A Reduced Order Model for Preliminary Design and Performance Prediction of Radial Turbopumps

摘要

A reduced order model for preliminary design and noncavitating performance prediction of radial turbopumps is illustrated. The model expresses the 3D incompressible, inviscid. irrotational flow through helical blades with slow axial variations of the pitch and backsweep by superposing a 2D cross-sectional axial vorticity correction to a fully-guided flow with axisymmetric stagnation velocity in the meridional plane. Application of the relevant governing equations yields a set of constraints for the axial evolution of the blade pitch and backsweep that allows for the closed form definition of the impeller geometry and fiowfield in terms of a reduced number of controlling parameters. In turn, mass and momentum conservation are used to account for the mixing of the flow leaving the impeller and its coupling with 2D reduced order models of the flow in the diffuser (if any) and the volute, thus generating the information necessary for completing the geometric definition of the machine and for determining its ideal noncavitating performance in accordance with the resulting fiowfield. Preliminary validation of the present model shows that, as a consequence of the neglect of viscous effects, the resulting dependence of the slip factors on the flow coefficient of the machine exceeds those obtained from theoretical/semi-empirical formulas reported in literature for centrifugal pumps, but correctly capture their trend. Inclusion of flow losses and experimental validation of the model are under way at Alta S.p.A..