Journal
JOURNAL OF FLUID MECHANICS
Volume 934, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2021.1022
Keywords
shear-flow instability; jets
Categories
Funding
- Russian Science Foundation [20-19-00404]
- Russian Science Foundation [20-19-00404] Funding Source: Russian Science Foundation
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This paper studies the development of perturbations in a submerged air jet with a round cross-section and a long laminar region. The results of experiments are in good agreement with theoretical calculations, demonstrating that small perturbations closely follow the predictions of inviscid linear stability theory.
We study the development of perturbations in a submerged air jet with a round cross-section and a long laminar region (five jet diameters) at a Reynolds number of 5400 by both inviscid linear stability theory and experiments. The theoretical analysis shows that there are two modes of growing axisymmetric perturbations, which are generated by three generalized inflection points of the jet's velocity profile. To validate the results of linear stability theory, we conduct experiments with controlled axisymmetric perturbations to the jet. The characteristics of growing waves are obtained by visualization, thermoanemometer measurements and correlation analysis. Experimentally measured wavelengths, growth rates and spatial distributions of velocity fluctuations for both growing modes are in good agreement with theoretical calculations. Therefore, it is demonstrated that small perturbations to the laminar jet closely follow the predictions of inviscid linear stability theory.
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