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UBC Theses and Dissertations

A computational framework for flow-induced vibrations of propeller blades in cavitating flows Darbhamulla, Nihar Bhardwaj


In the current work, we present a finite-element computational framework for Fluid-Structure Interaction problems subjected to the coupling of unsteady cavitating flows with flexible structures. We build upon a previously developed stabilized variational framework for multiphase FSI by incorporating a dynamical structural solver based on the modal decomposition of the structure. In the first part of the work, we present the validation of the current framework for conducting Large Eddy Simulations (LES) of cavitating flows past rigid structures. We identify the resolution criteria for dynamic subgrid-scale LES based on the re-entrant jet momentum - a prominent phe- nomenon associated with cavity-shedding in the wake of immersed bodies. The validated framework is then used to elucidate the features of cavitating flow past a rigid hydrofoil. In particular, we iden- tify features of sheet-cavitating flow which enable the transition to cloud cavitation. Further, we evaluate the instabilities driving sheet-cavity breakdown and establish the vortical structures which drive cloud cavity collapse, and quantify the frequencies observed over the course of a cavitation cycle. In the second part of the work, we present the validation of the framework for LES of cavitating flows past flexible structures. Based on the validation study conducted over a flexible NACA66 rectangular hydrofoil, we elucidate the role of cavity and vortex shedding in the structural dynamics at three different cavitation numbers. We identify a broad spectrum frequency band whose central peak does not correlate to the frequency content of the cavitation dynamics or the natural fre- quencies of the structure, indicating the induction of unsteady flow patterns around the hydrofoil. Finally, we discuss the coupled fluid-structure dynamics during a cavitation cycle associated with the promotion and mitigation of cavitation.

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