Experimental investigation on the characteristics of buoyant plume movement in a stairwell with multiple openings

•The location of neutral plane was determined by experiment.•The location of neutral plane was calculated by a calculated model.•The temperature distribution in stairwell was studied.•Discharge coefficient of the stairwell was calculated. A set of burning experiments were conducted in a 1/3 scale stairwell to investigate the characteristics of fire induced buoyant plume movement in a 12-storey stairwell with three vents. Results show that the temperature of fire plume generally decreases with height in the stairwell on the steady state, and the distribution of smoke temperature in stairwell is mainly determined by the heat release rate (HRR) of fire source. The variation trends of temperature and velocity profiles measured at the middle opening were used to determine the location of neutral plane, and the determined results were confirmed by the pictures of flow field (lightened by the laser sheet). Based on the temperature distribution in stairwell and theoretical analysis, the location of neutral plane in the stairwell was calculated and the results were in good agreements with experimental results. The location of the neutral plane was mainly affected by the height of the middle opening. For cases with the same middle opening, the heat release rate of fire source weakly affected the location of neutral plane. Based on experimental results, the discharge coefficient of the stairwell with three openings (0.41) was obtained.