The evolution equation for the flame surface density in turbulent premixed combustion

The mean reaction rate in flamelet models for turbulent premixed combustion depends on two basic quantities: a mean chemical rate, called the flamelet speed, and the flame surface density. Our previous work had been primarily focused on the problem of the structure and topology of turbulent premixed flames, and it was then determined that the flamelet speed, when space-averaged, is only weakly sensitive to the turbulent flow field. Consequently, the flame surface density is the key quantity that conveys most of the effects of the turbulence on the rate of energy release. In flamelet models, this quantity is obtained via a modeled transport equation called the Sigma-equation. Past theoretical work has produced a rigorous approach that leads to an exact but unclosed formulation for the turbulent Sigma-equation. In the exact Sigma-equation, it appears that the dynamical properties of the flame surface density are determined by a single parameter, namely the turbulent flame stretch. Unfortunately, the turbulent flame stretch as well as the flame surface density is not available from experiments, and, in the absence of experimental data, little is known on the validity of the closure assumptions used in current flamelet models. Direct Numerical Simulation (DNS) is the alternative approach to get basic information on these fundamental quantities. In the present work, three-dimensional DNS of premixed flames in isotropic turbulent flow is used to estimate the different terms appearing in the Sigma-equation. A new methodology is proposed to provide the source and sink terms for the flame surface density, resolved both temporally and spatially throughout the turbulent flame brush. Using this methodology, our objective is to extract the turbulent flame stretch from the DNS data base and then perform extensive comparisons with flamelet models. Thanks to the detailed information produced by the DNS-based analysis, it is expected that this type of comparison will not only underscore the shortcomings of current models, but also suggest ways to improve them

Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry

The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories

Towards Data-Driven Operational Wildfire Spread Modeling: A Report of the NSF-Funded WIFIRE Workshop

This report presents a record of the discussions that took place during the workshop entitled “Towards Data-Driven Operational Wildfire Spread Modeling” held on January 12-13, 2015, at the University of California, San Diego. The workshop was organized as part of WIFIRE, a collaborative project sponsored by the National Science Foundation (NSF) between San Diego Supercomputer Center, Calit2's Qualcomm Institute and Jacobs School of Engineering at the University of California at San Diego (UCSD) and the Department of Fire Protection Engineering at the University of Maryland (UMD). The objective of WIFIRE is to build a cyberinfrastructure for real-time and data-driven simulation, prediction and visualization of wildfire behavior (see http://wifire.ucsd.edu). WIFIRE is funded by NSF Award #1331615 as part of the Interdisciplinary Research in Hazards and Disasters (Hazards SEES) program. The objectives of the WIFIRE workshop were: (1) to identify technical barriers and milestones that need to be overcome in order to develop validated data-driven wildfire spread models and make them operational; and (2) to bring together leading representatives of the wildfire research community, the geosciences community and the fire science community. The wildfire research community has relevant expertise on wildfire operations; the geosciences community has relevant expertise on large-scale effects in wildfires (e.g., the coupling with atmospheric phenomena); the fire science community has relevant expertise on flame-scale effects in wildfires (e.g., the response of the fire to changing local conditions). The workshop was organized around four main topical areas and corresponding breakout groups, including operational rate-of-spread models for wildfire spread, CFD models, wildfire data, and data assimilation (see Appendix A for a description of the WIFIRE workshop program). Our goal in this report is to document and share the substance and scope of the workshop discussions and to thereby invite the wider research community to support, engage in, and contribute to the general effort to develop operational data-driven tools for wildfire spread predictions.The National Science Foundation via Award #1331615 as part of the Interdisciplinary Research in Hazards and Disasters (Hazards SEES) program

Call for participation in the second workshop organized by the IAFSS Working Group on Measurement and Computation of Fire Phenomena

Early 2015, a new initiative called ‘‘the IAFSS Working Group on Measurement and Computation of Fire Phenomena’’ (aka the MaCFP Working Group) was launched (http://www.iafss.org/macfp/). This initiative is endorsed and supported by the International Association for Fire Safety Science (IAFSS, http://www.iafss. org). The first workshop organized by the MaCFP Working Group was held in June 2017 as a pre-event to the 12th IAFSS Symposium in Lund, Sweden. Details are found on https://iafss.org/3770-2/ and in Ref. [1]. The primary objective of this letter is to engage the members of the fire research community to participate in the second MaCFP workshop, scheduled on April 25–26 2020 as a pre-event to the 13th IAFSS Symposium in Waterloo, Canada (http://iafss2020.ca). Continued updated information on the MaCFP Working Group effort is found at http:// www.iafss.org/macfp/

Call for participation in the second workshop organized by the IAFSS Working Group on Measurement and Computation of Fire Phenomena

status: publishe

Call for participation in the second workshop organized by the IAFSS Working Group on measurement and computation of fire phenomena

Early 2015, a new initiative called ‘‘the IAFSS Working Group on Measurement and Computation of Fire Phenomena’’ (aka the MaCFP Working Group) was launched (http://www.iafss.org/macfp/). This initiative is endorsed and supported by the International Association for Fire Safety Science (IAFSS, http://www.iafss. org). The first workshop organized by the MaCFP Working Group was held in June 2017 as a pre-event to the 12th IAFSS Symposium in Lund, Sweden. Details are found on https://iafss.org/3770-2/ and in Ref. [1]. The primary objective of this letter is to engage the members of the fire research community to participate in the second MaCFP workshop, scheduled on April 25–26 2020 as a pre-event to the 13th IAFSS Symposium in Waterloo, Canada (http://iafss2020.ca). Continued updated information on the MaCFP Working Group effort is found at http:// www.iafss.org/macfp/

Call for Participation in the Second Workshop Organized by the IAFSS Working Group on Measurement and Computation of Fire Phenomena

status: publishe

Call for participation in the first workshop organized by the IAFSS working group on measurement and computation of fire phenomena

A new initiative, endorsed and supported by the International Association for Fire Safety Science (IAFSS, http://www.iafss.org), has been launched: "the IAFSS Working Group on Measurement and Computation of Fire Phenomena" (or the MaCFP Working Group). The primary objective of this letter is to engage the members of the fire research community to participate in the first workshop organized by the MaCFP Working Group and which is scheduled as a pre-event to the 12th IAFSS Symposium in Lund, Sweden, in June 2017 (http://www.iafss.org/save-the-date-12th-iafss-symposium/). Constantly updated information on the MaCFP Working Group effort is found at http://www.iafss.org/macfp/

Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry

The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories