Ellegaard et al.(1998, 1999) first demonstrated that the axial symmetry of the viscous hydraulic jump may be broken, resulting in steady polygonal jumps. The 0.5 cm nozzle radius corresponds to that used in the study of Ellegaard et al. and yielded the most regular polygonal jumps. Examples of the polygonal jump structures observed in the experiments of Bush et al. (2003, 2005) are presented in Fig 2. In their study glycerol–water solutions with viscosities of 10–40 cS were pumped at flow rates of 40–100 cc/s through source nozzles with diameters of 4–10 mm. The fluid impacted the center of a circular glass plate of diameter 36 cm that formed the base of a reservoir. The fluid then proceeded through the jump, and over the edges of the reservoir, whose depth was controlled by an outer wall of height 2–10 mm. Polygonal jumps shown in Fig.2 are some examples of type IIa jump.
Varying the nozzle size and test fluid allowed them to explore a new regime marked by steady stable structures that included oval, cat’s eye, bowtie, butterfly and clover-shaped jumps. Henceforth, all referred to as the ‘clover regime’. Shapes arising in the clover regime are presented in Fig 3. It was noted that the jumps arising in the clover regime are marked by the tiered structure characteristic of the Type II b jumps. Some polygonal and clover forms were subject to weak time-dependent fluctuations, typically characterized by a net rotational motion of the entire jump structure, or the propagation of wave-like disturbances towards a single point on the jump.
