Investigation of turbulence structures sustaining in axial flow along a thin cylinder

Abstract

We performed direct numerical simulations to investigate the characteristics of the turbulence structures in axial flow along a thin cylinder with small radii. In this study, the high-speed air flow in axial direction along a thin cylinder were simulated by solving the fundamental equations of compressible flow with density variations. Then, the velocity fluctuation intensities and the friction coefficient were compared to observe the turbulence structures. As a result, the turbulence seems to become laminar when the radius of the cylinder decreases because the vortex structures of the turbulence disappears and the turbulence structures is different from that of a flat plate. However, the friction coefficient at that time is consistent with the value of the prediction formula, and laminarization is not observed in terms of the friction coefficient. In summary, in the flow around a cylinder with the sufficiently small radius, it was found that although there was a tendency for the flow to become laminar, the flow was not completely laminarized and the structures with the characteristics of turbulence and laminar flow existed. Furthermore, the structures are sustained by the velocity streaks leaving surface of the cylinder.