a numerical model for the spatiotemporal evolution of the plasma-nanoparticle system. The model simulates a one-dimensional parallel-plate capacitively-coupled plasma. It includes solutions to electron and ion population balance equations, and Poisson's equation for the electric field, models stochastic particle charging, and self-consistently solves the aerosol general dynamic equation, including particle size- and charge-dependent coagulation (including the effect of image potentials), and particle transport by electrostatic forces, Brownian diffusion, ion drag and thermophoresis. In the present work this model is used to explore the effect of system parameters on the nanoparticle and plasma behavior. Parameters studied include pressure, temperature and temperature distribution, applied voltage and gas flow rate. In addition we examine the behavior of the system at long times, when particles are pushed by ion drag out of the center of the plasma, opening a void that allows fresh nucleation.

Girshick, Steven; Agarwal, Pulkit

2009-10-01

256

Numerical simulation of molecular uptake via electroporation.  

PubMed

A numerical study of electroporation-mediated molecular delivery is presented. The model consists of the Nernst-Planck equations for species transport, coupled with an asymptotic Smoluchowski equation for membrane permeabilization. The transfer of calcium ions into a Chinese Hamster Ovary cell is simulated. The results reveal important physical insights. First, for this particular case, ion electrophoresis plays an important role, and is an order of magnitude faster than free diffusion on a comparable time scale. Second, the maximum achievable concentration within the cell is reciprocally correlated with the extracellular electrical conductivity. This behavior is mediated by an electrokinetic mechanism known as field-amplified sample stacking. Through this mechanism, the intracellular ion concentration can reach a level higher than the extracellular one provided that the intra-to-extracellular conductivity ratio is greater than unity. The results corroborate well with data in the literature, and offer a mechanistic interpretation to previous experimental observations. This work is a step toward the quantification of molecular delivery via electroporation. PMID:21621484

Li, Jianbo; Lin, Hao

2011-04-28

257

NUMERICAL SIMULATIONS OF DRIVEN RELATIVISTIC MAGNETOHYDRODYNAMIC TURBULENCE  

SciTech Connect

A wide variety of astrophysical phenomena involve the flow of turbulent magnetized gas with relativistic velocity or energy density. Examples include gamma-ray bursts, active galactic nuclei, pulsars, magnetars, micro-quasars, merging neutron stars, X-ray binaries, some supernovae, and the early universe. In order to elucidate the basic properties of the relativistic magnetohydrodynamical (RMHD) turbulence present in these systems, we present results from numerical simulations of fully developed driven turbulence in a relativistically warm, weakly magnetized and mildly compressible ideal fluid. We have evolved the RMHD equations for many dynamical times on a uniform grid with 1024{sup 3} zones using a high-order Godunov code. We observe the growth of magnetic energy from a seed field through saturation at {approx}1% of the total fluid energy. We compute the power spectrum of velocity and density-weighted velocity U = {rho}{sup 1/3} v and conclude that the inertial scaling is consistent with a slope of -5/3. We compute the longitudinal and transverse velocity structure functions of order p up to 11 and discuss their possible deviation from the expected scaling for non-relativistic media. We also compute the scale-dependent distortion of coherent velocity structures with respect to the local magnetic field, finding a weaker scale dependence than is expected for incompressible non-relativistic flows with a strong mean field.

Zrake, Jonathan; MacFadyen, Andrew I. [Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

2012-01-01

258

Numeric Simulation of Plant Signaling Networks1  

PubMed Central

Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis.

Genoud, Thierry; Trevino Santa Cruz, Marcela B.; Metraux, Jean-Pierre

2001-01-01

259

Numerical Simulations of The Mantle Lithosphere Delamination  

NASA Astrophysics Data System (ADS)

Sudden uplift, extension, and increased igneous activity are often explained by rapid mechanical thinning of the lithospheric mantle (e.g., Kay and Kay (1993)). Two main thinning mechanisms have been proposed, convective removal of a thickened litho- spheric root or delamination at the favor of a crustal decoupling level. The latter mechanism was first defined by Bird (1979) as the whole mantle lithosphere peel- ing suddenly away from the crust by the propagation of a strongly localised shear zone, and sinking into the mantle. We perform 2-D numerical simulations of convection using a viscoplastic rheol- ogy with a viscosity depending strongly on temperature, depth, and composition (crust/mantle). The simulations develop in three steps. (1) We first obtain "classical" sublithospheric convection for a long period of time (100 Myrs), yielding a slightly heterogeneous lithospheric temperature structure. (2) At some time, in some simu- lations, a strong thinning of the mantle occurs progressively (in about 20 Myrs) in a small area (100 km wide). This process puts the asthenosphere in direct contact with the lower crust. (3) Large pieces of mantle lithosphere then quickly sink into the man- tle, by the horizontal propagation of a detachment level away from the "asthenospheric conduit". We determine the favourable parameters (crustal thicknesses, activation energies, and friction coefficients) to the initiation of delamination (step 2). We find that delamina- tion initiates in places where the Moho temperature is the higher, as soon as the crust and mantle viscosities are sufficiently low. Delamination may thus occur on Earth in orogenic settings when the crust is thick and the Moho temperature exceeds 8000C. We also perform simulations with variable crustal thicknesses, and show that if de- lamination occurs at the base of the deeper crust, it does not propagate along the base of the shallower crust. References: Bird, P., Continental delamination and the Colorado Plateau, J. Geophys. Res., 84, 7561-7571, 1979. Kay, R. W. and Kay, S. M., Delamination and delamination magmatism, Tectonophysics, 219, 177-189, 1993.

Morency, C.; Doin, M.-P.

260

An analysis of lower-dimensional approximations to the scalar dissipation rate using direct numerical simulations of plane jet flames  

SciTech Connect

The difficulty of experimental measurements of the scalar dissipation rate in turbulent flames has required researchers to estimate the true three-dimensional (3D) scalar dissipation rate from one-dimensional (1D) or two-dimensional (2D) gradient measurements. In doing so, some relationship must be assumed between the true values and their lower dimensional approximations. We develop these relationships by assuming a form for the statistics of the gradient vector orientation, which enables several new results to be obtained and the true 3D scalar dissipation PDF to be reconstructed from the lower-dimensional approximations. We use direct numerical simulations (DNS) of turbulent plane jet flames to examine the orientation statistics, and verify our assumptions and final results. We develop and validate new theoretical relationships between the lower-dimensional and true moments of the scalar dissipation PDF assuming a log-normal true PDF. We compare PDFs reconstructed from lower-dimensional gradient projections with the true values and find an excellent agreement for a 2D simulated measurement and also for a 1D simulated measurement perpendicular to the mean flow variations. Comparisons of PDFs of thermal dissipation from DNS with those obtained via reconstruction from 2D experimental measurements show a very close match, indicating this PDF is not unique to a particular flame configuration. We develop a technique to reconstruct the joint PDF of the scalar dissipation and any other scalar, such as chemical species or temperature. Reconstructed conditional means of the hydroxyl mass fraction are compared with the true values and an excellent agreement is obtained.

Chen, Jackie [Sandia National Laboratories (SNL); Sankaran, Ramanan [ORNL; Hawkes, Evatt R [Sandia National Laboratories (SNL)

2009-05-01

261

DNS and RANS Modeling of Dispersion in the Wake of an Obstacle  

NASA Astrophysics Data System (ADS)

We present a numerical study of the dispersion of a passive scalar in turbulent separated flows to establish the predictive capabilities of algebraic flux models against the standard eddy-diffusivity representation. The scalar dispersion from a point source over a wavy wall is initially investigated to carefully evaluate scalar flux models through comparisons with DNS data. The roof-top release of a passive plume from a wall-mounted cube in a turbulent boundary layer is then presented to demonstrate that algebraic models can also be applied successfully to atmospheric dispersion at street-scale. Despite the questionable validity of local-equilibrium conditions, the numerical experiments show that algebraic models provide a significant improvement for scalar dispersion simulations of complex flows with respect to the standard eddy-diffusivity model.

Philips, David; Rossi, Riccardo; Iaccarino, Gianluca

2009-11-01

262

Hierarchical formulations for numerical flow simulations  

NASA Astrophysics Data System (ADS)

A new hierarchical formulation for the equations of fluid motion is developed. The hierarchical nature of the new formulation is due to its ability to simulate all levels of fluid flow approximations, namely, inviscid irrotational isentropic flows (potential flow formulation), inviscid rotational non-isentropic flows (Euler formulation) and viscous heat conducting flows (Navier-Stokes formulation). The new formulation uses a potential flow solver as a base solver which is evaluated everywhere in the flow field, while convection/diffusion equations for entropy, vorticity and total enthalpy are only evaluated within limited domains of the flow field where rotational effects are present such as in regions containing shocks, boundary layers and/or wakes. This is accomplished by using a Helmholtz decomposition of the velocity vector into the gradient of a potential function plus a rotational component. The density and pressure are reformulated in terms of the speed and entropy. The new formulation identifies an acoustic mode, governed by the potential equation, from the convection/diffusion mode governing the entropy, vorticity and total enthalpy. This identification of modes together with the ability to restrict the evaluation of entropy, vorticity and total enthalpy to relatively small domains within the flow field offers several advantages over the traditional Euler and Navier-Stokes formulations from the point of view of upwinding, multigrid and the incompressible flow limit. To test the robustness, efficiency and accuracy of this new approach, several flow problems are simulated. These problems include 2-D shock wave/boundary layer interaction, 2-D inviscid and viscous flows over cylinders, 2-D inviscid and viscous flows over airfoils and 3-D inviscid and viscous flows over wings. The results obtained using the new formulation agree well with both experimental results and numerical results obtained from traditional Euler and Navier-Stokes formulations. Fast convergence rates are also achieved through the implementation of multigrid to the augmented potential equation which results in an order of magnitude reduction in work units as compared to single grid computations.

Wahba, Essam Moustafa

263

A high-order public domain code for direct numerical simulations of turbulent combustion  

NASA Astrophysics Data System (ADS)

A high-order scheme for direct numerical simulations of turbulent combustion is discussed. Its implementation in the massively parallel and publicly available PENCIL CODE is validated with the focus on hydrogen combustion. This is the first open source DNS code with detailed chemistry available. An attempt has been made to present, for the first time, the full set of evolution and auxiliary equations required for a complete description of single phase non-isothermal fluid dynamics with detailed chemical reactions. Ignition delay times (0D) and laminar flame velocities (1D) are calculated and compared with results from the commercially available Chemkin code. The scheme is verified to be fifth order in space. Upon doubling the resolution, a 32-fold increase in the accuracy of the flame front is demonstrated. Finally, also turbulent and spherical flame front velocities are calculated and the implementation of the non-reflecting so-called Navier-Stokes Characteristic Boundary Condition is validated in all three directions.

Babkovskaia, N.; Haugen, N. E. L.; Brandenburg, A.

2011-01-01

264

Numerical viscosity in hydrodynamics simulations in general relativity  

Microsoft Academic Search

We present an alternative method to estimate the numerical viscosity in simulations of astrophysical objects, which is based on the damping of fluid oscillations. We apply the method to general relativistic hydrodynamic simulations using spherical coordinates. We perform 1D spherical and 2D axisymmetric simulations of radial oscillations in spherical systems. We first calibrate the method with simulations with physical bulk

P. Cerdá-Durán

2010-01-01

265

Direct Numerical Simulation of electrochemical reactions in a turbulent electrolyte  

NASA Astrophysics Data System (ADS)

In electrochemical processes, such as industrial electrodeposition, the flow state can influence the mass transfer of the active chemical species in solution. This could lead to significant modifications of reaction kinetics at the electrode and obviously affects the global performance of the system. We aim here to describe via DNS the behavior of a turbulent electrolyte in a channel configuration where electrode are placed at each wall. Since the whole problem is governed by a full multiphysic coupling, we resolve in 3D and at each time step a set of equations constituted by 2 turbulent transport equations -momentum and a passive scalar- completed by the potential distribution resolution. These 3 distinct physics are coupled through the Butler-Volmer boundary condition which acts at the electrode/electrolyte interface and governs the whole electrochemical activity. We present the numerical methodology used in this work and all the quantitative results obtained. We also report significant differences with the literature, mainly on the mass transfer statistics, which tend to confirm that a fully coupled approach is necessary to obtain a reliable description of the physic involved in such electrochemical transformations.

Doche, Olivier; Bauer, Frederic; Tardu, Sedat

2010-11-01

266

DNS Measurements at the .CN TLD Servers  

Microsoft Academic Search

The domain name system (DNS) is a fundamental Internet's infrastructure. There have been several studies on DNS measurements such as server workload and deployment characteristics. In this paper, based on the traffic collection spanning a two days period, we present a detailed study of the key characteristics of the .CN top level domain (TLD) name servers which are located at

Yuchi Xuebiao; Wang Xin; Li Xiaodong; Yan Baoping

2009-01-01

267

Secure Domain Name System (DNS) Deployment Guide.  

National Technical Information Service (NTIS)

The Domain Name System (DNS) is a distributed computing system that enables access to Internet resources by user-friendly domain names rather than IP addresses, by translating domain names to IP addresses and back. The DNS infrastructure is made up of com...

R. Chandramouli S. Rose

2013-01-01

268

Impact of configuration errors on DNS robustness  

Microsoft Academic Search

During the past twenty years the Domain Name System (DNS) has sustained phenomenal growth while maintaining satisfactory performance. However, the original design focused mainly on system robustness against physical failures, and neglected the impact of operational errors such as misconfigurations. Our recent measurement effort revealed three specific types of misconfigurations in DNS today: lame delegation, diminished server redundancy, and cyclic

Vasileios Pappas; Zhiguo Xu; Songwu Lu; Daniel Massey; Andreas Terzis; Lixia Zhang

2004-01-01

269

DNS performance and the effectiveness of caching  

Microsoft Academic Search

This paper presents a detailed analysis of traces of DNS and associated TCP traffic collected on the Internet links of the MIT Laboratory for Computer Science and the Korea Advanced Institute of Science and Technology (KAIST). The first part of the analysis details how clients at these institutions interact with the wide-area DNS system, focusing on performance and prevalence of

Jaeyeon Jung; Emil Sit; Hari Balakrishnan; Robert Morris

2001-01-01

270

Dns cache poisoning-the next generation  

Microsoft Academic Search

The old problem of DNS cache poisoning has again reared its ugly head. While some would argue that the domain name system protocol is inherently vulnerable to this style of attack due to the weakness of 16-bit transaction IDs, we cannot ignore the immediate threat while waiting for something better to come along. There are new attacks, which make DNS

J. Stewart

2003-01-01

271

NUMERICAL NOISE PM SIMULATION IN CMAQ  

EPA Science Inventory

We have found that numerical noise in the latest release of CMAQ using the yamo advection scheme when compiled on Linux cluster with pgf90 (5.0 or 6.0). We recommend to use -C option to eliminate the numerical noise....

