scholarly journals Approaches to Modeling Bed Drag in Pine Forest Litter for Wildland Fire Applications

2021 ◽  
Author(s):  
Eric V. Mueller ◽  
Michael R. Gallagher ◽  
Nicholas Skowronski ◽  
Rory M. Hadden
Keyword(s):  
Velocity Profile ◽  
Traditional Approach ◽  
Wildland Fire ◽  
Forest Litter ◽  
Cfd Model ◽  
Fire Dynamics ◽  
Forchheimer Equation ◽  
Eddy Simulation ◽  
Cfd Models ◽  
Wide Range

AbstractModeling flow in vegetative fuel beds is a key component in any detailed physics-based tool for simulating wildland fire dynamics. Current approaches for drag modeling, particularly those employed in multiphase computational fluid dynamics (CFD) models, tend to take a relatively simple form and have been applied to a wide range of fuel structures. The suitability of these approaches has not been rigorously tested for conditions which may be encountered in a wildland fire context. Here, we focus on beds of Pinus rigida needle litter and undertake a two-part study to quantify the drag and evaluate the capabilities of a multiphase large eddy simulation CFD model, the NIST Fire Dynamics Simulator. In the first part, bed drag was measured in a wind tunnel under a range of conditions. The results were fit to a Forchheimer model, and the bed permeability was quantified. A traditional approach employed in the multiphase formulation was compared to the parameterized Forchheimer equation and was found to over-predict the drag by a factor of 1.2–2.5. In the second part, the development of a velocity profile above and within a discrete fuel layer was measured. Using the Forchheimer equation obtained in the first part of the study, the CFD model was able to replicate a qualitatively consistent velocity profile development. Within the fuel bed, the model appeared to under-predict the velocity magnitudes, which may be the result of unresolved pore-scale flow dynamics.

scholarly journals Computational modeling of fire safety in metro-stations

2021 ◽  
Author(s):  
Philip McKeen
Keyword(s):  
Fire Safety ◽  
Performance Based Design ◽  
Cfd Model ◽  
Fire Dynamics ◽  
Evacuation Modeling ◽  
Fire Dynamics Simulator ◽  
Cfd Models ◽  
Smoke Spread ◽  
Modeling Software ◽  
Computational Fluid Dynamics Cfd

This research investigates and attempts to quantify the hazards associated with fire in metrostations. The use of numerical simulations for the analysis of fire safety within metro-stations allows for the prediction and analysis of hazards within the built environment. Such approaches form the growing basis of performance based design (PBD), which can optimize design solutions. The simulations utilize Fire Dynamics Simulator (FDS), a Computational Fluid Dynamics (CFD) model and Pathfinder, an evacuation modeling software. The safety of underground metro-stations is analyzed through the simulation of smoke spread and egress modelling. CFD models of TTC’s Union Station and TransLink’s Yaletown Station are developed to allow for simulations of smoke spread scenarios. These models are evaluated in regards to the preservation of tenability and influence on the Available Safe Egress Time (ASET). The egress of metro-stations is modelled and analyzed to determine the Required Safe Egress Time (RSET).

scholarly journals Computational modeling of fire safety in metro-stations

2021 ◽  
Author(s):  
Philip McKeen
Keyword(s):  
Fire Safety ◽  
Performance Based Design ◽  
Cfd Model ◽  
Fire Dynamics ◽  
Evacuation Modeling ◽  
Fire Dynamics Simulator ◽  
Cfd Models ◽  
Smoke Spread ◽  
Modeling Software ◽  
Computational Fluid Dynamics Cfd

This research investigates and attempts to quantify the hazards associated with fire in metrostations. The use of numerical simulations for the analysis of fire safety within metro-stations allows for the prediction and analysis of hazards within the built environment. Such approaches form the growing basis of performance based design (PBD), which can optimize design solutions. The simulations utilize Fire Dynamics Simulator (FDS), a Computational Fluid Dynamics (CFD) model and Pathfinder, an evacuation modeling software. The safety of underground metro-stations is analyzed through the simulation of smoke spread and egress modelling. CFD models of TTC’s Union Station and TransLink’s Yaletown Station are developed to allow for simulations of smoke spread scenarios. These models are evaluated in regards to the preservation of tenability and influence on the Available Safe Egress Time (ASET). The egress of metro-stations is modelled and analyzed to determine the Required Safe Egress Time (RSET).

