This paper introduces a computational model that computes the time-dependent evolution of a non-equilibrium turbulence spectrum from the system size down to the viscous dissipation scale. Turbulence models for use with Computational Fluid Dynamics (CFD) have at best treated the inertial-range below the CFD resolution as if obeying a renormalizable or scale-similar equilibrium described by the Kolmogorov spectrum with a spectral energy density that scales as k–5/3. The “Coherent Structure Dynamics” (CSD) model introduced here addresses situations where the timescale for changes in the macroscopic fluid dynamics is short and thus the resulting turbulence is far from an equilibrium cascade because the turbulent small scales that drive the dissipation will not have had time to equilibrate. Such circumstances can be caused, for example, by strong shocks passing through passive density gradients or fuel injection into supersonic flows. Mixing on the molecular scale and thus chemical reactions will be delayed until the short scales in the velocity spectrum are energized. The CSD model is not derived from the Navier-Stokes equations. It is constructed to satisfy the important physical conditions of the problem including scale consistency of the inviscid, nonlinear, fluid-dynamic interactions between the coherent structures that actually comprise turbulence. In addition to treating the kinetic energy density as a function of scale size down to the Kolmogorov dissipation scale, a number density of coherent structures at each scale is introduced to account for the fact that the relative spacing of the structures comprising turbulence, particularly away from equilibrium, may not be the same at all scales. This dynamic system relaxes to the Kolmogorov spectrum with a definite pre-dissipative bump (the bottleneck). Two scaleindependent parameters in the model are calibrated using the Taylor-Green vortex problem. Examples are presented and tests of the model are discussed. _______________ Manuscript approved September 14, 2018. 2 Glossary: ρ mass density of the fluid (gm/cc). ν Kinematic viscosity of the fluid (gm/(sec cm) ). L%&% System scale length, 10 m in examples following. R( Length scale (cm) of the rotors in scale size bin k. The following variables change in time due to the stiff evolution equations . . . E( Energy density (ergs/cc) of rotors of size Rk (k = 0, kmax). Nk Number density of rotors (#/cc) of scale size Rk. ε( Energy in a single rotor of size Rk. ε( = 3πρR(V( = E(/N( The following derived quantities are also used . . . P( 4 Packing fraction for rotors of size Rk (dimensionless). P( 4 ≡ 3πR( N(. Thus E( ≡ 3πρR(V(N( = ρP( V( P( Packing fraction temporary. P( ≡ (P( )0/. = (3πR(N() V( Characteristic average velocity (energy weighted) of rotors of size R( .

First responders need a more or less instant estimate of danger zones resulting from accidental airborne releases of hazardous materials in order to take immediate action, to coordinate rescue teams and to protect the population and critical infrastructure. To fulfill the need for efficient access to reliable results in a first responders environment while maintaining sufficient dispersion modeling accuracy, pre-computed high-resolution CFD modeling can be combined with 'physical data reduction' in an emergency assessment tool. This approach, specific to the geometry of the city of Hamburg, has been adopted by the Fire Brigade in Hamburg, Germany.

This book is written by two well known active researchers in the topical area, in which the authors share their precious practical experience in numerical computation of reactive flows. The book contains 13 chapters, grouped by the authors into three parts. The first is for an introductory short course on modelling and simulation, the second on some more advanced topics in numerical simulation, and the third on simulating complex reacting flows. A strong feature of the book is its inclusion of some extensive discussion of the practical aspects of computational simulation, applicable to both non-reactive and reactive flows. This is reflected in the less formal narrative style of presentation in the whole book, featured particularly strongly in Chapter 3. Rather than centring the materials based on the numerical methods, the authors arranged the numerical methods around the physical processes to be simulated, such as convection, diffusion, reaction mechanism and radiation process. Although it looks a bit fragmented in the presentation of the numerical methods as compared with similar text books, it stresses the flow physics centred approach, which is essential for numerical modellers. The authors have tried to be comprehensive in the coverage of numerical methods. Unsurprisingly the authors' own early work on the flux-corrected transport (FCT) algorithm is featured strongly in the book. On the other hand, the widely used approximate Riemann solvers have been treated very briefly, which is a little disappointing. The book also touches upon some more recent progress in various areas including parallel computing, adaptive gridding, Lagrangian methods, compact schemes, wavelet methods and Boltzmann gaskinetic methods. No attempt has been made to provide the details of some of these more advanced topics but appropriate references have been given for the readers.

