Calculation of unsteady attached cavitation

Under certain conditions, the flow of a liquid around an obstacle, e.g. a hydrofoil, can cause an attached sheet of vapor, so-called sheet cavitation. The simulation of such an unsteady vapor sheet has been explored using an interface-capturing technique. For this technique the flow of a hypothetical mixture, part liquid, part vapor, is considered. In this flow the relation between density and pressure is specified through an equation of state, which has been chosen such that it gives an approximation of the actual physics of cavitation, i.e. that the density of the mixture equals the density of the liquid in non-cavitating flow regions, and the density of the vapor in cavitating flow regions. The major part of the flow field will be non-cavitating and have constant density. In this part of the flow field the artificial-compressibility technique is used to compute the flow. This technique is extended to allow the calculation of the flow in the vapor region. The computational method based on this mathematical model of cavitating flows can simulate the flow around two-dimensional airfoils. Results show that the method can reliably simulate incompressible, steady and unsteady flow and the initial growth phase of attached sheet cavitation.