Abstract
Nonlinear waves excited in the axisymmetric swirling flow passing through a long cylindrical tube are considered. The waves are excited either by an obstacle on the tube axis or by the local expansion/contraction of the tube wall. The applicability of the weakly and strongly nonlinear theories is discussed by comparing their predictions with the solution of the fully nonlinear navier-Stokes equations. In the case of the solid-body rotation, the onset of the axial flow reversal when the resonantly excited wave amplitude becomes large is well predicted by the strongly nonlinear theory by Grimshaw & Yi. On the other hand, when the incoming flow does not have a solid-body rotation and has a swirl such as the Burgers vortex, the resonantly excited waves are well described by the weakly nonlinear theory, i.e., the forced KdV equation.
