Numerical simulation of a tidal turbine based hydrofoil with leading-edge tubercles

The tubercles along the leading edges of the humpback whale flippers can provide these large mammals with an exceptional maneuverability. This is due to the fact that the leading-edge tubercles have largely a 3D benefit for the finite hydrofoils, which can maintain the lift, reduce the drag and delay the stall angle. Newcastle University launched a series study to improve a tidal turbine’s performance with the aid of this concept. This paper presents a numerical simulation of the tested hydrofoil, which is representative of a tidal turbine blade, to investigate the flow around the foil and also to numerically model the experiment. This hydrofoil was designed based on an existing tidal turbine blade with the same chord length distribution but a constant pitch angle. The model tests have been conducted in the Emerson Cavitation Tunnel measuring the lift and drag. The results showed that the leading-edge tubercles can significantly improve the performance of the hydrofoil by improving the lift-to-drag ratio and delaying the stall. By applying Shear Stress Transport (SST), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) via using the commercial CFD solver, Star-CCM+, the tested hydrofoil models were simulated and more detailed flow information has been achieved to complement the experiment. The numerical results show that the DES model is in close agreement with the experimental results. The flow separation pattern indicates the leading-edge tubercles can energize the flow around the hydrofoil to keep the flow more attached and also separate the flow into different channels through the tubercles

Stereoscopic PIV aided wake simulation of a catamaran research vessel using a dummy-hull model in a medium size cavitation tunnel

The rising marine environmental concern has recently targeted underwater radiated noise. Amongst various sources present on-board, propeller cavitation noise is known to be the dominant source that may be harmful to marine biodiversity. To be able to minimize anthropogenic noise footprint, full-scale and model-scale test campaigns are the most reliable tools to measure or predict the noise sound pressure level. Within this framework, hydro-acoustic cavitation tunnel experiments carry utmost importance for model-scale tests. Due to limited space of the cavitation tunnel, a shortened dummy-hull is often used, even though the flow passing through the propeller plane of the dummy model does not represent a fully developed wake. This paper presents a wake simulation methodology for a shortened dummy-hull model of Newcastle University research vessel “The Princess Royal” with the aid of Stereoscopic Particle Image Velocimetry (SPIV) in Emerson Cavitation Tunnel. With such method, after three iterations sufficient similarity between target wake and simulated wake has been achieved. Adopted approach has been found to be significantly effective in terms of reducing the time and the iterations during wake simulation process

Hydrodynamic performance and appendage considerations of wave-piercing planing craft overlapping waves and porpoising

This work addresses the numerical study of wave-piercing planing hull and related hydrodynamic performance as the appendages. From the half century ago, the interest in high-speed planing crafts has been advanced toward maintaining performance stably. The main reasons to make it hard are instability motion occurring from porpoising and wave condition. Porpoising is mainly due to overlap the heaving and pitching motion with certain period, which is caused by instable pressure distribution and changing longitudinal location of center of gravity. In addition, in wave condition, encountering wave disturbs going into planing mode. This paper presents numerical results of wave-piercing planing hull in porpoising and wave condition. Numerical simulation is conducted via Reynolds Averaged Navier-stokes (RANS) with moving mesh techniques (overset grid), performed at different wave condition. The numerical results reveal motion characteristics overlapping porpoising and wave condition. At first, motions on low wavelength region show resonance on this condition, and some appendages enhance the motion amplitude larger than original values. Finally, this resonance was suppressed by stern appendages. However, momentum generated from stern appendages increases motions in high wavelength region. This effective motion corresponds with vertical accelerations from CG