Effect of periodical injection of branching flows perpendicular to the laminar main now is investigated experimentally and numerically, The periodical injection forms a regular alternative layer of main flow fluid and branching now fluid. The boundary between main flow fluid and the branching flow fluid is stretched and folded by the parabolic laminar velocity profile in the main now. The importance of the duty ratio of the branching flow injection, the number of branching flows and the phase of branching flows are discussed.