Gas Transport Into Vortex Cavities

The research presented in this thesis aims at understanding how gases influence the cavitating vortex generated by a wing tip in a stationary flow. Gases in the flow occur as non-condensible microbubbles as well as gases dissolved in the liquid. They are typically abundant in surface flows. For studying how dissolved gases influence a cavitating...

Simulation of cavitation and surface erosion on marine propellers

Cavitation is the formation of vapor pockets in a liquid due to a pressure drop or an increase in speed. Cavitation nuisance can be disastrous for mechanical components, and therefore needs to be controlled from an early design stage. However, predicting cavitation dynamics using CFD (Computational Fluid Dynamics) and therefore the performance...

Application of machine learning to design low noise propellers

Over 90% of international trade is carried out over seas. Shipping is currently the cheapest mode of transoceanic transport. The traffic density of shipping lanes on seas, oceans, and also rivers is likely to increase. Consequently, the GHG, NOx, SOx and noise emissions from shipping will rise making it more difficult to meet stricter emission...

Towards predicting cavitation noise using scale-resolving simulations: The importance of inflow turbulence

There is increasing attention for the effects of anthropogenic underwater radiated noise (URN) on marine fauna. This is expected to lead to regulations with respect to the maximum permitted sound emissions of ships. It is known that cavitating tip vortices, generated by ship propellers, are some of the key contributors to URN. Consequently,...

Cavitation implosion loads from energy balance considerations in numerical flow simulations

Cavitation erosion is a problem in the design of a wide range of fluid machinery involving liquid flows. Ship propellers, rudders, hydro pumps and turbines or diesel injectors are some of the most prominent examples. Cavitation occurs at locations of high local flow velocity, where the pressure may drop so low that the liquid phase vaporizes....

Influence of inland vessel stern shape aspects on propulsive performance: Derivation of insights and guidelines based on a computational study

This research focuses on identifying the most important stern shape aspects, with regard to resistance and propulsion power, of inland ships. Such information should help designers to determine which hull form aspect to adjust in case design requirements need them to do so. The information is obtained by firstly conducting a large series of CFD...

Hydro-elastic analysis of flexible marine propellers

Higher efficiencies, higher cavitation inception speeds and reduced acoustic signature are claimed benefits of flexible composite propellers. Analysing the hydrodynamic performance of these flexible propellers, implies that a coupled fluid-structure interaction (FSI) computation has to be performed. An FSI coupling can be monolithic, which means...

Dynamics of Vortex Cavitation

This thesis describes the mechanisms with which tip vortex cavitation is responsible for broadband pressure fluctuations on ship propellers. Hypotheses for these are described in detail by Bosschers (2009). Validation is provided by three main cavitation-tunnel experiments, one on a model propeller and two on a stationary wing. These have...

Ship Drag Reduction by Air Cavities

On the effect of turbulence on bubbles: Experiments and numerical simulations of bubbles in wall-bounded flows

Previous research has shown that the addition of gas bubbles to a turbulent boundary layer in water can reduce the local skin-friction drag by up to 80%. Application of this technique to ships seems promising, but to date no significant drag reductions are obtained on full-scale ships. More knowledge about the drag reduction mechanism is...

Assessment of Cavitation Erosion with a Multiphase Reynolds-Averaged Navier-Stokes Method

Cavitation erosion is one of the remarkable catastrophic consequences of cavitation. Predicting the cavitation aggressiveness quantitatively and predicting the most probable location of cavitation erosion are complex problems that currently still motivate an important amount of basic and applied research in the fields of hydrodynamics, physics...

Prediction of propeller-induced hull-pressure fluctuations

The cavitating propeller often forms the primary source of noise and vibration on board ships. The propeller induces hydroacoustic pressure fluctuations due to the passing blades and, more importantly, the dynamic activity of cavities in the propeller’s immediate vicinity. The accurate prediction of the resulting vibratory hull-excitation forces...

Control of Propeller Cavitation in Operational Conditions

Off design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase for instance leads to a higher engine loading, and can also easily lead to a decrease of cavitation inception speed with respect to calm water conditions. Wakefield variations due to ship motions, waves and manoeuvres also have effect on...

The structure of three-dimensional sheet cavitation

The interaction between diesel engines, ship and propellers during manoeuvring