模型船後流乱れとプロペラへの影響

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The unsteady phenomena of the flow around the hull of ships have begun to come into question as their forms become fuller and fuller. For example, we know unstable phenomenon in the self-propulsion test of full ship models discovered by Watanabe, the problem about remarkably great irregular vibrating propeller forces, unsteady propeller cavitation problem and so forth. These phenomena are likely to be related to the turbulence in the flow field of ships or model ones. Townsin and Boes pointed out that the turbulence in flow is not negligible in the field of ship hydrodynamics. The authors attempted in the present work to obtain empirical informations about the turbulence in the wake of a model ship at first and, next, to estimate its influence on unsteady propeller forces. The measurement of velocity of the flow behind the model ship of a full form was carried out in the towing tank. The three dimensional components of velocity were measured employing 5-hole Pitot tube device, whose pressure output was detected by the electronic pressure transducer responsive to rapid change of pressure. The analyzed results have shown that the intensity of the turbulent flow is more than 50% of mean velocity in the region of strong wake near the central vertical plane, and that the low frequency components below 10 Hz are powerful in the power spectra of the turbulence. The influence of the turbulence in the flow on a propeller forces was estimated applying the unsteady airfoil theory for the case that the tested model ship was equipped by a 5-bladed propeller. This estimation has revealed that the irregular noise part due to the turbulence in the flow occupies 80% of power of the total fluctuation of unsteady thrust and torque. The irregular variations of unsteady lift, thrust and torque were simulated by the computor, the results of which are similar to some experimental data mearsured by Kumai and others.
社団法人日本船舶海洋工学会の論文

模型船後流乱れとプロペラへの影響

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