We studied numerically impingement of vertical liquid jets of moderate Reynolds number for both Newtonian and non-Newtonian liquids to clarify the structure formation of circular hydraulic jump and the phenomenon of jet buckling. First, we have studied the hydraulic jump characteristics and governing parameters for a laminar water jet. Moreover, different types of hydraulic jump have been investigated by varying the height of a circular wall around the bed in flow downstream. The results show that a circular hydraulic jump has two kinds of steady states which can be reached by changing wall height. Next, we studied the impingement of a non-Newtonian liquid jet on a solid surface. In this case, we observe that instead of having a significant hydraulic jump, jet buckling phenomenon happens. The results were used in order to achieve a better understanding of the jet buckling phenomenon and the conditions in which this phenomenon happens.