^{1,a}, Uwe Iben

^{2}, Martin Güntner

^{3}and Rudolf Schilling

^{3}

^{1}Institute of Hydraulic Machinery, Ruhr-University Bochum, Universitätstr.150, D-44801 Bochum.

^{a}romuald.skoda@ruhr-uni-bochum.de

^{2}Robert Bosch GmbH, Corporate Research and Advance Engineering, Postfach 106050, D-70049 Stuttgart

^{3}Institute of Fluid Mechanics, Technische Universität München, Boltzmannstr. 15, D-85748 Garching

Since compressible methods are well suited for the prediction of cavitating flows [4], we successfully utilise explicit density-based solvers and evaluate the probability of cavitation erosion by a statistical analysis of the transient wall load [3]. However, the explicit method suffers from extremely high CPU times due to the numerical time step restriction (CFL condition), i.e. the ratio of the cell size and the speed of sound define the time step. Implicit methods do not have such a strict time step restriction. With respect to cavitation erosion, we aim at evaluating the potential of implicit pressure-based methods to save CPU time by systematically increasing the time step.

For a NACA0015 hydrofoil we increase the CFL number up to CFL = 2000. We find that the flow field as well as the wall load are only moderately effected by the increased time step size up to CFL = 200. For a plane micro channel flow that is a simplified model of Diesel injection systems, we consider the influence of the outlet pressure on cavitation erosion by a wall load analysis. The result is not significantly effected by an increase of CFL = 1 to CFL = 100.

As a conclusion, the increase of the time step size by two orders of magnitude does not change the prediction quality of the wall load significantly. Implicit methods have therefore generally the potential to minimize the CPU time for the prediction of cavitation erosion by a reduction of the number of time steps. In further research, the matrix operations must be optimised to reduce the CPU effort per time step, and we recommend focussing on implicit density-based schemes.