Effect of Peierls transition in armchair carbon nanotube on dynamical behaviour of encapsulated fullerene

The changes of dynamical behaviour of a single fullerene molecule inside an armchair carbon nanotube caused by the structural Peierls transition in the nanotube are considered. The structures of the smallest C20 and Fe@C20 fullerenes are computed using the spin-polarized density functional theory. Significant changes of the barriers for motion along the nanotube axis and rotation of these fullerenes inside the (8,8) nanotube are found at the Peierls transition. It is shown that the coefficients of translational and rotational diffusions of these fullerenes inside the nanotube change by several orders of magnitude. The possibility of inverse orientational melting, i.e. with a decrease of temperature, for the systems under consideration is predicted.Comment: 9 pages, 6 figures, 1 tabl

Effect of Surface Roughness on Boundary Layer Transition and Far Field Noise

Surface roughness elements are often used to force laminar to turbulent transition during aerodynamic and aeroacoustic experiments in wind tunnels. The statistical features and frequency content of the forced turbulent boundary layer can influence the far-field trailing edge noise. To study this dependence, boundary layer transition induced by randomly distributed roughness elements and a zigzag strip of the same height over a NACA 0012 airfoil is investigated experimentally. The effects of roughness type on the near-field flow topology, transition location, and far-field noise are addressed. At a fixed roughness height, the distributed roughness elements are less effective in forcing transition than the zigzag trip at low freestream velocity (u∞ < 20 m/s). As u∞ increases, the transition front for the distributed roughness elements moves close to the roughness location, reaching the same or even further upstream location compared with the zigzag strip. The far-field noise intensity depends on the transition location. For u∞ < 20 m/s, a higher noise level is measured for the distributed roughness with respect to the zigzag strip. Whereas, for u∞ <20m/s, the earlier onset of transition leads to a lower noise level for the distributed roughness elements with respect to the zigzag strip. The data confirms that an adequate characterization of the state of the boundary layer is necessary when measuring far-field noise in wind tunnel experiments.Wind Energ