The turbulence cascade in the near wake of a square prism. (20th July 2017)

• Record Type: Journal Article
• Authors: Alves Portela, F.; Papadakis, G.; Vassilicos, J. C.
• Is Part Of: Journal of fluid mechanics. Volume 825(2017)
• Page Start: 315
• Page End: 352
• Publication Date: 2017-07-20
• Subjects: turbulence theory, -- turbulent flows, -- wakes; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2017.390
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : We present a study of the turbulence cascade on the centreline of an inhomogeneous and anisotropic near-field turbulent wake generated by a square prism at a Reynolds number of $Re=3900$ using the Kármán–Howarth–Monin–Hill equation. This is the fully generalised scale-by-scale energy balance which, unlike the Kármán–Howarth equation, does not require homogeneity or isotropy assumptions. Our data are obtained from a direct numerical simulation and therefore enable us to access all of the processes involved in this energy balance. A significant range of length scales exists where the orientation-averaged nonlinear interscale transfer rate is approximately constant and negative, indicating a forward turbulence cascade on average. This average cascade consists of coexisting forward and inverse cascade behaviours in different scale-space orientations. With increasing distance from the prism but within the near field of the wake, the orientation-averaged nonlinear interscale transfer rate tends to be approximately equal to minus the turbulence dissipation rate even though all of the inhomogeneity-related energy processes in the scale-by-scale energy balance are significant, if not equally important. We also find well-defined near $-5/3$ energy spectra in the streamwise direction, in particular at a centreline position where the inverse cascade behaviour occurs for streamwise oriented length scales.