Fire Development in An Underground Corridor — Studies on Ceiling-jet Flow and Flashover Mechanism

1. Fire Development in An Underground Corridor — Studies on Ceiling-jet Flow and Flashover Mechanism Mr. Songyang Li STATE KEY LABORATORY OF FIRE SCIENCE, China Dept. of Energy Sciences, Lund University, Sweden

2. Overview Introduction 1 Fire-induced Ceiling-jet Flow 2 Multi-section model of Flashover 3 Fire simulation 4

3. Introduction • Education Background 2006-2011, University of Science and Technology of China, in fire safety science, as a Ph.D. student. 2010-2011, Lund University, as a exchange student. • Research interests Confined fire dynamics (compartment, underground space, tunnel fires) Fire Simulation • Project experiences Mechanism of flashover happened in regular compartment fires and tunnel fires Fire investigation and reconstruction Fire assessment and performance-based design of industrial, civil and military constructions

4. Introduction • University of Science and Technology of China USTC was founded by the Chinese Academy of Sciences (CAS) in 1958 in response to the urgent need for the national economy, defense construction, and education in science and technology. It was moved to Hefei city in 1970 during the period of Cultural Revolution. • Academics USTC has undertaken a large batch of national projects since its founding. 23 departments, the Special Class for the Gifted Young, three national research institutions

5. Introduction • State Key Laboratory of Fire Science SKLFS was founded in 1989 in USTC. 8 research divisions: Building fire, Forest and urban fire, Industrial fire, Fire assessment, Fire chemistry, Fire detection, Fire suppression, Fire simulation It won two Follow-up Prize in the National Achievement Awards in Science and Technology, including "Early Fire Intelligent Monitoring System for Large Space Buildings " and "An Artificial Monitoring and Policy-making Support System for Preventing and Reducing the Calamities of Anhui Province"

6. Research Objective • Fire Safety of tunnel and other underground corridor Until 2008, there are 1782 road tunnels (704km) and 6876 rail tunnels (3670km) in China Daegu subway fire, in South Korea in 2003, 198 killed Baku rail tunnel fire, in Azerbaijan in 1995, 300 killed • Characteristics of Fire Behavior in tunnel Long and enclosed structure, fire products are confined to transfer in one or two directions Ceiling and wall insulate heat from outside Smoke and heat are difficult to exhaust • Objectives Fire dynamics at pre-flashover and post-flashover period Mechanism of flashover in this long and confined space Application in fire assessment and fire reconstruction

7. Fire Development • Four stages of regular fire: The growth or pre-flashover stage, flashover, the fully-developed or post-flashover stage, the decay period • Flashover is a rapidly occurring transitional event in the development of a confined compartment fire

8. Tunnel Fire Experiments • 5 m long reduced-scale corridor Pre-flashover and post-flashover 50 sets of tests in terms of fuel types, HRR, fire location and ventilation • Measurement Temperature, Mass loss rate, gas concentration, thermal radiation flux

9. Fire plume model • Conservation equations Mass, Momentum, Energy, State • Fire plume Axisymmetric, Infinite linear • Characteristic scale • Solutions of Gaussian profile

10. Ceiling-jet Flow • 3 types of ceiling-jet flow: Pointsource + radial flow Linear source + one-dimensional flow (confined in a corridor) • Point source + one-dimensional flow (confined in a corridor) • 2 types of fire influence the ceiling-jet flows: Weak fire, the plume impinges the ceiling (pre-flashover) Strong fire, the flame impinges the ceiling (post-flashover)

11. Ceiling-jet Model I • Linear source + one-dimensional flow • Time averaged 2D flow model in fire growth stage in terms of steady temperature, velocity and smoke thickness • It is divided into 4 regions: • Region (I): fire plume region • Region (II): turning region during plume impingement • Region (III): one-dimensional shooting flow region under the ceiling • Region (IV): one-dimensional tranquil flow region under the ceiling

12. Conservation Equations Richardson Number: Wall temperature factor:

13. Scaling treatment Final ODEs: Correlation for density defect and velocity:

14. Solutions of Model I Numerical solutions of dimensionless characteristic velocity Numerical solutions of Richardson number and thickness of ceiling-jet Numerical solutions of dimensionless temperature defect

15. Ceiling-jet Model II • Point source confined in a corridor • Use radial model together with one-dimensional model to describe it • It is divided into 6 regions • Regions (I), (II) and (III) follows the previous study of radial flow, (IV) is described by a set of correlations, (V) and (VI) is calculated through one-dimensional flow model.

16. Ceiling-jet Model II Location of density jump the model (II) is valid if , where the transition from shooting flow to tranquil flow happens at a distance . , a new model is required to describe the flow. , the hydraulic jump moves away from the impingement point and becomes weaker. Besides, with increasing the flow will finally degenerate to an unconfined radial ceiling-jet Numerical solutions of Richardson number and thickness of ceiling-jet

17. Ceiling-jet Model II Longitudinal distribution of characteristic ceiling-jet temperature and comparison with experimental results Longitudinal distribution of characteristic ceiling-jet velocity

18. Multi-section Model of Flashover Division of a tunnel Side view of a CV Mass Equation: Energy Equation: Fire located CV

19. Typical Result of simulation • Major input data • 5 m corridor, 0.5×0.5m2 • Heptane, 15×15cm2 • 10 Sections • Result and Discussion Temperature increase sharply until it arrives at a steady value It will experiences a fluctuation period It reduce dramatically along the corridor at a given time Temperature history during flashover

20. Fire simulation with SIMTEC • SIMTEC (Simulation of Thermal Engineering Complex) is a large complex CFD software package developed by Dr. ZhenghuaYan in Lund University, Sweden. Including RANS and LES Unstructured mesh is valid More options for combustion, radiation models Using a separate set of solid and gas grid system

21. Pre-processing

22. Temperature contours of modeling results

23. Comparison of temperature

24. Comparison of Gas concentration CO2 CO

25. Conclusion and Future Work • Ceiling-jet flow model Develop a ceiling-jet flow model induced by a line fire source Propose a wall temperature factor Scaling treatment Analyze the location of density jump FW: Develop a model to describe the ceiling-jet flow induced by a strong fire, where the flame extends under the ceiling • Flashover model Propose a multi-section idea, and combine with classical nonlinear theory Propose a function to simulate the transition from fuel-controlled fire to ventilation-controlled fire FW: Consider smoke layer thickness and thermal radiation effect

26. Tack såmycket谢谢！