A stereo PIV measurement of a model ship wake in a towing tank with uncertainty assessment
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Abstract
Detailed information of the flow around a ship is essential for designing the hull because it is related to the propeller performance, maneuverability, and vibration. Thus, lots of experimental and computational researches have been executed to measure or analyze the stern flow of vessels. In this paper, the newly installed underwater SPIV system in Seoul National University Towing Tank is introduced with its measurement results and estimated uncertainty. The SPIV system was installed on the towing carriage which runs along side rails of the towing tank. With the underwater SPIV system, the uniform flow, made by running the towing carriage without a model, was firstly measured to investigate the uncertainty assessment. Uniform flow measurement results for each direction of the coordinate system were analyzed to estimate the random error and systematic error, following the ASME test uncertainty. The reference speed for the longitudinal and transverse uniform flow measurement was set to 1.0m/s and 1.5m/s, which is general towing speed range of model ships in the towing tank. In the uniform flow measurement results, the systematic error, the difference of ensemble-averaged speed and reference speed from the encoder of the towing carriage, was below 1.5% of the towing speed and the random error, derived from the standard deviation of the ensemble-averaged speed, was 4% of the reference speed. After the uncertainty assessment, the nominal wake, the flow on the propeller location with absence of the propeller, was measured and results were compared with experiment results with 5-holes Pitot tube from other towing tank. The model ship was KVLCC2, of which hull design and dimension are open to public. The scale of the model ship was 1/100, and the Froude number was 0.142 in the design speed. SPIV results showed good agreement with existing results and have advantages such as depiction of turbulence properties and reduction of the experiment-operating time.