Spectral proper orthogonal decomposition analysis of the turbulent wake of a disk at Re = 50 000

To study coherent structures and low-dimensional modes in turbulent shear flows we apply spectral proper orthogonal decomposition (SPOD) to simulation data from the turbulent wake of a disk at a Reynolds number of 50,000. Two principal constituents are found: a vortex shedding (m=1) and a double helix (m=2) mode. The SPOD spectrum illustrates the dominance of the leading eigenvalues. The turbulent kinetic energy and Reynolds stress profiles, when reconstructed at different downstream locations, show that the Reynolds shear stress exhibits strong low-rank behavior. The streamwise evolution of modal constituents reveals a transition from the m=1 mode in the near wake to m=2 in the far wake.