ИСТИНА

In this experimental study, we investigate the flow of a laminar, submerged, round air jet and introduction of the controlled excitations to it. The jet is generated by a special device with low exit turbulent fluctuations level, an extended laminar region (no less than 5D), and a substantial jet diameter. The use of this unique device allows us to conveniently introduce and monitor the evolution of small perturbations far downstream using laser-sheet visualization technique, hot-wire anemometry, and PIV measurements. In this paper, we focus on examining the growth of non-modal perturbations. To stimulate this mechanism, we propose the introduction of specific thin wavy structures (deflectors) into the jet, creating a roller-like transverse motion. Based on the acquired experimental data, we unequivocally identify the non-modal "lift-up" growth mechanism of the introduced disturbances. The development of perturbations qualitatively corresponds with theoretically calculated optimal perturbations. Additionally, we investigate the interaction between the non-modal linear mechanism and the previously studied modal mechanism, aiming to find a possibility to reduce the growth of modal perturbations.