Flow mechanism study and geometrical parameters analysis of fluidic oscillators based on pressure-sensitive paint measurements and modal analysis

The present study optimized some novel fluidic oscillator designs, measured their internal-external fluid dynamics, and used modal analysis to reveal their underlying oscillation mechanisms. It also investigated the effects of structural parameters on their fluid dynamics (including inlet-wedge width ww\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${w}_{w}$$\end{document}, feedback-channel inlet width wf\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${w}_{f}$$\end{document}, and mixing-chamber Coanda surface). The time-resolved internal-external pressure fields of the oscillators were determined by using pressure-sensitive paint (PSP) measurement. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) were used for modal analysis and phase reconstruction. The time-averaged pressure field and phase reconstruction results reveal that recirculation bubbles inside the mixing chamber and the feedback flow have underpinned the mechanism of formation of internal and external continuous sweeping flows. The modal analysis results reveal the spatial modal structures and their time evolution, which dominated the internal-external flow pattern. The inlet-wedge width and feedback-channel inlet diameter were found to be the structural parameters affecting feedback flow and recirculation bubble size and thereby influenced flow characteristics such as jet oscillation frequency and divergence angle. Different Coanda surfaces altered the recirculation bubbles and feedback flow of the mainstream, thereby influencing the formation mechanism of the sweeping jet.