The present work is an experimental and theoretical investigation of the possible forces of fluid dynamic origin that can act on a turbomachine rotor particularly when it is situated off its normal center position. An experimental facility, the Rotor Force Test Facility, has been designed and constructed in order to measure these kinds of forces acting on a centrifugal pump impeller when the latter is made to whirl in a slightly eccentric circular orbit. The rotor speed, eccentric orbital radii and whirl speed could be varied independently. The scope of the present experimental work consists of measuring quasi-steady forces on the impeller as it whirls slowly about the axis of the pump rotation. These forces are due to interaction between the impeller and volute; they are decomposed into force components relative to the geometric center of the volute and to those proportional to displacement from this center. These latter are interpreted as stiffness matrices. These matrices were measured on two widely differing volute types and both were found to have the property of being skew-symmetric. It can be shown that a stiffness matrix of this type can lead to dynamic instability of the impeller shaft system in certain circumstances. This new experimental finding may explain some operational problems of "high speed" hydraulic machinery.
In the theoretical part of this thesis, a somewhat more physical model of a rotor pump is proposed other than has been used heretofore in most works namely an actuator disk having infinitely many blades. As a simplification it is assumed that the flow field is irrotational. Forces and stiffness matrices are calculated on this basis but the stiffness matrix so found does not reveal the skew-symmetric property of the experiments.