272

A novel algorithm for DNS/LES of compressible turbulent flows  

NASA Astrophysics Data System (ADS)

A non-dissipative, robust, implicit algorithm is proposed for direct numerical and large-eddy simulation of compressible turbulent flows. The algorithm addresses the problems caused by low Mach numbers and under-resolved high Reynolds numbers. It collocates variables in space to allow easy extension to unstructured grids, and discretely conserves mass, momentum and total energy. The Navier-Stokes equations are non-dimensionalized using an incompressible scaling for pressure, and the energy equation is used to obtain an expression for the velocity divergence. A pressure-correction approach is used to solve the resulting equations such that the discrete divergence is constrained by the energy equation. As a result, the discrete equations analytically reduce to the incompressible equations at very low Mach number; i.e. the algorithm overcomes the acoustic time-scale limit without preconditioning or solution of an implicit system of equations. The algorithm discretely conserves kinetic energy in the incompressible inviscid limit, and is robust for inviscid compressible turbulence on the convective time-scale. These properties make it well-suited for DNS/LES of compressible turbulent flows. A parallel, structured grid flow solver was developed and used to apply the algorithm to acoustic propagation, the incompressible Taylor problem, periodic shock tube problem, laminar compressible boundary layer, isotropic turbulence and turbulent channel flow. The results are compared to analytical solution and experiment as appropriate. The simulations suggest that the algorithm is very promising for DNS/LES of compressible turbulent flows. Keywords: compressible turbulence, direct numerical simulation, large-eddy simulation, all-Mach number, non-dissipative, discrete energy conservation.

Hou, Yucheng

273

Numerical Simulation of Two Phase Flows.  

National Technical Information Service (NTIS)

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 treatmen...

M. S. Liou

2001-01-01

274

Particle Dispersion in a Transitional Axisymmetric Jet: A Numerical Simulation  

Microsoft Academic Search

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

275

Particle dispersion in a transitional axisymmetric jet: A numerical simulation  

Microsoft Academic Search

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

276

Numerical simulations of a relativistic magnetron  

Microsoft Academic Search

A two-dimensional particle-in-cell (PIC) simulation is used to study the self-consistent evolution of the space-charge cloud in a high-power magnetron. In the simulation, a rotating reference frame reduces the field solution to an inversion of Poisson's equation, which is solved in a cylindrical geometry. The particles are moved relativistically. The simulation is applied to the A6 magnetron, which is the

James C. Weatherall

1990-01-01

277

Detonation front theories: Using high-resolution DNS to define extended asymptotic scalings and models  

SciTech Connect

When the detonation reaction-zone length, {eta}{sub r}, is short in comparison to the dimensions of the explosive piece being burnt, the detonation can be viewed as a propagating surface (or front) separating burnt from unburnt material. If the product of the shock curvature, {kappa} and {eta}{sub r} is small (i.e., the scaled shock curvature satisfies the {vert_bar}{kappa}{eta}{sub r}{vert_bar} {much_lt} 1), then to leading order the speed of this surface, D{sub n}({kappa}) is a function only of {kappa}. It is in this limit that the original version of the asymptotic detonation front theory, called detonation shock dynamics (DSD), derives the propagation law, D{sub n}({kappa}). In this lecture, the authors compare D{sub n}({kappa})-theory with the results obtained with high-resolution direct numerical simulations (DNS), and then use the DNS results to guide the development of extended asymptotic front theories with enhanced predictive capabilities.

Aslam, T.D.; Bdzil, J.B.

1998-02-01

278

A hybrid simulation of numerical transmission systems  

Microsoft Academic Search

A general procedure for simulating the transmission of a lengthy sequence of symbols while analytically taking into account the effect of thermal noise and other interference is described. Computing time for the simulation is reduced by assuming periodicity of the transmitted sequence, by employing the Fast Fourier Transform for calculation, and by taking better advantage of the computer's memory capacity.

G. Jacovitti; P. Mandarini

1977-01-01

279

Numerical simulation of air flow in the human nasal cavity.  

PubMed

A highly automated method was used to construct numerical models of six 3-D human right nasal cavities from computed tomography data. Steady state airflow simulations were performed with computational fluid dynamics software for quiet breath on the six models. The method is validated with particle simulations. Simulation results from each of the six studies are compared. PMID:17281527

Wang, Kezhou; Denney, Thomas S; Morrison, Edward E; Vodyanoy, Vitaly J

2005-01-01

280

Numerical simulations of asteroid signals on the GAIA focal plane  

NASA Astrophysics Data System (ADS)

We present a numerical algorithm, based on a ray-tracing technique, to simulate the signals produced by asteroids crossing the fields of view of the GAIA astrometric detectors. The basic concepts of the simulation and their implementation in a numerical code are described, and some results are shown. We also present some computations of the photocenter displacement produced by extended objects having a given surface luminosity distribution, corresponding to asteroids obeying different possible scattering laws. A major application of our numerical simulator is to carry out a quantitative analysis of the actual capability of GAIA to obtain direct and accurate measurements of the apparent angular sizes of detected asteroids.

Dell'Oro, A.; Cellino, A.

2006-01-01

281

Rigorous Formulation of Two-Equation Heat Transfer Model of Turbulence Using Direct Simulations  

Microsoft Academic Search

A rigorous two-equation heat transfer model has been constructed with the aid of the most up-to-date direct numerical simulation (DNS) data for wall turbulence with heat transfer. The DNS data indicate that the near-wall profile of the dissipation rate, ?1, for the temperature variance, kt (= t¯ \\/2), is completely different from the existing model predictions. In this study, we

H. Hattori; Y. Nagano

1998-01-01

282

Numerical simulation of biped locomotion robot.  

National Technical Information Service (NTIS)

The Human Acts Simulation Program (HASP) has been performed since 1987 at JAERI. In this program, a human-shaped robot reads and understands instructions written in natural languages such as Japanese, planning and producing a required sequence of actions,...

E. Kume

1991-01-01

283

Numerical simulation of irradiation hardening in Zirconium  

NASA Astrophysics Data System (ADS)

A phase field model is developed to simulate interactions between gliding dislocations and irradiation induced damage loops (i.e., vacancy and self-interstitial loops) in Zirconium. Pinning contact interactions and long-range elastic interactions are simulated, with populations of defects generated based on experimental observations of typical damage microstructures in irradiated Zr. The model is employed to simulate irradiation hardening as a function of damage loop density. We find that the stress fields of damage loops contribute significantly to their effective obstacle strength, and that the elastic interactions cause the dependence of critical resolved shear stress on damage loop number density to deviate from analytical predictions of dispersed barrier hardening. The simulation predictions of the yield strength agree well with experimental measurements for different damage loop densities.

Boyne, A.; Shen, C.; Najafabadi, R.; Wang, Y.

2013-07-01

284

Numerical simulations of a relativistic magnetron  

SciTech Connect

A two-dimensional particle-in-cell (PIC) simulation is used to study the self-consistent evolution of the space-charge cloud in a high-power magnetron. In the simulation, a rotating reference frame reduces the field solution to an inversion of Poisson's equation, which is solved in a cylindrical geometry. The particles are moved relativistically. The simulation is applied to the A6 magnetron, which is the prototype for the new class of relativistic magnetrons. Good agreement is found with published experimental results. The simulation is used to study the effect of power extraction on efficiency, the role of the wave magnetic field on saturation, and relativistic effects on magnetron operation. Interaction regions within the charge cloud are identified.

Weatherall, J.C. (Pomona Div., General Dynamics, Pomona, CA (US))

1990-06-01

285

Numerical Simulation of an Ice Age Paleoclimate.  

National Technical Information Service (NTIS)

In order to simulate the climate of an ice age, a two-level, quasi-goestrophic, spectral general circulation model for the northern hemisphere is developed. Horizontal diffusion and vertical shearing stresses are incorporated along with a diabatic heating...

F. N. Alyea

1972-01-01

286

Polarization transmission at RHIC, numerical simulations  

SciTech Connect

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

287

Numerical simulations of gas turbine combustion  

Microsoft Academic Search

A numerical investigation of gas turbine combustion is conducted using the KIVA-3V code. Off-design conditions and spray parameters have significant effects on flow patterns, kinetic reactions and spray dynamics in the combustor, which consequently influences combustion performance and NOx emissions. This study provides insight into physical and chemical processes in combustion, and evaluates variations of combustion performance and NOx emissions

Ke Su

2002-01-01

288

Numerical simulation of saltwater intrusion experiment  

Microsoft Academic Search

We have modeled laboratory experiments of saltwater intrusion, similar to the so-called Henry Problem, using TOUGH2\\/EOS7. In general, the simulation showed good agreement to the experiment including the transient advancement and the final profile of the saltwater wedge that showed little dispersion in a homogeneous case. In a two-layer heterogeneous case, however, the simulation could not reproduce the experiment in

K. Karasaki; K. Maekawa

2007-01-01

289

Large eddy simulations of spatially growing subsonic and supersonic turbulent round jets  

Microsoft Academic Search

This paper presents an application of large eddy simulations (LESs) using the filtered structure function model to spatially developing compressible round jets issuing from a perturbed upstream velocity profile close to a top hat. For centreline Mach number M = 0.9 and Reynolds number Re = 3600, the numerical solution compares satisfactorily against a forced-jet direct numerical simulation (DNS) and

Mohamed Maidi; Marcel Lesieur

2005-01-01

290

A Priori Analysis of Subgrid Mass Flux Vectors from Massively Parallel Direct Numerical Simulations of High Pressure H2/O2 Reacting Shear Layers  

NASA Astrophysics Data System (ADS)

Direct Numerical Simulations (DNS) are conducted for temporally developing reacting H2/O2 shear layers at an ambient pressure of 100atm. The compressible form of the governing equations are coupled with the Peng Robinson real gas equation of state and are solved using eighth order central finite differences and fourth order Runge Kutta time integration with resolutions up to ˜3/4 billion grid points. The formulation includes a detailed pressure dependent kinetics mechanism having 8 species and 19 steps, detailed property models, and generalized forms of the multicomponent heat and mass diffusion vectors derived from nonequilibrium thermodynamics and fluctuation theory. The DNS is performed over a range of Reynolds numbers up to 4500 based on the free stream velocity difference and initial vorticity thickness. The results are then analyzed in an a priori manner to illustrate the role of the subgrid mass flux vector within the filtered form of the governing equations relevant to Large Eddy Simulations. The subgrid mass flux vector is found to be a significant term; particularly within localized regions of the flame.

Foster, Justin; Miller, Richard

2011-11-01

291

Protecting BGP Routes to Top Level DNS Servers  

Microsoft Academic Search

The Domain Name System (DNS) is an essential part of the Internet infrastructure and provides fundamental ser- vices, such as translating host names into IP addresses for Internet communication. The DNS is vulnerable to a num- ber of potential faults and attacks. In particular, false rout- ing announcements can deny access to the DNS service or redirect DNS queries to

Lan Wang; Xiaoliang Zhao; Dan Pei; Randy Bush; Daniel Massey; Allison Mankin; Shyhtsun Felix Wu; Lixia Zhang

2003-01-01

292

Numerical simulation of compressible flows with application to noise control  

Microsoft Academic Search

Spatial direct numerical simulations of compressible plane jets exhausting into parallel streams are examined. The inviscid mathematical model captures the most dynamically important, large-scale mixing events, such as vortex roll-up and pairings. Two-dimensional simulations employ the fully explicit (2-4) method, while three- dimensional simulations use implicit spatial compact differencing with Runge-Kutta time-advancement. All simulations utilize characteristic-based boundary conditions. Shear layer

Robert Stephen Reichert

1998-01-01

293

Numerical Simulation of Chern-Simons Inflation  

NASA Astrophysics Data System (ADS)

In this talk we show numerical results of the Chern-Simons Inflation Model proposed by Alexander, Marciano and Spergel. In this model, the Chern-Simons interaction of vector fields plays a central role in generating the inflationary epoch. According to the model, Inflation begins with a plasma made of interacting gauge fields and fermions. The Chern-Simons interaction then drives energy from the initial random spectrum into a narrow-band of frequencies at superhorizon scales. The fermion current also amplifies the gauge field at superhorizon scales. These gauge fields when combined with the Friedman equations can be broken into a system of hyperbolic equations and modeled numerically. We show that the amplification of horizon sized gauge fields produces the conditions to cause more than 60 e-folds of inflation.

Garrison, David; Preston, Annie; Alexander, Stephon

2012-03-01

294

Numerical simulation of in situ bioremediation  

SciTech Connect

Models that couple subsurface flow and transport with microbial processes are an important tool for assessing the effectiveness of bioremediation in field applications. A numerical algorithm is described that differs from previous in situ bioremediation models in that it includes: both vadose and groundwater zones, unsteady air and water flow, limited nutrients and airborne nutrients, toxicity, cometabolic kinetics, kinetic sorption, subgridscale averaging, pore clogging and protozoan grazing.

Travis, B.J.

1998-12-31

295

Unsteady PTV velocity field past an airfoil solved with DNS: Part 2. Validation and application at Reynolds numbers up to Re ? 104  

NASA Astrophysics Data System (ADS)

Hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS) is introduced in the series of two papers. Particle velocities on a laser-light sheet acquired with time-resolved PTV in a water tunnel are supplied to two-dimensional DNS with time intervals corresponding to the frame rate of the PTV. Hybrid velocity fields then approach those representing the PTV data in the course of time, and the reconstructed velocity fields satisfy the governing equations with the resolution comparable to numerical simulation. In part 2, by extending the capabilities of the hybrid simulation to higher Reynolds numbers, we simulate flows past the NACA0012 airfoil over ranges of Reynolds numbers ( Re ? 104) and angles of attack (-5° ? ? ? 20°) and validate the proposed technique by comparing with experimental results in terms of the lift and drag coefficients. We also compare the results with unsteady Reynolds-averaged Navier-Stokes (URANS) simulation in two-dimensions and show the advantages of the hybrid simulation against two-dimensional URANS.

Suzuki, Takao; Sanse, Akira; Mizushima, Takashi; Yamamoto, Fujio

2009-12-01

296

Numerical simulation of high enthalpy shock tunnel  

NASA Astrophysics Data System (ADS)

One of the most important problems on a development of a reentry vehicle is the prediction of real gas effect. In order to obtain the real gas data of reentry by ground test, the hypervelocity wind tunnel having extremely high reservoir condition, in which temperature and pressure are up to 10,000K and 1,500atm, is required. A free piston shock tunnel is the most useful facility which can produce such hypervelocity flow. The National Aerospace Laboratory is planning to develop the large free piston shock tunnel which can simulate the reentry of HOPE. In the present paper, CFD applications to the design and operation of the free piston shock tunnel are studied. The two topics are presented. One is the quasi-1D simulation to predict actual performances of free piston shock tunnels. Other is the axisymmetric 2D simulation of the reflected shock-boundary layer interactions to clarify the mechanism of the driver gas contamination.

Itoh, Katsuhiro; Takahashi, Masahiro

1994-06-01

297

Numerical simulation of magmatic hydrothermal systems  

NASA Astrophysics Data System (ADS)

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.

