Characterizing turbulence-interface interaction in a two-phase mixing layer

When two parallel gas and liquid streams meet at the exit of the separator plate, the velocity difference between the two triggers a shear instability at the interface. When turbulence is present in the gas inlet, the interaction between the inlet gas turbulence and the interface will influence the development of shear instability, including the selection of the most unstable mode and the transition from convective to absolute instability. The modified shear instability will in turn influence the formation of longitudinal interfacial waves, the transverse Rayleigh-Taylor instability on the wave crest, and multiphase turbulence statistics downstream. Both direct numerical simulation (DNS) and linear stability analysis have been conducted in the present study to investigate the effect of inlet gas turbulence intensity. In stability analysis, the Orr-Sommerfeld equation was solved to analyze the spatio-temporal viscous modes, and the turbulent eddy viscosity model has been used to represent the effect of inlet gas turbulence intensity. The effective gas viscosity, namely the sum of eddy viscosity and molecular viscosity, increases with the inlet gas turbulence intensity, which will in turn influence two dimensionless parameters, Reynolds number and viscosity ratio, which determine the stability. The effects of these two parameters will be investigated systematically. The results indicated that the modification of Re is dominant. In DNS the mass-momentum consistent volume-of-fluid method has been used to capture the sharp gas-liquid interface, and the pseudo turbulence at the gas inlet is generated by digital-filter approach. The stability model well captured the increasing trend of most-unstable frequency with inlet gas turbulence intensity, as observed in DNS.