LES of turbulent cavitating flows using the homogeneous mixture model

Abstract

The objective of this dissertation is to develop LES (large-eddy simulation) capabilities to study cavitation in complex hydrodynamic geometries. A fully-compressible homogeneous mixture model with a finite rate mass transfer is used in the simulations. The ability of the homogeneous mixture approach to capture resolved small-scale vapor bubbles is evaluated by a vapor bubble collapse problem. The effects of physical length scale, surface tension, driving pressure, and dimensionality of the problem are assessed using the parametric study. The finite rate effects of the cavitation model are discussed using the non-dimensional parameters and compared to the flow advection time scales. The expression for the finite rate mixture speed of sound is derived. Partial cavitation over incipient, transitory, and periodic regimes in the experimental sharp wedge configuration of Ganesh et. al. (2016) is investigated. The vapor void fractions obtained from LES shows very good agreement with X-ray measurements in each of the regimes. Physical mechanisms of cavity transition, both re-entrant jet and bubbly shock waves are captured in the LES. Conditions favoring the formation of either the re-entrant jet or the bubbly shock waves are studied through a detailed analysis of streamline curvature, vapor production, and vorticity transport. Flow over a five-bladed marine propeller is studied at design conditions. The assessment of propeller shaft orientation, numerical dissipation, the pressure drop in vortex cores, free-stream nuclei, and grid resolution revealed that the propeller performance is sensitive to the free-stream nuclei content, lower values showing a better comparison to the experiments. A numerical approach based on the preconditioning and the DTS is proposed to address the acoustic stiffness; thereby, enabling the low free-stream nuclei calculations. The novelty of the method lies in the application of preconditioning to a fully-compressible cavitation solver; where the characteristic-based filtering is modified based on the all-speed Roe-type scheme in addition to the traditional time-derivative matrix. The results are demonstrated for the unsteady flow over a cylinder under wetted and cavitation inception conditions, and the LES of low over a propeller under wetted conditions.