Structures in turbulent boundary layer flows investigated by tirne-resolved30 Lagrangian Particle Tracking using Shake-The-Box and FlowFit

Abstract

A great potential for minimizing fuel consumption is the reduction of total drag, consisting to a large extent of aerodynamic drag caused by turbulent boundary layers (TBL) along the entire surface of e.g. aircrafts. The understanding of the formation and the dynamics of very-large coherent structures or superstructures within TBLs and their influence on the drag producing wall shear stress is therefore an important research topic in aerodynamic flows at high Reynolds numbers not attainable by DNS. A further examination of the formation and evolution of such superstructures and their influence in the near-wall region is therefore of major interest for a better understanding of turbulent (wall bounded) flows in general. Shake-The-Box (STB) is a novel time-resolved 30 Lagrangian particle tracking method for densely seeded flows developed at DLR and is of particular use for such large scale investigations. STB overcomes the ill-posed reconstruction problem for 30 particle distributions at high seeding densities present for each single time-step (as known for tomo-PIV and PTV) by pre-solving the problem for each predicted time-step in a cascade of reduced complexity along a time series of images. As a result STB delivers accurate and dense 30 Lagrangian track data in large volumes. The velocity and acceleration information at the track positions can be used for a Navier-Stokes-regularized interpolation method (FlowFit) resulting in high resolution time-resolved 30 velocity gradient tensor information on a regular grid enabling combined Eulerian and Lagrangian investigations.