Effect of boundary layer on thrust deduction
Abstract
It is noted that methods of computing thrust deduction usually ignore viscous effects and assume that the flow field of the ship and propeller is irrotational. The computed values of the thrust deduction with and without the boundary layer and wake were compared. A streamlined body of revolution was selected, and a sink on the axis behind the body was used as a simple mechanism to simulate the suction at the stern induced by a propeller. When the boundary layer and wake are present, the thick boundary near the tail of the body is first calculated by a previously developed method in which the equation of a thick boundary layer and wake are solved numerically by finite differences, and the outer irrotational flow is obtained as the solution of an integral equation. An iteration procedure in which the inner and outer flows are successively adjusted converges to the desired solution. It was found that results obtained in the wake were not sufficiently accurate, so that a momentum analysis using a special control volume was used to calculate the viscous drag with and without the sink. The calculated values of the thrust deuction are C sub D = 0.00021 from irrotational flow and 0.00043 from the boundary layer potentialflow interaction method.
 Publication:

Iowa University Progress Report
 Pub Date:
 November 1981
 Bibcode:
 1981iowa.rept.....D
 Keywords:

 Boundary Layers;
 Flow Distribution;
 Ships;
 Thrust;
 Viscous Drag;
 Flow Resistance;
 Mathematical Models;
 Potential Flow;
 Propellers;
 Ship Hulls;
 Fluid Mechanics and Heat Transfer