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The velocity field downstream of an automotive vent is one of the key parameters of passenger comfort. Two theoretical approaches (using analytical-empirical equations, and based on computational fluid dynamics) were applied to calculate the velocity of a jet emerging from a real rectangular benchmark ventilation outlet with adjustable blades. The computational simulations were performed by solving the Reynolds-averaged Navier–Stokes equations (RANS) with the realizable k-ε turbulence model and by Large Eddy Simulation (LES). The results were validated by experimental data acquired by constant temperature anemometry (CTA). The validation comprised a comparison of axial velocity decay, scalar velocity field, angles of jet inclination, and profiles of velocity and turbulence intensity. The study was performed for the isothermal free jet and attached jet, where surrounding walls simulated confinement in a car cabin. The analytical empirical equation by Rajaratnam can be successfully used also to determine the throw of the jet, which is favourable, especially in light of the fact that both computational methods were not very accurate in velocity decay predictions. Root mean square errors for the free jet, and attached jet (expressed for calculations made according to Rajaratnam, and by LES and RANS with respect to the experimentally measured values) were 0.50, 0.85, 0.87 m s−1, and 0.52, 0.30, 0.65 m s−1, respectively. The LES method was more accurate than RANS in predicting the velocity profiles. The average percentage error of LES, and RANS is 6.3%, and 17.4%, respectively however, the calculation time was almost 27 times higher for LES. [Display omitted] • The LES/RANS method is suitable for evaluating the flow field downstream of the automotive vent. • Rajaratnam's equation provides the best accuracy of axial velocity decay. • Both CFD methods (LES and RANS) provided good predictions of turbulence intensity. [ABSTRACT FROM AUTHOR]

The inhalation route has a substantial influence on the fate of inhaled particles. An outbreak of infectious diseases such as COVID-19, influenza or tuberculosis depends on the site of deposition of the inhaled pathogens. But the knowledge of respiratory deposition is important also for occupational safety or targeted delivery of inhaled pharmaceuticals. Simulations utilizing computational fluid dynamics are becoming available to a wide spectrum of users and they can undoubtedly bring detailed predictions of regional deposition of particles. However, if those simulations are to be trusted, they must be validated by experimental data. This article presents simulations and experiments performed on a geometry of airways which is available to other users and thus those results can be used for intercomparison between different research groups. In particular, three hypotheses were tested. First: Oral breathing and combined breathing are equivalent in terms of particle deposition in TB airways, as the pressure resistance of the nasal cavity is so high that the inhaled aerosol flows mostly through the oral cavity in both cases. Second: The influence of the inhalation route (nasal, oral or combined) on the regional distribution of the deposited particles downstream of the trachea is negligible. Third: Simulations can accurately and credibly predict deposition hotspots. The maximum spatial resolution of predicted deposition achievable by current methods was searched for. The simulations were performed using large-eddy simulation, the flow measurements were done by laser Doppler anemometry and the deposition has been measured by positron emission tomography in a realistic replica of human airways. Limitations and sources of uncertainties of the experimental methods were identified. The results confirmed that the high-pressure resistance of the nasal cavity leads to practically identical velocity profiles, even above the glottis for the mouth, and combined mouth and nose breathing. The distribution of deposited particles downstream of the trachea was not influenced by the inhalation route. The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route or flow rate. On the other hand, the deposition hotspots were identified by both CFD and experiments in the second bifurcation in both lungs, and to a lesser extent also in both the third bifurcations in the left lung. • Limits of current methods in prediction of flow and high-resolution deposition in an airway geometry were investigated. • Experiments and simulations performed on a replica of airways - nasal and oral cavity and seven generations of TB branching. • The influence of the inhalation route on the flow field was negligible downstream of the glottis. • The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route. • Deposition hotspots identified in the second bifurcation in both lungs, and in both third bifurcations in the left lung. [ABSTRACT FROM AUTHOR]

