Computational Fluid Dynamics (CFD) is a very important tool for the study of complex fluidflows and the design of hydraulic fluid flow machinery. At the same time, experimentalanalysis is very difficult to perform. Thus, for a better understanding of the behaviour of suchcomplex flows, including turbulence, unsteadiness and cavitation, a suitable knowledge ofCFD is indispensable. Generally, the specific applications of CFD codes for solving this typeof engineering problems are not well documented and a previous work for the acquirement ofthe CFD code capabilities is necessary.This work presents numerical investigation concerning complex unsteady flows, includingturbulence and cavitation. The main objective was to acquire deeper knowledge about thesoftware potentials for solving this kind of flows. To reach this objective several cases havebeen studied with a commercial CFD code (Fluent v6.1). The turbulence models being usedwere mainly the Spalart-Allmaras, the Standard k-ε, and the k-ω model [1], [2], [3], [4]. Theutilized cavitation model was from Singhal, 2002 [5]. Based on long term considerations, thisinvestigation aims at the application of the acquired knowledge and experience for furtherinvestigations relative to the cavitation phenomena in real fluid flow machines.Several steps were necessary to understand the suitable simulation process of unsteadyturbulent cavitating flows. The case of an unsteady and turbulent, non-cavitating flow arounda 2D circular cylinder was studied as a first step using different turbulence models atReynolds numbers around the critical drag-crisis region. Compared with experimental data,the results are quite divergent, but similar numerical researches (J.S.Cox et al., 1997, [6],M.M.Zdravkovich, 1997, [7]) revealed comparable conclusions as does the present work.Mainly 3D effects are the cause of the non accuracy of the findings (e.g. P.D.Ditlevsen, 1996)[8].As a second step, the cavitation phenomena has been studied in several applications. First,the full cavitation model implemented in Fluent (Singhal, 2002) has been tested comparingfindings with corresponding experimental data. The first case was a steady, cavitating flowthrough a sharp-edged orifice by Nurick, 1976 [9]. Further, the unsteady turbulent flow arounda 2D NACA 0015 hydrofoil has been simulated using the cavitation model. This work wasbased on the publications by Kubota, 1992 [10] and Berntsen et al., 2001 [11]. Resultsrevealed that depending on the case, the cavitation model offers useful results, but only in aqualitative way. Accurate fittings with experiments are obtained only in few cases. Thetheoretical validity of the present cavitation model could be questioned. Future work consistsof the prediction of damage caused by cavitation (comparing numerical results withexperimental databases e.g. Escaler, 2001) using adequate software tools. The final goal isto apply the knowledge obtained to damage prediction in turbomachinery.