Numerical investigation of backdraft development and mitigation process based on LES
- Alternative Title
- 백드래프트 전개 및 저감과정에 대한 LES 기반의 수치적 검토
- Abstract
- The backdraft is a hazardous event of a fire that occurs in an under-ventilated enclosed region. Backdraft is a serious threat to the firefighters and to the people who are present near the location. Due to the complexities and dangers involved in performing backdraft experiments only a limited number of studies have been carried out with its fundamental physics. However, the evolution of numerical simulation approaches provides a better advantage of studying the dangerous fire phenomena in a safe manner at a less expense. Thus, in this numerical study of backdraft, Fire Dynamics Simulator (FDS) version, 6.3.2 developed by NIST was used as a computational tool. Large Eddy Simulation (LES) turbulence model with Eddy Dissipation Concept (EDC) simple chemistry, combustion model and GRAY gas radiation model was adopted in FDS to investigate the backdraft development process, critical condition of backdraft and its mitigation process by water mist.
The prediction performance of the LES with EDC simple chemistry model was evaluated for backdraft. Computations were carried out to visualize the development and behavior of the backdraft phenomena inside a reduced-scale compartment with a window opening geometry. Predicted results were compared with the previous numerical study performed by using Direct Numerical Simulation (DNS) turbulence model with 3-step finite rate chemistry, performed by Park et al. Comparative results have shown that LES with EDC simple chemistry model can predict the backdraft development process qualitatively at an efficient computational cost.
The critical conditions of backdraft were numerically investigated for methane fuel for the same reduced-scale compartment with a door opening geometry. Compartment dimensions, fuel composition and the temperature inside the compartment was specified based on the experiment conducted by Weng et al. Numerical pressure predictions showed a resonable trend with the experimentally measured pressure. Also, the severity of backdraft increases with the increase of fuel concentration remaining inside the compartment.
A computational study was carried out to investigate the mitigation of backdraft using water mist. The same reduced scale compartment with door opening geometry used in the previous study was used in this simulation. Initially, backdraft development process was investigated without the effect of water mist. For the same geometry and fuel composition effect of water mist on backdraft was investigated. The comparative results showed that spraying water mist suppresses the further flame propagation and reduces the compartment temperature and unburned fuel concentration by means of evaporation and dilution. A strong fireball exiting the compartment was completely suppressed.
- Issued Date
- 2017
- Awarded Date
- 2017. 2
- Type
- Dissertation
- Publisher
- 부경대학교 대학원
- Affiliation
- 부경대학교 대학원
- Department
- 대학원 안전공학과
- Advisor
- 오창보
- Table Of Contents
- Chapter 1 - Introduction 1
1.1 Research Background 1
1.1.1 Backdraft development process 3
1.2 Literature review 5
1.2.1 Backdraft experiments 5
1.2.2 Numerical simulations of backdraft 10
1.3 Research objective 16
Chapter 2 - Numerical Methodology 18
2.1 Governing equations 18
2.1.1 The fundamental conservation equations 19
2.2 Numerical model 21
2.2.1 Turbulence model 21
2.2.2 Combustion model 26
2.2.3 Radiation model 29
2.3 Conditions of numerical simulation 32
2.4 Backdraft scenario 35
Chapter 3 - Computational study of backdraft phenomena using LES approach with EDC model 37
3.1 Numerical conditions 38
3.2 Result and Discussion 40
3.2.1 Temperature 40
3.2.2 Methane mass fraction 42
3.2.3 Compartment pressure 45
3.2.4 Local flame structure 47
Chapter 4 - Computational study of critical condition for the occurrence of backdraft in compartment fires 49
4.1 Numerical conditions 50
4.2 Result and Discussion 52
4.2.1 Temperature 52
4.2.2 Methane mass fraction 55
4.2.3 Compartment pressure 57
Chapter 5 - Numerical investigation of water mist effects on the backdraft behavior 59
5.1 Numerical conditions 60
5.2 Result and Discussion 62
5.2.1 Temperature 62
5.2.2 Methane mass fraction 65
5.2.3 Compartment pressure 67
5.2.4 Local flame structure 69
Chapter 6 - Conclusion 72
6.1 Computational study of backdraft phenomena using LES approach with EDC model 73
6.2 Computational study of critical condition for the occurrence of backdraft in compartment fires 74
6.3 Numerical investigation of water mist effects on the backdraft behavior 75
6.4 Future work 76
Acknowledgment 77
Reference 79
- Degree
- Master
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