Abstract: 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 k-e 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.

Key words: CFD, gas effect, gas-liquid two-phase flow, Strouhal number, vortex street, vortex topology