Numerical study on thermally driven smoke flow characteristics in long tunnels under natural ventilation

• The paper focuses on the flow structures and mass flow rates of thermally driven smoke flows induced by fires in long transportation tunnels under natural ventilation. The important influencing factors including heat release rate (HRR), tunnel width and height, are taken into consideration. The mechanism of the smoke flow movement is explored. The results show that for a fire in a long naturally ventilated transportation tunnel, there exists a critical point which is dependent on HRR and tunnel geometry. This critical point is defined as the location where the smoke layer thickness and the outgoing mass flow rate increase towards it and decrease after it. Further, it is found that the critical point moves farther away from the fire source in a wider or higher tunnel, while it lies closer to the fire source for a higher HRR. A correlation is proposed to estimate the location of the critical point. The outgoing mass flow rates along the tunnel are calculated using the two-layer flow model and well-mixed flow model of thermally driven flows, and the results indicate that these models produce satisfactory predictions of the mass flow rates if the vertical temperature profile is known. © 2023 The Authors

Nyckelord

Critical point

Long tunnel

Mass flow rate

Smoke flow structure

Tunnel fire

Flow rate

Flow structure

Mass transfer

Smoke

Ventilation

Heat release

Long tunnels

Mass-flow rate

Natural ventilation

Release rate

Smoke flows

Thermally driven

Tunnel fires

Fires

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