This paper addresses the following question: Can an airborne cloud of a chemical or other unwanted agent be neutralized effectively in an urban geometry by injecting a suitable reacting “remediant” into the cloud in sufficient amounts and at appropriate locations? The transport and dispersion of potentially dangerous, contaminants is controlled principally by the wind in an outdoor environment, its turbulent gusts, and how this complex airflow interacts with the geometry of the buildings and terrain. The possible effectiveness of reactive agent neutralization, or mitigation, is a complex matter involving chemical reaction of the agent and the remediant, progressive dilution of the two reactants, and fluid dynamic mixing of the reactants over time. Anyone contemplating in situ remediation needs to know where and when to deliver a remediant and what amounts are necessary.

Accidental and deliberate releases of harmful substances pose a tremendous challenge to first responders because of the large number of possible casualties and the resulting potential environmental and economic damage in densely populated areas. Within minutes after a release, countermeasures must be taken to protect the population and environment adequately. This requires the exposed area, travel time of pollutants and possible exposure levels to be known in advance with sufficient accuracy in complex urban and industrial terrain where accidental releases are possible. This paper introduces an innovative and efficient concept for a more reliable local-scale hazmat dispersion modelling in the context of emergency response, developed at NRL. Using the current implementation of this approach for first response professionals in the city of Hamburg as an example, an overview of the emergency response tool CT-Analyst Hamburg is presented. Unique features of the tool such as source location reconstruction based on available measured data or the simulation of pollutant retention time in built-up terrain are discussed. The extensive efforts undertaken to carefully and reliably validate the first responder's tool are described. Both, the underlying CFD-LES simulations as well as the CT-Analyst tool have been validated extensively using high-resolution test data sets generated in special boundary layer wind tunnel facilities and available field test data.

This paper describes the design, implementation, and use of integrated chemical plume-models in virtual training systems. The US Naval Research Laboratory has linked its CT-Analyst® software, a high-fidelity real-time plume modeling tool, with VBS2, a widely-used virtual gaming and training program, to produce new training capabilities that were previously unavailable. This work benefits two different but overlapping training scenarios: 1) tactical training for large-scale chemical gas attacks with a specific focus on crowd management, and 2) handler-focused training for users interested in working with IED-detecting dogs. The use of accurate, faster-than-real-time plume modeling enhances the virtual training systems to provide broader realistic support to the simulation and training communities.

First responders need a more or less instant estimate of danger zones resulting from accidentally released hazardous materials in order to take immediate action, to coordinate rescue teams and to protect human population and critical infrastructure. To fulfill the need for a sufficient dispersion modeling accuracy while maintaining efficient access to reliable results in a first responders environment, systematic high resolution pre-accidental LES modeling can be combined with ’physical data reduction’ in an emergency assessment tool. A typical example of such an approach adjusted to the geometry of the Hamburg inner city area will be presented. It gives a glimpse into the application of LES-modeling for real-world problems.

A new research platform, the Air Traffic Monotonic Lagrangian Grid, has been developed to serve as a simulation tool for easy and fast testing of various air traffic system concepts. The underlying algorithm is the Monotonic Lagrangian Grid, which is a fast nearest-neighbors interaction algorithm used for sorting and tracking many moving and interacting objects. The nodes of the Monotonic Lagrangian Grid represent the locations of individual aircraft, and the grid moves at each time step as the aircraft move. The model is used to simulate a 24 h period of air traffic flow in the National Airspace System, during which there are 41,594 flights, and this requires only 79 s of wall-clock time on a single processor of a 1.3 GHz Altix. An analysis is presented of the number of nearest-neighbor nodes that must be checked to ensure adequate separation among aircraft. An investigation of the effect of removing waypoints from aircraft trajectories indicates that this may result in a significant reduction in total flight time. Finally, the model is compared with the traditional Latitude - Longitude grid approach, in which the airspace volume is partitioned into fixed stationary grid cells. Results of the comparison indicate that the main advantage of the Monotonic Lagrangian Grid method is that it is a general sorting algorithm that can sort on multiple properties, providing more computational efficiency.

This year, 2013, marks the 40th anniversary of the journal article "Flux-Corrected Transport I. SHASTA, A Fluid Transport Algorithm That Works" by Jay Boris and David Book [1]. Flux-Corrected Transport (FCT) removed a serious roadblock to advances in Computational Fluid Dynamics (CFD) by enabling the accurate treatment of strong, time-dependent shock problems in blast, reactive-flow, and combustion physics, and in aerodynamics and astrophysics. Steep gradients in conserved fluid variables could now be convected across a computational grid without the appearance of spurious oscillations and physically impossible negative values. The nonlinear "flux-correction" algorithm introduced in FCT imposes the physical properties of conservation, locality, causality, and monotonicity on the numerical solutions for convection without adding a great deal of numerical diffusion. This article shows that implementing these physical properties in solving the continuity equation through high-resolution FCT also results in a serviceable Large-Eddy Simulation treatment of turbulent flows without need for additional "subgrid turbulence models." We have named this simplified approach Monotone Integrated Large Eddy Simulation (MILES). (C) 2013 Elsevier Ltd. All rights reserved.

