Annular hydraulic jumps

A stream of swirling water descending a vertical Perspex tube was obstructed near its exit from the apparatus. In this way hydraulic ‘jumps’ were formed with an unbroken air core extending on both sides of the discontinuity. As in an open horizontal channel, three kinds of jump were seen: (i) purely undular, (ii) partly undular and partly turbulent, (iii) fully turbulent. Photographs were taken and simple measurements made. The motion was very unsteady, and little accuracy can be claimed for the readings, but they were found to be fairly consistent with the assumptions of solid-body rotation and uniform axial velocity.