On some physics to consider in numerical simulation of erosive cavitation

This paper discusses several mechanisms in erosive cavitation, which are all important to capture, and study, when assessing the risk of erosion. In particular we introduce the concept of primary and secondary cavitation in order to put emphasis on a particular class of mechanisms: cavitation created in the secondary flow field governed by, e.g., a shedding or collapse of a primary created cavity. These secondary cavities are almost always erosive and have previously not been well described in the literature. The role of cloud cavitation is partly reconsidered and a hypothesis for development of vortex group cavitation, a type of secondary cavitation, is presented. An underlying part of the discussion is how the described cavitation mechanisms influence numerical simulation of cavitation nuisance.http://deepblue.lib.umich.edu/bitstream/2027.42/84223/1/CAV2009-final180.pd

INVESTIGATION OF NUMERICAL SCHEMES IN AIR CAVITY COMPUTATIONS

ABSTRACT: Air cavity and air chamber concepts have been proven to be an efficient way for drag reduction in low-speed ships. Series of experiments were conducted in the SSPA cavitation tunnel to simulate the working conditions of an air filled cavity under the hull of a ship. In this paper, study is extended with a numerical validation using a CFD Open Source solver, OpenFOAM R (OF). Volume of fluid (VOF) approach, which uses phase volume fraction (α) is used to compute the incompressible two-phase viscous flow. The influence of different numerical methodologies on the advection of α is studied. Different schemes from diffusive first-order to higher order TVD (Total Variation Dimensioning) schemes like SUPERBEE are tested. Results are also drawn from counter-gradient convective flux implementation in OF VOF approch. Conclusions are drawn from the wave profile, wave sloshing pressure force and viscous force. It was observed that, as more compressive interface capturing methods were used, the aft force was better predicted but distorts the wave profile and under predicts the beach plate force

Particle swarm optimization: an alternative in marine propeller optimization?

<p>This article deals with improving and evaluating the performance of two evolutionary algorithm approaches for automated engineering design optimization. Here a marine propeller design with constraints on cavitation nuisance is the intended application. For this purpose, the particle swarm optimization (PSO) algorithm is adapted for multi-objective optimization and constraint handling for use in propeller design. Three PSO algorithms are developed and tested for the optimization of four commercial propeller designs for different ship types. The results are evaluated by interrogating the generation medians and the Pareto front development. The same propellers are also optimized utilizing the well established NSGA-II genetic algorithm to provide benchmark results. The authors' PSO algorithms deliver comparable results to NSGA-II, but converge earlier and enhance the solution in terms of constraints violation.</p

3D Unsteady Computations for Submarine-Like Bodies

Results from a computational study using Unsteady Reynolds Averaged Navier Stokes (URANS) models and Large Eddy Simulation (LES) of flows past submarine-like bodies are here presented. The aims are to evaluate URANS and LES for high-Re number hydrodynamic flows, to investigate the influence of the turbulence and subgrid turbulence modeling, and to discuss some features of submarine hydrodynamics. For this purpose we have chosen to examine the flow past a prolate spheroid at 10\ub0 and 20\ub0 angle of attack at a body length Re number of 4-106, and the flow past the DARPA-2 Suboff bare hull and fully appended hull configurations at a body length Re number of 12-106. For both cases experimental data is available for comparison. One finite element and one finite volume flow solver has been used - both with the capability of employing a range of turbulence models and with the capacity of using unstructured and hybrid grids. Better agreement between predictions and experimental data is obtained with LES than with the URANS models, but at a considerably higher price, due to the finer grids and finer temporal resolution in LES