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

2010-03-01

298

DNS of a spatially evolving hypersonic turbulent boundary layer at Mach 8  

NASA Astrophysics Data System (ADS)

This paper reports the direct numerical simulation (DNS) for hypersonic turbulent boundary layer over a flat-plate at Ma ?=8 with the ratio of wall-to-freestream temperature equal to 1.9, which indicates an extremely cold wall condition. It is primarily used to assess the wall temperature effects on the mean velocity profile, Walz equation, turbulent intensity, strong Reynolds analogy (SRA), and compressibility. The present high Mach number with cold wall condition induces strong compressibility effects. As a result, the Morkovin's hypothesis is not fully valid and so the classical SRA is also not fully consistent. However, some modified SRA is still valid at the far-wall region. It is also verified that the semi-local wall coordinate y* is better than conventional y + in analysis of statistics features in turbulent boundary layer (TBL) in hypersonic flow.

Liang, Xian; Li, XinLiang

2013-07-01

299

Numerical Simulation of Reactive Flow in Internal Combustion Engines.  

National Technical Information Service (NTIS)

Multidimensional numerical simulations of the reactive fluid flow in an internal combustion engine cylinder are useful in helping engine designers obtain insight into the physical mechanisms governing efficiency and pollutant formation. A comprehensive nu...

L. D. Cloutman J. K. Dukowicz J. D. Ramshaw

1980-01-01

300

Numerical Simulation and Immersive Visualization of Hairpin Vortices.  

National Technical Information Service (NTIS)

To better understand the vortex dynamics of coherent structures in turbulent and transitional boundary layers, we consider direct numerical simulation of the interaction between a flat-plate-boundary-layer flow and an isolated hemispherical roughness elem...

H. M. Tufo P. F. Fischer M. E. Papka K. Blom

1999-01-01

301

Defining predictive maturity for validated numerical simulations  

Microsoft Academic Search

The increasing reliance on computer simulations in decision-making motivates the need to formulate a commonly accepted definition for “predictive maturity.” The concept of predictive maturity involves quantitative metrics that could prove useful while allocating resources for physical testing and code development. Such metrics should be able to track progress (or lack thereof) as additional knowledge becomes available and is integrated

François Hemez; H. Sezer Atamturktur; Cetin Unal

2010-01-01

302

Numerical simulations of motorcycle helmet impact tests  

Microsoft Academic Search

The main objective of this study was to simulate experimental impact tests on a commercially available motorcycle helmet and to develop a virtual design tool. The mechanical properties of the shell and the foam liner of the helmet were estimated from existing material data taken from the open literature. The material data were adjusted to match the temperature conditioning of

M. Aiello; U. Galvanetto; L. Iannucci

2007-01-01

303

Numerical simulation of laser full penetration welding  

Microsoft Academic Search

A three dimensional finite element model has been developed to dynamically simulate the laser full penetration welding process. The parametric design capabilities of the finite element code ANSYS (revision 5.4) were employed for this purpose. The model calculates the transient temperature profile and the dimensions of the fusion zone during the welding process. The heat source was parameterized by the

Komeil Kazemi; John A. Goldak

2009-01-01

304

Numerical simulation for a centrifugal heart pump  

Microsoft Academic Search

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

Keiji Yano

1997-01-01

305

Numerical simulation of rough-surface aerodynamics  

Microsoft Academic Search

Computational fluid dynamics (CFD) simulations of flow over surfaces with roughness in which the details of the surface geometry must be resolved pose major challenges. The objective of this study is to address these challenges through two important engineering problems, where roughness play a critical role---flow over airfoils with accrued ice and flow and heat transfer over turbine blade surfaces

Xingkai Chi

2005-01-01

306

Numerical Simulations of Europa Hydrothermal Plumes  

Microsoft Academic Search

The liquid water interiors of Europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor, leading to the development of buoyant hydrothermal plumes. These plumes potentially control icy surface geomorphology, and are of interest to astrobiologists. We have performed a series of simulations of these plumes using the

J. C. Goodman; E. Lenferink

2009-01-01

307

Refined numerical models for multidimensional type Ia supernova simulations  

Microsoft Academic Search

Following up on earlier work on this topic (Reinecke et al. \\\\cite{reinecke-etal-99a},a), we present an improved set of numerical models for simulations of white dwarfs exploding as type Ia supernovae (SNe Ia). Two-dimensional simulations were used to test the reliability and numerical robustness of these algorithms; the results indicate that integral quantities like the total energy release are insensitive to

M. Reinecke; W. Hillebrandt; J. C. Niemeyer

2002-01-01

308

Numerical Simulation of PU Foaming Flow in a Refrigerator Cabinet  

Microsoft Academic Search

We have developed a numerical method for unsteady three-dimensional (3D) simulation of rigid polyurethane (PU) foaming flow in a refrigerator cabinet in this study. The governing equation for the compressible foaming flow is approximated with the Navier-Stokes equation, which means the foaming flow is assumed to be Newtonian. Numerical methods of simulation for unsteady compressible PU foaming flow with a

Young Bae Kim; Kyung Do Kim; Sang Eui Hong; Jong Goo Kim; Man Ho Park; Ju Hyun Kim; Jae Keun Kweon

2005-01-01

309

A pseudospectral numerical scheme for the simulation of natural flows  

Microsoft Academic Search

A pseudo-spectral numerical scheme based on a variational formulation was developed for the three-dimensional, time-dependent direct simulation of natural flows. Pseudo-spectral methods were selected due to their higher accuracy and suitability for complex flow simulations. The specific problem of Rayleigh-Bénard convection was chosen to illustrate the numerical scheme and investigate the problem of heat transfer in buoyancy- driven flows. The

Laila Guessous

1999-01-01

310

NUMERICAL METHODS FOR THE SIMULATION OF HIGH INTENSITY HADRON SYNCHROTRONS.  

SciTech Connect

Numerical algorithms for PIC simulation of beam dynamics in a high intensity synchrotron on a parallel computer are presented. We introduce numerical solvers of the Laplace-Poisson equation in the presence of walls, and algorithms to compute tunes and twiss functions in the presence of space charge forces. The working code for the simulation here presented is SIMBAD, that can be run as stand alone or as part of the UAL (Unified Accelerator Libraries) package.

LUCCIO, A.; D'IMPERIO, N.; MALITSKY, N.

2005-09-12

311

Numerical simulation of cross field amplifiers  

SciTech Connect

Cross field amplifiers (CFA) have been used in many applications where high power, high frequency microwaves are needed. Although these tubes have been manufactured for decades, theoretical analysis of their properties is not as highly developed as for other microwave devices such as klystrons. One feature distinguishing cross field amplifiers is that the operating current is produced by secondary emission from a cold cathode. This removes the need for a heater and enables the device to act as a switch tube, drawing no power until the rf drive is applied. However, this method of generating the current does complicate the simulation. We are developing a simulation model of cross field amplifiers using the PIC code CONDOR. We simulate an interaction region, one traveling wavelength long, with periodic boundary conditions. An electric field with the appropriate phase velocity is imposed on the upper boundary of the problem. Evaluation of the integral of E{center dot}J gives the power interchanged between the wave and the beam. Given the impedance of the structure, we then calculate the change in the traveling wave field. Thus we simulate the growth of the wave through the device. The main advance of our model over previous CFA simulations is the realistic tracking of absorption and secondary emission. The code uses experimental curves to calculate secondary production as a function of absorbed energy, with a theoretical expression for the angular dependence. We have used this code to model the 100 MW X-band CFA under construction at SLAC, as designed by Joseph Feinstein and Terry Lee. We are examining several questions of practical interest, such as the power and spectrum of absorbed electrons, the minimum traveling wave field needed to initiate spoke formation, and the variation of output power with dc voltage, anode-cathode gap, and magnetic field. 5 refs., 8 figs.

Eppley, K.

1990-01-01

312

Shocks induced by laser driven flyer plates: 2. numerical simulations  

Microsoft Academic Search

We present numerical simulations of shocks and damage induced by laser-driven flyer plates impacting metallic targets. A theoretical description of the different physical processes is included in the 1-D laser-matter numerical code FCI1. Good correlations between numerical and experimental results are obtained. Flyer plate velocities of few km\\/s and impact pressures greater than 1 Mbar are reached. In relation with

B. Cazalis; C. Boissière; G. Sibille

1996-01-01

313

Numerical simulation of melting of ice around a horizontal cylinder  

Microsoft Academic Search

The problem of outward melting of ice around a horizontal isothermal cylinder is considered. A numerical model in which natural convection induced in the molten water encompassing density inversion is taken into consideration has been developed. Via finite-difference solution of the melting model, numerical simulation of melting of ice has been performed for the cylinder surface temperature T(i) = 4,

C. J. Ho; S. Chen

1986-01-01

314

Numerical simulations of a low power microchannel thermal cycling reactor  

Microsoft Academic Search

A roadblock to the development of stand-alone microscale biomedical and chemical analysis systems is the relatively high heating power requirement of the microscale reactors, which typically exceeds the capability of low cost batteries. In this study, a microchannel thermal cycling reactor design using in-channel heating and passive cooling is proposed and a numerical model has been developed. Numerical simulations were

David Erickson; Dongqing Li

2002-01-01

315

On Numerical Simulation of Propagation of Solitons in Microstructured Media  

Microsoft Academic Search

Wave propagation in microstructured media is simulated numerically making use of two different models. In the first case a Korteweg-de Vries type equation is used for modeling 1D wave motion in granular materials. In the second case a Boussinesq type equation is applied for modeling 1D wave motion in Mindlin type microstructured solids. Both equations are integrated numerically under localized

A. Salupere; L. Ilison; K. Tamm

2008-01-01

316

Direct numerical simulation of heat transfer over riblets  

Microsoft Academic Search

Riblets are well-known as a passive mean for drag reduction in turbulent flow conditions, but their effectiveness for heat transfer is quite controversial. In this paper we present the numerical results for fully developed laminar and turbulent flow and heat transfer in a channel with triangular riblets. The turbulent study is performed by means of direct numerical simulation at a

E Stalio; E Nobile

2003-01-01

317

Numerical simulation of gas injection for upstructure oil drainage  

Microsoft Academic Search

This study describes the development and application of a 2-dimensional numerical model capable of simulating a gas injection project for upstructure oil drainage. The partial differential equations are approximated by the finite difference method. The numerical model stimulates the fully implicit 3-phase flow of oil, water, and gas. A simultaneous solution of the pressure and saturation distributions is done by

Strickland

1976-01-01

318

Numerical Simulation Applied to Micromixer Design  

NASA Astrophysics Data System (ADS)

We describe the development of new microfluidic components designed to optimize mixing. The components use pressure-driven flow and consist of a microchannel with surface features (such as diagonal grooves, chevron-shaped grooves, and herringbone-shaped grooves) cut into the top and/or bottom of the channel. We describe a fast advection routine used to predict the transport of passive scalars through the components and the various metrics used to characterize the effectiveness of a proposed design. We also present mixer designs optimized for our chosen metrics over our feature set and compare the numerical predictions with experimental results.

Mott, David; Markus, Daniel; Howell, Peter

2005-11-01

319

Efficient numerical algorithm for multiphase field simulations.  

PubMed

Phase-field models have emerged as a successful class of models in a wide variety of applications in computational materials science. Multiphase field theories, as a subclass of phase-field theories, have been especially useful for studying nucleation and growth in polycrystalline materials. In theory, an infinite number of phase-field variables are required to represent grain orientations in a rotationally invariant free energy. However, limitations on available computational time and memory have restricted the number of phase-field variables used in the simulations. We present an approach by which the time and memory requirements are drastically reduced relative to standard algorithms. The proposed algorithm allows us the use of an unlimited number of phase-field variables to perform simulations without the associated burden on computational time or memory. We present the algorithm in the context of coalescence free grain growth. PMID:16486310

Vedantam, Srikanth; Patnaik, B S V

2006-01-19

320

Numerical simulation of saltwater intrusion experiment  

NASA Astrophysics Data System (ADS)

We have modeled laboratory experiments of saltwater intrusion, similar to the so-called Henry Problem, using TOUGH2/EOS7. In general, the simulation showed good agreement to the experiment including the transient advancement and the final profile of the saltwater wedge that showed little dispersion in a homogeneous case. In a two-layer heterogeneous case, however, the simulation could not reproduce the experiment in one aspect. In the experiment, the fast-moving colored saltwater traveling in the higher permeability layer was observed encroaching into the lower permeability layer below. However, at this writing, we have not been able to reproduce this phenomenon, which could be caused by some instability or heterogeneity within the layers.

Karasaki, K.; Maekawa, K.

2007-12-01

321

Numerical simulations of the ionospheric interchange instability  

SciTech Connect

The nonlinear dynamics and spectral characteristics of the ionospheric interchange instability are studied numerically and analytically. A two-dimensional model is derived. The model is valid for both the collision-dominated regime and the inertia-dominated regime. Numerical solutions for the evolution of rising plasma bubbles, unstable plasma strata, and driven plasma irregularities are presented and discussed for both regimes. In the collisional regime, the principal result is that the evolution of the instability tends to an anisotropic state consisting of nearly sinusoidal (quasi-periodic) variation along the horizontal direction, and steepened (shock-like) structures propagating in the vertical direction along the extreme of the quasi-periodic structures. In the inertial regime, if the coupling between the density and the vorticity equations is weak, the instability leads to an isotropic turbulent state which has the same characteristics as the two-dimensional Navier-Stokes turbulence with a passive scalar. For strongly driven interchange instability, enstrophy invariance is violated and only an energy-cascade inertial subrange is observed. Results are compared with in-situ rocket and satellite measurements of the intermediate-wavelength equatorial F-region irregularities.

Zargham, S.

1988-01-01

322

Numerical simulation of unsteady separated flows  

NASA Astrophysics Data System (ADS)

Two unsteady flows dominated by the occurrence of separation are simulated through the use of the discrete vortex model. The first of these is a sinusoidally oscillating flow about a circular cylinder at a Keulegan-Carpenter number of K = 10. The vortex model has been combined with the boundary layer calculations and the positions of the separation and stagnation points, the evolution of the wake, the velocity and pressure distributions, and the instantaneous forces have been calculated and compared, whenever possible, with those obtained experimentally. The model has successfully simulated the occurrence of the transverse half Karman vortex street. The calculated positions of the vortices are in good agreement with those obtained experimentally. The measured and calculated in-line forces and the differential pressure distributions showed reasonably good agreement. The second simulation dealt with a rapidly decelerating flow about a two-dimensional sharp-edged camber. An extensive study of the velocity field in the vicinity of the singular points led to the development of a novel method for the introduction of vorticity at variable time intervals. The measured and calculated characteristics of the flow, such as the evolution of the wake and the forces acting on the camber, were found to be in excellent agreement.

Mostafa, Samir I.

