Numerical and experimental investigation on the resistance of a human upper airway

A study to decrease pressure loss by the introduction of a swirling flow

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Abstract

This report comprises the research entitled 'Numerical and experimental investigation on the resistance of a human upper airway'. The objective of this research is: To investigate the effects of a swirl producing inlet on the pressure drop in a simplified human upper airway model at high ow rates, by means of numerical simulations and experiments. In the literature study done by the author Hak (2014b) it is found that during exercise up to 15% of the maximum oxygen uptake (V O2;max) is spent by the breathing muscles. The breathing muscles support the breathing process by moving the diaphragm, creating a low pressure in the thoracic region, thereby starting the inflow of air. Since the human upper airway is featured by a complex shape, associated with highly three-dimensional ow patterns, it has a relatively high ow resistance compared to the remainder of the airways. If the ow pattern would be influenced by passive ow control in the form of a breathing aid, the pressure drop could be reduced, thereby decreasing the demand on the breathing muscles. The result is that more O2 can be used in the skeletal muscles and thus the anaerobic-threshold is postponed. This lead to the following main research question: What kind of swirl generating mouthpiece device can influence the inhaled ow, such that a pressure drop reduction is achieved, during intensive exercise? The research started off with an identification and simulation of the the upper airway ow. Typical human upper airway ow behavior which cause losses in pressure are found to be jetlike ow, re-circulating ow, detached ow, secondary ows such as Dean ow. If the upper airway is highly idealized, it can be seen as 'elbow pipe', a pipe with a 90o bend. Dean vortices and boundary layer separation in bent pipe ow are responsible for pressure losses. For the setting up of the simulation, the process of breathing is translated into boundary conditions. Simpli_cations and assumptions are done to the usual periodic behavior of breathing: a stationary inhalation rate is assumed, and only inspiration is considered. The compliance of the airway is not taken into account for simplicity and the ow rate is based on that of an exercising male adult

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