76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023;
Washington, DC
Session L35: Multiphase Flows: Turbulence
8:00 AM–10:36 AM,
Monday, November 20, 2023
Room: 202A
Chair: Francesco Zonta, Vienna Univ of Technology
Abstract: L35.00001 : Characterizing turbulence-interface interaction in a two-phase mixing layer*
8:00 AM–8:13 AM
Abstract
Presenter:
Tanjina Azad
(University of South Carolina)
Authors:
Tanjina Azad
(University of South Carolina)
Yue Ling
(University of South Carolina)
In a mixing-layer induced by two parallel streams of gas and liquid, the velocity difference between the two streams introduces a shear instability at the gas-liquid interface. The interaction between the turbulence in the fast gas stream and the interface modulates the shear interfacial instability, including the selection of the most unstable mode and the transition from convective to absolute instabilities. Consequently, the modified shear instability exerts its influence downstream, impacting the formation of longitudinal interfacial waves, the occurrence of transverse Rayleigh-Taylor instability at the wave crest, and the statistical characteristics of multiphase turbulence. In the present study, both linear stability analysis and direct numerical simulation (DNS) are conducted to investigate the effect of inlet gas turbulence intensity. In the linear 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. In DNS, the 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 the digital-filter approach. As the inlet gas turbulence intensity increases, the effective gas viscosity rises, resulting in a decrease of the Reynolds number and an increase in the gas-to-liquid viscosity ratio. The effects of these two parameters on interfacial instability have been investigated systematically. The results indicate that modification in Re is more important. We have chosen a benchmark case where the instability is convective in the absence of gas inlet turbulence. When Re decreases, the interfacial instability transitions from convective to absolute regimes. A new weak-absolute regime is identified, for which the absolute mode dominates the perturbations induced at the inlet, but its frequency varies with the inlet perturbation amplitude. In contrast, the frequency of the absolute mode will not be influenced by the inlet perturbations when the interfacial instability is in the absolute regime.
*This research is supported by NSF.