低含气率气液两相流涡街特性研究

Vortex Street Characteristics of Two-phase Flow with Low Gas Fraction

气液两相涡街现象广泛存在于生产实际中,由于相间作用,研究变得较为复杂。通过数值模拟和实流试验,对水平管低含气率情况下气相对两相涡街的影响进行研究。建立三维计算流体力学(Computational fluid dynamics,CFD)仿真模型,采用VOF多相流模型和RNG?-?湍流模型,模拟气液两相钝体绕流。仿真与试验结果在定量频率上具有良好的一致性。结合仿真与试验结果,从近尾迹流场与涡拓扑、斯特劳哈尔数两方面,对不同含气率两相涡街特性进行对比研究。结果表明,在稳定涡街范围内,随着气相含率增大,对涡街起重要作用的滞止区长度增大,导致斯特劳哈尔数线性减小;同时,涡街周期性和信号质量变差,涡街能量降低,这是由于涡中心吸入密度小、速度大的气泡,造成涡的旋转能量降低,进而影响涡街的稳定性。

Gas-liquid two-phase vortex street widely exists in productions, which is rather complicated due to the complex phase-interactions. Numerical simulations and real flow experiments are carried out to study the gas effects to two-phase vortex street in low gas fraction of horizontal pipeline. A 3-D computational fluid dynamics（CFD） modeling is carried out to simulate the gas-liquid two-phase flow around a bluff body using a volume of fluid（VOF） mutli-phase model and RNG ？-？ turbulence model. The simulation results indicate a good consistency with experiments in the quantitative frequency. Combined with simulation and experimental results, the two-phase vortex street characteristics of different gas fractions are studied from the near wake flow field and vortex topology, the Strouhal number two perspectives. The results indicate that under stable vortex street, the dominant length of stagnant region increases with gas fraction, which leads to the linear decrease of Strouhal number; Meanwhile, the periodicity and signal quality of vortex street deteriorate, and the energy of vortex street reduces, this is because the air bubbles of small density and high speed are trapped by vortex core, which results in the reduction of vortex rotational energy, and further influences the stability of vortex street.