CFD Prediction of Hydraulic Effects on External Ultrasonic Flowmeters: A Case Study

2006 ◽  
Author(s):  
Don Augenstein ◽  
Herb Estrada ◽  
Ernie Hauser ◽  
Ed Madera ◽  
Steven Keijers ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Nuclear Power ◽  
Power Level ◽  
Scale Model ◽  
Calibration Model ◽  
Test Results ◽  
Cfd Model ◽  
Flow Meters ◽  
Calibration Test ◽  
Cfd Models

External ultrasonic flow meters installed in a nuclear power plant feedwater system were suspected of containing a conservative bias (high reading) despite having been calibrated in a scale model laboratory test. Several independent measures of plant power level indicated that the bias could be as high as 2.0%. The first step in resolving the discrepancy was the construction of a computational fluid dynamics (CFD) model of the hydraulic configurations in which the flow meters were tested in the lab. The CFD model closely matched the original calibration test results. The CFD model for real plant geometry including certain upstream hydraulic features predicted calibration changes of the same sign and order of magnitude as the suspected bias. These upstream elements were absent in the original hydraulic model test. As a consequence of this finding, these additional features were included in new hydraulic calibration tests. Some effects predicted by the CFD model were verified and traceably confirmed, while others were contradicted by the data from the new model. Final calibration test results confirmed the presence of a bias, although not of the magnitude originally suspected. The calibration results provide a traceable measurement basis for use of the flow meters within their specified accuracy after correction for the bias. By use of a chordal ultrasonic flowmeter, velocity profile (pointed-ness) and swirl rates were measured during the tests. The tests, together with the velocity profile information from the CFD simulations, provided insights into the errors and omissions in the original calibration model tests and the assumptions on which the model was based. Finally the calibration tests highlight the strengths and limitations of CFD models for work of this kind.

scholarly journals Current Wildland Fire Patterns and Challenges in Europe: A Synthesis of National Perspectives

2021 ◽  
Vol 14 ◽  
pp. 117862212110281
Author(s):  
Nieves Fernandez-Anez ◽  
Andrey Krasovskiy ◽  
Mortimer Müller ◽  
Harald Vacik ◽  
Jan Baetens ◽  
...  
Keyword(s):  
Land Use ◽  
Large Scale ◽  
Wildland Fire ◽  
Human Life ◽  
Local Analysis ◽  
Wildland Fires ◽  
Fire Statistics ◽  
Quantitative Evidence ◽  
Wide Range ◽  
Fire Patterns

Changes in climate, land use, and land management impact the occurrence and severity of wildland fires in many parts of the world. This is particularly evident in Europe, where ongoing changes in land use have strongly modified fire patterns over the last decades. Although satellite data by the European Forest Fire Information System provide large-scale wildland fire statistics across European countries, there is still a crucial need to collect and summarize in-depth local analysis and understanding of the wildland fire condition and associated challenges across Europe. This article aims to provide a general overview of the current wildland fire patterns and challenges as perceived by national representatives, supplemented by national fire statistics (2009–2018) across Europe. For each of the 31 countries included, we present a perspective authored by scientists or practitioners from each respective country, representing a wide range of disciplines and cultural backgrounds. The authors were selected from members of the COST Action “Fire and the Earth System: Science & Society” funded by the European Commission with the aim to share knowledge and improve communication about wildland fire. Where relevant, a brief overview of key studies, particular wildland fire challenges a country is facing, and an overview of notable recent fire events are also presented. Key perceived challenges included (1) the lack of consistent and detailed records for wildland fire events, within and across countries, (2) an increase in wildland fires that pose a risk to properties and human life due to high population densities and sprawl into forested regions, and (3) the view that, irrespective of changes in management, climate change is likely to increase the frequency and impact of wildland fires in the coming decades. Addressing challenge (1) will not only be valuable in advancing national and pan-European wildland fire management strategies, but also in evaluating perceptions (2) and (3) against more robust quantitative evidence.

scholarly journals Mass and Heat Transfer Coefficients in Automotive Exhaust Catalytic Converter Channels

Catalysts ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 507
Author(s):  
Chrysovalantis C. Templis ◽  
Nikos G. Papayannakos
Keyword(s):  
Heat Transfer ◽  
Flow Reactor ◽  
Catalytic Converter ◽  
Reaction Rates ◽  
Cfd Model ◽  
Automotive Exhaust ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Mass And Heat Transfer

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two dimensional computational fluid dynamic (2-D CFD) model developed in Comsol Multiphysics, taking into account catalytic rates of a real catalytic converter. The effect of channel size and reaction rates on mass and heat transfer coefficients and the applicability of the proposed correlations at different conditions are discussed. The correlations proposed predict very satisfactorily the mass and heat transfer coefficients calculated from the 2-D CFD model along the channel length. The use of a one dimensional (1-D) simplified model that couples a plug flow reactor (PFR) with mass transport and heat transport effects using the mass and heat transfer correlations of this study is proved to be appropriate for the simulation of the monolith channel operation.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Compressor Performance and Operability in Swirl Distortion

2010 ◽  
Author(s):  
Yogi Sheoran ◽  
Bruce Bouldin ◽  
P. Murali Krishnan
Keyword(s):  
Gas Turbine ◽  
Complex Geometry ◽  
Full Range ◽  
Axial Compressor ◽  
Cfd Model ◽  
Generator System ◽  
Sliding Mesh ◽  
Wide Range ◽  
Compressor Performance ◽  
The Impact

