Jakub Cichowicz

An experimental study of unsteady hydrodynamics of a single scull

The effect of hull dynamics on the hydrodynamic performance of a single scull is investigated via a combination of field trials and tank tests. The location of laminar-turbulent transition in unsteady flow is explored via several series of hot-film measurements on the bow of a full-scale single scull in unsteady flow in both towing tank and field-trial conditions. Results demonstrate that the measured real-world viscous-flow behaviour can be successfully reproduced in the tank using an oscillating sub-carriage to reproduce the surging motion measured in the field trials. It can be seen that there is a strong link between turbulence and acceleration; results show that the link is relatively insensitive to mean velocity, but that small changes in acceleration time-histories can have a marked effect, as can the presence of small waves. The impact of the location of laminar turbulent transition is investigated by way of a series of resistance tests, both with free transition and with transition forced by turbulence stimulation at two different locations. Results indicate that an aft movement of 200 mm of the location of transition can reduce resistance by almost 0.5 per cent. Unsteady tests using the oscillating sub-carriage indicate that unsteady effects add around 3 per cent to the total mean resistance with free transition.

Realistic evaluation of hull performance for rowing shells, canoes, and kayaks in unsteady flow.

Abstract In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic performance of rowing shells as well as canoes and kayaks. An approach was developed to generate data in a towing tank using a test rig capable of reproducing realistic speed profiles. The impact of unsteady shallow-water effects on wave-making resistance was examined via experimental measurements on a benchmark hull. The data generated were used to explore the validity of a computational approach developed to predict unsteady shallow-water wave resistance. Comparison of measured and predicted results showed that the computational approach correctly predicted complex unsteady wave-resistance phenomena at low oscillation frequency and speed, but that total resistance was substantially under-predicted at moderate oscillation frequency and speed. It was postulated that this discrepancy arose from unsteady viscous effects. This was investigated via hot-film measurements for a full-scale single scull in unsteady flow in both towing-tank and field-trial conditions. Results suggested a strong link between acceleration and turbulence and demonstrated that the measured real-world viscous-flow behaviour could be successfully reproduced in the tank. Thus a suitable tank-test approach could provide a reliable guide to hull performance characterization in unsteady flow.