Polygonal hydraulic jump on microdecorated surfaces

We report on the hydraulic jump resulting from the impact of a water jet onto topographically patterned surfaces, i.e. arrays of cylindrical micron-size posts arranged on square or hexagonal lattices. By varying the topographic features (height of the posts, lattice distance) and the jet properties (size of the nozzle, flow rate), we obtain a variety of stable shapes including hexagons, eight corner stars and circles. We rationalize our results by taking into account a fluid velocity that depends on the orientation of the lattice.