Experimental visualisation of flow structures in the hydraulic jump region of circular jets

Free-surface liquid jets impinging onto a horizontal plate exhibit a circular hydraulic jump (CHJ). The jump intensity affects the flow structures in the jump region. The gradual increase of the jump strength, e.g., by increasing the height of an obstacle downstream of the jump for otherwise constant parameters, can successively increase the jump intensity and lead to different flow structures in the jump region. The following jump types have been observed both numerically and experimentally: type (0) without any recirculation zones, (1a) with a separation bubble on the plate, (1b) with a roller underneath the interface (only observed numerically), (2) with both a roller and a separation bubble in the jump region. All the experimental studies have qualitatively determined the flow structures in the jump region. In this study, the Particle Image Velocimetry (PIV) method is applied to an already-developed experimental setup for stationary CHJs. The use of fluorescent particles enables precise determination of the flow structures in the jump region in terms of the recirculation zones and their dimensions to verify the occurrence of type (1b) jumps.