Oscillatory flow in a symmetric bifurcation airway model.

Flow in a symmetric bifurcation model of analytically known geometry was investigated experimentally under oscillatory flow conditions. The duration of the inspiratory and expiratory phases were set to be equal during the oscillatory period. A two velocity component laser Doppler anemometer was used to interrogate the flow field. Three different flow rates through the bifurcation were investigated. The peak Reynolds numbers, based on peak flow rates, were 700, 1278, and 2077. The Womersley number was set to 4.3 and it was kept at the same value for the three different flow rates. The results suggest that under the conditions studied a quasisteady flow assumption for oscillatory flow is valid for only about 50% of the oscillatory period, or it is limited to represent the oscillatory flow only in the vicinity of peak inspiration and peak expiration. Complex transport phenomena that occur during the transition between the respiratory phases cannot be elucidated and analyzed by quasisteady equivalents.