Inlet swirl distortion has become a major area of concern in the gas turbine engine community. Gas turbine engines are increasingly installed with more complicated and tortuous inlet systems, like those found on embedded installations on Unmanned Aerial Vehicles (UAVs). These inlet systems can produce complex swirl patterns in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a database containing the impact of a range of swirl distortion patterns on a compressor performance and operability. A recent paper presented by the authors described a versatile swirl distortion generator system that produced a wide range of swirl distortion patterns of a prescribed strength, including bulk swirl, twin swirl and offset swirl. The design of these swirl generators greatly improved the understanding of the formation of swirl. The next step of this process is to understand the effect of swirl on compressor performance. A previously published paper by the authors used parallel compressor analysis to map out different speed lines that resulted from different types of swirl distortion. For the study described in this paper, a computational fluid dynamics (CFD) model is used to couple upstream swirl generator geometry to a single stage of an axial compressor in order to generate a family of compressor speed lines. The complex geometry of the analyzed swirl generators requires that the full 360° compressor be included in the CFD model. A full compressor can be modeled several ways in a CFD analysis, including sliding mesh and frozen rotor techniques. For a single operating condition, a study was conducted using both of these techniques to determine the best method given the large size of the CFD model and the number of data points that needed to be run to generate speed lines. This study compared the CFD results for the undistorted compressor at 100% speed to comparable test data. Results of this study indicated that the frozen rotor approach provided just as accurate results as the sliding mesh but with a greatly reduced cycle time. Once the CFD approach was calibrated, the same techniques were used to determine compressor performance and operability when a full range of swirl distortion patterns were generated by upstream swirl generators. The compressor speed line shift due to co-rotating and counter-rotating bulk swirl resulted in a predictable performance and operability shift. Of particular importance is the compressor performance and operability resulting from an exposure to a set of paired swirl distortions. The CFD generated speed lines follow similar trends to those produced by parallel compressor analysis.

Experimental Investigation of Subsonic Turbulent Flow Over Single and Double Backward Facing Steps

1962 ◽  
Vol 84 (3) ◽  
pp. 317-325 ◽  
Author(s):  
D. E. Abbott ◽  
S. J. Kline
Keyword(s):  
Experimental Investigation ◽  
Velocity Profile ◽  
Flow Pattern ◽  
Reynolds Numbers ◽  
Area Ratio ◽  
Single Step ◽  
Reattachment Length ◽  
Double Step ◽  
Wide Range ◽  
Geometric Variables

Results are presented for flow patterns over backward facing steps covering a wide range of geometric variables. Velocity profile measurements are given for both single and double steps. The stall region is shown to consist of a complex pattern involving three distinct regions. The double step contains an assymmetry for large expansions, but approaches the single-step configuration with symmetric stall regions for small values of area ratio. No effect on flow pattern or reattachment length is found for a wide range of Reynolds numbers and turbulence intensities, provided the flow is fully turbulent before the step.

Performance Characterization of a Twin Scroll Volute for Turbocharging Applications

2018 ◽  
Author(s):  
Carlo Cravero ◽  
Mario La Rocca ◽  
Andrea Ottonello
Keyword(s):  
Experimental Data ◽  
Scientific Literature ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Automatic Design ◽  
Cfd Model ◽  
Radial Turbine ◽  
Wide Range ◽  
Partial Admission

The use of twin scroll volutes in radial turbine for turbocharging applications has several advantages over single passage volute related to the engine matching and to the overall compactness. Twin scroll volutes are of increasing interest in power unit development but the open scientific literature on their performance and modelling is still quite limited. In the present work the performance of a twin scroll volute for a turbocharger radial turbine are investigated in some detail in a wide range of operating conditions at both full and partial admission. A CFD model for the volute have been developed and preliminary validated against experimental data available for the radial turbine. Then the numerical model has been used to generate the database of solutions that have been investigated and used to extract the performance. Different parameters and indices are introduced to describe the volute aerodynamic performance in the wide range of operating conditions chosen. The above parameters can be used for volute development or matching with a given rotor or efficiently implemented in automatic design optimization strategies.

scholarly journals Improvement of CFD models of tunnel fire development based on experimental data

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 705-716 ◽  
Author(s):  
Barbara Vidakovic ◽  
Milos Banjac
Keyword(s):  
Experimental Data ◽  
Combustion Process ◽  
Burning Surface ◽  
Physical Structure ◽  
Cfd Model ◽  
Change Rate ◽  
Flamelet Model ◽  
Tunnel Fire ◽  
Cfd Models ◽  
Combustion Processes

This paper, dealing with the problems of mathematical description of the tunnel fire development process with the use of experimental data, outlines the procedure of correction of the existing and obtaining of an improved CFD model package. The improved CFD model was developed on the basis of detailed analysis and comparison of experimental and numerical results, through consideration of the physical structure of all processes affecting combustion. During the analysis it was noticed that the existing CFD model in the part covering combustion based on the so-called steady laminar flamelet model, treats the combustion process almost as a direct correlation between the processes of mixing gasses and heat release rate. This potential deficiency has been overcome by correction of the model in the section defining boundary condition for the burning surface and by establishing a direct correlation between the measured value of the fuel mass change rate and the amount of heat released from burning surface. In this way a modification of complex stoichiometric combustion processes was avoided, while providing the model that better describes and predicts the course of events in this type of complex, anisotropic and turbulent flow of gases in the tunnel.

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