Stern propeller interaction with a streamline body of revolution

Article type: Research Article

Authors: Korvin-Kroukovsky, B.V.

Abstract: The present paper is the second of a series dealing with the calculation of the wake fraction and thrust deduction behind a body having a stern propeller. It is divided into two parts. In Part I the derivation of expressions for the fluid velocities in the propeller inflow are given together with tables and curves of the velocities computed from these expressions. In Part II, the potential flow about the stern of a streamline body of revolution (U.S. Airship Akron) is determined by means of a source-sink distribution, and the resultant surface pressures are compared with published experimental data. A hypothetical propeller installation is then specified, and the effect of the propeller inflow on the sink distribution, and the resultant propeller wake fraction and thrust deduction are computed using calculated data for the potential flow, and using published boundary-layer data for the frictional part of the wake fraction. The “nominal” and “effective” wake fractions are compared partly quantitatively and partly qualitatively. The effect of the propeller inflow on the sink distribution representing the body and on the potential wake fraction induced by this distribution is shown to be negligible. The predominating items of difference between the nominal and potential wake fractions appear to stem from the errors inherent in conventional computational and experimental practices, and in the case of an axisymmetric body, these can easily be accounted for. The signs of these errors are such as to cause good correlation between the values of the two wake fractions and to make both of them somewhat lower than the true wake fraction. The potential wake fraction is found to be 13%, the total wake fraction 28%, and the thrust deduction coefficient 17%. Trial computations made with assumed resistances of 50% and 150% of the normal model resistance, and with the boundary-layer thickness correspondingly adjusted, indicate that the thrust deduction is sensibly independent of resistance and of boundary-layer thickness. It is demonstrated that, by far, the largest part of the thrust deduction comes from parts of the hull in close proximity to the propeller. For instance, about 75% of the thrust deduction is found to be generated within a radius equal to less than three propeller radii from the propeller center. The present report, dealing with axisymmetric flow, is considered as an introduction to the subsequent work which will deal with the propeller of a normal ship (Victory), including the broader aspects of circumferential nonuniformity of thrust distribution. The study was conducted at the Experimental Towing Tank, Stevens Institute of Technology, under Office of Naval Research Contract No. N6onr-24705, sponsored by the Bureau of Ships under Project No. NS715-102, and technically administered by the Director, David Taylor Model Basin.

DOI: 10.3233/ISP-1956-31701

Journal: International Shipbuilding Progress, vol. 3, no. 17, pp. 3-24, 1956