1987-06-01

323

DNS measurements at a root server  

Microsoft Academic Search

The Domain Name System (DNS) prescribes domain names to be used in network transactions (email, web requests, etc.) instead of IP addresses. The root of the DNS distributed database is managed by 13 root nameservers. We passively measure the performance of one of them: F.root-servers.net. These measurements show an astounding number of bogus queries: from 60-85% of observed queries were

Nevil Brownlee; K. C. Claffy; E. Nemeth

2001-01-01

324

Protecting browsers from dns rebinding attacks  

Microsoft Academic Search

DNS rebinding attacks subvert the same-origin policy of browsers and convert them into open network proxies. We survey new DNS rebinding attacks that exploit the inter- action between browsers and their plug-ins, such as Flash Player and Java. These attacks can be used to circumvent firewalls and are highly cost-eective for sending spam e- mail and defrauding pay-per-click advertisers, requiring

Collin Jackson; Adam Barth; Andrew Bortz; Weidong Shao; Dan Boneh

2007-01-01

325

Using numerical simulation with rapid prototyping and investment casting  

NASA Astrophysics Data System (ADS)

This article presents an approach to making an aluminum automobile prototype by integrating numerical simulation and rapid prototyping into investment casting. Following the integrated prototype procedure, a sound aluminum (Al-Si-7Mg) manifold prototype with excellent contour and an acceptable surface finish was made with only one casting trial. This study indicated that the potential of the rapid prototyping-investment casting coupling could be more effective with the aid of integrated numerical simulation, and numerical optimization of the casting parameters aids in minimizing the risk of casting failure and avoiding the iterative casting trials.

Wuis, M.; Schädlich-Stubenrauch, J.; Wagner, I.; Sahm, P. R.

2000-08-01

326

Numerical simulation of electrospray in the cone-jet mode.  

PubMed

We present a robust and computationally efficient numerical scheme for simulating steady electrohydrodynamic atomization processes (electrospray). The main simplification assumed in this scheme is that all the free electrical charges are distributed over the interface. A comparison of the results with those calculated with a volume-of-fluid method showed that the numerical scheme presented here accurately describes the flow pattern within the entire liquid domain. Experiments were performed to partially validate the numerical predictions. The simulations reproduced accurately the experimental shape of the liquid cone jet, providing correct values of the emitted electric current even for configurations very close to the cone-jet stability limit. PMID:23005852

Herrada, M A; López-Herrera, J M; Gañán-Calvo, A M; Vega, E J; Montanero, J M; Popinet, S

2012-08-08

327

Direct numerical simulation of round turbulent jets in crossflow  

Microsoft Academic Search

Direct numerical simulation is used to study a round turbulent jet in a laminar crossflow. The ratio of bulk jet velocity to free-stream crossflow velocity is 5.7 and the Reynolds number based on the bulk jet velocity and the jet exit diameter is 5000. The mean velocity and turbulent intensities from the simulations are compared to data from the experiments

Suman Muppidi; Krishnan Mahesh

2007-01-01

328

Numerical Simulations of Magnetic Vortices In High Temperature Superconductors  

Microsoft Academic Search

Numerical simulations of magnetic vortices in high temperature superconductors are discussed. The behaviour of the depinning force as a function of the number of vortices, defects, and the angle of the defects is presented. The structure of pinned and moving vortex systems are also explored. Our simulations show the complex interplay of disorder and interactions in dynamical systems.

Mike E. Gallamore; Grant E. McCormack; Thomas P. Devereaux

329

Numerical simulation of ablative Rayleigh-Taylor instability  

Microsoft Academic Search

Numerical simulations over a wide range of parameters of the linear stability of an ablating laser-produced plasma show a linear decrease in the growth rate with increasing ablation velocity. Simulations in planar and spherical geometries, with red and blue laser light, at high and low intensities, and at high and low accelerations, all seem to nearly follow a consistent law

John H. Gardner; Stephen E. Bodner; Jill P. Dahlburg

1991-01-01

330

Numerical simulation of ablative Rayleigh–Taylor instability  

Microsoft Academic Search

Numerical simulations over a wide range of parameters of the linear stability of an ablating laser-produced plasma show a linear decrease in the growth rate with increasing ablation velocity. Simulations in planar and spherical geometries, with red and blue laser light, at high and low intensities, and at high and low accelerations, all seem to nearly follow a consistent law

John H. Gardner; Stephen E. Bodner; Jill P. Dahlburg

1991-01-01

331

Numerical Simulations in Cosmology II: Spatial and Velocity Biases  

Microsoft Academic Search

We give a summary of recent results on spatial and velocity biases in cosmological models. Progress in numerical techniques made it possible to simulate halos in large volumes with a such accuracy that halos survive in dense environments of groups and clusters of galaxies. Halos in simulations look like real galaxies, and, thus, can be used to study the biases

Anatoly Klypin

2000-01-01

332

Numerical simulation of electromagnetic turbulence in tokamaks  

SciTech Connect

Nonlinear two- and three-fluid equations are written for the time evolution of the perturbed electrostatic potential, densities, vector potential, and parallel ion motion of collisional and trapped electron plasmas in tokamak geometry. The nonlinear terms arise from the E x B/sub 0/ convection (d/dt = partial/partialt+v/sub E/ x del/sub perpendicular/) and magnetic flutter (del-tilde/sub parallel/ = del/sub parallel/+(B/sub perpendicular//B/sub 0/) x del/sub perpendicular/). Simplified two-dimensional (k/sub perpendicular/) mode coupling simulations with a fixed average parallel wavenumber (k/sub parallel/ = 1/Rq) and curvature drift (..omega../sub g/ = (L/sub n//R)..omega../sub asterisk/ ) characteristic of outward ballooning are performed. Homogeneous stationary turbulent states of the dissipative drift and interchange modes from 0< or =..beta..<..beta../sub crit/ for both the collisional and trapped electron plasmas are obtained. Transport coefficients associated with E x B and magnetic motions are calculated. The problem of simulating plasmas with high viscous Reynolds number is treated with an absorbing mantle at the largest wavenumbers.

Waltz, R.E.

1985-02-01

333

Numerical Simulation of Ultracold Neutral Plasma Clouds.  

NASA Astrophysics Data System (ADS)

In recent experiments, Killian et al. [Phys. Rev. Lett. 83, 4776 (1999)] produced ultracold neutral plasmas by photoionizing small clouds of laser cooled atoms. This paper presents the results of novel molecular dynamic simulations for the early time evolution ( ~ 50 plasma periods) of such plasmas. The simulations are challenging because it is necessary to follow three-body recombination into weakly bound (high n quasi-classical) Rydberg states, and the time scale for such states is short compared to that for the plasma dynamics. Contrary to earlier speculation, we observe no evidence of strong correlation even if the initial value of the coupling parameter ( ?e = e^2 / akTe ) is much larger than unity. Rapid electron heating reduces the value of ?e to less than unity (in a plasma period), as the electrons fall into the Coulomb wells of neighboring ions. The rate of three-body recombination is in reasonable agreement with the traditional formula, R = 3.9 × 10-9sec-1[n; (cm-3)]^2 [ Te (^circ K)]-9/2, but care must be taken to use the correct temporally evolving temperature, T_e. Interestingly, a byproduct of three-body recombination is the production of very energetic electrons ( \\varepsilon >> kTe ) that are ejected from the cloud and form a surrounding halo.

Kuzmin, S. G.; O'Neil, T. M.

2001-10-01

334

2D Numerical Simulations of Soil Nail Walls  

Microsoft Academic Search

In practice, numerical simulations of soil nail walls are often carried out to assess the performance and stability. In the\\u000a present study, implications of the use of advanced soil models, such as hardening soil model and hardening soil with small-strain\\u000a stiffness model to simulate the behavior of in situ soil on the overall response of simulated soil nail wall have

Vikas Pratap Singh; G. L. Sivakumar Babu

2010-01-01

335

Numerical simulation of length-limited parametric sound beam  

NASA Astrophysics Data System (ADS)

This study proposes a numerical simulation method that predicts nonlinear propagation of ultrasound beams in order to estimate the sound field of parametric array in the time domain. Basically, the method resorts to solving numerically and compactly the governing equations in a compressible viscous fluid using the Yee algorithm finite-difference time domain method. The simulation indicates a narrow audible sound beam which is a feature of the parametric array. Additionally, a length-limited parametric sound beam, which is proposed by Hedberg et al. [C. M. Hedberg et al., Acoust. Phys. 56, 637-639 (2010)], is numerically simulated as a model application. A pair of parametric sound sources generates the length-limited sound beam by control of the amplitudes and initial phases of the sources. The simulation shows a narrow truncated array length-limited sound beam.

Nomura, Hideyuki; Hedberg, Claes M.; Kamakura, Tomoo

2012-05-01

336

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

337

Numerical Simulation of Unsteady Driven Cavity Flow  

NASA Astrophysics Data System (ADS)

A numerical study is performed on the flow of an incompressible fluid driven in a square cavity. The behavior of unsteady flows beyond the first Hopf bifurcation is investigated. The first Hopf bifurcation is localized at \\mathit{Re}cr1=7987± 0.2% with the fundamental frequency fB=0.4519, in good agreement with the previous studies. A secondary Hopf bifurcation occurs at \\mathit{Re}cr2=9575± 3%, which generates a quasi-periodic solution with two incommensurable frequencies fB and fH, up to the annihilation of fB at \\mathit{Re}cr3=10975± 2%. While quasi-periodic flow is observed for \\mathit{Re}cr2?\\mathit{Re}?\\mathit{Re}cr3 on this solution branch, another branch of the periodic solution with fundamental frequency fL (

Osada, Takuya; Iwatsu, Reima

2011-09-01

338

Primitive numerical simulation of circular Couette flow  

SciTech Connect

The azimuthal-invariant, 3-d cylindrical, incompressible Navier-Stokes equations are solved to steady state for a finite-length, physically realistic model. The numerical method relies on an alternating-direction implicit (ADI) scheme that is formally second-order accurate in space and first-order accurate in time. The equations are linearized and uncoupled by evaluating variable coefficients at the previous time iteration. Wall grid clustering is provided by a Roberts transformation in radial and axial directions. A vorticity-velocity formulation is found to be preferable to a vorticity-stream function approach. Subject to no-slip, Dirichlet boundary conditions, except for the inner-cylinder rotation velocity (impulsive start-up) and zero-flow initial conditions, nonturbulent solutions are obtained for sub- and supercritical Reynolds numbers of 100 to 400 for a finite geometry. An axially-stretched model solution is shown to asymptotically approach the 1-d analytic Couette solution at the cylinder midheight. Flowfield change from laminar to Taylor-vortex flow is discussed as a function of Reynolds number.

Hasiuk, J.F.

1988-01-01

339

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

340

Numerical Simulation of Colliding Ion Acoustic Solitons  

NASA Astrophysics Data System (ADS)

The ion acoustic wave dispersion relation ?= k Cs we are familiar with, is in the long wave length limit. Inclusion of short wave-length (Debye length) scale through Poisson equation gives rise to the Korteweg de Vries (KdV) equation. We simulate propagation of solitary waves by solving the KdV equation in one dimensional and two dimensional planer geometries (Kadomtsev-Petviashvili equation).ootnotetext B.B.Kadomtsev, Doklady Akademii Nauk SSSR 192, 753 (1970).^,ootnotetextY.Nishida and T.Nagasawa, Phys. Rev. Lett. 42, 379 (1979). On the other hand, a different nonlinear term, ponderomotive force gives rise to Langmuir solitons by the interaction between high frequency Langmuir waves and low frequency ion acoustic waves.ootnotetextV.E.Zhaharov, Sov. Phys. JETP 35, 908 (1972). We discuss our studies on 1d-1v Vlasov-Poisson system employing the splitting schemeootnotetextC.Z.Cheng and G.Knorr, J. Comput. Phys. 22, 330 (1976). (by the method of characteristics).

Nishimura, Y.; Chen, Y. H.; Cheng, C. Z.

2011-11-01

341

Analysis of turbulent transport and mixing in transitional Rayleigh-Taylor unstable flow using direct numerical simulation data  

NASA Astrophysics Data System (ADS)

Data from a 1152×760×1280 direct numerical simulation (DNS) [N. J. Mueschke and O. Schilling, ``Investigation of Rayleigh-Taylor turbulence and mixing using direct numerical simulation with experimentally measured initial conditions. I. Comparison to experimental data,'' 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; Mueschke, Nicholas J.

2010-10-01

342

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

343

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

344

Numerical Simulation of Ice Accretions Based on Unstructured Grids  

NASA Astrophysics Data System (ADS)

An Eulerian method to numerically simulate ice accretions on airfoils based on unstructured grids has been presented. The Euler Equations are employed to solve the flowfields of the airfoils. The governing equations for droplets are solved based on the velocity distribution of the airflow to obtain the collection efficiency on the airfoil surfaces. The different freezing models are employed to simulate the freezing processes of the rime and glaze ice in order to calculate the ice amount. The ice accretions on a NACA 0012 airfoil have been simulated and the comparison with the experimental data indicates that the simulated method presented is feasible and effective.

Zhang, Q.; Gao, Z. H.

2011-09-01

345

Finite-rate chemistry and transient effects in Direct Numerical Simulations of turbulent non-premixed flames  

SciTech Connect

Three-dimensional Direct Numerical Simulations (DNS) of turbulent non-premixed flames including finite-rate chemistry and heat release effects were performed. Two chemical reaction models were considered: (1) a single-step global reaction model in which the heat release and activation energy parameters are chosen to model methane-air combustion, and (2) a two-step reaction model to simulate radical production and consumption and to compare against the single-step model. The model problem consists of the interaction between an initially unstrained laminar diffusion flame and a three-dimensional field of homogeneous turbulence. Conditions ranging from fast chemistry to the pure mixing limit were studied by varying a global Damkoehler number. Results suggest that turbulence-induced mixing acting along the stoichiometric line leads to a strong modification of the inner structure of the turbulent flame compared with a laminar strained flame, resulting in intermediate species concentrations well above the laminar prediction. This result is consistent with experimental observations. Comparison of the response of the turbulent flame structure due to changes in the scalar dissipation rate with a steady strained laminar flame reveals that unsteady strain rates experienced by the turbulent flame may be responsible for the observed high concentrations of reaction intermediates.

Mahalingam, S. [Colorado Univ., Boulder, CO (United States). Dept. of Mechanical Engineering; Chen, J.H. [Sandia National Labs., Livermore, CA (United States); Vervisch, L. [Institut de Mecanique des Fluides, Numeriques (France)

1994-01-01

346

Numerical Simulation of Anisotropic Preheating Ablative Rayleigh-Taylor Instability  

NASA Astrophysics Data System (ADS)

The linear growth rate of the anisotropic preheating ablative Rayleigh-Taylor instability (ARTI) is studied by numerical simulations. The preheating model ?(T) = ?SH[1 + f(T)] is applied, where f(T) is the preheating function interpreting the preheating tongue effect in the cold plasma ahead of the ablative front. An arbitrary coefficient D is introduced in the energy equation to study the influence of transverse thermal conductivity on the growth of the ARTI. We find that enhancing diffusion in a plane transverse to the mean longitudinal flow can strongly reduce the growth of the instability. Numerical simulations exhibit a significant stabilization of the ablation front by improving the transverse thermal conduction. Our results are in general agreement with the theory analysis and numerical simulations by Masse [Phys. Rev. Lett. 98 (2007) 245001].

