Measuring Internal Forces in a Hydraulic Jump with a Load Cell

The hydraulic jump is a dynamic phenomenon characterized by three-dimensional motions and energy dissipation. Despite extensive research of the air-water flow properties and interactions of free-surface movements, flow aeration and turbulence, the understanding of the internal processes in hydraulic jumps remains limited. Herein the present study used a novel approach to directly measure the internal forces on a water-filled sphere submerged within the hydraulic jump roller. The sphere was connected to a six-axis load cell with a truss structure designed to remove the effect of the natural frequency of the overall system while allowing the measurement of the characteristic frequencies inside the jump roller. Profiles of internal forces were measured at different cross-sections along the hydraulic jump. The results showed larger internal forces and force fluctuations within the roller region close to the jump toe, which was consistent with the high flow velocities within this region and the formation of vortices. The internal forces decreased in the downstream direction. At each measurement location, the characteristic frequencies were estimated showing a close agreement with results of previous studies. Novel data of transverse and vertical forces, force fluctuations and frequencies were recorded for the first time. The results highlighted the ability of the new measurement system to directly measure the internal three-dimensional motions and dissipative processes inside the jump roller.