Coupling of three- and one-dimensional hydraulic flow simulations

•Coupling of one- and three-dimensional flow domains to reduce computational effort.•Wave propagation into normal direction is well captured.•Tolerating moderate perpendicular flow fluctuations.•Information from solving the Riemann problem for heterogeneous flux functions.•Discontinuous fluxes at interface. Commonly, severely reduced system models are used to predict the performance of industrial hydraulic systems as injection, brake or pump systems. These simulations are usually based on zero- and one-dimensional mathematical models describing the flow path of the technical system. To take into account parts with inherently three-dimensional flow structures like cavitation and the induced pressure wave propagation it is desirable to couple parts with the reduced system models directly with three-dimensional subregions. The coupling is subtle since the three-dimensional part should be small and often contains fluctuations tangential to the coupling interface, not aligned to the main flow direction. In this paper we propose a novel three-to-one-dimensional coupling, which is quite robust in these situations and does not generate artificial effects at the coupling interface. Due to locally defined coupling variables in virtual cells, the transition from three to one space dimension is modelled by a discontinuity of the non-normal components of the numerical momentum fluxes. Simulations of industrial applications shown are hydraulic flows with high pressures with use of a barotrop equation of state that allows for cavitation. We show that the proposed method tolerates moderate crossflow fluctuations without generating oscillations and reflections.