不同弯管角度和入口速度下管道内压缩空气泡沫流动研究

Numerical study on the flow behavior of compressed air foam in pipes with different bending angles and inlet velocities

理解和预测管道内压缩空气泡沫流体的流动规律,有利于消防工作者根据火灾类型和规模铺设合适的管路以及选用合理的泡沫流体。本文采用CFD仿真模拟分析了不同弯管角度和泡沫流体入口速度对管道内压缩空气泡沫流动行为的影响。研究发现,随着弯管角度的增加,出口段的内壁流速呈现3种变化现象:涡旋和回流现象、回流现象、近似直管流动现象。随着弯管角度增大,弯头转折点的泡沫流体平均速度逐渐增大。由于离心作用,更多的泡沫流体被挤压加速,导致泡沫流体在弯头处的平均速度均大于入口流速,并且在弯管角度θ≥120°时,由于低速区的消失,2种泡沫入口流速下均出现平均速度增长率相对更大的现象。发现泡沫流经弯管时,动力黏度呈现非单调演化趋势。当泡沫流经弯头时,由于弯头的阻碍作用,使流速降低,出现低黏度区间,导致局部黏度下降至2 kg/(m·s)以内(约为稳定段黏度的1/3)。

Understanding and predicting the flow law of com-pressed air foam fluid in the pipeline is helpful for fire fighters to lay appropriate pipelines and select reasonable foam fluid accord-ing 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 in-creases,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 ef-fect,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 av-erage 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 el-bow,due to the obstruction of the elbow,the flow rate de-creases,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 viscos-ity range.