Spray generation for liquid wall jets over smooth and rough surfaces

Abstract

This is an experimental investigation of the filaments and drops generated at the free surface of liquid wall jets formed over smooth- and sand- roughened surfaces. The jet characteristics and the geometric properties of the filaments and drops were measured from images captured using high-speed digital cameras. A statistical investigation of the various properties revealed the characteristic behavior of the filaments and drops as a function of the relative wall roughness, wall curvature and jet inertia. For this investigation, the wall jet Reynolds number ranged from 2.6 x 10(exp 4) to 4.5 x 10(exp 4), the Froude number from 19 to 33 and the Weber number from 1600 to 4700. The emphasis herein was on the physics of the process rather than the development of empirical relationships. As such, the results indicate that spray generation from a wall jet is a boundary-layer-driven phenomenon, requiring that the jet be in a highly supercritical state (Fr >> 1). Wall roughness reduces the minimum necessary level of supercriticality, but it is not a prerequisite condition for the formation of drops. Whileincreasing the jet inertia enhances the drop formation process, concave wall curvature tends to reduce the quantity and the energy of the drop forming events