Effects of the wall heat flux on the flow characteristics of large-scale coherent structures in a pipe with enhanced heat transfer

Abstract

In this study, we use stereoscopic particle image velocimetry (SPIV) to measure the internal instantaneous flow field of a typical pipe with enhanced heat transfer (a single-start spirally corrugated pipe with a pitch-to-diameter ratio S/D = 2.22) with and without a wall heat flux for Reynolds number ReD = 10000 and 25000. Proper orthogonal decomposition (POD) is used to extract the large-scale structures of the internal flow field. The POD results for the flow in the spirally corrugated pipe are employed to quantitatively analyze the turbulent kinetic energy (TKE) and Reynolds shear stress (RSS) using the corresponding results for a straight circular pipe as a benchmark. The results reveal the flow patterns of the large-scale motions in the flow field of spirally corrugated pipes are not sensitive to the wall heat flux and Reynolds number. Nevertheless, convective heat transfer can boost the energy content of large-scale coherent structures in a spiral pipe because of an increase in in-plane velocity fluctuations. Furthermore, the large-scale coherent structures of the swirling flow are reflected in multiple Q2 and Q4 events, which contribute positively to the net RSS. However, convective heat transfer reduces the contribution of these structures to the total RSS through the various parameters associated with these events.