Superposition of Constant and Oscillatory Flows in a Rigid Cylindrcal Tube: Influence of Entrance Effects

The interaction of constant and oscillatory flows in a cylindrical tube was studied theoretically and verified experimentally. The impedance of the tube predicted on the basis of a model dealing with this interaction was in good agreement with the observed values (between 2 and 32 Hz) provided the influence of entrance effects was taken into account. The study shows that the influence of a constant flow on oscillatory impedances is of minor importance within this range of frequencies. Entrance effects however, result in an overestimation of steady and oscillatory resistances. The latter increase with steady tlow, twice as rapidly for oscillatory as for steady flow resistance.