Experimental characterization and modelling of a cavitating centrifugal pump operating in fast start-up conditions

Sébastien Duplaa (1) , Olivier Coutier-Delgosha (1) , Antoine Dazin (1) , Gérard Bois (1) , Guy Caignaert (1)

1 LML - Laboratoire de Mécanique de Lille - FRE 3723

The start-up of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behavior is reached. The pump transient behaviour induces significant pressure fluctuations which may result in partial flow vaporization, i.e. cavitation. An existing experimental test rig has been updated in the LML laboratory (Lille, France) for the start-ups of a centrifugal pump. The study focuses on cavitation induced during the pump start-up. Instantaneous measurement of torque, flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behaviour during rapid starting periods. Three different types of fast start-up behaviours have been identified and have been presented at ISROMAC 12 (Duplaa et al, 2008). According to the final operating point, the start-up is characterized either by a single drop of the delivery static pressure, by several low-frequency drops, or by a water hammer phenomenon that can be observed both a the inlet and outlet of the pump. A physical analysis to explain these three different types of transient flow behaviour has been recently proposed (Duplaa et al, 2010). In the present paper, a modelling of the fast start ups in cavitating conditions is proposed. It consists of a two steps adaptation of fast start-up model in non cavitating conditions proposed by Dazin et al (2007). For that, fast X-rays imaging has been performed in the impeller with the collaboration of the French Atomic Agency (CEA) in order to determinate the high frequency evolution of the volume fraction during fast the start-ups. Although the results of the modelling presented here are not definitive, they are very promising.

Mots clés: Turbomachinery; Cavitation; Transient; Modeling

Domaines: Milieux fluides et réactifs

Sébastien Duplaa, Olivier Coutier-Delgosha, Antoine Dazin, Gérard Bois, Guy Caignaert. Experimental characterization and modelling of a cavitating centrifugal pump operating in fast start-up conditions. 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery - ISROMAC-13, Apr 2010, Honolulu-Hawaii, United States. pp. 22-29. ⟨hal-00904965⟩