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Brine Water Experiments on Transient Flow and Evolution to Multiple States in Inclined Tunnel Fire with Forced Longitudinal Flow


The transient flow characteristics in inclined tunnel fire considerably influence occupant evacuation. We conducted brine water experiments to investigate transient smoke movement characteristics and their evolution into multiple final flow states in an inclined tunnel fire. The flow pattern exhibited a downward trend was the expected flow pattern. The experiment results indicated that before longitudinal mechanical force was activated in the inclined tunnel, the thickness of the current was nearly uniform. When longitudinal mechanical force was activated, the propagation velocity of the upstream longitudinal current declined, and then the back-layering reached its maximum length. During the naturally ventilated stage, the propagation velocity of the downstream and upstream current were approximately proportional to the cubic root of the source buoyancy flux, respectively. In the longitudinally ventilated stage, the modified Richardson number \(Ri^{\prime}\) defined as Eq. (16) were used to analyze the head propagation velocity of both the downstream and upstream currents, and then the empirical models were proposed based on the experimental data. Multiple final flow states existed even under identical longitudinal force and source buoyancy flux; distinct steady flow states were resulted from different initial conditions, that is, distinct longitudinal force activation times. If the buoyant fluid eventually evolved into the expected pattern and flowed out from the downstream end of the tunnel, the initial condition did not considerably influence the reduced gravity distribution in the final steady state.Please confirm the affiliationsI have confirmed.Please check and confirm the short title.Yes, I have checked and confirmed.

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\(B\) :

Buoyancy flux (m4/s3)

\(B_{0}\) :

Source buoyancy flux per unit width (m3/s3)

c :

Dye concentration at the concerned point (g/L)

c 0 :

Dye concentration at the source (g/L)

\(C_{p}\) :

Specific heat of air (J/kg K)

E :

Fire power (W)

g :

Acceleration of gravity (m/s2)

\(g^{\prime}\) :

Reduced gravity (m/s2)

\(H\) :

Tunnel height (m)

\(Q_{0}\) :

Volume flux per unit width of the source (m2/s)

\(T_{0}\) :

Temperature of ambient air (K)

T :

Smoke temperature (K)

V :

Velocity of longitudinal airflow (m/s)

W :

Tunnel width (m)

\(\rho\) :

Density of buoyant fluid (kg/m3)

\(\rho_{0}\) :

Ambient fluid density (kg/m3)


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The authors acknowledge support from the National Natural Science Foundation of China (NSFC) under Grant No. 51976017.

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Correspondence to Dong Yang.

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Li, P., Yang, D. Brine Water Experiments on Transient Flow and Evolution to Multiple States in Inclined Tunnel Fire with Forced Longitudinal Flow. Fire Technol 59, 743–765 (2023).

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  • Transient evolution
  • Initial condition
  • Multiplicity
  • Inclined tunnel fire
  • Longitudinal ventilation