Experiments of an inducer with symmetric slits were conducted. The purpose of the study is to explore the suppression effect on cavitation instabilities by slits. The slits are located in a throat position in each blade and it means symmetric slits. The experiments are done through measuring pressure fluctuation in the flow field and shaft displacement and visualization using high speed camera. In this study, the head performance, the suction performance, the cavity length and the occurrence range and the strength of the cavitation instabilities are compared with the results of inducer without slit. As a result, the slit in throat position does not give bad effect on head performance, improves suction performance, and has a relation to suppression of oscillation of cavitation instabilities because of the suppression effect of cavity length, although the occurrence range of super-synchronous rotating cavitation unfortunately increases because the cavity develops slowly.
The phenomenon that a cavity rotates faster than the rotational speed of the pump in the direction of rotation is called super-synchronous rotating cavitation (super-S RC). It is known that super-S RC is often observed in rocket turbopumps, but that it is rare to be observed in industrial pumps. Therefore, we form a hypothesis that its occurrence is related to the rotational speed of pumps. In this study, experiments of an inducer were conducted at four rotational speed at Kakuda Space Center in the Japan Aerospace Exploration Agency. The pressure fluctuation and the rotor vibration were measured, and the propagation velocity ratio of super-S RC and the frequency of unsteady cavitation in the super–S RC were determined at each rotational speed. As a result, when the cavitation number is the same, the propagation velocity ratio is almost the same regardless of the rotational speed of the inducer. It means that the faster the rotational speed, the faster the unsteady cavitation oscillates in the inducer despite the condition of the same cavitation number. It indicates that rotating cavitation does not occur under a certain rotational speed because of the limitation of the frequency of unsteady cavitation, which is known in hydrofoil.
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