Flow Velocity and Water Layer Thickness at Vertical Ring Mesh Structures

Abstract

Vertically assembled ring meshes serve as barriers against explosive threats, in particular when overflowing water completely covers the mesh. The author measured the flow velocity over these structures using Surface Structure Image Velocimetry and subsequently determined the water layer thickness by taking into account discharges in the range 1.0 L/s≤Q≤4.5 L/s. The water proceeds through and over the mesh and forms surface surges at lower discharges. The surges disappear for higher discharges and induce plain water curtains. Based on a momentum balance equation, a theoretical approach was derived to describe the flow dynamics. The free parameters, e.g., the surface roughness of the metal rings and the deflection angle at the rings, were analyzed and compared with the experimental data. The main finding of this study was that the flow velocity remained constant at w≈0.54 m/s, whereas the water thickness increased linearly between 1.0 and 4.6 mm with increasing discharge. As a consequence, ring meshes should be supplied with the highest possible discharge to achieve the greatest mitigating effect against blast wave threats.