Wang, Li-Feng; Ye, Wen-Hua; Li, Ying-Jun

2010-02-01

347

Dynamics of scalar dissipation in isotropic turbulence: a numerical and modelling study  

Microsoft Academic Search

The physical mechanisms underlying the dynamics of the dissipation of passive scalar fluctuations with a uniform mean gradient in stationary isotropic turbulence are studied using data from direct numerical simulations (DNS), at grid resolutions up to 5123. The ensemble-averaged Taylor-scale Reynolds number is up to about 240 and the Schmidt number is from 1 8 to 1. Special attention is

P RAKASH V EDULA; P. K. Y EUNG

2001-01-01

348

Study on the numerical schemes for hypersonic flow simulation  

NASA Astrophysics Data System (ADS)

Hypersonic flow is full of complex physical and chemical processes, hence its investigation needs careful analysis of existing schemes and choosing a suitable scheme or designing a brand new scheme. The present study deals with two numerical schemes Harten, Lax, and van Leer with Contact (HLLC) and advection upstream splitting method (AUSM) to effectively simulate hypersonic flow fields, and accurately predict shock waves with minimal diffusion. In present computations, hypersonic flows have been modeled as a system of hyperbolic equations with one additional equation for non-equilibrium energy and relaxing source terms. Real gas effects, which appear typically in hypersonic flows, have been simulated through energy relaxation method. HLLC and AUSM methods are modified to incorporate the conservation laws for non-equilibrium energy. Numerical implementation have shown that non-equilibrium energy convect with mass, and hence has no bearing on the basic numerical scheme. The numerical simulation carried out shows good comparison with experimental data available in literature. Both numerical schemes have shown identical results at equilibrium. Present study has demonstrated that real gas effects in hypersonic flows can be modeled through energy relaxation method along with either AUSM or HLLC numerical scheme.

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

2009-10-01

349

Numerical simulation of dynamic fracture and failure in solids  

SciTech Connect

Numerical simulation of dynamic fracture and failure processes in solid continua using Lagrangian finite element techniques is the subject of discussion in this investigation. The specific configurations in this study include penetration of steel projectiles into aluminum blocks and concrete slabs. The failure mode in the aluminum block is excessive deformation while the concrete slab fails by hole growth, spallation, and scabbing. The transient dynamic finite element code LS-DYNA2D was used for the numerical analysis. The erosion capability in LS-DYNA2D was exercised to carry out the fracture and failure simulations. Calculated results were compared to the experimental data. Good correlations were obtained.

Chen, E.P.

1994-05-01

350

Meshless numerical simulation for fully nonlinear water waves  

NASA Astrophysics Data System (ADS)

A meshless numerical model for nonlinear free surface water wave is presented in this paper. An approach of handling the moving free surface boundary is proposed. Using the fundamental solution of the Laplace equation as the radial basis functions and locating the source points outside the computational domain, the problem is solved by collocation of only a few boundary points. Present model is first applied to simulate the generation of periodic finite-amplitude waves with high wave-steepness and then is employed to simulate the modulation of monochromatic waves passing over a submerged obstacle. Good agreements are observed as compared with experimental data and other numerical models.

Wu, Nan-Jing; Tsay, Ting-Kuei; Young, D. L.

2006-01-01

351

Numerical simulation of the Langevin equation for skewed turbulence  

SciTech Connect

In this paper the authors present a numerical method for the generalized Langevin equation of motion with skewed random forcing for the case of homogeneous, skewed turbulence. The authors begin by showing how the analytic solution to the Langevin equation for this case can be used to determine the relationship between the particle velocity moments and the properties of the skewed random force. They then present a numerical method that uses simple probability distribution functions to simulate the effect of the random force. The numerical solution is shown to be exact in the limit of infinitesimal time steps, and to be within acceptable error limits when practical time steps are used.

Ermak, D.L. [Lawrence Livermore National Lab., CA (United States); Nasstrom, J.S. [EG and G Energy Measurements Inc., Pleasanton, CA (United States)

1994-12-01

352

Numerical simulation of tethered DNA in shear flow.  

PubMed

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. PMID:21508485

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

2011-04-20

353

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

354

Numerical simulation of protein stamping process driven by capillary force.  

PubMed

Numerical simulations based on first-principle conservation laws of mass and momentum are performed to observe flow characteristics during the stamping process. The protein solution is transferred by a new design of microstamps with microchannels and printed on a bottom substrate. Furthermore, key physics of the stamping process and the control factors achieving uniform spot size can be identified and optimized after these simulations. PMID:16696302

Lin, Shih-Chang; Tseng, Fangang; Chieng, Ching-Chang

2002-09-01

355

Numerical viscosity in hydrodynamics simulations in general relativity  

Microsoft Academic Search

We present an alternative method to estimate the numerical viscosity in\\u000asimulations of astrophysical objects, which is based in the damping of fluid\\u000aoscillations. We apply the method to general relativistic hydrodynamic\\u000asimulations using a spherical coordinates. We perform 1D-spherical and 2D-\\u000aaxisymmetric simulations of radial oscillations in spherical systems. We\\u000acalibrate first the method with simulations with added bulk

Pablo Cerdá-Durán

2009-01-01

356

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

357

Solid freeform fabrication of aluminum alloy components: Numerical simulations  

Microsoft Academic Search

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

358

Numerical Simulation of Friction Stir Welding by Natural Element Methods  

Microsoft Academic Search

In this work we address the problem of numerically simulating the Friction Stir Welding process. Due to the special characteristics\\u000a of this welding method (i.e., high speed of the rotating pin, very large deformations, etc.) finite element methods encounter\\u000a several difficulties. Meshless methods somewhat alleviate this problems, allowing for an updated Lagrangian framework in the\\u000a simulation. Accuracy is not affected

I. Alfaro; L. Fratini; E. Cueto; F. Chinesta

2008-01-01

359

Numerical simulation of friction stir welding by natural element methods  

Microsoft Academic Search

In this work we address the problem of numerically simulating the Friction Stir Welding process. Due to the special characteristics\\u000a of this welding method (i.e., high speed of the rotating pin, very large deformations, etc.) finite element methods (FEM)\\u000a encounter several difficulties. While Lagrangian simulations suffer from mesh distortion, Eulerian or Arbitrary Lagrangian\\u000a Eulerian (ALE) ones still have difficulties due

I. Alfaro; G. Racineux; A. Poitou; E. Cueto; F. Chinesta

2009-01-01

360

Numerical simulation of a premixed turbulent V-flame  

SciTech Connect

We present three-dimensional, time-dependent simulations of a full-size laboratory-scale rod-stabilized premixed turbulent V-flame. The computations use an adaptive projection method based on a low Mach number formulation that incorporates detailed chemical kinetics and transport. The simulations are performed without introducing models for turbulence or turbulence chemistry interaction. We outline the numerical procedure and experimental setup, and compare computed results to mean flame location and surface wrinkling statistics gathered from experiment.

Bell, John B.; Day, Marc S.; Grcar, Joseph F.; Lijewski, Michael J.; Johnson, Matt R.; Cheng, Robert K.; Shepherd, Ian G.

2003-07-27

361

Numerical simulation of low pressure die-casting aluminum wheel  

Microsoft Academic Search

The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC) of an aluminum wheel. By analyzing the mold-fi lling and solidifi cation stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim\\/spoke

Mi Guofa; Liu Xiangyu; Wang Kuangfei; Fu Hengzhi

362

Controlling numerical diffusion in reservoir simulation using Flux Corrected Transport  

SciTech Connect

Flux Corrected Transport (FCT) is a technique developed to reduce numerical diffusion around shock fronts which has not previously been used in reservoir engineering. The first section of this paper describes the application of FCT techniques to solving a one dimensional waterflooding problem, and shows how to include FCT in an IMPES simulator. A second feature of our program is the implicit timesplit treatment of capillary pressure effects. A comparison between laboratory data and simulator results is included, and good agreement is obtained.

Carr, A.H.; Christie, M.A.

1983-11-01

363

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

SciTech Connect

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

364

Numerical simulation of thrust reverser for rear mounted engine  

Microsoft Academic Search

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

365

Experimental and Numerical Simulations of Tsunami-Structures Interaction  

Microsoft Academic Search

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

366

Numerical Simulations of Fluidic Flowmeter with Large Measurement Range  

Microsoft Academic Search

A fluidic flowmeter with new structure is designed in this work on the basis of the traditional ones in order to obtain wide measurement range. This fluidic flowmeter has the diffuser wall with polygonal line and it has the performance of adaptability and stability. The CFD software FLUENT is employed to the numerical simulations of the fluidic flowmeter. The linear-relationship

Dailiang Xiel; Ting Fang; Guona Li; Guowei Liang

2007-01-01

367

Numerical simulation of the stamping process through microchannels  

Microsoft Academic Search

This study proposes a stamper array chip with embedded microchannels that delivers fixed size and shape liquid samples to a bottom chip for quantitative biodiagnosis and bioassays. The transfer process and physics are analyzed by solving first-principle equations numerically. The simulation proves that the surface tension force inside a microchannel plays an important role in driving the liquid fluid from

Shih-Chang Lin; Fangang Tseng; Ching-Chang Chieng

2003-01-01

368

Numerical simulation of protein stamping process driven by capillary force  

Microsoft Academic Search

Numerical simulations based on first-principle conservation laws of mass and momentum are performed to observe flow characteristics during the stamping process. The protein solution is transferred by a new design of microstamps with microchannels and printed on a bottom substrate. Furthermore, key physics of the stamping process and the control factors achieving uniform spot size can be identified and optimized

Shih-Chang Lin; Fangang Tseng; Ching-Chang Chieng

2002-01-01

369

Numerical simulation and experimental observations of initial friction transients  

SciTech Connect

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

370

ITER TF coil double pancake assembly: Laser welding numerical simulation  

Microsoft Academic Search

In the frame of the ITER coils production, one crucial point is the cover plate welding to complete a coil layer, the so called double pancake (DP). The scope of the activity here described is the assessment of the deformation induced by this laser welding through a FE numerical simulation, in order to find the welding sequence that minimize the

F. Lucca; E. Briani; C. Gianini; C. Jong; J. Knaster; A. Marin

2011-01-01

371

Wind Tunnel to Flight: Numerical Simulations of Hypersonic Propulsion Systems  

Microsoft Academic Search

Uncertainties in the flight conditions and limitations of ground based facilities create inherent difficulties in assessing the performance of hypersonic propulsion systems. We use numerical simulations to investigate the correlation of wind-tunnel measurements (Steelant et al., 2006) and flight data (Hass et al., 2005) for the HyShot vehicle; the objective is to identify potential engine unstart events occurring under different

Gianluca Iaccarino

2009-01-01

372

Numerical simulation of laminar hypersonic flows about an ellipsoid  

Microsoft Academic Search

The laminar hypersonic flow about a double ellipsoid, which idealizes the nose and cockpit of a spacecraft, were numerically simulated. The calculation method solves the three dimensional thin layer Navier-Stokes equations in a conservative formulation on a surface oriented calculation grid using an implicit\\/explicit finite difference technique. The conservative formulation allows the correct calculation of embedded compression shocks, while the

S. Riedelbauch; B. Mueller

1988-01-01

373

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

374

Numerical simulation of a variable speed refrigeration system  

Microsoft Academic Search

This work presents two numerical models to simulate the transient and steady state behavior of a vapor compression refrigeration system. The condenser and the evaporator were divided into a number of control volumes. Time dependent partial differential equations system was obtained from the mass, energy and momentum balances for each control volume. As the expansion valve and the compressor both

R. N. N. Koury; L. Machado; K. A. R. Ismail

2001-01-01

375

Numerical simulations of shock-induced mixing and combustion  

SciTech Connect

In this paper we use numerical simulation to investigate shock-induced ignition and combustion of a hydrocarbon gas. The focus of this paper is on quantifying the effect of fidelity in the chemical kinetics on the overall solution. We model the system using the compressible Navier Stokes equations for a reacting mixture. These equations express conservation of species mass, momentum, total energy.

Bell, John B.; Day, Marc S.; Kuhl, A.

2003-07-27

376

Numerical simulation of isothermal flow in axisymmetric turbulent opposed jets  

Microsoft Academic Search

A numerical simulation has been carried out to study the steady and unsteady flow in axisymmetric turbulent opposed jets. The study is based on the solution of the complete Navier–Stokes equations and turbulence models using a finite volume technique. The tridiagonal matrix algorithm (TDMA) is used to solve the discretization equations. The pressure–velocity coupling is achieved using the SIMPLE method.

A. Abdel-Fattah

2011-01-01

377

Numerical Simulations of Interaction between Stellar Wind and Interstellar Medium  

Microsoft Academic Search

Hydrodynamic interaction between supersonic spherical wind emitted from an astronomical object and a uniform streaming flow is simulated numerically assuming the flow to be axisymmetric, adiabatic and inviscid. Examples of such a phenomenon are a comet in the solar wind, and the solar wind or a stellar wind in an interstellar medium. Three cases of the incident flow, i.e., subsonic,

Takuya Matsuda; Yuzo Fujimoto; Eiji Shima; Keisuke Sawada; Takashi Inaguchi

1989-01-01

378

NUMERICAL SIMULATION OF THREE-DIMENSIONAL TUFT CORONA AND ELECTROHYDRODYNAMICS  

EPA Science Inventory

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...

