Abstract: The mathematical model and numerical method of firefighting foam spread over deep liquid pools were established, and the transient process of firefighting foam spread was analyzed. The effects of the initial conditions, foam rheological behaviors and liquid properties on the foam spreading process were studied. The results show that the propagation velocity of the foam front gradually decays as the foam layer spreads downstream. A higher initial foam velocity or foam layer thickness at the inlet favors foam spreading, which results in increased foam front velocity, and the foam spreads further at a given moment. Affected by the yield stress of the firefighting foam, the foam layer spreads forward in a plug-like flow. The effect of liquid viscosity on foam spreading is not monotonic. If the liquid viscosity is low and the turbulent boundary layer dominates, an increase in liquid viscosity is beneficial for foam spreading; otherwise, the laminar boundary layer dominates, the increase in liquid viscosity will hinder foam spreading.

Key words: firefighting foam, Herschel-Bulkley fluid, deep liquid pools, foam spread, boundary layer flow