Development of a 3D PTV algorithm for the investigation of characteristic flow structures in the upper human bronchial tree
The flow in the upper bronchial tree is highly unsteady and three dimensional. In order to capture the characteristic flow patterns inside a model of the upper human conducting airways, a three dimensional Particle Tracking Velocimetry evaluation algorithm is developed and tested. At first, the general concept as well as the single routines to obtain three dimensional particle trajectories are described. Before discussing experimental results, the algorithm is used to process synthetic data to estimate the limits and errors of the reconstruction. Images with a particle density of up to 0.01 particles per pixel are evaluated. For a stepwise particle reconstruction it is shown, that for the whole range about 95% of all particles could be reconstructed with a fraction of ghost particles below 10% Experiments are conducted using a transparent silicone lung model of the upper human airways. Characteristic flow parameters feature those of normal breathing with a Womersley number of a 3.0 and a Reynolds number of about Re 2000. The results reveal the capability of the particle tracking algorithm to reconstruct important flow features during breathing Fig. 1 Reconstructed particle trajectories for an oscillating frequency of 0.15 Hz and a tidal volume of 500 ml. Image a) shows flow conditions at peak inspiration, image b) at peak expiration. Trajectories are color coded in respect to their local absolute velocity |u|