Shake-The-Box - Dense 3D Lagrangian particle tracking for turbulence research

Abstract

hake-The-Box (STB) is a novel time-resolved 3D Lagrangian particle tracking method for densely seeded flows. The STB algorithm has been developed at DLR Göttingen in the past three years and uses the prediction of 3D particle distributions for each subsequent time-step as a mean to seize the temporal domain for accurate track reconstructions based on time series of particle images from few camera projections. Exploiting the temporal information enables the processing of densely seeded flows (up to and beyond 0.1 particles per pixel with a nearly complete suppression of ghost particles). Such high particle trajectory densities are a necessary precondition for interpolating the corresponding time­resolved 3D velocity vector field onto a regular grid using Navier-Stokes-constraints. Such a non-linear data assimilation method named FlowFit has been developed at our group in parallel to STB and tested already successfully: For example, unsteady 3D pressure distributions have been calculated from interpolated 3D acceleration fields. The STB method has been applied to wall bounded turbulence in air and water and to a m3-scale experiment using Helium-Filled-Soap-Bubbles (HFSB) as tracers. The results demonstrate that with STB valuable data for turbulence characterization with outstanding temporal and spatial resolution especially in (wall bounded) shear flow can be obtained.