Experimental Characterization of Unsteady Forces Triggered by Cavitation on a Centrifugal Pump †

The paper presents an experimental campaign aimed at the characterization of the relationship between cavitation-induced instabilities and forces acting on the shaft, relevant to space application turbopumps. The experiments have been carried out on a six-bladed unshrouded centrifugal turbopump. Pressure fluctuations are analyzed in their frequency content for understanding the instability nature (axial, rotating) and their main characteristics (e.g., amplitude, rotating direction). The spectral analysis of the force components highlights a strong relationship of the z-component (along the rotating axis) with axial instabilities. On the other hand, rotating cavitation may involve force oscillations along all the three components leading to unwanted and dangerous fluctuating unbalances perpendicular to the rotating axis.