No AccessTechnical NoteEffect of the Initial Turbulence Level on an Underexpanded Supersonic JetJ. Liu, K. Kailasanath, J. P. Boris, N. Heeb, D. Munday and E. GutmarkJ. LiuLaboratories for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D.C. 20375, K. KailasanathLaboratories for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D.C. 20375, J. P. BorisLaboratories for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D.C. 20375, N. HeebUniversity of Cincinnati, Cincinnati, Ohio 45221, D. MundayUniversity of Cincinnati, Cincinnati, Ohio 45221 and E. GutmarkUniversity of Cincinnati, Cincinnati, Ohio 45221Published Online:19 Feb 2013https://doi.org/10.2514/1.J051949SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Gutmark E. and Ho C., "Preferred Modes and the Spreading Rates of Jets," Physics of Fluids, Vol. 26, No. 10, Oct. 1983, pp. 2932–2938. doi:https://doi.org/10.1063/1.864058 PHFLE6 1070-6631 CrossrefGoogle Scholar[2] Hussain A. K. M. F. and Zedan M. F., "Effects of the Initial Condition on the Axisymmetric Free Shear Layer: Effects of the Initial Fluctuation Level," Physics of Fluids, Vol. 21, No. 9, 1978, pp. 1475–1481. doi:https://doi.org/10.1063/1.862410 PHFLE6 1070-6631 CrossrefGoogle Scholar[3] Long D., McDonald T. and Maye P., "Effect of Inlet Flow Conditions on Noise and Performance of Supersonic Nozzles," AIAA Paper 2010-3920, 2010. LinkGoogle Scholar[4] Bogey C. and Bailly C., "Influence of Initial Turbulence Level on the Flow and Sound Fields of a Subsonic Jet at a Diameter-Based Reynolds Number of 105," Journal of Fluid Mechanics, Vol. 701, June 2012, pp. 352–385. doi:https://doi.org/10.1017/jfm.2012.162 JFLSA7 0022-1120 CrossrefGoogle Scholar[5] Bogey C. and Bailly C., "Influence of the Nozzle-Exit Boundary-Layer Thickness on the Flow and Acoustic Fields of Initially Laminar Jets," Journal of Fluid Mechanics, Vol. 663, Nov. 2010, pp. 507–538. doi:https://doi.org/10.1017/S0022112010003605 JFLSA7 0022-1120 CrossrefGoogle Scholar[6] Cacqueray N., Bogey C. and Bailly C., "Direct Noise Computation of a Shocked and Heated Jet at a Mach Number of 3.30," AIAA Paper 2010-3732, 2010. Google Scholar[7] Bogey C., Marsden O. and Bailly C., "Large-Eddy Simulation of the Flow and Acoustic Fields of a Reynolds Number 105 Subsonic Jet with Tripped Exit Boundary Layers," Physics of Fluids, Vol. 23, No. 3, 2011, pp. 1–20. doi:https://doi.org/10.1063/1.3555634 PHFLE6 1070-6631 CrossrefGoogle Scholar[8] Pokora C. D., McMullan W. A., Page G. J. and McGuirk J. J., "Influence of a Numerical Boundary Layer Trip on Spatial-Temporal Correlations within LES of a Subsonic Jet," AIAA Paper 2011-2920, 2011. Google Scholar[9] Boris J. P., A Fluid Transport Algorithm That Works, Computing as a Language of Physics, Centre for Theoretical Physics, Trieste, Italy, 1972, pp. 171–189. Google Scholar[10] Lohner R., Patnaik G., Boris J. P., Oran E. S. and Book D. L., "Applications of the Method of Flux-Corrected Transport to Generalized Meshes," Tenth International Conference on Numerical Methods in Fluid Dynamics Lecture Notes in Physics 264, edited by Zhuang F. G and Zhu Y. L., Springer–Verlag, New York, 1987, pp. 428–434. Google Scholar[11] Boris J. P., "On Large Eddy Simulation Using Subgrid Turbulence Models, Whither Turbulence?," Turbulence at the Crossroads: Lecture Notes in Physics 357, edited by Lumley L. J., Springer–Verlag, New York, 1990, pp. 344–353. CrossrefGoogle Scholar[12] Liu J., Kailasanath K., Ramamurti R., Munday D., Gutmark E. and Lohner R., "Large-Eddy Simulations of a Supersonic Jet and Its Near-Field Acoustic Properties," AIAA Journal, Vol. 47, No. 8, 2009, pp. 1849–1864. doi:https://doi.org/10.2514/1.43281 AIAJAH 0001-1452 LinkGoogle Scholar[13] Munday D. and Gutmark E., "Flow Structure and Acoustics of Supersonic Jets from Conical Convergent-Divergent Nozzles," Physics of Fluids, Vol. 23, No. 11, 2011, p. 116102. doi:https://doi.org/10.1063/1.3657824 PHFLE6 1070-6631 CrossrefGoogle Scholar[14] Shapiro A. H., The Dynamics and Thermodynamics of Compressible Fluid Flow, Vol. 1, Wiley, New York, NY, 1953, pp. 153–154. Google Scholar[15] Lyrintzis A., "Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field," International Journal of Aeroacoustics, Vol. 2, No. 2, 2003, pp. 95–128. doi:https://doi.org/10.1260/147547203322775498 1475-472X CrossrefGoogle Scholar Previous article Next article

