Velocity field characterization of single-phase flows across a tube bundle through spatial filter velocimetry

Abstract

This paper presents experimental vector velocity fields of external flows across a tube bundle to characterize the flow structure and elucidate the main mechanisms of turbulence generation. The experiments were conducted in a tube bundle test section composed of 20 rows of 4 tubes with 20 mm O.D. arranged in a normal triangular configuration with a transversal pitch per diameter ratio of 1.25. The experiments were conducted under single-phase flows with Reynolds numbers ranging from 210 to 19560, comprising transitional and turbulent flow regimes. The vector velocity fields were obtained through the Spatial Filter Velocimetry (SFV) technique, resulting in maximum spatial and temporal resolutions of 2.1 samples/mm and 49.6 kHz, respectively. The velocity measurements obtained through SFV enabled the analysis of the flow development, the vector velocity field, the flow turbulence, the velocity fluctuation along the time, and the effects of the mechanism of momentum transport on the pressure gradient. The obtained results indicate that the flow separation and the repeated intersection of opposite flows are the most relevant sources of turbulence. Moreover, the analysis of the terms of the RANS equations reveals that the convective terms are the most relevant terms for the pressure gradient.