The Influence of Leading-Edge Tubercles on the Wake Flow Dynamics of a Marine Rudder

Abstract

The impact of two tubercle leading-edge (TLE) modifications on the turbulent wake of a representative marine rudder at Reynolds number 2.26×10 6 was analysed numerically using Detached-Eddy Simulations. TLE have been shown to alter the flow profile over aero/hydrofoils through the generation of streamwise counter-rotating vortex pairs behind the tubercles, which can enhance the lifting performance. This paper studies the formation of these vortex pairs and their impact on the wake structures behind the rudder to find out if vortex interaction can reduce the tip vortex.The tubercles enhanced lift for angles of attack (AOA) 10º and above, but at the cost of a large drag penalty that reduced the rudders' lift-to-drag ratio. The formation of the distinctive streamwise counter-rotating vortex pairs behind the tubercles was shown. Due to the inherent spanwise flow component of finite-span lifting surfaces the vortices were generated at unequal strength and only positive vortices were maintained in the wake. The vortices facilitated flow compartmentalisation over the rudder suction side which broke up the trailing-edge vortex sheet and confined the spanwise flow separation over the rudder surface as AOA increased. The tubercles confined flow separation closer to the rudder tip which caused a tip-offloading effect that minimised the initial tip vortex strength. Large elements of streamwise counter-rotating vorticity formed around the localised stall cells of the TLE rudders that interacted with the tip vortex downstream, introducing elliptical instabilities further weakening the tip vortex and changing its trajectory.

Leading-Edge Tubercles Applied Onto a Flapped Rudder

“…The tubercle amplitude was fixed at 5% Cnom and the wavelength at 36% Cnom resulting in 4 tubercles covering the LE. This geometry configuration performed well in a previous study by the authors [18] investigating an all-movable rudder of similar planform shape and foil section. Furthermore the TLE was designed in a "crest configuration" where it terminates on a crest at the rudder tip, which can minimise the tip vortex generation [19].…”

“…The TLE concept has already been successfully applied to rudders and other marine applications, such as tidal turbine blades, propellers, or ducts, where it showed improved flow attachment, prolonged post-stall lift, as well as cavitation mitigation capabilities [9], [15]- [18].…”

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

“…While rudders are used to manoeuvre the boat, foils are used to lift the hull above water level. Modifications to both rudders and foils have been developed consistently and some examples include flapped rudders, flapped foils, flettner rudders, active rudders, tubercle rudders [51,52].…”

Experimental investigation on the effect of Leading Edge Tubercles on the Performance of Marine Propellers in fully wet condition

“…The study stressed that the modified rudder did not worsen self-propulsion performance of the vessel at zero deflection angle while it was markedly superior in deflected conditions up to large incidences in the post stall regime. While most of the studies focused on the hydrodynamic loads and modification of wall flow due to the vortex pairs generated by tubercles, (Troll et al, 2021) analyzed their effect on the dynamics of the wake past a marine rudder by Improved Delayed Detached Eddy Simulations (IDDES). The system of vortex pairs interfere with the vorticity shed past the trailing edge and the compartmentalization of the flow alters the distribution magnitude and vorticity of the wake system.…”