Image processing using proper orthogonal and dynamic mode decompositions for the study of cavitation developing on a NACA0015 foil

• Published in: Experiments in fluids 2016-10, Vol.57 (10), p.1-25, Article 157
• Main Authors: Prothin, Sebastien, Billard, Jean-Yves, Djeridi, Henda
• Format: Article
• Language: English
• Subjects: Bifurcations; Cavitation; Computational fluid dynamics; Decomposition; Dynamics; Engineering; Engineering Fluid Dynamics; Engineering Sciences; Engineering Thermodynamics; Fluid flow; Fluid- and Aerodynamics; Fluids mechanics; Foils; Heat and Mass Transfer; High Reynolds number; Holes; Image processing; Instability; Mechanics; Proper Orthogonal Decomposition; Research Article; Reynolds number; Robustness (mathematics); Shedding; Shock wave propagation
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-016-2246-1

The purpose of the present study is to get a better understanding of the hydrodynamic instabilities of sheet cavities which develop along solid walls. The main objective is to highlight the spatial and temporal behavior of such a cavity when it develops on a NACA0015 foil at high Reynolds number. Experimental results show a quasi-steady, periodic, bifurcation domain, with aperiodic cavity behavior corresponding to σ /2 α values of 5.75, 5, 4.3 and 3.58. Robust mathematical methods of signal postprocessing (proper orthogonal decomposition and dynamic mode decomposition) were applied in order to emphasize the spatio-temporal nature of the flow. These new techniques put in evidence the 3D effects due to the reentrant jet instabilities or due to propagating shock wave mechanism at the origin of the shedding process of the cavitation cloud.