This is the accepted version of the paper.This version of the publication may differ from the final published version.Permanent repository link: https://openaccess.city.ac.uk/id/eprint/21817/ Link to published version: http://dx. AbstractThe present paper focuses on the simulation of the high-velocity impact of a projectile impacting on a water-jet, causing the onset, development and collapse of cavitation. The simulation of the fluid motion is carried out using an explicit, compressible, density-based solver developed by the authors using the OpenFOAM library. It employs a barotropic two-phase flow model that simulates the phase-change due to cavitation and considers the co-existence of noncondensable and immiscible air. The projectile is considered to be rigid while its motion through the computational domain is modelled through a direct-forcing Immersed Boundary Method. Model validation is performed against the experiments of Field et al. [1], who visualised cavity formation and shock propagation in liquid impacts at high velocities. Simulations unveil the shock structures and capture the high-speed jetting forming at the impact location, in addition to the subsequent cavitation induction and vapour formation due to refraction waves. Moreover, model predictions provide quantitative information and a better insight on the flow physics that has not been identified from the reported experimental data, such as shock-wave propagation, vapour formation quantity and induced pressures. Furthermore, evidence of the Richtmyer-Meshkov instability developing on the liquid-air interface are predicted when sufficient dense grid resolution is utilised. 45 cavitation erosion development.Along the same lines, the theoretical study of [31], has analytically examined the liquid drop impacts on solid surfaces, while the experiments reported in [1] for liquid droplets impacting on a solid surface, reveal the strong effects of com-the nozzle, in: 10th International Cavitation Symposium, 2018.
In the current study, an immersed boundary method for simulating cavitating flows with complex or moving boundaries is presented, which follows the discrete direct forcing approach. Although the immersed boundary methods are widely used in various applications of single phase, multiphase, and particulate flows, either incompressible or compressible, and numerous alternative formulations exist, to the best of the authors' knowledge, a handful of computational works employ such methodologies on cavitating flows. The herein proposed method, following previous works of the author's group, tries to fill this gap and to solidify the development of a computational tool of a simple formulation capable to tackle complex numerical problems of cavitation modeling. The method aims to be used in a wide range of applications of industrial interest and treat flows of engineering scales. Therefore, a validation of the method is performed by numerous benchmark test-cases, of progressively increasing complexity, from incompressible low Reynolds number to compressible and highly turbulent cavitating flows. K E Y W O R D Scavitation, diesel injector, direct forcing, immersed boundary method, turbulence modeling INTRODUCTIONWithin the framework of computational fluid dynamics, applications of industrial interest often refer to flows in complex geometries or around moving bodies; their simulation may be numerically challenging and computationally expensive. Many cases of cavitating flows fall into that category. For example, cavitation formation in diesel injector nozzles with moving needle, gear pumps, or propellers mounted under ship hauls, refer to problems with moving geometrical parts and include different geometrical features with wide range of length scales and topological features that impose severe constraints in mesh generation. The conventional strategy of generation of boundary-conforming grids for such problems, may become demanding and time consuming. When the numerical simulation involves moving parts with large displacements, common conformal grid strategies result in remeshing of the entire domain in every time-step, 1 or deforming the grid and adding or removing cell-layers when a desired cell size is reached. 2 In the case of marine propellers, to accommodate their rotational motion, either the entire computational domain would be rotated accordingly, 3 or a multi-region mesh would be used, which lets the part of the grid that conforms with the propeller blades to slide with regards to the global domain. 4 Another approach of over-set grids 5 (also known as Chimera grids), employs multiple overlapping 3092
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