Inhaled asbestos fibres have been implicated in causal relationships with increased frequencies of non-malignant pleural disease, asbestosis, mesothelioma and lung cancer. Replacement fibres are considered to be less harmful, however, their health effects are not fully understood. The objective of the present work was to implement and apply numerical fibre tracking techniques in order to simulate the deposition of fibres in a complex oro-pharyngeal-laryngeal-bronchial system at different inhalation flow rates and compare the results with the outcomes of recent measurements performed in the same geometry. Two different approaches for the estimation of drag force were considered. Simulated deposition efficiency values agreed reasonably well with the experimentally determined values, however, the drag model which considers the anisotropic nature of the geometry of fibres performed better than the one which accounted only for the their non-spherical shape. The highest values of deposition density correlated well with the location of primary lesions observed in pathological studies. • Deposition of inhaled man-made vitreous fibres in different segments of the airways at three airflow rates was modelled. • Two different drag force models were implemented. • Simulated deposition fractions were compared to the results of deposition measurements in the same airway replica. • Good agreement of numerical and experimental data was found, though simulated upper airway deposition was slightly higher. • The location of segments with high deposition density correlated with the sites of the observed airway lesions. [ABSTRACT FROM AUTHOR]

Regional deposition of glass fibers was investigated in a physically realistic, human respiratory tract replica. The replica begins with the oral cavity and includes the airways up to the 7th generation of the tracheobronchial tree. Uniform diameter glass fibers were classified by length using a dielectrophoretic classifier and introduced into the replica at three steady-state flow rates (15, 30, and 50 LPM). A novel automatic image processing method was utilized to speed up the sample analysis and make it more reproducible. Fractional deposition was high in the oral cavity and the upper respiratory airways. Deposition density was higher in the first few generations of the tracheobronchial tree. Deposition efficiencies were compared with published data and good agreement was obtained. Our data confirmed that the deposition efficiency increased with increasing Stokes number indicating that impaction was the main deposition mechanism. The experimental data were used to propose new empirical models predicting fiber deposition in the tracheobronchial tree. [ABSTRACT FROM AUTHOR]

Quantification of airway deposition of aerosol particles is essential for the assessment of health risks of detrimental particles. Knowledge of deposition distribution is important also in the case of treatment with aerosolised drugs. It is also worth considering that deposition of inhaled particles in severe asthmatics can be different from the deposition in healthy subjects due to the modified breathing parameters, airway geometry and lobar flow distribution. The aim of this study was to apply combined experimental and numerical techniques to quantify the upper airway and bronchial deposition of the inhaled microparticles in healthy individuals in comparison with asthma patients. Idealised and realistic physical and digital replicas of the human airways were constructed. Deposition fractions and efficiencies of inhaled polydisperse mannitol and chitosan particles in different airway sections were measured and calculated. Deposition fraction of polydisperse mannitol particles in the idealised airway geometry assuming breathing conditions of healthy subjects was 21.9% and 18.3% when determined experimentally and by numerical simulations, respectively. Experimental measurements of deposition fraction of chitosan particles in the same geometry, but assuming breathing parameters characteristic of severe asthmatics yielded 32%, while simulations provided 30.1% for the same conditions. Extrathoracic deposition fraction of mannitol particles in healthy subjects measured in the realistic geometry was 71.1%, while bronchial deposition fraction was 5.3%. The corresponding simulations yielded 76.2% and 8.9% deposition fractions in the upper and bronchial airways, respectively. There was a good agreement between the experimental and simulation deposition results also in the different predefined sections of the airways. Present pilot study proved that lobar flow redistribution due to severe asthma significantly modified the deposition distribution of micro-particles. Although the present results refer only to small groups of healthy and asthmatic individuals, it clearly demonstrates the capability of carefully validated models to simulate the deposition of micron-size particles in larger populations of both groups. • Deposition distribution of micro-particles in idealised and realistic upper and central airways was measured and simulated. • Deposition distribution of micro-particles in idealised and realistic upper and central airways was measured and simulated. • Good agreement of numerical and experimental data was found. • The modified breathing of asthmatics significantly changed the deposition distribution of micro-particles. • Combination of numerical and experimental techniques can be a powerful tool of the quantification of particle deposition. [ABSTRACT FROM AUTHOR]