Unsteady numerical simulations were carried out over two different configurations: first, in venturi geometry and then, in a blade cascade of an aircraft inducer. Cavitating flow in the venturi exhibited the instability due to detachment of cavitation sheet in a static geometry. For this case, it was necessary to modify the turbulence model in order to allow the formation of a re-entrant jet at cavitation closure, which causes the cavitation detachment followed by the convection of vapour sheet in main flow, and its disappearance downstream. Cavitating flow in the two-blade inducer, for various sigma values and flowrates, predicted three types of cavitation behaviour on the blade cascade: (a) stable behaviour with symmetrical cavitation length; (b) stable behaviour with non-symmetrical cavitation length; (c) cyclical unstable behaviour with non-symmetrical cavitation length. Cavitation length behaviour was symmetrical and stable for a high flowrate of Q = 0.97 Q_nom. Alternate blade cavitation was observed for lower flowrates, when the l/h ratio was higher than about 65 per cent. Finally, the rotating cavitation was observed only for a partial flowrate of Q = 0.56_nom, where the calculations were carried out using RNG kappa-epsilon model and RNG kappa-epsilon modified model. Numerical results showed three different mechanisms of cavitation instabilities. 1. Self-oscillation of the cavitation sheet owing to the interaction between the recirculation flow and the cavity surface in the venturi geometry. 2. Rotating cavitation owing to the interaction of the sheet cavitation in a blade with the leading edge of the neighbour blade in blade cascade. 3. Coupling of the rotating cavitation and the self-oscillating of the cavitation sheet in blade cascade. The results showed unstable cavitation lengths with similar behaviours as in results presented in references for cavitating flow in four-blade inducer using different physical model and numerical codes based on different computational methods.