Whole-Hutchison-thesis.pdf (4.15 MB)
The use of hot-films to characterise flow regimes on a sailing yacht hull-guidance for scaling
thesisposted on 2023-05-27, 13:00 authored by Hutchison, C
Within the yacht testing community there has been a continuing interest in and concern with, the effectiveness of techniques used to extrapolate model scale resis- tance tests to full scale values. While there are many aspects which influence the effectiveness of scaling results from model yacht experiments; this thesis has inves- tigated the use of hot-films to characterise boundary layer state so as to provide guidance in selection of model scale. A primary focus of this thesis was to ensure the method selected to characterise the boundary layer was suitable for commercial testing programs. The methodology included a robust technique for the installation and application of glue-on hot-film sensors and a modified data analysis method. The hull form used for this research was based on an International America's Cup Class yacht. The hull type has several features desirable in researching yacht hy- drodynamics including; non-immersed transom, minimal distortion to the hull lines and high aspect ratio foils. From data obtained from the hot-film sensors a series of conclusions were made. With turbulence stimulation, the on body flow was found to be fully turbulent for all Froude numbers tested (0.05 to 0.46). This implies that with appropriate boundary layer stimulation, the state of the boundary layer is not a limiting factor in the testing of a 1/8th scale IACC yacht model. The hot-film data also showed that the change in Cf due to waves generated by the hull were half that of the change due to natural transition. The lower limits of applicability of the Grigson flat plate friction line were also examined using this experimental data. For the 1/8th scale model tested these limits lie at a model ReL = 2:6 _ 106 (Froude num- ber of 0.27) as opposed to that reported in his paper as ReL = 1:5 _ 106 (Froude number of 0.15). In general it was concluded that if a yacht hull-form is slender with fair lines and no immersed transom and testing is at model speeds above 1.28 m/s (Froude number of 0.27) then it is possible to use a simple analytical approach to decide the correct model scale. If there is concern that there might be an issue with transition be- haviour it has been shown that it is possible and relatively simple to use hot-films to verify the boundary layer state.
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