FLOW TRANSITION IN BENDS AND APPLICATIONS TO AIRWAYS

The transitional character of fluid flow in a bend has been studied using a computational fluid dynamics software package, FIDAP. In particular, we have addressed factors affecting the developing lengths of velocity patterns. Axial velocities, secondary currents, and isovelocity contours were selected to characterize developing flows. The findings established that developing lengths are functions of Dean numbers. The results of this work can be used to model transport processes for developing flows in curved tubes such as are components of, for example, aerosol instrumentation, industrial processes or respiratory systems. For demonstration purposes simulations were performed for curved airways within human lungs. The Horsfield et al. (1971, J. Appl. Physiol. 31, 207-217) and Horsfield (1991, In The Lung: Scientific Foundations, Vol. 1, (Edited by Crystal, R. G., West, J. B., Barnes, P. J., Cherniack, N. S. and Weibel, E. R.), pp. 721-727. Raven Press, New York) lung morphologies were used to describe airway shapes and dimensions. For sedentary breathing conditions, airways are regions of developing flow which indicates that models in the literature assuming developed flow conditions are not appropriate. The findings have important implications to inhalation toxicology and aerosol therapy.