ABSTRACT
Local surface aeration processes are complex phenomena which depend sensitively upon many parameters. The boundary geometry and the absolute scales of geometry and flow rates are extremely important. In most cases of local aeration, air entrainment takes place at a discontinuity of the free surface at which substantial velocity differences are encountered. In a hydraulic jump, for instance, the air is entrained exclusively at the toe of the surface roller. The inception of air entrainment is governed by the condition that the free surface is penetrated and interrupted by the impinging flow. Air entrainment will commence when inertial and gravity forces override the resisting forces due to viscosity and surface tension. The effect of surface tension is overcome as a result of an increase in the flow rate or height of fall or both. Air is entrained to greater depths and, with increasing turbulence, is broken into finer and finer bubbles.
