NUMERICAL INVESTIGATION OF CAVITATING FLOW

Two main types of cavitation can be observed in hydraulic machinery: S heet cavitation which consists of a vapour region adjacent to the body surface and cloud cavitation formed by small cavitation bubbles. The different physical properties of these two cavitation types are treate d by two individual models. The investigation of sheet cavitation conc entrates on. the direct numerical simulation of the vapor/liquid inter face. Working with overlapping grids a Chimera grid scheme is applied to describe the geometry of the vapor sheet. The incompressible flow f ield is determined by a two-dimensional Navier-Stokes code in combinat ion with the turbulence model of Baldwin-Lomax. The cloud cavitation m odel is based on an averaged two-phase model: In a macroscopic view th e fluid is assumed to be viscous and compressible characterized by the volume averaged void fraction. At the microscopic scale clusters of s mall spherical cavitation bubbles are considered. The two models for s heet and cloud cavitation are applied lo cavitating pour in convergent -divergent channels and around NACA hydrofoils and the results are com pared with experiments.