Abstract: In order to study the negative pressure field formed on the surface of the oil desk during the combustion of the fire whirl in the naturally driven four-sided slit fire whirl device, under the condition of simplified hypothesis, the negative pressure field model produced in the combustion process of fire cyclone was established. The radius and strength of vortex core of fire whirlwind were calculated. The radius of the small-scale vortex core formed in the laboratory is positively correlated with the size of the oil pan. The relationship between vortex core strength and vortex core radius can be expressed by exponential function, and aerodynamic mechanism is the dominant mechanism to determine the mass combustion rate of fire cyclone.

Key words:  fire cyclone, negative pressure field, vortex core radius, vortex core strength, negative pressure suction