Influence of Periodic Unsteady Effects on Flow and Performance Prediction on an Axial High Pressure Compressor

Abstract

A numerical assessment of unsteadiness and information losses due to boundary conditions, especially the rotor-stator interface treatment in an axial high pressure compressor (HPC) is proposed. Steady and unsteady computations are performed on a three-stage axial HPC with a 3D Navier-Stokes code. The steady simulation is based upon periodic boundary condition for azimuthal frontiers and the mixing plane approach which averages circumferentially the information coming from the adjacent blade row. The unsteady one uses the phase-lag method for both azimuthal frontiers and rotor-stator interface. The unsteady simulation highlights the wake effects in the stator passage due to the wakes released by the rotor and the potential effects on the wall pressure of the rotor blades due to the stator blades. The comparison between the steady and the time-averaged unsteady simulations shows a good agreement in the information transfer at the rotor-stator interface. The main discrepancy appears in the static pressure field on the rotor side of the interface, due to the inability of the steady computation to capture the potential effects. The radial profiles and the performances obtained with these two simulations are very similar. Thus a steady computation results in flow field and performance predictions with a sufficient accuracy. This comparison confirms the validity of using the mixing plane approach for HPC design.