The preliminary design of axial pumps and turbines based on analytical solutions of the flow field

This paper is the conclusive step of an authors’ research on the inverse methods (Navarro, 1992, Navarro and Masi 1997). It provides a method for the preliminary design of axial turbomachines operating with incompressible fluids. The method gives the turbomachine geometry which agrees with the desired parameters of global performance, namely specific work, flow rate and rotating speed. The initial assumption are the volume and hydraulic efficiency and the blades number. The process is completely two-dimensional. It is composed of the sequential modelling of the meridian plane and an arbitrary number of cylindrical surfaces of the blade passages. Therefore it is not a technique of design optimisation, but its aim is to overcome the classic one-dimensional Euler theory of turbomachinery, which is still the fundamental instrument for preliminary design. The article starts introducing the hypothesis, which allow the potential models of the meridian and cascade surfaces for axial pumps and hydraulic turbines. The meridian and the blade to blade flow fields obtained by the models are discussed. Then the dependencies are solved between the fluid-dynamics design parameters and the analytical variables of the two models. Finally, as example, the paper shows the preliminary design of the rotor and the casing of a pump and a turbine.