Dynamics of corotating vortex filaments Part 2: experimental results

The interactions of pairs of corotating vortex filaments have been investigated experimentally in a water tunnel. The time history of the motion of each filament has been recorded at several downstream locations to analyze its spatial and temporal behavior. Two sets of data are presented in which the vortices have been excited over a range of frequencies using a shaker. The excitation frequency and its multiples have been shown to be present in the downstream flow. At each downstream position, the filaments have been shown to move along preferred directions, suggesting their tendency to form planar waves, inclined relative to the line connecting them. The amplitudes of these waves have been shown to grow, implying unstable interaction between the vortices. The angles of the planes containing the motion have been presented and compared with the predictions of two analytical models. The scatter in the data prevented quantitative comparison with the analytical predictions. However, the flow is shown to contain all of the essential features predicted by two analytical models.