Abstract

Results of a proper orthogonal decomposition of a turbulent pipe flow generated by direct numerical simulation are presented. The flow field is decomposed into its optimal basis functions as found by solving a Fredholm integral whose kernel is the two-point velocity autocorrelation tensor. The energy, structure, and dynamics of the basis functions are examined. The basis functions are categorised into two classes and six subclasses based on their wavenumber and coherent vorticity structure, and compared to similar results found in turbulent channel flow. The turbulent pipe flow is generated by a direct numerical simulation of the Navier-Stokes equations using a spectral element algorithm at a Reynolds number Re_tau=150 and a domain length of ten diameters (L/D=10). Evidence of very-large-scale motions will also be presented, as well as preliminary results from a corresponding investigation using a new large-domain (L/D=100) simulation.