Temporal evolution of dominant flow structures in turbulent channel flow

The flow of a viscous incompressible fluid in a plane channel is simulated numerically with the use of a computational code for the numerical integration of the unsteady three-dimensional Navier-Stokes equations. The numerical method is based on a mixed spectral-finite difference algorithm. The calculations in the two homogeneous directions (the streamwise and the spanwise) are performed in Fourier space and second-order finite differences are used in the direction orthogonal to the solid walls. A turbulent-flow database representing the turbulent statistically steady state of the velocity field through 10 viscous time units is assembled at a nominal friction Reynolds number Reτ = 180 and the coherent structures of turbulence are extracted from the fluctuating portion of the velocity field with the use of the Proper Orthogonal Decomposition technique (POD). The temporal evolution of a number of the most energetic POD modes is visualized, unveiling the mechanisms of interaction between dominant flow structures in wall-bounded turbulent flows.