Coherent structures of the flow around a surface-mounted cubic obstacle in turbulent channel flow

The coherent structures of the flow developing around a surface-mounted cubic obstacle placed in turbulent channel flow (Re=40.000 based on bulk velocity and channel half-width) are investigated. The technique of the proper orthogonal decomposition is applied to extract the coherent structures of the flow from a database obtained with the use of a finite volume computational code for the numerical integration of the three-dimensional time-dependent incompressible Navier–Stokes equations; for turbulence modeling the LES approach is followed and the RNG subgrid-scale closure is used. The three-dimensional time-dependent velocity field is computed and 100 non-dimensional time steps of the turbulent statistically steady state are considered. The decomposition is performed on two appropriate subdomains around the cubic obstacle and a “reduced” velocity field, reflecting the contribution of the most energetic eigenfunctions of the decomposition, containing up to 95% of the turbulent kinetic energy of the original flow field, is reconstructed; results are presented in terms of vorticity showing the temporal dynamics of the coherent structures in the selected subdomains.