379

A NUMERICAL MODEL FOR THE SIMULATION OF EXTERNAL GEAR PUMPS  

Microsoft Academic Search

External gear pumps are the most widely employed source of power in hydraulic applications, allowing good performance and low manufacturing costs. The present paper reports the description of a numerical model for the simulation of these kind of machines, developed by the authors. The model has been implemented using the software AMESim ® , introducing new in-house C++ models, with

Paolo CASOLI; Andrea VACCA; Germano FRANZONI

2005-01-01

380

A numerical simulation for the omega band formation  

Microsoft Academic Search

The formation of the omega bands and torch structures in the recovery phase of a substorm is numerically simulated. The kinetic energies of auroral particles are substantially provided by nonadiabatic acceleration in the tail current sheet. The magnetic drift flux (in the adiabatic sense) of the plasma sheet ions increases with decreasing invariant latitude; it starts to increase significantly around

T. Yamamoto

2011-01-01

381

NUMERICAL SIMULATIONS OF SEVERE SIROCCO EVENTS AT SARAJEVO INTERNATIONAL AIRPORT  

Microsoft Academic Search

During strong or severe sirocco episodes, pilots at Sarajevo International Airport often report significant turbulence that can cause difficulties during the landing procedures. Measurements at two airport locations show that these episodes are accompanied by strong wind gusts. This study examines several such episodes that occurred between 22 November and 6 December 2005. Numerical simulations of selected sirocco events were

Lada Gabela

382

Numerical Simulation of Supersonic Combustion for Hypersonic Propulsion  

Microsoft Academic Search

Recently, renewed interest on the scramjet engine has been demonstrated through the many international activities along the several Asia-Pacific countries. Here, a short review of current activities on supersonic combustion in a scramjet engine will be addressed followed by the discussions on the review of numerical simulation on supersonic combustion phenomena related with scramjet engine combustors and ram accelerator. Emphasis

In-Seuck Jeung; Jeong-Yeol Choi

383

NUMERICAL SIMULATION OF INFILTRATION THROUGH UNSATURATED LAYERED SOIL COLUMN  

Microsoft Academic Search

The effect of changing permeability at the interface for common residual soils, namely Silty Sand, Fine Sand and Gravelly Sand was investigated by conducting numerical simulations of vertical infiltration tests on two layered soil columns of Silty Sand over Fine Sand, and Silty Sand over Gravelly Sand. The results show that water movement across interface between the two layered soils

Azman Kassim; Nurly Gofar; Lee Min Lee

2008-01-01

384

Single and double plate impact welding: Experimental and numerical simulation  

Microsoft Academic Search

This paper presents an experimental study and a numerical simulation of impact welding of single and double aluminium plates using a gas gun. The study shows the differences in the bonding quality of the two impacting flyer plates. In general the bonded area between the two flyer plates is less than that between the leading flyer and the target. The

M. Chizari; L. M. Barrett

2009-01-01

385

NUMERICAL SIMULATION OF AFTERBURNING OF THERMOBARIC EXPLOSIVE PRODUCTS IN AIR  

Microsoft Academic Search

To predict the blast performance of thermobaric warhead, numerical modeling of secondary burning after detonation of thermobaric explosives is investigated. We select TNT containing small quantity of aluminum as a candidate thermobaric explosive. The combustion process is modeled by the fast reaction for gas and aluminum vapor and the finite-rate burning for aluminum particle. The simulations are performed by the

C.-K. Kim; J.-S. Hwang; K.-S. Im

386

Ab initio molecular simulations with numeric atom-centered orbitals  

Microsoft Academic Search

We describe a complete set of algorithms for ab initio molecular simulations based on numerically tabulated atom-centered orbitals (NAOs) to capture a wide range of molecular and materials properties from quantum-mechanical first principles. The full algorithmic framework described here is embodied in the Fritz Haber Institute \\

Volker Blum; Ralf Gehrke; Felix Hanke; Paula Havu; Ville Havu; Xinguo Ren; Karsten Reuter; Matthias Scheffler

2009-01-01

387

NUMERICAL SIMULATION OF EXPLOITATION OF SUPERCRITICAL ENHANCED GEOTHERMAL SYSTEM  

Microsoft Academic Search

S The process of heat transfer during the fluid filtration in rocks of magma-geothermal system of Mutnovsky volcano was studied by the method of numerical simulation. The distribution of temperature, pressure, fluid phase state and its phases' velocities were obtained. The character of dependence of the calculated geothermal gradient and geometry of supercritical fluid region on the form of magma

Roman I. Pashkevich; Vitaly V. Taskin

388

A numerical model for simulating mechanical behavior of flexible fibers  

Microsoft Academic Search

A numerical method is developed for simulating the mechanical behavior of flexible fibers. A circular crossed fiber is represented by a number of cylindrical segments linked by spring dash-pot systems. Segments are lined up and bonded to each neighbor. Each bond can be stretched or compressed by changing the bond distance. Bending deflection and twist movement occur, respectively, in the

Zemin Ning; John R. Melrose

1999-01-01

389

Numerical simulation of hot stamping of quenchable boron steel  

Microsoft Academic Search

Quenchable boron steel is a new type of ultra-high-strength steel used for automotive parts to reduce the weight of automobiles and maintain the safety requirements. On the basis of experimental data of mechanics and thermal physical properties, a material model under hot stamping condition of quenchable steel was set up, and the numerical simulation to the whole hot stamping process

Z. W. Xing; J. Bao; Y. Y. Yang

2009-01-01

390

Modeling and Numerical Simulation of a Complete Hydroelectric Production Site  

Microsoft Academic Search

For many years the EPFL Laboratory for Electrical Machines develops SIMSEN, a numerical software package for the simulation in transient and steady-state conditions of electrical power systems and adjustable speed drives, having an arbitrary topology. SIMSEN is based on a collection of modules, each corresponding to one system component (machines, converters, transformers, control devices, etc.). This contribution presents the extension

C. Nicolet; P. Allenbach; J.-J. Simond; F. Avellan

2007-01-01

391

The numerical simulation of the hydrodynamics of Barbamarco Lagoon, Italy  

Microsoft Academic Search

A three-dimensional numerical model in finite differences was used to simulate the transport and mixing in Barbamarco Lagoon, Italy. The field data for the boundary conditions and for the conditions within the lagoon are described in an earlier paper by Ramirez and Imberger [Hydrodynamics of a shallow lagoon: Barbamarco Lagoon, Italy, submitted, 2000]. In general, the model reproduced the main

Isabel Ramirez; Jorg Imberger

2002-01-01

392

Numerical Simulation of Particle Flow in a Sand Trap  

Microsoft Academic Search

Sand traps are used to measure Aeolian flux. Since they modify the surrounding wind velocity field their gauging represents an important challenge. We use numerical simulations under the assumption of homogeneous turbulence based on FLUENT to systematically study the flow field and trapping efficiency of one of the most common devices based on a hollow cylinder with two slits. In

A. D. Araújo; J. S. Andrade Jr.; L. P. Maia; H. J. Herrmann

2008-01-01

393

Numerical Simulation of I-type Spherule Formation  

NASA Astrophysics Data System (ADS)

Numerical simulations for atmospheric entry of spherules are performed to calculate the time dependence of velocity, altitude, spherules' radii and temperature. They indicate that the strong apparent gravitational acceleration due to atmospheric drag results in exposure of metallic cores to the air during melting and oxidation of spherules. Two major types of internal structures of Fe-Ni spherules are explained by this model.

Yada, T.; Sekiya, M.; Nakamura, T.; Takaoka, N.

1996-03-01

394

Numerical modeling and simulation of wheel radial fatigue tests  

Microsoft Academic Search

A computational methodology is proposed for fatigue damage assessment of metallic automotive components and its application is presented with numerical simulations of wheel radial fatigue tests. The technique is based on the local strain approach in conjunction with linear elastic FE stress analyses. The stress–strain response at a material point is computed with a cyclic plasticity model coupled with a

Mehmet Firat; Recep Kozan; Murat Ozsoy; O. Hamdi Mete

2009-01-01

395

Water and heat fluxes in desert soils: 2. Numerical simulations  

Microsoft Academic Search

Transient one-dimensional fluxes of soil water (liquid and vapor) and heat in response to 1 year of atmospheric forcing were simulated numerically for a site in the Chihuahuan Desert of Texas. The model was initialized and evaluated using the monitoring data presented in a companion paper (Scanlon, this issue). Soil hydraulic and thermal properties were estimated a priori from a

Bridget R. Scanlon; P. C. D. Milly

1994-01-01

396

Water and heat fluxes in desert soils 2. Numerical simulations  

Microsoft Academic Search

Transient one-dimensional fluxes of soil water (liquid and vapor) and heat in response to 1 year of atmospheric forcing were simulated numerically for a site in the Chihuahuan Desert of Texas. The model was initialized and evaluated using the monitoring data presented in a companion paper (Scanlon, this issue). Soil hydraulic and thermal properties were estimated a priori from a

Bridget R. Scanlon; P. C. D. Milly

1994-01-01

397

Numerical simulation of charge coupled device operation, abbreviated form  

Microsoft Academic Search

The research consisted of a detailed theoretical study of the operation of both surface and buried channel charge coupled devices (CCD). In the case of surface charge coupled devices, the primary results were: the development of the technologically important push clock clocking scheme, the numerical simulation of the operation of two and four phase overlapping gate CCD, the estimation of

A. M. Mohsen; Y. Diamon; C. A. Mead

1974-01-01

398

A review of numerical simulation of hydrothermal systems.  

USGS Publications Warehouse

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

399

Experimental evaluation of numerical simulation of cavitating flow around hydrofoil  

Microsoft Academic Search

Cavitation in hydraulic machines causes different problems that can be related to its unsteady nature. An experimental and numerical study of developed cavitating flow was performed. Until now simulations of cavitating flow were limited to the self developed “in house” CFD codes. The goal of the work was to experimentally evaluate the capabilities of a commercial CFD code (Fluent) for

Matevž Dular; Rudolf Bachert; Bernd Stoffel; Brane Širok

2005-01-01

400

NUMERICAL SIMULATION OF NATURAL GAS-SWIRL BURNER  

SciTech Connect

A numerical simulation of a turbulent natural gas jet diffusion flame at a Reynolds number of 9000 in a swirling air stream is presented. The numerical computations were carried out using the commercially available software package CFDRC. The instantaneous chemistry model was used as the reaction model. The thermal, composition, flow (velocity), as well as stream function fields for both the baseline and air-swirling flames were numerically simulated in the near-burner region, where most of the mixing and reactions occur. The results were useful to interpret the effects of swirl in enhancing the mixing rates in the combustion zone as well as in stabilizing the flame. The results showed the generation of two recirculating regimes induced by the swirling air stream, which account for such effects. The present investigation will be used as a benchmark study of swirl flow combustion analysis as a step in developing an enhanced swirl-cascade burner technology.

Ala Qubbaj

2005-03-01

401

Aggregation in an expanding cloud: experiments and numerical simulations  

NASA Astrophysics Data System (ADS)

We have set-up an experimental device and a numerical model to study aggregation of an aerosol (titanium oxide) expanding in the atmosphere. By mean of scanning microscopic analysis, it is shown that agglomerated aerosol forms fractal clusters of fractal dimension of about 1.75. The numerical simulations quantitatively confirm this geometrical feature. We show how our numerical results can complete some points which are not available in experiments. Nous avons construit un dispositif expérimental et un modèle numérique pour étudier l'agrégation d'un aérosol (oxyde de titane) en expansion dans l'atmosphère. A partir de l'analyse de photographies prises au microscope électronique à balayage, on montre que l'aérosol aggloméré forme des amas fractals de dimension fractale de l'ordre de 1,75. Les simulations numériques confirment quantitativement cette particularité géométrique. Nous montrons comment nos résultats numériques peuvent compléter quelques points qui ne sont pas accessibles à l'expérience.

Dziedzinl, Françoise; Botet, Robert

1991-03-01

402

Numerical simulation of a surface barrier discharge in air  

SciTech Connect

The development of a surface barrier discharge in air at atmospheric pressure under the action of a constant voltage of different polarity is simulated numerically. When the polarity of the high-voltage electrode is negative, the discharge develops as an ionization wave that moves along the dielectric surface. When the polarity is positive, the discharge develops as a streamer that first moves above the dielectric surface and then comes into contact with and continues to develop along it. In the case of a high-voltage electrode of positive polarity, the discharge zone above the dielectric surface is approximately five times thicker than that in the case of negative polarity. The characteristic aspects of numerical simulation of the streamer phase of a surface barrier discharge are discussed. The numerical results on the density of the charge stored at the dielectric surface and on the length of the discharge zone agree with the experimental data.

Solov'ev, V. R.; Konchakov, A. M.; Krivtsov, V. M.; Aleksandrov, N. L. [Moscow Institute of Physics and Technology (Russian Federation)

2008-07-15

403

Numerical simulation of flow-induced bi-directional oscillations  

NASA Astrophysics Data System (ADS)

Flow-induced vibration (FIV) by vortex shedding behind a submerged cylinder can lead to damage of nuclear components. With respect to such a serious scenario, various experiments and numerical simulations have been conducted to predict the vibration phenomena. Especially in simulation, the immersed finite element method (IFEM) is a promising approach to solve fluid-structure interaction problems because it needs less computational resources. In this paper, two-dimensional motions of cylinders are simulated by using IFEM to obtain their vibration characteristics. Three benchmark tests such as flow past a fixed circular cylinder, in-line oscillation of a circular cylinder and flow-induced vibration with uni-directional motion are performed to verify the proposed numerical method. Furthermore, bi-directional motions of two horizontally and vertically arranged cylinders as well as that of a single cylinder in fluid flow are analyzed, and then key findings are fully discussed.

Lee, Hyun-Boo; Lee, Tae-Rin; Chang, Yoon-Suk

2013-02-01

404

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

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) are conducted of a model hydrocarbon nitrogen mixing layer under supercritical conditions. The temporally developing mixing layer configuration 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 variables, including the pressure, internal energy, enthalpy, heat capacity, and speed of sound along with additional terms associated with the generalized heat and mass transport vectors. The Peng Robinson formulation is based on pure-species reference states accurate to better than 1% relative error through comparisons with highly accurate state equations over the range of variables used in this study (600 [less-than-or-eq, slant] T [less-than-or-eq, slant] 1100 K, 40 [less-than-or-eq, slant] p [less-than-or-eq, slant] 80 atm) and is augmented by an accurate curve fit to the internal energy so as not to require iterative solutions. The DNS results of two-dimensional and three-dimensional layers elucidate the unique thermodynamic and mixing features associated with supercritical conditions. Departures from the perfect gas and ideal mixture conditions are quantified by the compression factor and by the mass diffusion factor, both of which show reductions from the unity value. It is found that the qualitative aspects of the mixing layer may be different according to the specification of the thermal diffusion factors whose value is generally unknown, and the reason for this difference is identified by examining the second-order statistics: the constant Bearman Kirkwood (BK) thermal diffusion factor excites fluctuations that the constant Irwing Kirkwood (IK) one does not, and thus enhances overall mixing. Combined with the effect of the mass diffusion factor, constant positive large BK thermal diffusion factors retard diffusional mixing, whereas constant moderate IK factors tend to promote diffusional mixing. Constant positive BK thermal diffusion factors also tend to maintain density gradients, with resulting greater shear and vorticity. These conclusions about IK and BK thermal diffusion factors are species-pair dependent, and therefore are not necessarily universal. Increasing the temperature of the lower stream to approach that of the higher stream results in increased layer growth as measured by the momentum thickness. The three-dimensional mixing layer exhibits slow formation of turbulent small scales, and transition to turbulence does not occur even for a relatively long non-dimensional time when compared to a previous, atmospheric conditions study. The primary reason for this delay is the initial density stratification of the flow, while the formation of strong density gradient regions both in the braid and between-the-braid planes may constitute a secondary reason for the hindering of transition through damping of emerging turbulent eddies.

