Revision as of 12:38, 17 May 2020

Airflow in the human upper airways

Application Challenge AC7-02 © copyright ERCOFTAC 2020

Test Data

Overview of Tests

PIV measurements were performed at six different planes within the lung replica (see Fig. 6). The first three planes were located within the inlet tube with the aim to determine the exact inlet conditions. Plane IV corresponds to the central plane of the oral cavity and the pharynx. Note that this plane is tilted by 2o from the exact vertical orientation. The larynx and the upper trachea were imaged by plane V, and plane VI covers the main bifurcation and bronchi. Both planes are vertical. For all of the measurement stations, the mean velocity and turbulent kinetic energy fields from the in-plane velocity components are determined (see section 4 and equations 8-11).

Locations of the PIV measurement planes I-VI. (a) Measurement planes near the inlet: I-xy plane, II-xz plane, III-yz plane. (b) Measurement planes in mouth-throat (IV-xy plane tilted by 2o from the exact vertical orien- tation), trachea (V-xy plane) and main bifurcation and bronchi (VI-yz plane).

Description of experiment

The lung model was placed in an open liquid tank with a piston diaphragm pump attached to a linear actuator to achieve a quasi-stationary inspiratory flow. The stroke of the piston followed a cyclic triangular function with an adjustable falling constant slope and thus constant velocity to match different flow rates during inspiration. The employed working fluid is a mixture of water/glycerine (43:57 mass ratio, $\rho =1150kg/m^{3},\,\nu =8.4\cdot 10^{-6}m^{2}/s$ at $20^{o}C$ ), which exactly matches the refractive index of the silicone model. Neutrally buoyant polyamide particles ( $d_{p}=50\mu m$ ) were used as tracer particles (Stokes number Stk ≈ 0.002). Particle images were recorded using a CCD camera (pco.1600, PCO) with a resolution of 1600px x 1200px in double-frame mode. A total number of 688 image pairs were acquired for each measurement. Illumination was provided by a double-pulse Nd:YAG laser ( $\lambda$ = 532nm, MinilitePIV, Continuum, 10 mJ per pulse). Images were evaluated by DaVis 8 (LaVision). The final grid size is 32 x 32px (planes I-III) and 16 x 16px (planes IV-VI), respectively, both with 50% overlap.

Boundary conditions

The mouth inlet and distal outlets of the lung model are open to the surrounding liquid. Thus liquid can enter and leave the model without any additional resistances or compliances. The local pressure at the mouth inlet corresponds to the barometric pressure plus the pressure of the water column above the model which is approximately 10cm. Accordingly, the pressure at the distal outlet increases by the additional water column which corresponds to the total model height of about 50cm. During inspiration, liquid is sucked into the model from the tank. The distance between tank's walls and the inlet of the model is about 15cm. The specific inlet conditions found in the experiment are presented in Fig. 6.

Figure 7: Inlet flow conditions of the experiments as determined by the PIV measurements. Illustrated is the mean in-plane velocity magnitude at the planes I (a), II (b) and III (c) for a flowrate of 60 L/min. The velocity along the profile lines depicted in (a) and (b) are plotted in (d) and(e), respectively (PIV (o) and LES1 (-)).

Measurement errors

Contributed by: P. Koullapis^a, J. Muela^b, O. Lehmkuhl^c, F. Lizal^d, J. Jedelsky^d, M. Jicha^d, T. Janke^e, K. Bauer^e, M. Sommerfeld^f, S. C. Kassinos^a —
^aDepartment of Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia, Cyprus
^bHeat and Mass Transfer Technological Centre, Universitat Politècnica de Catalunya, Terrassa, Spain
^cBarcelona Supercomputing center, Barcelona, Spain
^dFaculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic
^eInstitute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Freiberg, Germany
^fInstitute Process Engineering, Otto von Guericke University, Halle (Saale), Germany