DOI: 10.1615/THMT-18
ISBN Print: 978-1-56700-468-7
ISBN Online: 978-1-56700-467-0
ISSN Print: 2377-2816
On the early onset of transition in circular-orifice baffled tubes: an experimental study
RÉSUMÉ
This paper presents an experimental study of the flow pattern in tubes with equally-spaced circular-orifice baffles. Particle Image Velocimetry (PIV) technique is employed in order to obtain the velocity field in the symmetry plane of a region between two consecutive baffles (cell tank). With Reynolds number extending from Re=100 to Re=650, the fully laminar regime and unstable regime are described by means of the turbulent intensity, mean velocity fields and Proper Orthogonal Decomposition (POD). These tools have been able to detect the onset of transition at Re=200. POD has been used for detecting the coherent structures of the flow. The first modes represent the instability of the main stream which oscillates periodically. This oscillation is responsible for the increase in the Nusselt number at relatively low Reynolds numbers (above 200), what proves the important relation between flow structures and heat transfer.