Miller, Richard S.; Harstad, Kenneth G.; Bellan, Josette

2001-06-01

405

Direct numerical simulation of a transitional supercritical binary mixing layer: heptane and nitrogen  

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) of a supercritical temporal mixing layer are conducted for the purpose of exploring the characteristics of high-pressure transitional mixing behaviour. The conservation equations are formulated according to fluctuation-dissipation (FD) theory, which is consistent with non-equilibrium thermodynamics and converges to kinetic theory in the low-pressure limit. According to FD theory, complementing the low-pressure typical transport properties (viscosity, diffusivity and thermal conductivity), the thermal diffusion factor is an additional transport property which may play an increasingly important role with increasing pressure. The Peng Robinson equation of state with appropriate mixing rules is coupled to the dynamic conservation equations to obtain a closed system. The boundary conditions are periodic in the streamwise and spanwise directions, and of non-reflecting outflow type in the cross-stream direction. Due to the strong density stratification, the layer is considerably more difficult to entrain than equivalent gaseous or droplet-laden layers, and exhibits regions of high density gradient magnitude that become very convoluted at the transitional state. Conditional averages demonstrate that these regions contain predominantly the higher-density, entrained fluid, with small amounts of the lighter, entraining fluid, and that in these regions the mixing is hindered by the thermodynamic properties of the fluids. During the entire evolution of the layer, the dissipation is overwhelmingly due to species mass flux followed by heat flux effects with minimal viscous contribution, and there is a considerable amount of backscatter in the flow. Most of the species mass flux dissipation is due to the molecular diffusion term with significant contributions from the cross-term proportional to molecular and thermal diffusion. These results indicate that turbulence models for supercritical fluids should primarily focus on duplicating the species mass flux rather than the typical momentum flux, which constitutes the governing dissipation in atmospheric mixing layers. Examination of the passive-scalar probability density functions (PDFs) indicates that neither the Gaussian, nor the beta PDFs are able to approximate the evolution of the DNS-extracted PDF from its inception through transition. Furthermore, the temperature species PDFs are well correlated, meaning that their joint PDF is not properly approximated by the product of their marginal PDFs; this indicates that the traditional reactive flow modelling based on replacing the joint PDF representing the reaction rate by the product of the marginal PDFs is not appropriate. Finally, the subgrid-scale temperature species PDFs are also well correlated, and the species PDF exhibits important departures from the Gaussian. These results suggest that classic PDFs used in atmospheric pressure flows would not capture the physics of this supercritical mixing layer, either in an assumed PDF model at the larger scale, or at the subgrid scale.

Okong'o, Nora A.; Bellan, Josette

2002-08-01

406

Numerical techniques for parallel dynamics in electromagnetic gyrokinetic Vlasov simulations  

NASA Astrophysics Data System (ADS)

Numerical techniques for parallel dynamics in electromagnetic gyrokinetic simulations are introduced to regulate unphysical grid-size oscillations in the field-aligned coordinate. It is found that a fixed boundary condition and the nonlinear mode coupling in the field-aligned coordinate, as well as numerical errors of non-dissipative finite difference methods, produce fluctuations with high parallel wave numbers. The theoretical and numerical analyses demonstrate that an outflow boundary condition and a low-pass filter efficiently remove the numerical oscillations, providing small but acceptable errors of the entropy variables. The new method is advantageous for quantitative evaluation of the entropy balance that is required for obtaining a steady state in gyrokinetic turbulence.

Maeyama, S.; Ishizawa, A.; Watanabe, T.-H.; Nakajima, N.; Tsuji-Iio, S.; Tsutsui, H.

2013-11-01

407

Collapse of a Liquid Column: Numerical Simulation and Experimental Validation  

NASA Astrophysics Data System (ADS)

This paper is focused on the numerical and experimental analyses of the collapse of a liquid column. The measurements of the interface position in a set of experiments carried out with shampoo and water for two different initial column aspect ratios are presented together with the corresponding numerical predictions. The experimental procedure was found to provide acceptable recurrence in the observation of the interface evolution. Basic models describing some of the relevant physical aspects, e.g. wall friction and turbulence, are included in the simulations. Numerical experiments are conducted to evaluate the influence of the parameters involved in the modeling by comparing the results with the data from the measurements. The numerical predictions reasonably describe the physical trends.

Cruchaga, Marcela A.; Celentano, Diego J.; Tezduyar, Tayfun E.

2007-03-01

408

ConfiDNS: Leveraging Scale and History to Detect Compromise  

Microsoft Academic Search

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

409

Serving DNS Using a Peer-to-Peer Lookup Service  

Microsoft Academic Search

The current domain name system (DNS) couples own- ership of domains with the responsibility of serving data for them. The DNS security extensions (DNSSEC) allow verificaton of records obtained by alternate means, open- ing exploration of alternative storage systems for DNS records. We explore one such alternative using DHash, a peer-to-peer distributed hash table built on top of Chord. Our

Russ Cox; Athicha Muthitacharoen; Robert T. Morris

2002-01-01

410

A DNS study on the stabilization mechanism of a turbulent lifted ethylene jet flame in highly-heated coflow  

SciTech Connect

Direct numerical simulation (DNS) of the near-field of a three-dimensional spatially-developing turbulent ethylene jet flame in highly-heated coflow is performed with a reduced mechanism to determine the stabilization mechanism. The DNS was performed at a jet Reynolds number of 10,000 with over 1.29 billion 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. The Damkoehler number and chemical explosive mode (CEM) analysis also verify that auto-ignition occurs at the flame base. 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 similar to a previous study (Yoo et al., J. Fluid Mech. 640 (2009) 453-481) with hydrogen/air jet flames. It is also observed that the present lifted flame base exhibits a cyclic 'saw-tooth' shaped movement marked by rapid movement upstream and slower movement downstream. This is a consequence of the lifted flame being stabilized by a balance between consecutive auto-ignition events in hot fuel-lean mixtures and convection induced by the high-speed jet and coflow velocities. This is confirmed by Lagrangian tracking of key variables including the flame-normal velocity, displacement speed, scalar dissipation rate, and mixture fraction at the stabilization point.

Yoo, Chun S [Sandia National Laboratories (SNL)

2011-01-01

411

Numerical simulation of shock interaction with above-ground structures  

NASA Astrophysics Data System (ADS)

This final report for DNA contract DNA 001-89-C-0098 for the time period May 15, 1989 to Dec 31, 1992 describes the results of several of the computations conducted under this research effort. The numerical simulations conducted simulated shock wave diffraction phenomenon about complex-geometry two-dimensional and three-dimensional structures. Since a significant part of this effort was composed of parametric studies that have been delivered to the sponsors, the Defense Nuclear Agency and the Air Force Ballistic Missile Organization (BMO), and conducted under the now defunct Rail Garrison project, we included in this report a detailed description of the results of the major computations, and a brief summary of all the repetitive computations. The final report is divided into three sections. Chapter 1 describes in detail the two-dimensional numerical methodology and typical two-dimensional computation, i.e., the application of the numerical methodology to the simulation of shock interaction with a typical 2-D train (a 2-D cut at the center of a 3-D train). Chapter 2 describes the numerical development of a passive shock reflector, a major effort undertaken in this project. The objective of this effort was to design a passive device that, while allowing the ventilation of the enclosure under steady conditions, will prevent blast waves impinging on the wall from entering the enclosure when the structure is impacted by a shock.

Baum, Joseph D.; Lohner, Rainald

1994-05-01

412

DNS Extensions to Support IP Version 6  

Microsoft Academic Search

This document defines the changes that need to be made to the Domain Name System (DNS) to support hosts running IP version 6 (IPv6). The changes include a resource record type to store an IPv6 address, a domain to support lookups based on an IPv6 address, and updated definitions of existing query types that return Internet addresses as part of

S. Thomson; C. Huitema; V. Ksinant

1995-01-01

413

DNS Root\\/gTLD Performance Measurements  

Microsoft Academic Search

The Internet Domain Name System (DNS) is an essential part of the Internet infrastructure. Each web site or email lookup involves traversing a tree-structured distributed database to complete the mapping from a hostname to an IP address. The root and top level domain (TLD) nameservers form the highest level of authority over the Internet naming hierarchy, and are thus potentially

Nevil Brownlee

2001-01-01

414

Secure Domain Name System (DNS) Dynamic Update  

Microsoft Academic Search

This document proposes a method for performing secure Domain Name System (DNS) dynamic updates. The method described here is intended to be flexible and useful while requiring as few changes to the protocol as possible. The authentication of the dynamic update message is separate from later DNSSEC validation of the data. Secure communication based on authenticated requests and transactions is

B. Wellington

2000-01-01

415

Improving Response Deliverability in DNS(SEC)  

Microsoft Academic Search

The Domain Name System provides a critical service on the Internet, where it allows host names to be translated to IP addresses. However, it does not provide any guarantees about authenticity and origin integrity of resolution data. DNSSEC attempts to solve this through the application of cryptographic signatures to DNS records. These signatures generally result in larger responses compared to

Broek van den Gijs; Rijswijk van Roland; Aiko Pras; Anna Sperotto

2012-01-01

416

Graphics interfaces and numerical simulations: Mexican Virtual Solar Observatory  

NASA Astrophysics Data System (ADS)

Preliminary results associated to the computational development and creation of the Mexican Virtual Solar Observatory (MVSO) are presented. Basically, the MVSO prototype consists of two parts: the first, related to observations that have been made during the past ten years at the Solar Observation Station (EOS) and at the Carl Sagan Observatory (OCS) of the Universidad de Sonora in Mexico. The second part is associated to the creation and manipulation of a database produced by numerical simulations related to solar phenomena, we are using the MHD ZEUS-3D code. The development of this prototype was made using mysql, apache, java and VSO 1.2. based GNU and `open source philosophy'. A graphic user interface (GUI) was created in order to make web-based, remote numerical simulations. For this purpose, Mono was used, because it is provides the necessary software to develop and run .NET client and server applications on Linux. Although this project is still under development, we hope to have access, by means of this portal, to other virtual solar observatories and to be able to count on a database created through numerical simulations or, given the case, perform simulations associated to solar phenomena.

Hernández, L.; González, A.; Salas, G.; Santillán, A.

2007-08-01

417

Numerical Simulations of One-dimensional Microstructure Dynamics  

SciTech Connect

Results of numerical simulations of one-dimensional wave propagation in microstructured solids are presented and compared with the corresponding results of wave propagation in given layered media. A linear microstructure model based on Mindlin theory is adopted and represented in the framework of the internal variable theory. Fully coupled systems of equations for macro-motion and microstructure evolution are rewritten in the form of conservation laws. A modification of wave propagation algorithm is used for numerical calculations. It is shown how the initial microstructure model can be improved in order to match the results obtained by both approaches.

Berezovski, M.; Berezovski, A.; Engelbrecht, J. [Centre for Nonlinear Studies, Institute of Cybernetics at Tallinn University of Technology, Akadeemia tee 21, 12618 Tallinn (Estonia)

2010-05-21

418

Numerical Simulations of Turbulent Convection with Background Rotation and Stratification  

NASA Astrophysics Data System (ADS)

Direct numerical simulation using a Fourier-Legendre spectral element method and about six million points have been performed. Bouyancy flux, with a flux Rayleigh number of about 10^9, is introduced at a localized region along the top boundary of a three-dimensional computational box. The ambient fluid is in a solid body rotation with linear stable stratification. Vortices have been observed in the horizontal plane. The possible mechanism for the formation of these vortices is by either barotropic or baroclinic stability. Using numerical data and experimental correlation, we identify the latter being the more likely scenario.

Chan, Daniel

1997-11-01

419

Characterizing electron temperature gradient turbulence via numerical simulation  

SciTech Connect

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

420

Characterizing Electron Temperature Gradient Turbulence Via Numerical Simulation  

SciTech Connect

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

421

Numerical simulation study on the flow field of porous hydrofoil  

NASA Astrophysics Data System (ADS)

Because cavitation and cavitation erosion will caused significant impact to the security and stability of hydro turbine, so changing geometric structure to reduce the risk of cavitation is considered. Punching many holes on the hydrofoil is adopted. By using RNG ? - ? turbulence model and SIMPLEC algorithm, the flow field around hydrofoil and porous hydrofoil are simulated based computational fluid dynamics(CFD). The numerical simulation result-velocity and pressure field of hydrofoil with different geometry are compared and analysed. This study introduces geometry optimization ideas to researchers for improving cavitation phenomenon in water turbine.

Yu, F. R.; Zhang, L. X.

2012-11-01

422

Numerical simulation of laser-induced heating on multilayers  

NASA Astrophysics Data System (ADS)

Numerical simulation and analysis of the temperature distributions in multilayers under laser irradiation have been reported. Using finite element method (FEM), we have developed 2D and 3D programs, and calculated the temperature distributions under irradiation of immovable or laterally movable laser beams. The simulated results show that the maximum temperature rise appears at where the most laser energy deposition is. The results also show that when the moving velocity of laser beam is not so fast, the maximum temperature rise would not descend much compared with immovable irradiation.

Hu, Peng; Chen, Faliang

2013-05-01

423

Numerical aspects in the simulation of thermohydraulic transients in CICCs  

NASA Astrophysics Data System (ADS)

This paper gives a brief description of the model commonly used to simulate thermo-hydraulic transients in Cable-in-Conduit Conductors (CICC's), in particular quench initiation and evolution. A discussion on the mathematical and physical characteristics of the system of equations is the starting point to assess the difficulties and advantages of methods used for the numerical solution of this class of problems. The crucial points in the simulation of quench are highlighted, they are associated with the fluid flow and the presence of moving boundaries. The implications for a selection of an optimally suited solution method are discussed.

Bottura, L.

1995-03-01

424

Numerical code for Monte-Carlo simulation of ion storage  

SciTech Connect

A numerical code for simulation of evolution of ion distribution functions during storage process has been proposed. The code based on Monte-Carlo method and 'macroparticle' type simulation allows to estimate growth rates of the beam emittance and momentum spread due to an intrabeam scattering and an interaction with the stripping target for beams with non-Gaussian distribution function and permits to follow the process of particle losses as well. The algorithm of the code has been described, the code has been tested and results of its application to TWAC project have been given and discussed.

Alekseev, N.; Bolshakov, A.; Mustafin, E.; Zenkevich, P. [Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, Moscow (Russian Federation)

1999-06-09

425

Numerical code for Monte-Carlo simulation of ion storage  

NASA Astrophysics Data System (ADS)

A numerical code for simulation of evolution of ion distribution functions during storage process has been proposed. The code based on Monte-Carlo method and «macroparticle» type simulation allows to estimate growth rates of the beam emittance and momentum spread due to an intrabeam scattering and an interaction with the stripping target for beams with non-Gaussian distribution function and permits to follow the process of particle losses as well. The algorithm of the code has been described, the code has been tested and results of its application to TWAC project have been given and discussed.

Alekseev, N.; Bolshakov, A.; Mustafin, E.; Zenkevich, P.

1999-06-01

426

Numerical simulation of three-dimensional tuft corona and electrohydrodynamics  

SciTech Connect

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 individual tufts is considerably higher even at a low average current level and, therefore, could contribute to both the formation of back corona in the collected-dust layer and the generation of the secondary flow. Numerical simulation for three-dimensional tuft corona is successfully solved. The electrical characteristics of tuft corona are investigated, and the structure and role of the three-dimensional secondary flow and EHD in relation to transport of the fine particles are described.

Yamamoto, T.; Sparks, L.E.

1986-01-01

427

Numerical Linear Device: Numerical simulation of turbulent plasmas in linear devices  

NASA Astrophysics Data System (ADS)

Structural formation mechanisms in magnetically confined plasmas are crucial issues in plasma physics. We have been developing a 3-dimensional numerical simulation code called Numerical Linear Device (NLD), which models a simple cylindrical plasma configuration. The 3-field (density, potential and parallel velocity of electrons) reduced fluid model is adopted. Using this code, quantitative comparison of turbulence characteristics with experimental results, such as identification of the observed instabilities, nonlinear saturation level of turbulence, wavenumber spectra and balance of momentum transport are analyzed. For describing the competition between drift and interchange modes, gravitation terms due to the magnetic curvature are added. Parameter scan predicts the experimental condition for excitation of turbulence. It is found that ion-neutral collision is an important parameter to excite drift wave turbulence, and ion viscosity weakly stabilizes the turbulence. Nonlinear simulation gives saturated turbulence. Turbulence characteristics of linear devices LMD and ECH in Kyushu Univ. and CSDX in UCSD will be discussed.

