Exploratory study on the roller effect of direct hydraulic jumps

Can a direct hydraulic jump also be generated if the surface roller is substituted with a corresponding inset? This and related questions are considered in the note, to understand the role of the roller. Based on recent findings relating to the classical hydraulic jump, its modification using bottom and surface insets is reconsidered using laboratory experimentation. The results of these tests are reported below using mainly photography and basic hydraulic computations. It is further demonstrated that the roller may not be separated from the hydraulic jump in a free surface arrangement. This would greatly simplify observations, because the standard two-phase flow including an air-water mixture flow would become a one-phase flow consisting of only water flow. The implications of this result are discussed. This work has exploratory character and should stimulate a further discussion on the main flow features of direct hydraulic jumps.