Lagrangian coherent structures and mass transport in T-junctions

The mechanisms of air water two-phase flow and phase distribution in T-junctions are studied using Lagrangian methods such as the Lagrangian Coherent Structure (LCS) and the particle tracking method. First, the air water two-phase flow field in the T-junctions is numerically simulated. In particular, characteristics such as phase distribution, pressure distribution, and streamline diagrams in mixing and separating regions are captured. Then, the ridges in finite-time Lyapunov exponent fields are extracted as LCSs. The mass transport process is discussed through contrasting the phase distribution and the LCSs. In the mixing region, the air water interfaces almost coincide with the attracting LCSs. At the same time, the attracting LCSs can demonstrate the evolution process of the vortices, which is crucial for the mixing of phases. In the separating region, employing the particle tracking method reveals that particles are entrained by the most attractive LCSs, while repelling LCSs demarcate regions with distinct flow directions, thereby playing a pivotal role in phase separation. In summary, we investigated mass transport in air water two-phase flow in T-junctions from the perspective of LCSs.