§** †† The impact of the turbulence level at the nozzle exit on the jet flow and far-field noise level has been investigated using large-eddy simulations (LES) and the Ffowcs Williams & Hawkings (FW-H) surface integral method. The jet exit flow condition is slightly underexpanded. Both the random perturbations inside the nozzle and the nozzle surface roughness are used to increase the turbulence level. Increasing the turbulence level at the nozzle exit increases the shear-layer spreading, reduces the screech intensity and also decreases slightly the far-field noise level. The LES predictions of the shock-cell structures and the jet core lengths agree well with the measurement data. In addition, the impact of grid resolution used in both the jet flow and the near-field acoustic propagation region has also been investigated. It is found that the grid resolution used in the shear layer impacts the numerical predictions more than those used in the other regions. Adding an adequate amount of turbulence level at the nozzle exit greatly improves the predictions using a coarser grid resolution in the shear layer. Furthermore, the far-field noise predictions agrees well with measurement data, and the contribution from the end cap is found small, but it is sensitive to the mesh size used in the integration.

First responders need a more or less instant estimate of danger zones resulting from accidentally released hazardous materials in order to take immediate action, to coordinate rescue teams and to protect human population and critical infrastructure. To fulfil the need for a sufficient dispersion modelling accuracy while maintaining efficient access to reliable results in a first responders environment, systematic high resolution pre-accidental LES modelling can be combined with 'physical data reduction' in an emergency assessment tool. A typical example of such an approach adjusted to the geometry of the Hamburg inner city area will be presented.

The Air Traffic Monotonic Lagrangian Grid (ATMLG) is used to simulate a 24 hour period of air traffic flow in the National Airspace System (NAS). During this time period, there are 41,594 flights over the United States, and the flight plan information (departure and arrival airports and times, and waypoints along the way) are obtained from an Federal Aviation Administration (FAA) Enhanced Traffic Management System (ETMS) dataset. Two simulation procedures are tested and compared: one based on the Monotonic Lagrangian Grid (MLG), and the other based on the stationary Latitude-Longitude (LatLong) grid. Simulating one full day of air traffic over the United States required the following amounts of CPU time on a single processor of an SGI Altix: 88 s for the MLG method, and 163 s for the Lat-Long grid method. We present a discussion of the amount of CPU time required for each of the simulation processes (updating aircraft trajectories, sorting, conflict detection and resolution, etc.), and show that the main advantage of the MLG method is that it is a general sorting algorithm that can sort on multiple properties. We discuss how many MLG neighbors must be considered in the separation assurance procedure in order to ensure a five-mile separation buffer between aircraft, and we investigate the effect of removing waypoints from aircraft trajectories. When aircraft choose their own trajectory, there are more flights with shorter duration times and fewer CD&R maneuvers, resulting in significant fuel savings.

First responders need a more or less instant estimate of danger zones resulting from accidentally released hazardous materials in order to take immediate action, to coordinate rescue teams and to protect human population and critical infrastructure. To fulfil the need for a sufficient dispersion modelling accuracy while maintaining efficient access to reliable results in a first responders environment, systematic high resolution pre-accidental LES modelling can be combined with 'physical data reduction' in an emergency assessment tool. A typical example of such an approach adjusted to the geometry of the Hamburg inner city area will be presented.