水下排气两相流动及气泡粒径分布的数值模拟

Simulation on the gas-liquid two-phase flow and bubble diameter distribution in an underwater exhaust system

对某内燃机水下排气管道的排气过程进行了数值模拟,以预测CO_2经过排气管道处理后的气泡直径分布,期为管道的优化设计提供参考。气液两相流动模型采用Euler模型,湍流模型采用Realizable k-ε模型,考虑了气泡的分裂与聚合的粒径分布采用群体平衡方程计算。计算结果表明:在所研究的几何条件与流动参数范围内,CO_2气泡在管道中的非连续流动会因为有浮力作用使其逐渐集中到管道上方从而导致气泡粒径变大,孔板下部开孔对气泡破碎效果有限。管道出口处粒径在4 mm以下的气泡体积分数的时均值为0.466。

Numerical simulation of internal-combustion engine was carried out to predict the diameter distribution of exhaust CO2 bubble after the treatment,in order to help optimizing the exhaust pipe designation. Euler model and Realizable k-ε model were used for simulating gas-liquid two-phase flow and modeling turbulence. Population Balance Equation was adopted to calculate the distribution of bubble diameter considering coalescence and break-up of bubbles. The distribution of the bubble diameter and the effect of multi-orifice on the CO2 bubbles breaking were analyzed. The results showed that,the discontinuous flow of CO2 bubbles in the pipeline would be gradually concentrated to the upper part of the pipe due to the buoyancy effect,which led to the coalescence of bubbles,and made the orifices on the lower part of the plates superfluous. At the outlet of the pipe,the time-averaged volume fraction of all the bubbles whose size was lower than 4 mm was 0.466.