Control and / or Mitigation of the Turbulence Generated by Marine Control Surfaces

Moritz Troll, in the Department of Naval Architecture, Ocean and Marine Engineering at the University of Strathclyde is using ARCHIE-WeSt to investigate the control and / or mitigation of the turbulence generated by Marine Control Surfaces (MCS) for his PhD project. MCS typically are foil-shaped appendages to ships and underwater vehicles and include rudders, fin stabilisers, and submarine hydroplanes, amongst others. Whilst playing a critical role in the manoeuvring of most marine vehicles, they also significantly contribute to the generation of the turbulent wake adding to the vessel’s resistance, underwater noise radiation and can also make it more detectable. MCS turbulence mostly occurs due to boundary layer separation and the formation of sheet vortices behind the control surface trailing edge which roll up to form a strong and distinct tip vortex caused by pressure imbalances between the foil sides.

Whale movement. Picture Source: https://www.grantthomasphotography.com

This project therefore researches novel mechanisms (retrofitting flow conditioning devices) or design strategies (best practices) to improve an MCS’ performance regarding the turbulent wake. This is done via a biomimetic approach, using a so-called Tubercle Leading Edge (TLE) which displays sinusoidal bumps along the leading edge, resembling humpback whale flippers.

Left: Q-Criterion visualization of turbulent wake behind foil with tubercle leading edge. Middle and Right: streamline visualization of of flow around foil with tubercle leading edge. All at AOA = 10 deg;

TLE describe a relatively new concept, currently subject to extensive research in the field of hydrodynamics and aerodynamics. TLE have shown to enhance lift and largely delay stall. This is achieved through the formation of counter-rotating streamwise vortices when the incoming fluid flow is deflected into the troughs between two adjacent tubercles. These vortices energise the flow over the foil suction side, whilst confining flow separation to the areas behind tubercle troughs and generally reducing 3D flow effects. Having recognised the potential of the TLE the project now focusses on studying how the formation of these streamwise vortices can be controlled and exploited to eventually largely reduce the strength of the tip vortices, which form the most distinctive part of an MCS’ turbulent wake.

This project is going to combine the state-of-the-art experimental marine hydrodynamic tests with high fidelity computational fluid dynamics simulation to evaluate and optimise MCS design or provide best practise to operate these control surfaces. The sail and sailplanes (forward control surfaces) of the Joubert / BB2 open-source submarine concept model provide the basis for the analysis. Currently, multiple TLE configurations are assessed via Detached Eddy Simulations in Star-CCM+, where ARCHIE-WeSt proves to be an indispensable resource.

For more information about the project contact Mr Moritz Troll (moritz.troll@strath.ac.uk) or his PhD supervisor and Lecturer at the Department of Naval Architecture, Ocean and Marine Engineering at the University of Strathclyde Dr Weichao Shi (weichao.shi@strath.ac.uk).

Figure: Flow separation and vortex shredding from stalled flow downstream from tubercle through (top), re-attached flow downstream from tubercle crest (bottom) at AOA = 10 deg.