We analyse unsteady cavity dynamics, cavitation patterns and instability mechanisms governing partial cavitation in the flow past a sharp convergent–divergent wedge. Reproducing a recent reference experiment by numerical simulation, the investigated flow regime is characterised by large-scale cloud cavitation. In agreement with the experiments, we find that cloud shedding is dominated by the periodic occurrence of condensation shocks, propagating through the two-phase medium. The physical model is based on the homogeneous mixture approach, the assumption of thermodynamic equilibrium, and a closed-form barotropic equation of state. Compressibility of water and water vapour is taken into account. We deliberately suppress effects of molecular viscosity, in order to demonstrate that inertial effects dominate the flow evolution. We qualify the flow predictions, and validate the numerical approach by comparison with experiments. In agreement with the experiments, the vapour volume fraction within the partial cavity reaches values${>}80\,\%$for its spanwise average. Very good agreement is further obtained for the shedding Strouhal number, the cavity growth and collapse velocities, and for typical coherent flow structures. In accordance with the experiments, the simulations reproduce a condensation shock forming at the trailing part of the partial cavity. It is demonstrated that it satisfies locally Rankine–Hugoniot jump relations. Estimation of the shock propagation Mach number shows that the flow is supersonic. With a magnitude of only a few kPa, the pressure rise across the shock is much lower than for typical cavity collapse events. It is thus far too weak to cause cavitation erosion directly. However, by affecting the dynamics of the cavity, the flow aggressiveness can be significantly altered. Our results indicate that, in addition to classically observed re-entrant jets, condensation shocks feed an intrinsic instability mechanism of partial cavitation.

A fully compressible numerical approach, combined with a homogeneous mixture model is applied to the simulation of the cavitating flow around the model propeller VP1304. The formally inviscid approach resolves the coupled behavior of phase transition and wave dynamics. It thus captures collapse-induced instantaneous pressure loads and associated shock wave dynamics and allows for an assessment of material erosion. Our contribution focuses on a validation of the chosen approach with experimental and numerical investigations conducted in the frame of the Potsdam Propeller Test Case 2011. The obtained results show good agreement for the computed propeller efficiency, blade pressure distribution and observed cavitation pattern. A mesh alignment technique improves the accuracy of the propeller wake structure and enables the prediction of a cavitating trailing tip vortex. The investigations show that cavity dynamics cause instantaneous surface loads, originating from a periodic shedding of the suction side root cavity. Furthermore, stochastic collapse events lead to broad band noise. An investigation of the maximum pressure allows for a qualitative assessment of erosion risk.

Our contribution focuses on the evaluation of cavitation aggressiveness on the cavitating model propeller VP1304 by numerical simulation. To this respect, we employ a density-based, finite volume method, based on a barotropic, homogeneous mixture model. Fully accounting for two-phase compressibility, collapse-induced instantaneous peak pressures and associated wave dynamics are captured by the chosen approach.The maximum instantaneous pressures registered on material surfaces allow for a qualitative identification of erosion-sensitive areas. Furthermore, a collapse detection algorithm is applied for an automated recording of isolated cavity collapse events. Impact load spectra showing rate and intensity distributions of recorded collapses is utilized for a quantitative evaluation of cavitation aggressiveness. While the cavitating tip vortex is stable and does not lead to collapse events in the vicinity of the propeller, material erosion can be expected in the suction side root region due to a highly unsteady root cavitation.

We evaluate the suitability of micro vortex generators for the passive flow control of shock-wave/turbulent boundary layer interactions. For this purpose, implicit large eddy simulations using the adaptive local deconvolution method are performed. The flow configuration consists of an oblique shock with deflection angle β = 9.5°, impinging on a turbulent boundary layer at Ma∞ = 2.31 and Re = 67.4 · 103. Analysis focuses on the assessment of the relative displacement between the control devices and the shock system, the complex flow structure behind the devices and the low-frequent motions of the separated region.