The vortex lattice method is applied to calculations of the aerodynamic characteristics of propellers. A blade of the propeller is divided into many trapezoidal panels, and each panel is represented by a spiral horse shoe vortex in which a bound vortex is placed on the 1/4chord line of the panel, and a pair of wake vortices is emitted from the both ends of the bound vortex. The circulation strength of these vortices can be obtained by the boundary conditions which describe the tangency condition of the flow at 3/4-chord point. The forces acting on each panel are calculated by KUTTA-JOUKOWSKI theorem. Thrust, torque and efficiency of the propeller are obtained by summing up all forces. Although the flow is assumed to be inviscid and incompressible, the effect of displacement velocity, the effect of compressibility by PRANDTLGLAUERT similarity rule and the effect of drag force introduced into the force calculations using experimental data are examined. Furthermore, utilizing the efficiency of each panel, total efficiency of propeller is improved by increasing or decreasing pitch angle of the blade. The following results are derived by these calculations. (1) The power coefficients agree well with the experimental values for the conventional type of propeller, however, for ATP theoretical values are larger than experimental results. (2) The efficiencies are larger than the experimental values for all types of propeller. Including the drag forces into calculations, theoretical values for the conventional type of propeller agree well with the experimental values, but are still larger for ATP. (3) For the reason of disagreement described in (1) and (2), it can be considered that the inflow to the blade is inclined by nacelle. (4) In middle subsonic range, the power coefficients increase, and the efficiencies decrease by application of PRANDTLGLAUERT similarity rule. (5) Varying pitch angle distribution along the spanwise direction, the section efficiency increases with reduction of the pitch angle and vice versa.
This paper describes an experimental study of the flow past blunt obstacle placed on a plane boundary. The experiment was carried out in an N.P.L. blow-down type wind-tunnel having a working section of 400mm×400mm×2, 000mm in size at the REYNOLDS number 4.74×104. The surface-pressure distributions on a sphere, hemisphere cylinder and circular cylinder were measured and the drag and lift coefficients were determined by integration of the surface pressure. The vortices generated in the flow-field around an obstacle have also been observed. Since a hemisphere cylinder is seen to be a hybrid of a sphere and a circular cylinder, the results for hemisphere-cylinder were compared with those for a sphere and a circular cylinder.