Bubble measurements downstream of hydraulic jumps

A phase Doppler anemometer (PDA) system was used to measure the velocity pr ofiles and air bubble size distributions downstream of two-dimensional hydr aulic jumps for different upstream flow conditions in a 1.92 m long laborat ory flume. The PDA detected bubbles from 1 to 500 mum in diameter, and more were found at the bottom of the downstream flow near the elevation of the upstream free surface. This distribution was more marked for smaller bubble s, those with diameters less than 100 mum. The migration of the bubbles is controlled by the effects of buoyancy and by turbulent mixing; the relative magnitude of their effects on bubble distribution depends strongly on bubb le size, and also on the energy of the upstream flow. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.