6. Three-dimensional flow and numerical simulation

Quasi-three-dimensional modelling is still practised today at the machine pre-sizing stage; however, the advent of very powerful numerical codes and the associated computing resources is rapidly changing habits and providing invaluable and hitherto unsuspected information on the physics of internal flows. Many phenomena of three-dimensional origin and nature are now taken into account: the influence of operating clearances, various geometric imperfections, fully unstuck operation (partial flow), compression of complex fluids and in particular two-phase liquid-gas mixtures, operation in cavitating conditions, kinematic inlet distortions, calculation of pressure fluctuations linked to unsteady phenomena (rotor-stator interaction), etc.