Design and Analysis of High Speed Pumps

摘要

The motivation for this course is the worldwide growing interest in space propulsion and the increased use of more compact and lighter pumps in industrial applications. This search has led to an increased rotational speed up to the point where cavitation and rotordynamics become a major issue. The purpose of present lectures is to provide an overview of the present understanding about those phenomena and to discuss other aspects that are of major importance for advanced high speed pumps.nThe main consequences of cavitation are performance breakdown and hydraulic instabilities. Experiments on simplified models are described, revealing the origin of cavitation, the different forms under which it appears and the influence of thermal effects and nuclei content on its development. These findings are supported by overall performance measurements, unsteady pressure- and optical measurements in real rotating components. Numerical simulations on 2D models have been used to reveal the influence of numerical and physical parameters. First applications to high-speed rocket pump cavitation prediction are presented.nThe increased power density and the search for lighter pumps enhance also the risk for rotordynamic problems in which seals and bearings play a critical role. The flow mechanisms in the different types of fluid film bearings and seals are presented, emphasizing that the stability criteria for constant density fluids are considerably different from the ones for compressible gasses. A better understanding of them for hydrostatic and hydrodynamic bearings has resulted in an improved reliability and an extension of the field of applications, not only for cryogenic turbopumps but also for various oil free applications.nFlow instabilities such as rotating stall, surge, rotating cavitation and cavitation surge are discussed and compared with one- and two dimensional stability analyses. The lectures focus on the cause and characteristics of those instabilities with special attention to cavitation instabilities in inducers. They are illustrated by experimental results.nInlet distortion and impeller volute interaction may be an important source of mechanical excitation for impeller and shaft when operating at off design conditions. Both loss mechanisms and unsteady forces are better understood thanks to a more accurate modeling by means of Computational Fluid Dynamics (CFD).nA better physical description of the cavitation phenomena and the extension of the numerical cavitation models to 3D flow are challenging targets for the coming years.