Stabilization and Dynamic of Premixed Swirling Flames

Stabilization and Dynamic of Premixed Swirling Flames focuses on swirling flames in various premixed modes (prevaporized, stratified, partially, and fully premixed) for the combustor and the development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modelling of turbulent combustion, , and a complete overview of the topic of stabilization and combustion dynamics of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact on flame speed/combustion/mixing. It presents a theoretical framework for flame stabilization. The last chapter covers the design of a fully premixed injector for future jet engine applications.

• Provides a comprehensive review of stabilization mechanisms for prevaporized, stratified, partially and fully premixed flames
• Features a complete view of the challenges at the intersection of swirling flame/combustors, requirements and physics of fluids at work enabling the development of future gas turbine engine combustor
• Describes the phenomenology of premixed combustion, driving mechanisms of combustion instability, and various investigation approaches and includes the presentation of the very latest numerical results and analyses of flashback, lean blowout and combustion instabilities

Aerospace and mechanical engineers, researchers, masters' and PhD students in aero and mech engineering

Foreword ix

Preface xi

Introduction xiii

1. The Combustor 1

1. Overall Principle of the Gas Turbine Engine 1

1.1. Generalities and Overall Description 1

1.2. Components/Modules Technologies Description 12

1.3. Thermodynamics and Non-reacting Fluid Dynamics 16

2. Combustor Role, Requirements and Environment 26

2.1. Overall View 26

2.2. Design and Requirements 28

2.3. Combustor, injector and swirler designs 34

3. Combustor Architectures 47

3.1. RQL 49

3.2. LDI 50

3.3. LPP 51

3.4. LSI 53

3.5. LFP 53

4. Operating Conditions and Flight Envelope 54

2. Premixed Combustion for Combustors 59

1. Mathematical descriptions 59

1.1. Governing Equations of Reacting Flows 59

1.2. G-Equation Formalism 67

1.3. Decomposition in static and dynamic components 69

2. Physical-Chemical Description 69

2.1. Premixed Combustion Overview 69

2.2. Swirling Flames Overview 76

2.3. Acoustics Wave-Flame Interactions 79

2.4. Autoignition 81

2.5. Blowout 82

2.6. Chemical Kinetic 83

2.7. Combustion Noise 84

2.8. Combustion Instability 86

2.9. Flame Speed 87

2.10. Flame Stretch

2.11. Flammability Limits 89

2.12. Flashback 90

2.13. Ignition 90

2.14. Pollutants Emissions 91

2.15. Turbulent Combustion 92

2.16. Turbulent Mixing 94

3. Combustion modes 94

3.1. Overview 94

3.2. Pre-vaporized Mode 95

3.3. Partially Premixed Mode 98

3.4. Stratified Premixed Mode 99

3.5. Fully Premixed Mode 100

4. Effect of operating conditions on premixed combustion and impact on flame 101

4.1. Current operating conditions 101

4.2. Fuel, equivalence ratio and power settings engine matching 102

3. Premixed Swirling Flame Stabilization 109

1. Mechanisms and processes of stabilization 109

1.1. Definitions 110

1.2. Key stabilization mechanisms: local contributors 110

1.3. Local equivalence ratio 111

1.4. Flame stretch 113

1.5. Flame speed versus flow speed 114

1.6. Reaction rates 116

1.7. Vorticity 116

1.8. Temperature, pressure and density (Equation of State) 116

1.9. Governing equations 117

1.10. Role and impact of global flow/flame features 118

2. Framework for flame stabilization study: application 120

2.1. Numerical procedure 120

2.2. Statistically steady flame dynamics 123

3. Theoretical results on flame stabilization and propagation 139

3.1. Flowfield decomposition and theoretical approach: framework 140

3.2. Regimes and configurations 142

3.3. Expressions for laminar and turbulent planar flames in open tubes 142

3.4. Expressions for the static component of stabilized flame 145

3.5. Expressions for the dynamic component of stabilized flame 148

3.6. Swirling flame numerical simulations: results and discussion 155

3.7. Summary 160

4. Effect of operating conditions, swirl number and fuel on flame stabilization 161

4. Transient Combustion 165

1. Introduction 165

1.1. Definitions 165

1.2. Data sciences and data analysis 169

1.3. Measurements and diagnostics 172

2. Unsteady Premixed Combustion 173

2.1. Laminar unsteady premixed combustion 173

2.2. Turbulent premixed combustion 177

3. Combustor Engine Transient 184

4. Configuration Case Study 184

4.1. Methodology and Numerical Procedure 185

4.2. Time average versus instantaneous velocity field 186

4.3. Flashback 189

4.4. Lean blowout 191

4.5. Transient to limit cycle 202

5. Fundamentals mechanisms and link between steady and unsteady combustion) 207

5.1. Static and dynamic stability link 207

5.2. Static stability 209

5.3. Dynamic stability 210

6. Technologies and control for flame stabilization and combustion instability 211

6.1. State of the art 212

6.2. Effect of swirler position 215

6.3. Effect of geometry 217

6.4. Effect of operating condition, equivalence ratio and fuel 217

5. Swirling Flame Dynamic and Combustion Instability 219

1. Combustor Acoustics 219

1.1. Combustion instability loop 219

1.2. Network acoustics model 220

1.3. Acoustics codes 223

1.4. Upstream flow modulation versus self-sustained oscillations 223

1.5. Flow modulation and Navier-Stokes characteristics boundary conditions models

(NSCBC) 224

2. Modulated swirling flames dynamic 225

2.1. Flame responses 225

2.2. Flow dynamic mode conversion processes occurring upstream of the flame 239

2.3. Unsteady flame front dynamics 243

2.4. Combustion dynamics mechanisms 246

3. Combustion instability 260

3.1. Combustion instability prediction 260

3.2. Coupling and stability criteria 267

3.3. Longitudinal instabilities 268

3.4. Tangential instabilities 278

6. Design and Numerical Simulations Modeling 281

1. Context and challenges 281

2. Modeling of flow modulations in numerical simulations 282

2.1. Introduction 283

2.2. Combustor Dynamics Modulation Models 285

2.3. Inlet modulation in an isothermal duct 288

2.4. Application to a bluff-body stabilized flame 295

2.5. Conclusions 296

3. Modeling approaches and assumptions 296

3.1. Unsteady Reynolds Averaged Navier-Stokes 296

3.2. Large Eddy Simulations 299

4. Chemical kinetic 301

5. Turbulent combustion modeling 302

5.1. Thickened flame models 302

5.2. Flamelet models 303

5.3. Flame surface models 304

5.4. Probability Density Function models 304

6. A priori filtering for turbulent combustion model 305

6.1. Introduction 305

6.2. The a priori filtering method 308

6.3. DNS Preccinsta dataset 309

6.4. Results and discussion 310

6.5. Comparisons for the Thickened Flame model 317

6.6. Conclusions and perspectives 319

7. Fuel vaporization physics and modeling 322

8. Supercritical combustion regime at take-off conditions 323

7. Lean Fully Premixed (LFP) Injector Design 325

1. Design procedure 328

2. Innovation and concept definition 332

3. Modeling and sizing 334

3.1. Vaporizing unit 334

3.2. Premixing and premixing-stabilizing units 339

4. Conclusion 348

Conclusion and Perspectives 351