Implementation and validation of non-reflecting mixing plane on openfoam

Abstract

In this study, a non-reflecting mixing-plane methodology was developed and implemented in OpenFOAM for steady-state compressible turbomachinery simulations. Mixing-plane methods are widely used in turbomachinery analyses because they allow different blade rows to be simulated with reduced periodic domains instead of full-annulus geometries. However, conventional mixing-plane approaches may generate artificial reflections at the interface, especially in compressible flow fields where pressure waves, shocks, wakes, and strong circumferential non-uniformities are present. These reflections can affect the stability and accuracy of the solution. Therefore, the main aim of this work was to implement a characteristic-based non-reflecting mixing-plane treatment suitable for compressor simulations. The implemented method transfers flow information between upstream and downstream blade rows by circumferentially averaging the flow variables over radial bands. The averaged quantities are then used to reconstruct the boundary state at the opposite side of the interface. In order to reduce artificial reflections, the treatment is formulated using characteristic variables, which separate the incoming and outgoing wave information at the boundary. In addition, different averaging approaches and a mass-flow correction procedure were included to improve the consistency of the interface treatment. The implementation was developed within the OpenFOAM framework and integrated into a density-based compressible solver environment. The method was first tested on the NASA Stage 37 transonic compressor case. The results were compared with experimental data and with reference FineTurbo calculations. The global performance curves showed that the implemented method was able to reproduce the main pressure-ratio and efficiency trends with reasonable agreement. Local comparisons, including radial profiles and contour plots near the mixing-plane region, showed that the dominant wake structures, pressure variations, temperature distributions, and velocity trends were captured in a physically meaningful manner. Although differences were observed in local extrema and near-wall regions, the general behavior of the flow was consistent with the reference solution. The implementation was also applied to a multi-stage compressor configuration in order to investigate its behavior in a more complex turbomachinery environment. The results showed that the method was able to transfer the main flow structures through multiple blade rows without producing clear artificial reflection patterns at the mixing-plane locations. The pressure-ratio and efficiency trends were generally consistent with the reference calculations, although some differences remained in local values and operating range limits. Overall, the results indicate that the developed non-reflecting mixing-plane implementation provides a practical and usable steady-state interface treatment for compressible turbomachinery simulations in OpenFOAM. The method successfully combines the computational efficiency of mixing-plane modelling with a characteristic-based treatment aimed at reducing spurious wave reflections. Future work may include further validation on turbine cases, radial turbomachinery applications, more general mesh topologies, and improved conservative correction procedures.