EXPERIMENTAL STUDY OF THE NON-MODAL PERTURBATION GROWTH MECHANISM IN A LAMINAR SUBMERGED JET

Abstract

It is known that in wall-bounded flows, along with the growth of instability modes, the non-modal (algebraic) mechanism of linear growth plays an important role. In open flows, including submerged jets, the non-modal growth mechanism is theoretically studied only in the last decade; this mechanism has not yet been identified in experiments. In the present work, experiments on excitation of a non-modal “lift-up” growth mechanism are conducted. Special wavy structures (deflectors) are introduced into a laminar submerged jet of circular cross section, which excites a roller-like transverse movement. The data obtained unambiguously identify the non-modal “lift-up” growth of introduced disturbances. The development of perturbations in the experiment qualitatively corresponds to the theoretically calculated optimal perturbations. The features of the transition to turbulence caused by non-modal growth are considered.