Abstract: Understanding and predicting the flow law of compressed air foam fluid in the pipeline is helpful for fire fighters to lay appropriate pipelines and select reasonable foam fluid according to the fire type and scale. In this paper, CFD simulation is used to analyze the influence of different bending angles and foam fluid inlet velocity on the flow behavior of compressed air foam in the pipeline. Research has found that as the angle of the bend increases, the inner wall velocity of the outlet section exhibits three changes: vortex and reflux phenomenon, reflux phenomenon, and approximate straight pipe flow phenomenon. With the increase of bending angle, the average velocity of foam fluid at elbow turning point increases gradually. At the same time, due to centrifugal effect, more foam fluid is squeezed and accelerated, resulting in the average velocity of foam fluid at the elbow is greater than the inlet velocity. Due to the disappearance of the low-speed zone, the average speed growth rate is relatively higher under the condition of elbow angle θ≥120°. On the other hand, it is found that when foam flows through the bend, the dynamic viscosity presents a non monotonic evolution trend. When foam flows through the elbow, due to the obstruction of the elbow, the flow rate decreases, resulting in the local viscosity falling to within 2 kg/(m·s)(about 1/3 of the viscosity of the stable section), and a low viscosity range.

Key words: compressed air foam, fire extinguishing, Fluent simulation, bending angle, entrance speed, viscosity