The CFD assisted design and experimental testing of a wing-sail with high lift devices
A wingsail is a solid symmetrical aerofoil section which creates thrust in the same manner as a conventional sail. Wingsails may either be used as a sole power unit, e. g. for a yacht or catamaran, or as an auxiliary power unit on a larger craft, e. g. fishing vessels, cargo ships or passenger liners. To augment the thrust created by the wingsail, high lift devices are employed to increase both the maximum lift and the stall incidence of the aerofoil. A wingsail must be symmetrical and capable of creating an equal lift force with the flow approaching the leading edge from either side of the wing centreline, i. e. the wingsail surface must act as either the upper, or lower pressure surface. Initial experimental work proved that using a symmetrical slat as a leading edge high lift device both delayed the separation of flow over the wingsail upper surface and increased the effective camber of the aerofoil. To increase the thrust created still further, this leading edge high lift device was combined with a trailing edge high lift device, a symmetrical single slotted flap. Due to the large number of possible model configurations, a commercially available CFD package was introduced to assist with the design. A series of validation tests comparing the CFD with published and experimental results showed a qualitative agreement with these results. However, the CFD predictions were not sufficiently accurate to be used quantitatively. The computationally designed triple element model was tested experimentally. Lift, drag, pitching moment and pressure distribution measurements were taken from the model. The results of this testing showed that the triple element wingsail increased the plain wing Coax by 68% and the stall incidence by between 4* and 6'. The final triple element wingsail design also increased the thrust of a plain wingsail over the whole operating region. Thrust was increased by up to 83% at the wind angles where a wingsail is most efficient. The results also proved that a commercially available CFD package can be used as an effective and time saving tool for wingsail design.