Measuring Lagrangian particle tracks in densely seeded wall bounded turbulent flows using 4D-PTV “Shake-the-box”

Abstract

Turbulent wall bounded flows at aerodynamically relevant Reynolds numbers consist of manifold temporal and spatial scales and are essentially characterized by the self-organization and dynamics of coherent flow structures. The latter ones can be regarded as energy containing structures such as hairpin-like vortices and spanwise alternating wall bounded low- and high-speed streaks, which have been observed and extensively analysed in the past with both advanced experimental (e.g. PIV) and numerical methods (e.g. DNS). In many studies the role of coherent structures for the wall normal and spanwise fluid exchange has been highlighted mostly within an Eulerian frame of reference. In the present work the time series of already existing particle images achieved during two different applications of time-resolved tomographic PIV to wall bounded flows will be reprocessed applying the novel 4D-PTV algorithm “Shake-the-box” (STB) developed at DLR Göttingen. The series of 3D velocity vector data from conventional tomographic MART reconstructions and related correlation-based evaluation techniques will be compared to results of the STB algorithm for a) the flat plate turbulent boundary layer flow in a water tunnel at Re ~ 2460 and b) the turbulent flow in the shear layer region downstream of the 7th hill of the ERCOFTAC test case Nr. 81 in the “Periodic hill” water tunnel at TU Munich at Re = 33,000 gained during the EC project AFDAR. The advantages of the STB results compared to Tomo PIV will be highlighted in terms of accuracy, ghost-level, spatial resolution and the possibility to switch between the Eulerian and Lagrangian frame of reference. In the same sense these advantages and further potential benefits of the STB will be discussed for serving as a 4D measurement tool for characterizing wall bounded turbulence in future projects.