Application of an Improved Mixing Plane Approach for Steady-State Computations of Turbulent Flows in Turbomachinery

Steady-state simulations of turbomachinery often require the use of mixing planes in between blade rows to remove unsteady rotor-stator interactions. In multistage configurations with many mixing planes, the errors caused by this removal of information accumulate and make accurate predictions very challenging, especially at off-design operating conditions. In a recent publication, the effect of mixing planes on the production of turbulent kinetic energy is addressed with an additional differential equation. In this study, this modification is applied to steady-state simulations of a 4.5-stage and an 8.5-stage axial compressor. The boundary conditions are varied to assess the potential of this modification near the choke and surge limits of the compressors. Results are shown from simulations of both setups. The turbulent kinetic energy and eddy viscosity, as well as global performance parameters like efficiency and mass flow rate are evaluated. Based on these quantities, it is shown that the use of the modification leads to more accurate predictions compared to URANS simulations and allows for simulations closer to the surge limit. Furthermore, it is demonstrated that the modification underestimates the production of turbulent kinetic energy when a shock interacts with an upstream mixing plane.