Coherent Structure Analysis in a Backward Facing Step

Lagrangian coherent structures are a useful tool for characterizing the dynamical behavior of a turbulent flow, in particular, to identify evolution of vortices, and assess turbulent mixing in practical flows. In this work, large-eddy simulation of incompressible flow in a backward facing step with an inlet Re_τ of 395 is performed in order to identify and correlate formation and destruction of coherent structures with vortex shedding frequencies. The simulation is performed with OpenFOAM using second-order accurate spatial and temporal schemes. Forward and backward finite-time Lyapunov exponents are utilized for the identification of repelling and attractive structures, respectively.