Applications of Multi-Pulse Shake-The-Box 3D Lagrangian Particle Tracking to single- and multi-exposed recordings

Kurzfassung

Lagrangian particle tracking (LPT) enables the accurate measurement of position, velocity and acceleration of single seeding tracers imaged by a multiple camera system. The Shake-The-Box (STB) technique extended the capabilities of 3D particle tracking methods to higher seeding densities, thus providing access to the full velocity gradient tensor. The STB method, initially proposed for the reconstruction of time-resolved sequences of recordings, has been extended to the case of short recording sequences acquired by multi-pulse systems for the investigation of high-speed flows. The Multi-Pulse Shake-The-Box technique (MP-STB) exploits an iterative strategy to make up for the lack of time-resolved recordings and progressively simplify the reconstruction and tracking problem, therefore increasing the number of successfully identified particle tracks. Individual track fields from MP-STB can be exploited to describe the instantaneous flow structures by means of interpolation to a regular grid or collected into bins with an ensemble-average approach to produce highly spatially resolved statistics. Several applications of the MP-STB technique to turbulent boundary layer flows and to a high speed free jet in air are presented here. The experimental conditions are described together with the main processing parameters adopted for the iterative STB strategy. The multi-pulse recording sequences are obtained by means of two pulse separation techniques (polarization- and timing-based) and by adopting Multi-Exposed recordings. Results are shown in terms of instantaneous fields and flow statistics.