Rotation effect on near-wall turbulence statistics and flow structures

Abstract

Large eddy simulation (LES) of turbulent flow through an axially rotating pipe, coupled with nonlinear dynamic subgrid-scale (SGS) model, is carried out to investigate rotation effect on the near-wall turbulence characteristics and flow structures. In the rotating turbulent pipe flow, it is found that the tendency towards a relaminarized flow appears and the axial velocity fluctuation is suppressed; however, the azimuthal fluctuation is enhanced due to the presence of the pipe wall rotation. The joint probability density function (joint PDF) of the velocity fluctuations and the probability density function (PDF) of the helicity fluctuation are analyzed in detail. It is revealed that the resolved Reynolds stress and helicity fluctuation in the wall region are closely related to the correlation between the velocity and vorticity fluctuations and affected significantly by the rotation-induced azimuthal mean flow. Further, the budgets of resolved Reynolds stresses indicate that the rotation effect is responsible for the more active turbulent energy redistribution and the production of the azimuthal turbulence fluctuation. The near-wall inclined streaky structures with respect to the axial direction are ascribed to the spiral motion of the fluid induced by the rotating pipe. The turbulence characteristics revealed in this study are of great help for the understanding of physical fundamentals in the rotating turbulent flows and for the development of reliable turbulence model.