•A self-sustained oscillating cavitation pocket developing along a Venturi is computed and compared with experimental results.•One fluid compressible RANS simulations are performed based on a void ratio transport equation model.•The importance of traveling pressure waves in the physical mechanism is put in evidence.•The importance of considering a non-equilibrium state for the vapour phase is exhibited. Unsteady partial cavitation is mainly formed by an attached cavity which presents periodic oscillations. Under certain conditions, instabilities are characterized by the formation of vapour clouds convected downstream the cavity and collapsing in higher pressure region. Two main mechanisms have been identified for the break-off cycles. The development of a liquid re-entrant jet is the most common type of instabilities, but more recently, the role of pressure waves created by the cloud collapses has been highlighted. This paper presents one-fluid compressible simulations of a self-sustained oscillating cavitation pocket developing along a Venturi geometry. The mass transfer between phases is driven by a void ratio transport equation model. The importance of traveling pressure waves in the physical mechanism is put in evidence. Moreover, the importance of considering a non-equilibrium state for the vapour phase is exhibited.