Depth of penetration of bubbles entrained by an oscillated plunging water jet

Abstract

We present experimental measurements of the penetration depth of the bubble cloud generated by a plunging water jet, when this jet is oscillated parallel to the free surface. We demonstrate that when the Reynolds number is larger than 104 the penetration depth can be adequately described with the model introduced by Clanet and Lasheras (1997) for a non-oscillating jet tilted relative to the normal of the liquid surface, provided an effective inclination angle is introduced to account for the jet translation velocity. In the case of jets with a Reynolds number smaller than 104, we find that the penetration depth of the oscillated jet can be increased of up to 30% by moderate oscillation velocities. This increase of the penetration is due to the decrease of the mixing layer angle when the symmetry around the bubble cloud is broken by the oscillation. We finally discuss the shape of the overall region impacted by the oscillating bubble cloud. We show that there is a regime for which the penetration is maximum at the center of this region, and a regime for which the penetration is maximum at the periphery. We propose a cartography to predict when each regime is relevant.