Göran Bark

LES of unsteady cavitation on the delft twisted foil

In this paper, the cavitating flow around the Delft twisted hydrofoil with unsteady inflow condition is numerically simulated using Large Eddy Simulation in combination with a volume of fluid implementation to capture the liquid-vapor interface and Kunz’s model for the mass transfer between the phases. Main cavitation mechanisms, including periodic shedding of main and secondary cavities, side- and re-entrant jets, as well as the cavity extent and the lock-in effect between the inflow variation and the cavity are compared with experimental observations.

Hydrodynamic mechanisms controlling cavitation erosion

In this paper we consider development of cavitation erosion having its origin in sheet cavitation. The discussion includes generation of cloud cavitation from sheet cavitation and how a cloud collapse can be enhanced by energy cascading from the collapse of a glassy sheet cavity into the collapse of a cloud. A decomposition of the cavitation process into crucial parts results in formulation of a conceptual model for description and analysis of the generation of erosion by mixed glassy and cloud cavitation.

Numerical Simulations of the Cavitating Flow on a Marine Propeller

This paper deals with numerical simulations of the cavitating flow around a marine propeller operating in open water but mounted on an inclined shaft. The investigation is mainly based on both Large Eddy simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) in combination with a Volume-of-Fluid implementation to capture the liquid-vapour interface and a transport equation-based method for the mass transfer between the phases. Potential flow solver result will also be included to offer a complete picture of the general behaviour and capabilities of a range of computational methods with different levels of detail. Highspeed video recordings from experiments are available for detailed inspection.

A Procedure for Optimizing Cavitating Propeller Blades in a Given Wake

Abstract The blade geometry of a cavitating propeller in a given wake is optimized to maximize propeller efficiency and minimize propeller induced pressure fluctuations. The Keller criterion, the cavity volume and other constraints are considered in the optimization process. Such constraints are cavity area, cavity length and face side pressure. These are switched on separately or simultaneously to investigate their influence on cavitation and efficiency. The optimization starts from a near optimum propeller as well as from an off-design propeller. Results indicate that the present optimization technique can yield higher efficiency and lower pressure amplitude with tolerable cavitation for a cavitating propeller in a given wake.

Hydrodynamic Processes Controlling Cavitation Erosion

In this paper we consider development of cavitation erosion having its origin in the sheet cavitation on the hydrofoils and propeller blades. The discussion includes generation of cloud cavitation by processes related to sheet cavity dynamics and how a cloud collapse can be enhanced by energy cascading from the collapse of a sheet cavity into the collapse of a cloud. A decomposition of the cavitation process leads to the basis for a conceptual model for description and analysis of the generation of erosion by mixed glassy and cloud cavitation. This model is made up of ten Analysis Models identifying the large to moderately small-scale events to be traced for unfolding behaviors that can control erosion.

Numerical optimisation of propeller-hull configurations at full scale

Optimisation of propeller/hull configurations based on the Reynolds-Averaged Navier-Stokes (RANS) equations has been very rare so far due to the large computational effort required. Virtually no such optimisation has been carried out at full scale, where only a few RANS methods are at all applicable due to stability problems. The present paper introduces a newly developed RANS solver especially designed for stability and this solver is shown to work well at full scale. Through a link to a commonly used propeller analysis code, predictions of the viscous flow around the full scale ship with an operating propeller may be made. This is utilised in the work reported here, where the flow codes are introduced into a system for automatic optimisation. It is shown that even well designed propellers may be further improved, both in a fixed wake and in the wake behind a fixed hull.

Mesh Resolution Effects in Simulating Unsteady Sheet Cavitation

Abstract We present simulations of the cavitating flow on a NACA0015 hydrofoil in homogeneous and constant inflow. The simulations are performed using an incompressible implicit LES methodology with cavitation modelling based on a one-fluid mixture approach combined with a transport equation modelling including source terms for the mass transfer between the phases. We compare the flow development and spectral content of lift oscillations with experimental results from the literature. The study shows that a good qualitative as well as quantitative agreement is possible but requires a high mesh resolution, primarily in the wall normal direction, to avoid spurious cavitation dynamics in the simulated flow.