Development of a kayak race prediction including environmental and athlete effects

The aim of this study is to produce a simulator for sprint kayak racing which would allow the prediction of race times based on the physiological capabilities and mass of a given athlete. The simulator has been verified using established empirical data for the prediction of environmental effects and has been shown to be accurate, however verification of the physiological model is difficult to do by using general race data. An investigation into the fatigue model which has been implemented shows that further investigation is required to calibrate the simulator and produce more accurate results over a variety of distances. However, the simulator does show quite how sensitive the selection of appropriate level of effort is to the final race time for the 1000m

Tip gap noise mechanisms in ducted marine propellers due to unsteady flow features

Ducted propellers exist in both aerodynamic and hydrodynamic contexts, and the former has received significantly more attention than the latter. This thesis is aimed at identifying the key noise mechanisms in marine ducted propellers. The properties of the fluid media have a significant impact on the relative importance of noise producing flow features and the differences in likely noise sources for aerodynamic and hydrodynamic propellers are discussed. This thesis uses time-resolved simulations to investigate the unsteady flow features in the tip gap region of a ducted propeller. By inferring the important noise mechanisms it is possible to identify specific criteria which can be used to produce noise mitigating designs. A variety of simplified geometries have been investigated beginning with an open tipped foil to provide a base line case. The complexity of the case is progressively increased to investigate the impact of the tip gap height, the inclusion of a no slip condition on the boundary surface above the tip, and the impact of foil thickness and camber. The numerical simulations have been carried out using an open source computational fluid dynamics software with both time-averaged, and time-resolved simulations conducted. Post processing techniques such as vortex identification criteria and an acoustic analogy have been used to infer the primary noise sources in the tip gap region. Non-dimensional quantities have been used to investigate the flow features and have shown good agreement with previous numerical and experimental work. The studies found that the most likely cause of noise within the tip gap region is due to the unsteady flow structures being shed through the tip gap and scattered over the sharp edge of the tip. The size and strength of these structures is highly dependent on the tip gap size, and explains why reduced tip gaps are associated with reduced rotor tip noise. The vortex structures are shown to be an accurate indicator of the hydrodynamic surface pressure variations leading to a more intuitive metric to use for improved designs. A simple design modification is made to the blade with the aim of removing the vortex structures within the tip gap region in order to reduce the strength of the unsteady pressure fluctuations. This improved design reduced the surface pressure spectra by greater than 30dB at certain, key frequencies

Investigation into the tip-gap flow and its Influence on ducted propeller tip-gap noise using acoustic analogies

Ducted propellers are commonly used on naval vesselssuch as submarines as well as increasingly moreomnipresent autonomous underwater vehicles (AUVs).Understanding the noise signature of these vessels is ofcritical importance both from detection and concealmentperspective, but the detailed physics of how the tip of thepropeller blade interacts with the boundary layer on theduct are not sufficiently well understood. Present studyintroduces a series of simulations in which tip vorticesformed over finite-span lifting surfaces are investigatedwith the aim of better understanding interactions oftip-gap flow and its interaction with incident boundarylayers on radiated noise. Particular attention is devotedto characterising the nature of the incipient complex flowfeatures and their effect on the force coefficients, surfacepressure fluctuations. These reveal that variations offorce coefficients with tip-gap height may be used asan early indicator of tip vortex being suppressed as thegap is reduced. Use of the λ2criterion identifies theformation of strong, coherent vortical structures in the tipgap region. It is suggested that the interaction of thesestructures with the tip edges is likely to be in importantsource of noise, with a similar generation mechanism totrailing edge noise. Preliminary analysis of the acousticsignatures computed using Ffowcs Williams-Hawkingsacoustic analogy indicates high levels of directivity withmajority of the noise being generated by the foil ratherthan the duct. Presence of substantial amounts ofvorticity in the flow also suggests that accounting forthe non-linear quadrupole noise sources within the fluidmight be necessary to fully describe the noise pattern develope