Investigation of sheet to cloud cavitation dynamics using modal decomposition

The objective of this study is to apply modal decomposition methods to numerical simulations of sheet to cloud cavitation over a wedge. A homogeneous mixture model is employed, and the numerical method is first validated against experimental measurements, showing good agreement across a range of cavitation numbers. The simulations capture the two primary mechanisms known to destabilize the sheet cavity: the re-entrant jet mechanism and the condensation front mechanism. The results confirm that a homogeneous mixture model composed of incompressible liquid and vapor phases is adequate to capture the formation of a condensation front, suggesting that individual phase compressibility is not an essential condition for its formation. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are then used to analyze dominant flow structures within a single cavity shedding cycle. The modal analysis shows distinct spatial modes delineating the two instability routes. At relatively low cavitation numbers, the leading POD mode and DMD mode capture a wall-detached vapor structure that travels upstream as a condensation front, accompanied by pressure variations inside the partial cavity. At higher cavitation numbers, the dominant modes show a thin, wall-attached vapor structure that advances upstream as a re-entrant jet accompanied by pressure variations outside the partial cavity. The identification of these dominant spatial modes for each of the mechanisms presents an opportunity to design appropriate control strategies to modulate sheet to cloud cavitation transition at different cavitation numbers.