Lagrangian mixing simulation and quantification of scales

Abstract

This paper introduces Lagrangian Mixing Simulation (LMS), which is a new method that uses particles to track the flow front between two fluids in a mixer. The line formed by an ensemble of particles enables the calculation of the instantaneous rate of interfacial area generation between the fluids and the computation of segregation scales. LMS uses the Eulerian velocity field from CFD simulation, which has a spatial resolution determined from the flow dynamics, for the simulation of mixing at scales that are several orders of magnitude below the CFD gridscale. Since only the interface between the two fluids is simulated, the LMS is orders of magnitude faster than the flow field simulation. In this work, LMS is applied to 2D CFD simulations of the flow in Confined Impinging Jets (CIJ) reactors for Re = 100, 300 and 500. LMS shows that the interfacial area generation is exponential for chaotic flow regimes (Re = 300 and 500) and linear for steady flows (Re = 100). Moreover, LMS is able to simulate segregation scales smaller than 10−8 m, i.e., LMS result spans and overcomes the entire range of spatial scales that have physical meaning.