Instantaneous flow-distribution measurements of the equilibrium turbulent region in a circular pipe using ultrafast NMR imaging

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Abstract
A powerful flow visualization and measurement method has been developed using ultrafast NMR imaging. This technique enables one to measure instantaneous distribution of any velocity component in any cross-sectional plane. This method was applied to the equilibrium turbulent region, or ‘‘puff,’’ which is intermittently created by large disturbances in a circular pipe when the Reynolds number is around 2250. Instantaneous velocity component distributions were visualized and measured for two velocity components. The flow component parallel to the pipe axis clearly demonstrated the gross nature of the equilibrium puff and that perpendicular to the pipe axis visualized the detailed structures of vortices. Longitudinal vortices were clearly observed near the pipe wall at the upstream interface as well as around the pipe axis in the downstream region. The present measurements made for a single puff, in principle, agree with the ensemble-averaged results obtained in hot-wire measurements previously reported, both qualitatively and quantitatively.