Computational Fluid Dynamics in Fire Engineering (eBook)

Front Cover 1
Computational Fluid Dynamics in Fire Engineering: Theory, Modelling and Practice 4
Copyright 5
Table of Contents 6
Preface 12
Chapter 1: Introduction 14
1.1 Historical Development of Fire Modeling 14
1.2 Overview of Current Trends in Fire Modeling 17
1.3 Review of Major Fire Disasters and Impact on Fire Modeling 24
1.3.1 Kings Cross Fire 24
1.3.2 World Trade Center Fire 25
1.4 Application of Fire Dynamics Tools in Practice 30
1.5 Validation and Verification of Fire Dynamics Tools 36
1.6 Scope of the Book 39
Chapter 2: Field Modeling Approach 42
Part I Mathematical Equations 42
2.1 Computational Fluid Dynamics: Brief Introduction 42
2.2 Computational Fluid Dynamics in Field Modeling 44
2.3 Equation of State 48
2.4 Equations of Motion 50
2.4.1 Continuity Equation 51
2.4.2 Momentum Equation 53
2.4.3 Energy Equation 59
2.4.4 Scalar Equation 63
2.5 Differential and Integral Forms of the Transport Equations 65
2.6 Physical Interpretation of Boundary Conditions for Field Modeling 70
2.7 Numerical Approximations of Transport Equations for Field Modeling 72
2.7.1 Discretisation Methods 74
2.7.1.1 Steady Flows 74
2.7.1.2 Unsteady Flows 82
2.7.2 Solution Algorithms 84
2.7.2.1 Matrix Solvers 84
2.7.2.2 Pressure-Velocity Linkage Methods 87
2.7.3 Boundary Conditions 94
2.8 Summary 96
Part II Turbulence 98
2.9 What Is Turbulence? 98
2.10 Overview of Turbulence Modeling Approaches 99
2.11 Additional Equations for Turbulent Flow-Standard k-epsi Turbulence Model 103
2.12 Other Turbulence Models 106
2.12.1 Variant of Standard k-epsi Turbulence Models 109
2.12.2 Reynolds Stress Models 115
2.13 Near-Wall Treatments 119
2.14 Setting Boundary Conditions 123
2.15 Guidelines for Setting Turbulence Models in Field Modeling 126
2.16. Worked Examples on the Application of Turbulence Models in Field Modeling 127
2.16.1 Single-Room Compartment Fire 127
2.16.2 Influence of Gaps of Fire Resisting Doors on Smoke Spread 134
2.17 Summary 144
Chapter 3: Additional Considerations in Field Modeling 148
Part III Combustion 148
3.1 Turbulent Combustion in Fires 148
3.2 Detailed Chemistry versus Simplified Chemistry 152
3.3 Overview of Combustion Modeling Approaches 164
3.4 Combustion Models 166
3.4.1 Generalized Finite-Rate Formulation 166
3.4.1.1 Background Theory 166
3.4.1.2 Species Transport Equations 167
3.4.1.3 Laminar Finite-Rate Chemistry 174
3.4.1.4 Eddy Break-up and Eddy Dissipation 176
3.4.2 Combustion Based on Conserved Scalar 181
3.4.2.1 Description of Approach 181
3.4.2.2 Definition of Mixture Fraction 183
3.4.2.3 Flame Sheet Approximation 185
3.4.2.4 State Relationships 188
3.4.2.5 Probability Density Function (PDF) of Turbulence-Chemistry 192
3.4.2.6 Laminar Flamelet Approach 200
3.5 Guidelines for Selecting Combustion Models in Field Modeling 207
3.6 Worked Examples on the Application of Combustion Models in Field Modeling 209
3.6.1 Single-Room Compartment Fire 209
3.6.2 Two-Room Compartment Fire 215
3.7 Summary 221
Part IV Radiation 222
3.8 Radiation in Fires 222
3.9 Radiative Transfer Equation 225
3.10 Radiation Properties of Combustion Products 228
3.10.1 Gray Gas Assumption 229
3.10.2 Weighted Sum of Gray Gases Model 236
3.10.3 Other Models 240
3.11 Radiation Methods for Field Modeling 243
3.11.1 Monte Carlo 246
3.11.2 P-1 Radiation Model 250
3.11.3 Discrete Transfer Radiative Model 253
3.11.4 Discrete Ordinates Model 256
3.11.5 Finite Volume Method 263
3.12 Guidelines for Selecting Radiation Models in Field Modeling 265
3.13 Worked Examples on the Application of Radiation Models in Field Modeling 266
