Casestudy No: FTLCFD06

Introduction

This study examines fire and smoke behaviour in an enclosed underground parking facility using the Fire Dynamics Simulator (FDS). A fire was initiated at a single location within the car park to assess the performance of smoke control strategies employing jet fan-assisted mechanical ventilation. The study provides insights into how advanced CFD simulations can be used to evaluate fire safety measures and support performance-based design in such environments.

Computational Domain

The computational domain represents a large underground car park with realistic architectural features including columns, beams, inlet openings, and exhaust vents.
A single fire source representing a burning vehicle was located at one side of the domain. The simulation examined smoke rise, ceiling jet development, and the influence of jet fan airflow on smoke transport.

Figure 2: Computational domain

Mesh

A cartesian mesh was generated, refined near the fire and jet fans. The total cell count is approximately 4 million. Refinement zones were introduced to accurately capture velocity gradients, buoyant smoke flow, and ceiling jet patterns, particularly around regions of high temperature and high velocity.

Figure 3: Full domain Mesh with refinement regions

Numerical Model

The simulation was conducted using Fire Dynamics Simulator (FDS), which applies a Large Eddy Simulation (LES) turbulence model to resolve fire-induced air motion and thermal flow.

Fire Source:
A single vehicle fire was modelled with a prescribed Heat Release Rate (HRR) to represent a realistic car fire scenario. The HRR curve was defined as a controlled growth, steady burning, and decay phase, ensuring consistent smoke and heat generation throughout the analysis.

Ventilation System:
Jet fans were modelled as mechanical ventilation devices producing directional airflow. These fans provided longitudinal movement of air to push smoke toward the exhaust vents and maintain tenable conditions near the ground.

Boundary	Type / Description
Inlet	Open boundary for air
Outlet	Open exhaust
Jet Fans	Velocity inlets.
Walls / Floor / Ceiling	Adiabatic, no-slip solid surfaces
Fire Source	Prescribed Heat Release Rate (HRR)

Table 1 : Boundary conditions

Results and Discussion

The CFD simulation captured the complete evolution of smoke and air movement during the fire scenario. Initially, the fire plume rose vertically, forming a ceiling-attached smoke layer above the ignition region. As jet fans activated, the induced airflow redirected the smoke horizontally, transporting it toward the exhaust openings.

                                                 Figure 4: Smoke Visualization

                                                           Figure 5: Jet flow visualization

Figure 4 shows the smoke visualization within the domain. The jet fans effectively limited smoke accumulation near the fire source, promoting directional movement along the ceiling. This reduced stagnation and improved visibility in the lower regions of the car park.

Figure 5 presents the velocity contours, clearly illustrating the flow field generated by the jet fans. The contours highlight the longitudinal air movement, confirming the fans’ effectiveness in maintaining continuous smoke extraction pathways.

Conclusion

CFD simulation of fire and smoke behavior in an underground car park was performed using FDS to evaluate jet fan-assisted ventilation performance.

The study demonstrated:

• • Realistic simulation of smoke and airflow using FDS with a defined HRR fire source.

• • Jet fans effectively controlled smoke transport and improved ventilation efficiency.

• • Velocity contours showed consistent longitudinal flow aiding smoke extraction.

• • Boundary and geometric configuration influenced overall airflow and smoke clearance.

• • CFD proved to be a valuable tool for performance-based fire safety design in enclosed structures.

References

1. 1. Deckers, X., Haga, S., Sette, B., & Merci, B. (2012). Smoke control in case of fire in a large car park: Full-scale experiments. Fire Safety Journal. https://doi.org/10.1016/j.firesaf.2012.10.017

1. 1. McGrattan, K., Hostikka, S., Floyd, J., Baum, H., Rehm, R., Mell, W., & McDermott, R. (2008). Fire Dynamics Simulator (Version 5) – Technical Reference Guide. NIST Special Publication 1018-5. National Institute of Standards and Technology.

1. 1. Tilley, N., Deckers, X., & Merci, B. (2012). CFD study of ventilation velocity and smoke back-layering distance in car parks. Fire Safety Journal, 48, 11–20.

1. 1. Wu, Y., & Bakar, M.Z.A. (2000). Control of smoke flow in tunnel fires using longitudinal ventilation systems – a study of the critical velocity. Fire Safety Journal, 35(4), 363–390.

1. 1. Merci, B., & Shipp, M. (2012). Smoke and heat control for fires in large car parks: Lessons learnt from research? Fire Safety Journal. https://doi.org/10.1016/j.firesaf.2012.05.001

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