• calibrazione
• cavitazione
• dinamometro
• rotodinamica
• turbopompe

Cavitation and rotordynamic instabilities are two relevant phenomena in space engine turbopumps, and the related mechanisms are still lacking sufficiently accurate models. Experimentation and tests therefore do play a fundamental role. In the past few years, Centrospazio research laboratory in Pisa, Italy, has undertaken the design and construction of a test facility for carrying out experiments on turbopump impellers under fluid dynamic and inertial/thermal cavitation similarities, using water as the working fluid. Most recently, the facility has been upgraded to allow for measurement of steady and unsteady forces exerted by the fluid on inducers and pumps both under non cavitating and cavitating conditions.
Purpose of the present work is that of detailing the author’s activities undertaken to field the instrument for the measurement of loads, the extensimeter scale christened rotating dynamometer.
The first part provides a brief summary of the present theoretical and experimental knowledge on cavitation and rotordynamic instabilities, showing also the recent related test activities performed by Centrospazio and other research institutes.
Then the specifications and layout of the CPRTF (Cavitating Pump Rotordynamic Test Facility) and its components are described, with particular emphasis on the rotating dynamometer. The calibration, i.e. the building of the linear correspondence between the measured signals and the applied load, is thoroughly illustrated. The numerical reduction to extract the applied forces and moments is then shown, both for a reference frame fixed w.r.t. the dynamometer and one fixed w.r.t. the laboratory.
Finally, a numerical model for the prediction of axial natural flow oscillation in the test circuit is illustrated, and the good correlation with test data is then shown.