Characterization of the three-dimensional velocity field of a propeller wake using Lagrangian particle tracking

A Lagrangian description of the vortical flow in the wake of a propeller is presented in this work. Data from a volumetric-PIV measurement performed in the historic Garfield Thomas Water Tunnel was re-processed using LaVision's implementation of the Shake-the-Box (STB) particle tracking algorithm. The data was acquired at 2500 fps using four Phantom v1212 cameras in a linear arrangement and a Photonics DM-50 to illuminate the volume. The measurement volume has dimensions of 140 x 180 x 40 mm^3. The generic propeller rotated at 625 rpm with a thrust of up to 30lbs. Lagrangian descriptions of flows are often not considered from experimental data due to the many challenges of dealing with sparse or uneven grid spacing. However, using even basic Lagrangian statistics, such as single or dual particle dispersion, distinct structural features of the wake flow can be highlighted and analyzed. Furthermore, a scheme to detect trajectories that are within coherent wake vortices and also ones that are entrained is presented.