Abstract
Propeller pumps with small numbers of blades are usually designed by applying airfoil-strip theory using the tabulated properties of airfoils in a linear flow field of infinite extent. The velocity at each radius is taken as the relative velocity obtained by vector combination of the tangential velocity, the axial velocity, and the induced velocity at the mid-chord of the blade. For few blades the induced velocity at a blade resulting from the presence of other blades usually is ignored. Since the facilities and techniques at the authors’ disposal make it relatively easy to obtain pressure distributions on the moving elements of hydraulic machinery, a comparison was made between the calculated and measured pressure loading on a single-bladed axial-flow impeller. The results show that the design method used, which differs only in a minor way from the usual method given in the technical literature, gives a close approach to the actual loading at the design point. The experimental data are presented in sufficient quantity to show how the blade loading varies with flow rate over the whole of the blade and that the free-vortex condition is fairly well achieved in the neighborhood of the design point. Generally, it is concluded that the airfoil theory can give a close approximation to the performance and loading of a blade of a propeller pump in spite of the considerable departure from the ideal conditions for which it was developed.
