Characterization of the Velocity Field External to a Tube Bundle Using Spatial Filter Velocimetry Based on Variable Meshing Scheme

This paper presents results for the experimental vector velocity field obtained through spatial filter velocimetry in a triangular tube bundle with tubes of 20 mm O.D. and a transverse pitch of 25.2 mm. The experiments were conducted for single-phase water flows with Reynolds numbers ranging from 447 to 1842, and for air–water two-phase bubbly flow with liquid Reynolds number of 909 and gas Reynolds number of 42. The vector velocity field for each experimental condition was obtained using a variable meshing scheme to improve the spatial resolution in regions of low velocities. The results indicate that the variable meshing strategy is promising to increase the spatial resolution of the spatial filter velocimetry technique and to release from the constraint imposed by the uniform window sizes, especially for experimental data obtained with relatively low frame rates. Details of the flow structure of external flow across tube bundles, such as the near-wall velocity profiles, wake region and the effects of the gas buoyancy on vertical mean velocities are presented in this paper with high temporal and spatial resolution, which can be useful for validation of numerical models.