Pulse separation strategies for multi-pulse systems: 3D Lagrangian particle tracking with Shake-The-Box in turbulent boundary layers

The Shake-The-Box (STB) technique [1] opened the possibility to perform accurate Lagrangian particle tracking in 30 at relatively high seeding densities. The STB method relies on the availability of a sequence of time-resolved recordings, the Iterative Particle Reconstruction technique (IPR [2]) and particle prediction in order to provide accurate particle trajectories that can be used to measure particleposition, velocity and material acceleration. When dealing with high flow velocities typical of industrial and aerodynamics applications, where, due to the current limitations in terms of acquisition frequency, time­resolved data are not available, multi-pulse systems can be employed; the acquisition of a dual illumination and imaging system is synchronized in a staggered fashion in order to generate short sequences of time-resolved recordings (typically four). Recently, the STB technique has been extended to the case of multi-pulse data; an iterative STB processing strategy has been proposed by [3], where the sequential application of IPR and particle tracking is used to progressively reduce the complexity of the object tobe reconstructed (i.e. perceived imaged seeding density) and increase the number of successfully retrieved tracks. The principle of the iterative strategy has been demonstrated by means of synthetic experiments of isotropic turbulence and of a transonic base flow in [4] and the technique has been successfully applied to the experimental investigation of a turbulent boundary layer with adverse pressure gradient in air at 36 m/s [3] and to data from a transonic jet experiment at Mach 0.84 [5]