DESIGN OF NOZZLE PROPELLERS

The report presents a procedure for selecting the major design parameters of a nozzle propeller such that the unit will operate with maximum efficiency. Application of momentum theory leads to the optimum configuration of a nozzle propeller: guidevanes for axial exit and minimum kinetic losses, constant circulation in stator and rotor for maximum energy transfer. An evaluation of the efficiency of a nozzle propeller, taking into account both kinetic and frictional losses, results in diagrams which enable the designer to select optimum combinations of propeller diameter and rpm for maximum efficiency or, alternately, to predict the decrease in efficiency caused by the choice of non-optimum combinations of propeller diameter and rpm. Both accelerating and decelerating nozzle propellers have been considered. Comparison of the theoretical results with empirical data shows excellent agreement. The report presents further methods of computing, for a given set of design parameters, the nozzle contour as well as the flow pattern inside the nozzle taking in account the presence of a hub. (Author)