3.13.1 Single-Room Compartment Fire 266
3.13.2 Two-Room Compartment Fire 273
3.14 Summary 277
Chapter 4: Further Considerations in Field Modeling 280
Part V Soot Production 280
4.1 Importance of Soot Radiation 280
4.2 Overview and Limitations of Soot Modeling 282
4.3 Soot Models for Field Modeling 285
4.3.1 Single-Step Empirical Rate 285
4.3.2 Semi-Empirical Approach 289
4.4 Population Balance Approach to Soot Formation 298
4.4.1 What Is Population Balance? 298
4.4.2 Formulation of Transport Equations and Rate Mechanisms 301
4.5 Guidelines for Selecting Soot Models in Fire Modeling 312
4.6 Worked Examples on the Application of Soot Models in Field Modeling 313
4.6.1 Two-Room Compartment Fire 313
4.6.2 Multi-Room Compartment Fire 320
4.7 Summary 326
Part VI Pyrolysis 327
4.8 Importance of Pyrolysis in Fires 327
4.9 Phenomenological Understanding of Pyrolysis Processes 330
4.10 Physico-Chemical Description of Pyrolysis Processes 332
4.10.1 Pyrolysis of Cellulose 335
4.10.2 Pyrolysis of Hemicellulose 335
4.10.3 Pyrolysis of Lignins 336
4.10.4 Pyrolysis of Wood 336
4.11 Formulation of Governing Equations 337
4.11.1 Conservation of Energy for Wood Pyrolysis 337
4.11.2 Conservation of Mass for Wood Pyrolysis 339
4.11.3 Modeling Wood Pyrolysis Source Terms 342
4.11.4 Thermophysical Properties of Wood Pyrolysis 345
4.12 Practical Guidelines to Pyrolysis Models in Field Modeling 351
4.13 Worked Example on Ignition of Combustible of Charring Material in a Cone Calorimeter 352
4.14 Worked Example on Fire Growth and Flame Spread Over Combustible Wall Lining in a Single-Room Compartment 365
4.15 Summary 376
Chapter 5: Advance Technique in Field Modeling 380
5.1 Next Stages of Development and Application 380
5.2 Alternative Approach to Handling Turbulence 382
5.2.1 Direct Numerical Simulation (DNS) 382
5.2.2 Large Eddy Simulation (LES) 387
5.3 Favre-Averaged Navier-Stokes versus Large Eddy Simulation 406
5.4 Formulation of Numerical Algorithm 408
5.4.1 Explicit Predictor-Corrector Scheme 408
5.4.2 Combustion Modeling 415
5.4.3 Inclusion of Other Physical Models 421
5.5 Worked Examples on Large Eddy Simulation Applications 423
5.5.1 A Freestanding Buoyant Fire 423
5.5.2 Fire in a Single-room Compartment 431
5.6 Summary 435
Chapter 6: Other Challenges in Fire Safety Engineering 438
6.1 Fire Safety Evaluation and Assessment 438
6.1.1 Deviation from Prescriptive-Based Statutory Requirements 438
6.1.2 Adopting Performance-Based Methodologies 439
6.2 Overview of Emerging Technique in Field Modeling 445
6.3 Overview of Evacuation Modeling 452
6.4 Overview of Probabilistic Approach 454
6.5 Case Studies 456
6.5.1 The Predictive Capability of Artificial Neural Network Fire Model in a Single-Room Compartment Fire 457
6.5.2 The Application of CFD-Based Fire Model and Evacuation Model for Fire Safety Evaluation and Assessment 463
6.6 Future Developments in Fire Predictive and Assessment Models 470
6.7 Summary 472
Appendix A: Higher-Order Differencing Schemes and Time-Marching Methods 476
A.1 Higher-Order Differencing Schemes 476
A.2 Total Variable Diminishing (TVD) Schemes 478
A.3 Higher-Order Time-Marching Methods 482
Appendix B: Algebraic Equation System and CFD-Based Fire Model 486
B.1 Conversion of Governing Equation to Algebraic Equation System Using the Finite Volume Method 486
B.2 CFD-Based Fire Model 491
Appendix C: Advanced Combustion Modeling 492
C.1 Probability Density Function Method 492
C.2 Conditional Moment Closure 493
Appendix D: Relevant Tables for Combustion and Radiation Modeling 496
References 504
Further Suggested Reading 528
Index 530