Experience with Hot-Film Anemometry for Ship Model Nominal Wake Survey in a Towing Tank

Problems with the calibration and operation of hot-film anemometers in water have prevented their widespread application for towing tank measurements. The potential advantages of their use, in terms of their accuracy compared with pitot tubes and their low coot compared with laser-doppler anemometry, have yet to be fully exploited. Calibration experiments with several hot-film probes were done in a towing tank to investigate their characteristics. After an initial 'burn in' period of about 100 hours of operation, their calibration was found to be stable and repeatable, although it varied with the ambient water temperature. Nominal wake survey experiments were conducted be hind a model of a Newfoundland fishing vessel form by using a wedge-shaped single sensor hot-film probe and a dual sensor vee hot-film probe respectively. The model was towed at a speed of l.45m/s, which corresponded to a Froude number of 0.33 and full scale vessel speed of 6.4 knots. Levels of turbulence as well as mean velocity values in the wake were obtained. A comparison is made between sample results obtained by the use of the two different probes.