The tool assembly vibrates a casing string or drill string in a wellbore. The tool assembly includes a housing, an insert mounted in the housing as a fluidic agitator, and a cover fitted over the insert. The insert includes an inlet chamber, a vortex chamber, and a feedback chamber, and the fluid flow through the insert has a pressure profile with a plurality of levels determined by the feedback chamber. The strength and frequency of the pressure profile can be regulated by the feedback chamber according to position, size and asymmetry of the transition channels connected to the feedback chamber. The high strength and low frequency pressure pulses can be achieved in the limited space of the housing for placement of the inlet and outlet.