An efficient approach for computing the finite time Lyapunov exponent in complex three-dimensional flow based on the discrete phase model

We propose a method for computing the finite-time Lyapunov exponent (FTLE) based on the discrete phase model (DPM), which is integrated with a CFD solver and has several advantages as follows. Unlike the conventional method that calculates the fine velocity field first and then calculates the particle trajectory based on the velocity field, the particle position and velocity field in the resulting method are solved simultaneously in the CFD solver, which saves memory and improves the computational efficiency. The resulting method can be applied to arbitrarily complex three-dimensional flows, which helps to promote Lagrangian analysis in the complex flows in aerospace. The discrete phase model used in the resulting method is flexible and easy to be extended. For example, it can be extended from massless tracer particles to real particles with mass. The finite-time Lyapunov exponent is also used to evaluate the uniformity of scalar convection mixing, it is found that the larger the finite-time Lyapunov exponent at the mixture contact line, the longer the contact line for the next time period, indicating more uniform convective mixing. (c) 2023 Elsevier Masson SAS. All rights reserved.