Kasuya, Naohiro

2005-10-01

428

Numerical simulation of weakly ionized hypersonic flow over reentry capsules  

NASA Astrophysics Data System (ADS)

The mathematical and numerical formulation employed in the development of a new multi-dimensional Computational Fluid Dynamics (CFD) code for the simulation of weakly ionized hypersonic flows in thermo-chemical non-equilibrium over reentry configurations is presented. The flow is modeled using the Navier-Stokes equations modified to include finite-rate chemistry and relaxation rates to compute the energy transfer between different energy modes. The set of equations is solved numerically by discretizing the flowfield using unstructured grids made of any mixture of quadrilaterals and triangles in two-dimensions or hexahedra, tetrahedra, prisms and pyramids in three-dimensions. The partial differential equations are integrated on such grids using the finite volume approach. The fluxes across grid faces are calculated using a modified form of the Steger-Warming Flux Vector Splitting scheme that has low numerical dissipation inside boundary layers. The higher order extension of inviscid fluxes in structured grids is generalized in this work to be used in unstructured grids. Steady state solutions are obtained by integrating the solution over time implicitly. The resulting sparse linear system is solved by using a point implicit or by a line implicit method in which a tridiagonal matrix is assembled by using lines of cells that are formed starting at the wall. An algorithm that assembles these lines using completely general unstructured grids is developed. The code is parallelized to allow simulation of computationally demanding problems. The numerical code is successfully employed in the simulation of several hypersonic entry flows over space capsules as part of its validation process. Important quantities for the aerothermodynamics design of capsules such as aerodynamic coefficients and heat transfer rates are compared to available experimental and flight test data and other numerical results yielding very good agreement. A sensitivity analysis of predicted radiative heating of a space capsule to several thermo-chemical non-equilibrium models is also performed.

Scalabrin, Leonardo C.

429

Numerical model for learning concepts of streamflow simulation  

USGS Publications Warehouse

Numerical models are useful for demonstrating principles of open-channel flow. Such models can allow experimentation with cause-and-effect relations, testing concepts of physics and numerical techniques. Four PT is a numerical model written primarily as a teaching supplement for a course in one-dimensional stream-flow modeling. Four PT options particularly useful in training include selection of governing equations, boundary-value perturbation, and user-programmable constraint equations. The model can simulate non-trivial concepts such as flow in complex interconnected channel networks, meandering channels with variable effective flow lengths, hydraulic structures defined by unique three-parameter relations, and density-driven flow.The model is coded in FORTRAN 77, and data encapsulation is used extensively to simplify maintenance and modification and to enhance the use of Four PT modules by other programs and programmers.

DeLong, L. L.

1993-01-01

430

NUMERICAL SIMULATION OF OPEN WAVEGUIDE CONVERTERS USING FDTD METHOD  

Microsoft Academic Search

We study 3-dimensional asymmetric diffraction problems for waveguide-based electro-dynamic systems, radiating to infinite\\u000a free space. For calculations we utilize the FDTD (Finite Difference Time Domain) numerical simulation method with the UPML\\u000a (Unsplit Perfectly Matched Layer) absorbing boundary conditions. This paper states that the FDTD method, in spite of its relatively\\u000a low calculation speed, has an approved ability of solving certain

Maxim L. Kulygin; Gregory G. Denisov; Alexey V. Chirkov; Sergey V. Kuzikov

2006-01-01

431

Numerical Simulation of Three-Dimensional Tuft Corona and Electrohydrodynamics  

Microsoft Academic Search

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 individual tufts is considerably higher even at a low average current level and therefore could contribute to both the formation of back corona in the collected-dust layer and the generation of the secondary flow. Numerical simulation for

Toshiaki Yamamoto; Leslie E. Sparks

1986-01-01

432

Numerical Simulation of Ca 2+ “Sparks” in Skeletal Muscle  

Microsoft Academic Search

A three dimensional (3D) model of Ca2+ diffusion and binding within a sarcomere of a myofibril, including Ca2+ binding sites troponin, parvalbumin, sarcoplasmic reticulum Ca2+ pump, and fluorescent Ca2+-indicator dye (fluo-3), was developed to numerically simulate laser scanning confocal microscope images of Ca2+ “sparks” in skeletal muscle. Diffusion of free dye (D), calcium dye (CaD), and Ca2+ were included in

Yu-Hua Jiang; Michael G. Klein; Martin F. Schneider

1999-01-01

433

Numerical simulations of sea and land breezes at high latitudes  

Microsoft Academic Search

Few investigations of sea\\/land breezes (SB\\/LB) at high latitudes have been reported in the meteorological literature. However, internal reports at some Norwegian institutions, summarised recently by Grønås and Sandvik, show that SB\\/LBs, in combination with terrain-driven circulations, are frequent along the coast of Norway and Spitsbergen. In this paper, numerical simulations of SB\\/LBs for latitudes between 50° and 80°N have

Sigbjørn Grønås; Anne Dagrun Sandvik

1998-01-01

434

Numerical simulations of cloaking problems using a DPG method  

NASA Astrophysics Data System (ADS)

The paper reviews the construction of cloaks for 2D acoustic or electromagnetic waves using the Piola transform, and shows how the knowledge of the transform leads to the construction of a quasi-optimal test norm for the Discontinuous Petrov-Galerkin (DPG) method with optimal test functions for this class of problems. Numerical experiments for cylindrical and square cloaks illustrate the discussed concepts and demonstrate the effectiveness of the DPG method in cloak simulations.

Demkowicz, L.; Li, Jichun

2013-05-01

435

Numerical Simulation of Breaking Gravity Waves below a Critical Level  

Microsoft Academic Search

\\u000a The interaction of an internal gravity wave with a critical layer and the generation of turbulence are studied by three-dimensional\\u000a numerical simulations. Based on a successful comparison of a two-dimensional version of the model with experimental observations\\u000a (Thorpe, 1981), we discuss results obtained with two different models of viscosity. Although the variances of the turbulent quantities\\u000a are nearly the same,

Andreas Dörnbrack; Ulrich Schumann

436

Numerical simulation of diffuse radiowave scattering from planetary surfaces  

Microsoft Academic Search

Numerical finite-difference time-domain (FDTD) techniques offer a new approach to studying radiowave scattering from geophysical surfaces, for which theoretical models are difficult to construct and of limited interpretive use. FDTD simulation yields the near-scattered fields in the vicinity of discrete, wavelength-scale surface and subsurface objects having complex shape and material inhomogeneities; Huygens's principle allows extension to the far field. Accuracies

John Edward Baron

2002-01-01

437

Numerical simulation of weakly ionized hypersonic flow over reentry capsules  

Microsoft Academic Search

The mathematical and numerical formulation employed in the development of a new multi-dimensional Computational Fluid Dynamics (CFD) code for the simulation of weakly ionized hypersonic flows in thermo-chemical non-equilibrium over reentry configurations is presented. The flow is modeled using the Navier-Stokes equations modified to include finite-rate chemistry and relaxation rates to compute the energy transfer between different energy modes. The

Leonardo C. Scalabrin

2007-01-01

438

Numerical Simulation of Flow Control Over Airfoils Using Plasma Actuators  

Microsoft Academic Search

The goal of this work is to numerically simulate the application of weakly-ionized plasma actuators for improved aerodynamic performance of wings. Computations using the NASA Langley CFL3D unsteady thin layer Navier-Stokes solver have been carried out to calculate flow fields near NACA 0015 airfoil with plasma actuators installed on the suction surface in two different arrangements: one at the leading

Vladimir Voikov; Thomas Corke; Osamah Haddad

2004-01-01

439

Thermal stresses in multilayer ceramic capacitors: numerical simulations  

Microsoft Academic Search

Numerical simulations using a previously published model (see G.C. Scott and G. Astfolk, ASME J. Electron. Pack., vol.112, p.35-40, 1989) to characterize the development of thermal stresses in surface-mounted multilayer ceramic capacitors (MLCCs) are discussed. The model was used to investigate the effect of several important factors on the development of thermal stresses in MLCCs. These factors relate to the

G. C. Scott; G. Astfalk

1990-01-01

440

The MEGAFLOW Project — Numerical Flow Simulation for Aircraft  

Microsoft Academic Search

Some years ago the national CFD project MEGAFLOW was initiated in Germany, which combined many of the CFD development activities\\u000a from DLR, universities and aircraft industry. Its goal was the development and validation of a dependable and efficient numerical\\u000a tool for the aerodynamic simulation of complete aircraft which met the requirements of industrial implementations. The MEGAFLOW\\u000a software system includes the

C.-C. Rossow; N. Kroll; D. Schwamborn

441

Shock metamorphism on the ocean floor (numerical simulations)  

Microsoft Academic Search

Impact craters are unknown in deep-ocean basins. Important reasons for this are that the ocean crust is younger than continents and the impacts are weakened by the water column. Laboratory experiments can show specific features of water impacts. However, impact velocities are too small (<5km\\/s) with respect to planetary-scale asteroidal impacts (11.2–40km\\/s). Most numerical simulations of impacts deal primarily with

N. A. Artemieva; V. V. Shuvalov

2002-01-01

442

Numerical Simulation of Anisotropic Preheating Ablative Rayleigh-Taylor Instability  

Microsoft Academic Search

The linear growth rate of the anisotropic preheating ablative Rayleigh-Taylor instability (ARTI) is studied by numerical simulations. The preheating model kappa(T) = kappaSH[1 + f(T)] is applied, where f(T) is the preheating function interpreting the preheating tongue effect in the cold plasma ahead of the ablative front. An arbitrary coefficient D is introduced in the energy equation to study the

Li-Feng Wang; Wen-Hua Ye; Ying-Jun Li

2010-01-01

443

Numerical simulations for high-energy impact of thin plates  

Microsoft Academic Search

New approaches to the design of advanced aerospace systems requires an evaluation of extreme loading conditions and assessment of different possible failures scenario. One such scenario involves the high-energy foreign-object impact on relatively thin plates used in fuselage and wing applications. This paper describes a series of LS-DYNA numerical simulations for studying the impact and penetration of thin plates by

Damodar R. Ambur; Navin Jaunky; Robin E. Lawson; Norman F. Knight

2001-01-01

444

Numerical Simulations of the Metallicity Distribution in Dwarf Spheroidal Galaxies  

SciTech Connect

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

445

Numerical simulation of particle flow in a sand trap  

Microsoft Academic Search

Sand traps are used to measure Aeolian flux. Since they modify the surrounding wind velocity field their gauging represents\\u000a an important challenge. We use numerical simulations under the assumption of homogeneous turbulence based on FLUENT to systematically\\u000a study the flow field and trapping efficiency of one of the most common devices based on a hollow cylinder with two slits.\\u000a In

A. D. Araújo; J. S. Andrade Jr.; L. P. Maia; H. J. Herrmann

2009-01-01

446

Numerical Simulation In Magnetic Drug Targeting. Magnetic Field Source Optimization  

Microsoft Academic Search

\\u000a This paper presents numerical simulation model and results on magnetic drug targeting therapy. The study aims at investigating\\u000a the aggregate blood - magnetic carrier flow interaction with an external magnetic field. Another objective was finding the\\u000a optimal magnetic field source configuration that provides for flows that best assist in magnetic drug targeting. In order\\u000a to evaluate the effects we used

A. Dobre; A. M. Morega

447

Development of Brick and Mortar Material Parameters for Numerical Simulations  

Microsoft Academic Search

\\u000a Numerical simulation of brick and mortar masonry in the literature has been performed using homogenized material properties;\\u000a however, discrete material properties for brick and mortar for a constitutive model built into hydrocodes have been unavailable.\\u000a The Holmquist-Johnson-Cook (HJC) constitutive model for concrete captures pressure and strain rate dependent strength behavior\\u000a and void crushing damage behavior of brittle solids reasonably well,

Christopher S. Meyer

448

Numerical simulation of downhole temperature distribution in producing oil wells  

Microsoft Academic Search

An improved numerical simulation method is presented to calculate the downhole temperature distribution for multiple pay zones\\u000a in producing oil wells. Based on hydrodynamics and heat transfer theory, a 2-D temperature field model in cylindrical coordinates\\u000a is developed. In the model, we considered general heat conduction as well as the heat convection due to fluid flow from porous\\u000a formation to

Ying Shi; Yanjie Song; Hong Liu

2008-01-01

449

Novel accelerators employing high-current electron beams numerical simulations  

SciTech Connect

Numerical simulations codes are described which can be used to study the physical phenomena of high-current electron beams employed in some novel accelerator schemes. Examples are given of the study of transverse effects in the free electron laser part of a Two-Beam Accelerator, the study of ion guiding in a Relativistic Klystron, and a study of the acceleration phase of a Collective implosion Accelerator.

Fawley, W.M.; Teague, M.R.; Caporaso, G.J.; Yu, S.S.; Sessler, A.M.

1986-01-01

450

Issues in direct numerical simulation of plasma turbulence and transport  

NASA Astrophysics Data System (ADS)

The problem of direct numerical simulation of plasma turbulence in magnetic confinement systems such as a tokamak is important in gaining a theoretical understanding of anomalous transport of particles, energy, momentum and impurities in such systems. Two approaches to this question are being developed. The design philosophy and the basic numerical problems encountered and solved in the construction of a two-fluid, 3-D, electro-magnetic, finite difference, time evolution code, CUTIE, are outlined. The importance of qualitative consistency, time-reversal, conservation properties, phase mixing, and boundary conditions are illustrated in the context of both passive and active electrostatic turbulence. A separate study was undertaken to aid in the understanding of drift wave turbulence in tokamak plasmas. In this connection a 3-D, time-dependant, electrostatic drift wave code called DRIFT was written. This has features which take account of toroidicity, non-adiabaticity and magnetic shear. The resulting code is very flexible, and was used to solve the Hasegawa-Mima equation efficiently in 2-D. Results from time-dependant, 3-D calculation run on a Cray-2 are presented. The aim is to obtain a proper physical understanding of plasma turbulence in typical tokamak conditions by calculating the power spectra of the turbulent fluctuations and their transport consequences. It is believed that this can only be achieved by a step-by-step approach to the numerics, making sure that the calculated effects represent genuine physics and are not mere artifacts of the numerical simulation.

Thyagaraja, A.; Arter, W.; Haas, F. A.

1991-04-01

451

Characteristic boundary conditions for direct simulations of turbulent counterflow flames  

Microsoft Academic Search

Improved Navier–Stokes characteristic boundary conditions (NSCBC) are formulated for the direct numerical simulations (DNS) of laminar and turbulent counterflow flame configurations with a compressible flow formulation. The new boundary scheme properly accounts for multi-dimensional flow effects and provides nonreflecting inflow and outflow conditions that maintain the mean imposed velocity and pressure, while substantially eliminating spurious acoustic wave reflections. Applications to

C. S. Yoo; Y. Wang; A. Trouvé; H. G. Im

2005-01-01